M Pascal

M Xavier Carrier

MAUGE, ENSICAEN, Rapporteur Mme Françoise

Mauge Devant

IRCE M Daniel Bianchi

Mme Audrey Bonduelle

M Christophe Coperet

Eth Zürich

Membre Mme Christèle Legens

LUCK, TOTAL SA, Membre M Francis

Pour continuer, un grand merci aussi au département Catalyse Homogène (H.Olivier-Bourbigou). Merci plus particulièrement aux techniciens, qui m'ont prêté du matériel, m'ont permis d'utiliser l'IR, la RMN et la GC/MS. J'ai très souvent été chez vous sans faire parti de votre département, et merci vraiment pour votre accueil ! Enfin, parce qu'il est impossible de remercier tout le monde nominativement, merci à tous les membres de la division Physique et Analyses, dont les résultats d'analyses m'ont été d'une aide précieuse pour arriver au bout de ce manuscrit.

Merci aux secrétaires (en particulier Valérie), pour leur soutien, leur aide et leur disponibilité.

Je tenais aussi à remercier toutes les personnes avec qui j'ai pu participer à des activités extra-professionnelles grâce au CE. Merci à Eric et Serge, pour les 2 années à la section renforcement musculaire, merci à toute l'équipe du groupe salsa, en particulier Daniel, Patrice, Nico, Agnès, Camille et Hélo (:D), et un grand, grand merci à Jérôme de la section SAE, pour m'avoir redonné le goût de l'escalade, que j'avais oublié depuis 15 ans.

Un merci tout particulier aux thésards et à l'ADIFP. La « famille thésard » m'a vraiment permis d'avancer, dans les bons comme les mauvais moments. Impossible ici de citer tout le monde, mais un merci particulier à certains avec qui j'ai pu passer des moments hors du commun, à IFPEn, comme en dehors. Merci aux fistons : Bob (co-bureau de folie, avec nos sessions F.Cabrel déprimantes, ou sessions musiques « de film » planifiées le soir, à partir de 18h30-19h), Guillaume (et nos sessions discussions en OFF, sur le parking Dolomite, après un badgeage à l'arrachée) et Fabien. Merci à tous ceux de la pause café de 18h, qui n'ont pas encore été nommés : Ema (wua !), Maxime (achhh !), Alex, Alban, Gabi, et les autres. D'ailleurs, merci à la machine à café, et sa copine la machine à grignoter, pour nous avoir offert (ou pas vraiment…) de quoi prendre des forces pour les dernières heures de boulot. Merci encore à certains et certaines pour les grandes discussions, et le soutien mutuel, notamment Laurette la bouclette.

Au passage, je remercie tous les collègues thésards et post-doc de l'ETH, pour leur accueil chaleureux à chacun de mes passages, et les bonnes soirées passées ensembles. Merci en particulier à Maria C., Maxime, Giuseppe, Georges, Karol, Martin, Victor, et surtout David et Florent ! Merci aussi à Esther, pour toutes les formalités administratives.

Merci aussi à mes amis/es, sans qui je n'aurais jamais réussi à tenir le coup ces trois ans, que ce soit grâce au sport, aux sorties, ou à des moments plus tranquilles (Fred, Emilie, Antoine, Caro, Laura du thé, Laurelineuuu, …). Et surtout, des remerciements tous particuliers à

Dans un premier temps, je remercie Messieurs D.Guillaume et F.Bertoncini de m'avoir accueilli au sein de leur division et de leur département à IFPEn. Merci aussi aux membres du jury, d'avoir accepté de juger mon travail de thèse, dans les rapports, comme lors de la soutenance. Un grand merci aussi à mon directeur, Pascal, pour son encadrement, et son implication dans ce projet de thèse. Des remerciements particuliers aussi pour Christophe, pour sa disponibilité, pour le désir d'aller toujours plus loin qu'il me transmettait, pour son accueil à l'ETH Zürich et ses conseils. Enfin, pour terminer avec l'équipe encadrante, je remercie très chaleureusement Christèle et Audrey pour leur patience lors des réunions hebdomadaires, pour leur capacité à supporter mes « oui, mais… » et pour leur intransigeance, qui m'a permis de toujours chercher à faire mieux (« ne pas faire aussi bien que quelqu'un de moyen, mais mieux que l'excellence ! », n'est-ce pas Audrey ? :D).

Je remercie aussi tous les collègues du département Sulfure, pour leur bonne humeur, leur aide au labo, les repas toujours plus sympas et leur soutien. Des remerciements tous particuliers à Nathalie, ma référente dès mon arrivée. Merci pour ta bonne humeur sans faille, ta zènitude, et ta gentillesse ! Au passage, un grand merci à Sylvie, et Anne : vous m'avez accueilli pendant mes 8 premiers mois, et partager votre bureau a vraiment été une chouette aventure ! (votre ficus est toujours vivant :D). Merci aussi à Julie (désolé pour mes taquineries un peu franches), Véro, Georges, Marie-Paule, avec qui j'ai pu passer de bons moments au labo. Merci aussi à tous ceux que je n'ai pas cités, mais à qui je pense en rédigeant ces mots.

Des remerciements aussi à Dani, pour tout le boulot que j'ai pu lui donner en début de thèse (pièces de verrerie un peu étranges), pour sa gentillesse, et sa disponibilité.

Pour continuer, je souhaite remercier toutes les personnes avec qui j'ai pu travailler, et surtout échanger. De chaleureux remerciements à « papa » Philou, qui a su me « botter les miches » quand il fallait, mais aussi me conseiller, et surtout m'écouter. La thèse n'aurait surement pas été la même sans toi. Vraiment, merci, merci beaucoup ! Merci à tous les membres du laboratoire IR/RMN, et plus particulièrement à Mathieu et Laurent. Merci pour votre implication lors des discussions, et pour la rapidité avec laquelle j'ai pu avoir vos résultats d'analyse. C'est aussi grâce à vous, que nous thésards, nous pouvons aller plus vite et « plus haut ».

Pareillement, un grand merci à toutes les personnes du laboratoire de microscopie : ça a toujours été un plaisir de passer dans votre grand bureau et discuter de la beauté et de l'intérêt (:D) de la microscopie. Merci en particulier à Anne-Lyse, pour sa formation, et son accompagnement tout au long de la thèse. J'en profite aussi pour remercier Anne-Sophie et Maria, qui ont beaucoup contribuées à rendre la thèse plus « sexy » grâce aux belles images STEM-HAADF obtenues (et ouai, mieux que les Danois :p !)

Introduction générale

Le pétrole brut est transformé en raffinerie par une suite de procédés de séparation, de conversion et de dépollution. Tous ces procédés permettent in-fine d'obtenir des produits directement valorisables (méthane, butane, huiles, bitumes), des produits rassemblés dans le pool essence ou le pool Diesel, ou des molécules utilisables en pétrochimie.

Actuellement, l'appauvrissement des réserves pétrolières conventionnelles mondiales amène les producteurs à fournir des bruts de plus en plus lourds, et généralement plus chargés en hétéroatomes indésirables. Les raffineurs sont donc confrontés à deux défis majeurs : l'amélioration des procédés de conversion des coupes lourdes que constituent les résidus atmosphériques, ainsi que la mise aux spécifications des carburants (diminution des teneurs en soufre dans les carburants en dessous de 10 ppm, notamment). L'hydrotraitement (HDT) des produits raffinés est par conséquent une étape clé pour éliminer de ces impuretés, grâce à l'action combinée de catalyseurs et d'hydrogène dans des conditions plus ou moins sévères de température et pression. Schématiquement, le pétrole brut est distillé à pression atmosphérique pour donner des produits légers comme le gaz, les essences, des produits intermédiaires dits «distillats moyens» type gazole et kérosène et des produits plus lourds : les «résidus atmosphériques». La distillation de ces résidus à pression réduite permet d'obtenir les «distillats sous vide» (DSV) servant de base pour la production de carburants. Les composés non distillés forment une coupe appelée «résidus sous vide» (RSV), et serviront à la production de fiouls lourds et bitumes.

Actuellement, la répartition entre produits lourds, produits légers et intermédiaires après distillation des bruts n'est plus en phase avec la demande du marché. En effet, la demande en fuels lourds étant bien trop faible, les distillats sous vide doivent être transformés en composés plus légers pouvant servir de base à la production d'essence ou Diesel. Par ailleurs, l'importante diésélisation des parcs automobiles mondiaux contraignent les raffineurs à produire de plus en plus de distillats moyens afin de les raffiner in-fine en kérosène et gazole répondant aux spécifications demandées.

Les procédés catalytiques d'hydrotraitement, permettent de retirer les hétéro-éléments (soufre, azote, oxygènes...) indésirables, et mettent en oeuvre des catalyseurs dont la phase active est une phase sulfure mixte préparée à partir de tungstène (W) ou de molybdène (Mo), promue par du nickel (Ni) ou du cobalt (Co). Parmi ces catalyseurs, les phases mixtes NiWS sont reconnues pour être plus actives que les phases NiMoS et CoMoS en hydrogénation des aromatiques. Elles sont aussi actives que les phases NiMoS en hydrodéazotation, et plus performantes que les phases CoMoS.

Néanmoins, la sulfuration limitée du W par rapport au Mo conduit les industriels à préférer les catalyseurs à base de Mo. Ces catalyseurs (à base de W) sont conventionnellement préparés par imprégnation à sec à l'aide de précurseurs hétéro-polyanions. Or ces méthodes de préparation sont pour partie à l'origine des limites observées de la sulfuration du précurseur oxyde. L'enjeu de cette thèse réside donc dans la compréhension et l'amélioration de la sulfuration de catalyseurs à base de W. La thèse a donc pour objectif la rationalisation des différentes étapes de préparation de catalyseurs d'hydrotraitement de type NiWS depuis la préparation jusqu'au test catalytique par une approche moléculaire, ce qui permettra de proposer de nouvelles voies pour lever le verrou majeur lié à la mauvaise sulfuration du W. Au coeur de cette approche se situe l'utilisation d'une méthode de préparation originale, ayant recours à des composés moléculaires métallo-organiques bien-définis comme précurseurs de la phase sulfurée W, combinée à une analyse poussée par spectroscopie multiples (IR, RMN, XPS) et chimie computationnelle.

L'étude qui a été menée au cours de la thèse est détaillée dans ce manuscrit, qui est divisé en six grandes parties :

Dans la 1 ère partie, nous présentons une étude bibliographique centrée sur les catalyseurs sulfures, et la caractérisation de leur phase active. Parmi les diverses tentatives d'amélioration des catalyseurs d'hydrotraitement (Ni)W déposés sur support oxyde, nous développons plus particulièrement le mode de préparation par une approche dite moléculaire, ou de "chimie de surface contrôlée" (CSC). [Ballard, 1973;Yermakov and Kuznetsov, 1972;Basset andChoplin, 1983, Copéret et al., 2003;Wegener et al., 2011] Nous exposons ensuite les objectifs et la méthodologie de la thèse.

La 2 ème partie est consacrée à la description des modes de préparation de tous les matériaux catalytiques et présente également les techniques analytiques. La 3 ème partie traite de la préparation, de la caractérisation et d'une première évaluation des performances catalytiques (hydrogénation du toluène) de catalyseurs non-promus supportés sur silice-alumine amorphe (ASA) dits WS 2 /ASA. Ces catalyseurs ont été préparés par imprégnation d'alcoxydes de tungstène où le métal est au degré d'oxydation (V) ou (VI), et leurs performances catalytiques sont comparées à celles de catalyseurs préparés par voies conventionnelles, afin de déterminer le potentiel de la méthode de préparation dite de chimie de surface contrôlée.

La 4 ème partie présente l'étude approfondie de matériaux, préparés par voie CSC à partir d'alcoxyde de tungstène(V) déposé sur ASA. Nous montrons en particulier l'influence de la quantité de tungstène déposée sur la nature des espèces de surface, et proposons un ensemble de mécanismes réactionnels pouvant être à l'origine des espèces de surface observées.

La 5 ème partie détaille l'évolution des espèces alcoxydes de W supportés sur ASA non promus après sulfuration vers la phase active WS 2 . Ce chapitre permet la comparaison des catalyseurs CSC avec des références conventionnelles, séchées ou calcinées. Nous détaillons l'ensemble des résultats de caractérisation et tentons de corréler ces résultats aux différences d'activités observées en hydrogénation du toluène. La 6 ème et dernière partie présente la préparation, la caractérisation et l'évaluation catalytique de catalyseurs promus NiWS supportés sur ASA. Nous exposons les diverses voies de préparation suivies, les résultats de caractérisation des phases promues NiWS, ainsi que leurs performances catalytiques, qui sont mises en regard des analyses effectuées sur nos catalyseurs.

Nous terminons ce manuscrit par une conclusion générale et les perspectives envisagées pour la suite de ces travaux.

L'étude bibliographique (partie I) est rédigée en Français. Les autres parties sont rédigées en Anglais. Ballard, D.G.H., Advances in Catalysis (1973), 23, 263-275 Basset, J.M. andChoplin, A., Journal of Molecular Catalysis (1983), 21, 1-3, 95-108 Copéret, C.; Chabanas, M.; Petroff Saint-Arroman, R.; Basset, J.M., Angewandte Chemie International Edition (2003), 42, 2, 156-181 Wegener, S.L.; Marks, T.J.; Stair, P.C, Accounts of Chemical Research (2011), 45, 2, 206, 214 Yermakov Y.I. andKuznetsov B.N. Kinetika i Kataliz (1972) 13, 1355-1356.

Références bibliographiques

Partie I : Etude bibliographique

I.1. Généralités sur les procédés d'hydrotraitement

Le raffinage des produits pétroliers est un ensemble de procédés catalytiques mis en oeuvre pour séparer, transformer et purifier les coupes pétrolières brutes en produits valorisables comme carburants ou en molécules utilisables en pétrochimie.

La Figure 1 illustre la complexité du schéma de raffinage. Le pétrole brut est tout d'abord distillé à pression atmosphérique pour permettre d'obtenir séparément des produits légers (gaz, essences), des produits intermédiaires (distillats moyens) type gazole et kérosène et des produits plus lourds (résidus Atmosphériques). Une seconde distillation réalisée sous pression réduite permet d'obtenir une gamme de produits dits « distillats sous vide » (DSV), dont les points de coupe sont trop élevés pour être utilisés directement comme base carburants mais qui seront « craqués » dans les procédés de conversion pour être valorisés. Les composés non distillés dits « résidus sous vide » (RSV) servent notamment à la production de bitumes.

Deux procédés industriels permettent de transformer les DSV : le craquage catalytique, appelé FCC pour « Fluid Catalytic Cracking », qui permet d'obtenir majoritairement des essences de bonne qualité, et l'hydrocraquage qui permet de produire essentiellement des gazoles et kérosènes de bonne qualité. [Kaufmann et al., 2000;Mochida and Choi, 2004;Raybaud and Toulhoat, 2013, Ed. Technip, Paris]. Les contraintes imposées par le marché (demande faible en produits lourds) et les spécifications environnementales (teneurs en S inférieures à 10 ppm dans les carburants) obligent donc les raffineries à améliorer les procédés d'hydrocraquage, de conversion des résidus lourds, et les procédés d'hydrotraitement (HDT), procédés clés destinés à se débarrasser des hétéroatomes indésirables. Tous ces procédés sont opérés grâce à l'action combinée de catalyseurs et d'hydrogène dans des conditions plus ou moins sévères (température, pression). La pollution atmosphérique engendrée par les rejets de SO 2 , source des pluies acides, et l'empoisonnement des catalyseurs des pots catalytiques par le soufre issu de la combustion des carburants imposent notamment des réductions drastiques des taux de ce composé dans les carburants. Comme le soufre est l'hétéroatome le plus abondant dans les pétroles bruts [Schulz et al., 1999] l'hydrodésulfuration (HDS) poussée devient une réaction majeure des raffineries, afin de respecter les normes européennes toujours plus drastiques : moins de 10 ppm de S dans les carburants depuis 2009. [Directive européenne 2009/30/CE] L'azote est, quant à lui, présent dans des proportions 10 à 100 fois moins importantes que le soufre. L'élimination de ce composé (hydrodéazotation HDN) est absolument essentielle pour éviter l'empoisonnement des catalyseurs acides utilisés dans les procédés de conversion et notamment en hydrocraquage. Par ailleurs, il est probable que les futures normes européennes concernant les produits de combustion des composés azotés (NO x ) deviennent de plus en plus sévères, et incitent les raffineurs à diminuer les teneurs en azote dans les produits de raffinage (Norme Euro 6).

Parmi les procédés d'hydrotraitement, on peut aussi citer l'hydrodéoxygénation (HDO) et l'hydrodémétallation (HDM). L'HDO permet d'éliminer l'oxygène, notamment présent dans les coupes issues de la transformation de la biomasse. L'HDM des coupes de type résidus sous vide permet de retirer les métaux tels que le nickel ou le vanadium, qui constituent des poisons pour les catalyseurs d'hydrotraitement en général.

Les procédés d'hydrotraitement comprennent aussi des procédés d'hydrogénation (HYD).

I.2. Les catalyseurs d'hydrotraitement couramment utilisés

Les catalyseurs d'hydrotraitement couramment utilisés sont essentiellement des phases sulfures mixtes (car contenant au moins deux éléments) constituées de métaux du groupe VIB comme le molybdène et le tungstène, promus par des métaux du groupe VIII comme le nickel ou le cobalt. Les précurseurs de ces métaux sont déposés sur des supports oxydes présentant une surface spécifique importante comme la silice, l'alumine, ou les silice-alumines. Ils sont ensuite sulfurés pour générer la phase active.

Les catalyseurs d'hydrotraitement sont plus généralement préparés à partir de précurseurs de molybdène, notamment à cause de leur coût comparativement aux précurseurs à base de tungstène. A ce propos, la Figure 2 illustre la diminution globale du prix du molybdène ces huit dernières années, a contrario de celui du tungstène. Néanmoins, sur des supports de type alumine et sur des charges très soufrées, c'est avant tout la meilleure sulfurabilité et la meilleure réactivité du molybdène [Raybaud and Toulhoat, 2013, Ed. Technip, Paris] Cela peut expliquer pourquoi les phases NiWS supportées, bien que performantes en hydrogénation des aromatiques [Stanislaus and Cooper, 1994;Hensen et al., 2007] et en HDN [START_REF] Vazquez | [END_REF], sont peu utilisées dans le domaine du raffinage. Par contre, dans l'enchainement de catalyseurs du procédé d'hydrocraquage et notamment dans un schéma « maxi sélectivité en gazole », les phases NiWS déposées sur silice-alumine sont très utilisées.

I.3. La phase sulfure

I.3.a. Généralités et modèle(s) issu(s) de la littérature La phase sulfure présente une structure lamellaire, formée de feuillets de MS 2 (M = W, Mo).

La morphologie 2D de ces feuillets, leur empilement moyen (≈ 2 à 4) et leur taille moyenne (≈ 3 à 6 nm) dépendent des conditions de sulfuration.

La sulfuration induit une modification profonde de la phase oxyde (Figure 3) : les ligands oxygène sont remplacés par des atomes de soufre et le métal passe d'un degré d'oxydation +VI à +IV. Cette transformation provoque une réorganisation des espèces de surface, ainsi qu'un changement de l'environnement cristallographique du métal qui passe d'une structure octaédrique à une structure trigonale prismatique. Le procédé de sulfuration en phase gazeuse nécessite l'utilisation d'un composé soufré, très souvent du sulfure d'hydrogène (H 2 S), pur ou dilué dans un autre gaz (N 2 , H 2 ). En phase liquide, l'H 2 S utilisé pour la sulfuration des matériaux oxyde peut aussi être produit in-situ par décomposition de composés soufrés (éventuellement présents dans les essences et Diesels), en présence de dihydrogène. Par ailleurs, la gamme de températures utilisées industriellement se situe entre 300°C et 400°C.

Parmi les différents modèles de phase active le modèle historique de Kasztelan et al.

[ Kasztelan et al.,1984] décrit des feuillets MoS 2 ayant une morphologie hexagonale ou rhomboédrique pour laquelle la présence de promoteur provoquerait une modification de structure. Les résultats obtenus par les auteurs ne permettent pas de conclure sur le rôle exact du promoteur, mais montrent que les différentes réactions d'hydrotraitement (HYD et HDS) sont limitées par le nombre de sites métalliques de bord, ou de coins. Ce modèle est en accord avec celui proposé par Topsøe et al. [Topsøe et al., 1981, Topsøe andBrenner, 1983;Topsøe and Clausen, 1986] sur la base d'analyses de type spectroscopie Mössbauer sur des catalyseurs CoMo/Al 2 O 3 . Le modèle de Topsøe (catalyseur CoMo/Al 2 O 3 ) illustré par la Figure 4, propose la présence de cristallites MoS 2 sur lesquelles le promoteur (cobalt) vient en décoration sur les bords des feuillets, ou leurs coins. La phase active, reconnue comme permettant les réactions d'HDT mentionnées précédemment, est la phase « Co-Mo-S » dite « phase mixte ». [Kasztelan et al., 1983;van Veen et al., 1992;Gandubert et al., 2008] A ce propos, la terminologie « site mixte » désigne la juxtaposition, sur les bords des feuillets, d'un atome de molybdène (ou de tungstène) avec un atome de promoteur. Cependant, le catalyseur réel n'est pas idéal et tous les atomes introduits ne sont pas utilisés pour générer une phase mixte. Certains atomes de promoteur peuvent former des phases sulfures inactives, comme Co 9 S 8 ou encore Ni x S y (NiS ou Par la suite, Schweiger et al. [Schweiger et al., 2002] ont utilisé la théorie de la fonctionnelle de la densité (DFT) pour prédire la morphologie des feuillets MoS 2 non promus en fonction de la pression partielle en H 2 S du système. Ils ont montré que pour une atmosphère très sulfurante, i.e. pour une pression partielle en H 2 S (p(H 2 S)) élevée, les feuillets MoS 2 adoptaient une géométrie triangulaire. Au contraire, dans des conditions proches de celles utilisées dans les procédés d'HDS (p(H 2 S)/p(H 2 ) compris entre 0,0025 et 0,15), la morphologie des feuillets devenait hexagonale. Leurs calculs théoriques ont ensuite été confirmés par les analyses STM effectuées par Lauritsen et al. en 2004. [Lauritsen et al., 2004] La Figure 5 présente deux modèles géométriques de feuillets MoS 2 : un modèle hexagonal et un triangulaire. La morphologie des cristallites dépend de la stabilité des bords M (M-edge, plan Etude bibliographique 29 cristallin (1 ;0 ;-1) [Moses et al., 2007] ou S (S-edge, plan cristallin (-1 ;0 ;1) [Moses et al., 2007]) l'un par rapport à l'autre. Portela et al. [Portela et al., 1995] on étudié l'influence de la pression partielle en H 2 S sur la taille des cristallites MoS 2 de catalyseurs non promus MoS 2 /Al 2 O 3 . Les auteurs ont montré que la pression partielle en H 2 S modifie la taille des cristallites : l'étude du rapport atomique moyen Mo/Al obtenu par spectroscopie de type X-ray photoelectron spectroscopy (XPS) ainsi que des analyses d'adsorption d'oxyde d'azote suivie par spectroscopie infrarouge (IR) ont révélé qu'une sulfuration sous H 2 S pur provoquait une augmentation de la taille des cristallites, par rapport à une sulfuration sous un mélange 15 % vol. H 2 S/H 2 . Ces conclusions sont identiques à celles de

Baubet [Baubet, PhD thesis, Lyon, 2013] qui a étudié par microscopie à transmission électronique (MET) des catalyseurs MoS 2 /Al 2 O 3 , sulfurés sous H 2 S pur, ou sous un mélange 15 % mol. H 2 S/H 2 .

L'étude de catalyseurs promus CoMoS/Au(111) par STM (équipe de Lauritsen et al.

[ Lauritsen et al., 2001] a permis d'observer que la présence du promoteur favorise une morphologie de feuillet plus hexagonale que triangulaire. Ces résultats expérimentaux ont été confirmés par les calculs DFT de Schweiger et al. en 2002. [Schweiger et al., 2002] Ces Carlsson et al. [Carlsson et al., 2006] Cependant, les variations de morphologie observées dans le cas du W sembleraient moins marquées : l'ajout du promoteur ne provoquerait qu'une troncature plus importante des angles des triangles WS 2 mais n'entrainerait pas un passage vers une structure proche d'un hexagone.

derniers
Toutefois, l'analyse STEM-HAADF des systèmes NiWS est à ce jour moins poussée que celle des systèmes NiMoS dans la littérature. En parallèle, la mise en évidence de la localisation des atomes de promoteur sur les bords des feuillets sulfures par STEM-HAADF reste un défi. Les récents travaux récents travaux de microscopie STEM-HAADF de Deepak et al. [Deepak et al., 2011], réalisés sur des nanofils de CoMoS et CoWS déposés sur alumine, ont cependant montré qu'il semblait possible de révéler la position des atomes de (W)Mo et de Co en bordure des nanofils sulfurés (et par conséquent, d'observer l'existence des fameux sites mixtes). Pour résumer, ces travaux révèlent que la morphologie des feuillets dépend de la présence du promoteur, de la température de sulfuration ainsi que de la pression partielle en H 2 S.

Cependant, il convient de mettre en avant que la nature des supports utilisés pour les travaux Pecoraro et Chianelli [Pecoraro and Chianelli, 1981] couplés aux calculs de Toulhoat et Raybaud [Toulhoat and Raybaud, 1999] ont permis de définir une courbe en volcan (voir L'activité des phases sulfures est liée aux atomes de bord M-edge et S-edge, encore appelés sites de bords (Figure 5). La quantité de ces sites actifs varie avec la morphologie 2D des feuillets, qui est dictée par la stabilité de chacun des bords. Que ce soit pour des réactions d'HDS, ou d'HYD, différents sites actifs comme différentes espèces interviendraient dans le processus catalytique. Selon l'étude de Moses et al. [Moses et al., 2007], réalisée par calculs DFT sur des phases MoS 2 , les réactions d'HYD, participant au mécanisme réactionnel de l'HDS du thiophène, seraient préférentiellement localisées sur les bords M-edge des feuillets. Dans le cas de phases CoMoS, une étude comparative [Gandubert et al., 2008] entre expérience (catalyseurs CoMo/Al 2 O 3 ) et calculs par DFT, révèlerait que pour une réaction d'HYD du toluène, les sites actifs seraient principalement situés sur les bords M-edge. Par ailleurs, aucune étude n'a démontré que les sites de bords S-edge étaient totalement inactifs en HYD : leur influence, même moindre, peut donc être envisagée pour interpréter des résultats catalytiques. Les deux études précédentes mettent aussi en avant l'implication de différents sites : les CUS pour «coordinatively unsaturated sites», [Siegel, 1973;Gandubert et al., 2008] ou les Brim. [Topsøe et al., 2005;Moses et al., 2007] Les CUS représentent des sites de bord avec une lacune en soufre, et sont supposés être impliqués dans l'adsorption des molécules soufrées, et dans la rupture des liaisons S-C (HDS). Les sites Brim, au contraire, représentent des sites proches du bord, localisés sur la partie supérieure des feuillets sulfures, et ne présentent pas de lacune en soufre. De plus, la présence d'espèces de type M-SH, encore appelée sulfhydryls, est aussi invoquée. Leur domaine de stabilité sur les bords des feuillets est, par exemple, discuté dans les travaux théoriques (DFT) de Prodhomme et al. [Prodhomme et al., 2011] dans le cas des catalyseurs MoS 2 . L'implication des espèces sulfhydryls, et des sites métalliques de bords (sans distinction M-edge ou S-edge) dans le processus d'hydrogénation est résumée dans les travaux de Guernalec et al. [Guernalec et al., 2006], et leur modèle microcinétique de l'hydrogénation du toluène. Dans ce modèle, l'une des étapes comprend l'adsorption du cycle aromatique (toluène) sur un site métallique. Cette adsorption, dans le cas d'un site mixte CoMoS, seraient plus stable sur un atome de molybdène, d'après Gandubert et al. [Gandubert et al., 2008] [Ouafi et al., 1988] Des espèces similaires sont recensées à la surface de catalyseurs préparés à partir de molybdène. [Kasztelan et al., 1983 [Hensen et al., 2007] De plus, les différents supports oxydes (silice, silice-alumine, alumine) utilisés pour la préparation de catalyseurs d'hydrotraitement n'ont pas la même influence sur les espèces oxydes de surface. La silice, par exemple, n'est pas couramment utilisée comme support de catalyseurs d'hydrotraitement. En effet, ce support présente une acidité quasiment nulle, et il est admis qu'il ne développe pas une très forte affinité avec les métaux, ce qui conduit généralement à des catalyseurs présentant une phase métallique peu dispersée. [Kim et al., 1996] La silice-alumine et l'alumine sont plus communément utilisées, notamment de part leur acidité modérée ou forte, et de part la bonne dispersion du tungstène en surface. Cette meilleure répartition du tungstène sur la surface, comparé à un support silicique, a été associée à l'affinité du tungstène pour les parties aluminiques. [Vissenberg et al., 2000;van der Meer et al., 2004] Par ailleurs, l'étude de catalyseurs préparés sur silice-alumine a mis en évidence la présence d'espèces de surface similaire à celles observées sur alumine. [Dugulan et al., 2010] Enfin, il convient de mentionner l'éventuelle « dissolution » du support, en présence d'espèces ioniques en solution, le cas le plus connu étant la dissolution partielle de l'alumine au contact Il est reconnu que pour des catalyseurs supportés sur alumine, le tungstène est plus difficilement sulfurable que le molybdène [Breysse et al. 1988]. Ce phénomène a été associé à l'énergie de liaison W-O-Al relativement élevée [Scheffer et al., 1990] et al., 2002a;van der Vlies et al., 2002b] Dans le cas de catalyseurs à base de tungstène, préparés sur silice, Kim et al. [Kim et al., 1996] décrivent la formation de feuillets sulfures plus empilés et moins bien dispersés que sur alumine. Dans le cas de matériaux préparés sur silice-alumine, [Hensen et al., 2007] L'étape de sulfuration, qui permet finalement de former la phase active des catalyseurs d'hydrotraitement, ne permet pas de convertir 100 % de la phase oxyde en phase sulfure. La spectroscopie EXAFS pour « extended X-ray absorption fine structure » [Hensen et al., 2007] ainsi que la préparation de références adéquates et leur analyse par spectroscopie XPS, ont permis d'identifier trois différentes espèces chimiques présentes sur les catalyseurs sulfures, préparés à base de W : une espèce W (IV) , attribuée à une phase sulfure WS 2 , une phase réfractaire W (VI) attribuée à l'oxyde de départ, ainsi qu'une phase intermédiaire W (V) . Le débat concernant l'attribution de cette dernière phase à des espèces de type WS 3 [Payen et al., 1988;Sun et al., 2001;Hensen et al., 2007] ou oxysulfures type WO x S y [Payen et al., 1988;Sun et al., 2001;van der Vlies et al., 2002a;Hensen et al., 2007] est toujours ouvert.

I.4. Préparation conventionnelle et activation des catalyseurs sulfures

A l'heure actuelle, il n'existe donc pas de solution satisfaisante pour sulfurer de manière optimale des catalyseurs conventionnels à base de W : la préparation de catalyseurs à partir de précurseurs conventionnels ne permet pas de sulfurer le tungstène à plus de 60% rel. WS 2 sur silice-alumine (30 % pds. SiO 2 ). Parmi les voies d'amélioration de la sulfuration du tungstène, on peut citer l'augmentation de la température de sulfuration. Le taux de sulfuration du W est alors augmenté [Reinhoudt et al., 1998], au détriment de l'activité catalytique, ce qui est dû à l'effet de frittage des feuillets (augmentation de leur taille) qui diminue la quantité de phase active (atomes de bords). D'autres voies d'amélioration de la sulfuration sont envisageables, comme l'utilisation de précurseurs non conventionnels. Ces précurseurs seraient de petite taille (mononucléaires ou petit cluster) avec l'objectif d'améliorer leur répartition sur la surface du support lors de l'imprégnation. Ils pourraient aussi contenir un à plusieurs atomes de W avec un degré d'oxydation plus proche de celui du tungstène sulfuré (i.e. W (IV) ), pour éventuellement faciliter la sulfuration du métal. Une recherche bibliographique a permis de mettre en évidence de nombreux travaux traitant du dépôt de W et d'autres métaux via des précurseurs non conventionnels, appelés précurseurs métallo-organiques. Leur utilisation pour préparer de nouveaux matériaux nécessite cependant une méthodologie de préparation peu employée dans le domaine catalyseurs d'hydrotraitement. Cette approche relativement atypique dans la préparation de catalyseurs d'hydrotraitement est décrite et illustrée dans la partie I.5. L'utilisation de précurseurs non conventionnels permet d'envisager la préparation de catalyseurs par une approche dite de « chimie de surface contrôlée » (CSC), appelée traditionnellement « chimie organométallique de surface » (COMS) de part l'utilisation au départ de complexes organométalliques. [Ballard, 1973;Yermakov and Kuznetsov, 1973;Basset and Choplin, 1983;Copéret et al., 2003, Wegener et al., 2011] Cette approche requière le contrôle de l'état de surface du support, et le suivi étape par étape de la préparation du catalyseur.

I.5. Apport de la Chimie de Surface Contrôlée (CSC) : catalyseurs préparés par voie non conventionnelle

Chaque étape suivant le dépôt du composé doit être finement caractérisée, pour accéder à une compréhension des phénomènes chimiques au niveau moléculaire.

Lors de son dépôt sur un support oxyde, un précurseur métallo-organique peut se greffer ou être physisorbé. On appellera de manière général « greffage » lorsque le complexe moléculaire établit une liaison forte avec un(des) atome(s) de surface; il est souvent lié à la réaction d'échange entre un ou plusieurs des ligands anioniques du complexes avec un hydroxyle de surface du support oxyde (Figure 8). On appellera physisorption l'établissement d'interactions faibles de type van Der Waals entre une molécule et une surface. Comme précisé auparavant, les complexes métallo-organiques utilisés pour les greffages sont généralement sensibles, mais ils présentent certains avantages. [Copéret et al., 2003] Le premier provient de la possibilité de préparer des catalyseurs avec des sites de surface de structure bien définie, là où les méthodes classiques ne fonctionnent pas. Le second avantage provient de la possibilité de déposer le métal de manière bien plus homogène sur la surface.

L'utilisation de cette méthode de préparation permettrait de lever les interrogations sur la formation de la phase active, sa réactivité, les mécanismes de réaction, et les effets de synergie Tableau 2 : Fréquences des bandes de vibrations IR remarquables pour un support silicique. [START_REF] Vansant | Characterization and Chemical modification of the silica surface[END_REF] ν (cm Il existe huit formes cristallines d'alumines recensées à ce jour. Les alumines η, γ, δ, θ et α sont les plus connues et les plus employées mais nous ne détaillerons ici que le cas de l'alumine-γ. Deux modèles ont été proposés pour modéliser la structure de cette alumine-γ : un modèle spinelle [Pinto et al., 2004;Menendez-Proupin and Gutiérrez, 2005] et un modèle non spinelle. [Krokidis et al., 2001;Digne et al., 2004] La différence entre les deux repose sur la présence ou non de défauts de sites dans la structure.

Comme pour la silice, Il existe différents types d'hydroxyles de surface pour l'alumine. Les premiers travaux de Knözinger et al. [Knözinger and Ratnasamy, 1978] [Peri, 1965, Digne et al., 2004] et expérimentaux. [Knözinger and Ratnasamy, 1978;Busca et al., 1993] La Actuellement, la compréhension de la nature des sites de surfaces d'ASA reste un défi. La combinaison de résultats expérimentaux [Trombetta et al., 1998;Gora-Marek et al., 2005;Garrone et al., 2006;Crépeau et al., 2006] et de travaux théoriques [Garrone et al., 2006;Chizallet et al., 2009;Chizallet et al., 2010] a récemment permis de déterminer la nature de différents groupements hydroxyles présents en surface. Ces hydroxyles sont présentés dans la La température de deshydroxylation du support est alors un facteur très important pour orienter le type de greffage des complexes organométalliques.

La méthode CSC a été employée pour la préparation de catalyseurs à base de métaux comme Mo, W ou Re, actifs en métathèse des oléfines. [Chabanas et al., 2001, Mazoyer et al., 2010;Leroux et al., 2005a;Blanc et al., 2007] du greffage de complexes de métaux du groupe 4 (M = Ti [Rosier et al., 1997], Zr [Corker et al., 1996]) conduit à un mélange d'espèces comportant principalement une espèce tripodale (60-70%) (M = Ti [Bini et al., 2006], Zr, [Rataboul et al., 2004]) [Basset et al., 2010] L'approche moléculaire du dépôt de complexe organométallique a aussi permis la préparation de catalyseurs actifs en polymérisation des oléfines. On peut notamment citer la préparation de catalyseurs à base de titane comme ceux préparés par Grau et al., [Grau et al., 2013] dans le cadre de l'amélioration de catalyseur Ziegler-Natta préparés sur MgCl 2 , en présence de tétrahydrofurane (THF).

Pour terminer, il est intéressant d'évoquer le cas des complexes présentant des ligands alcoxydes, utilisés pour la préparation de catalyseurs d'époxydation (à partir de Ti(OiPr) 4 [Fraile et al., 1996]), de dépéroxidation (à partir de Ta(OMe) 5 [Petroff Saint-Arroman et al., 2008]) ou de métathèse (à partir de Mo(≡NAr)(=CHCMe 2 Ph)(OR) 2 où R = tBu ou Ar [Rendón et al., 2009]).

Ainsi, le dépôt sur SiO 2-500 (voie CVD, à 70°C) d'un complexe comme V(=NtBu)((CH 2 tBu)) 3 ne comportant pas de ligand alcoxy, génère un mélange quasi équimolaire d'espèces monopodales et bipodales [Wolke et al., 2001] Cette approche moléculaire a aussi été utilisée pour la préparation de catalyseurs d'hydrotraitement de type HDN [Harvey and Matheson, 1986], HYD [Thomas and Brenner, 1983;Eisen and Marks, 1994] ou HDS [Yermakov et al., 1981, Yermakov et al., 1984;Ishirara et al., 1994;[START_REF] Choi | Controlled surface modification of alumina-supported Mo and Co-Mo sulfides by surface organometallic chemistry[END_REF]Larabi et al., 2012]. Les supports les plus utilisés sont la silice et l'alumine.

Dans cette partie, les précurseurs métallo-organiques évoqués ne représentent qu'une infime partie des nombreuses espèces existantes. En effet, nous ne décrirons que l'utilisation de précurseurs carbonylés, du type M (0) (CO) 6 (M = Mo, W) et de précurseurs homoleptiques (ayant un seul type de ligand) neutres, du type M (x) R x (x = 2,4,5), avec M = W ou Mo et R étant un alkyl (C n H 2n+1 ), ou un ligand anionique comme un alcène (C n H 2n ), ou un alcoxyde (OC n H 2n+1 ).

D'après la littérature, il semblerait que l'imprégnation de précurseurs carbonylés M(CO) 6 (M = Mo, W) dans le pentane [Brenner and Burwell, 1978;Jaenicke and Loh, 1999] ou le benzène ne permette pas de déposer aisément d'importantes quantités de métal (< 2.2 % pds. métal, sur Partie I

50

alumine [Davie et al., 1972]), du fait de la faible solubilité de ces complexes et de leur faible réactivité vis-à-vis des groupements OH de surface. Cependant, ces composés sont photoactivables (irradiation sous UV) par échange de ligand avec, par exemple, du tétrahydrofurane (THF ou C 4 H 8 O) [Maeyama and Iwasawa, 1999] ou encore de la triphénylphosphine (PPh 3 ou P(C 6 H 5 ) 3 ). [Baibich et al., 1997;Sica et al., 1999] Cette approche permet de remplacer facilement un ligand carbonyle par un ligand plus labile, qui pourra aisément être échangé lors de son dépôt sur le support. A titre d'exemple, Sica et al. [Sica et al., 1999] [Suvanto et al., 1998;Perez-Cadenas et al., 2003], par un meilleur transport du précurseur au sein des pores du support ou par adsorption avec des sites spécifiques supposés bien dispersés [Suvanto et al., 1998]. Les nombreuses études par spectroscopie FT-IR [Zecchina et al., 1990;Busca et al., 1993;[START_REF] Raybaud | Catalysis by transition metal sulphides[END_REF]Suvanto et al., 1999]

Partie I

52

En outre, l'emploi de précurseurs moléculaires permettrait de mieux répartir le W [Perez-Cadenas et al., 2003] ([W(OEt) 5 ] 2 /charbon actif) et la phase sulfure (WS 2 /SiO 2 ou WS 2 /ASA) [Yermakov et al., 1981;Roukoss, 2009] à la surface du support, par rapport à une voie de préparation conventionnelle. Enfin, les caractéristiques structurales des feuillets semblent aussi être impactées par le degré d'oxydation du métal de départ. Pour un tungstène au degré +IV, il semblerait que la phase active soit composée de nanocristallites de taille inférieure à 1,0 nm et de monofeuillets allant de 1,5 à 5,0 nm. Pour un métal au degré d'oxydation inférieur, la taille moyenne est similaire alors que pour un degré d'oxydation supérieur (W (VI) ), la taille des cristallites observées est plus importante. [Yermakov et al., 1984] Les travaux présentés montrent que la préparation de catalyseurs d'hydrotraitement à base de W déposé par voie CSC permet généralement d'améliorer leur activité catalytique. Cela est notamment dû à la meilleure « sulfurabilité » de la phase métallique sur silice (comme sur alumine) en comparaison des catalyseurs conventionnels. Il semble aussi que cette voie non conventionnelle permette d'obtenir des tailles de cristallites différentes. Enfin, l'emploi de certains précurseurs métallo-organiques comme [W(OEt) 5 ] 2 a permis d'augmenter la dispersion des espèces de surface, sur les catalyseurs. I.5.d. Catalyseurs d'hydrotraitement promus, préparés par voie CSC Les méthodes de dépôt non conventionnelles de promoteurs sont identiques à celle utilisées pour le dépôt de la phase métallique Mo ou W.

Comme précisé précédemment, les précurseurs carbonylés sont aisément sublimables.

Pour cette raison, certaines études, comme celle de Suvanto et al., [1999] rapportent le dépôt par voie CVD de dicobalt (0) octacarbonyle, ou Co 2 (CO) 8 . La préparation de catalyseurs CoW/Al 2 O 3 [Suvanto et al., 1999] ou CoMo/Al 2 O 3-600 , [Kurhinen and Pakkanen, 2000] a permis de montrer que les solides obtenus sont actifs en HDS du thiophène, mais sont peu sélectifs.

Les équipes d'Okamoto [Okamoto et al., 2005, Okamoto et al., 2009] et Maugé [Maugé et al., 1989, Maugé et al., 1992] L'équipe de Maugé et al. [1989Maugé et al. [ , 1992] ] Parallèlement à l'emploi de la méthode CVD, certains auteurs ont étudié l'incorporation du promoteur par imprégnation. Vishwakarma et al. [Vishwakarma et al., 2007]

54

«sonochimique» par rapport aux références issues de précurseurs conventionnels. [Halbert et al., 1991] Des analyses MET [Zaikovskii et al., 1984] pratiquées sur des catalyseurs NiWS CSC ont permis d'observer des feuillets WS 2 avec une longueur moyenne de 2,5 nm avec un empilement moyen de 2. La présence de particules de tailles inférieures à 1,0 nm, aussi observées par MET par d'autres auteurs, ont été attribuées à des nanoparticules de WS 2 [Zaikovskii et al., 1984] ou à une phase oxysulfure non cristalline WO x S y . [Stockmann et al., 1995;Reinhoudt et al., 1998;Kooyman et al., 2001] Okamoto et al. [2009] ont d'ailleurs observé que ces particules étaient moins visibles quand la température de sulfuration augmentait.

Des analyses XPS effectuées sur des catalyseurs supportés sur ASA (30 % pds. SiO 2 ), préparés par co-imprégnation de [W(OEt) 5 ] 2 et nickel bis-méthylcyclopentadienyl (Ni(1-MeCp) 2 ), solubilisés dans l'hexane, ont confirmé la présence de phase WS 2 , NiWS et NiS [Roukoss et al., 2009]. L'utilisation de ces précurseurs a permis d'améliorer le taux de promotion (i.e. la quantité de Ni incorporée dans une phase NiWS) jusqu'à 17 % pour une phase WS 2 déposée par voie CSC. La quantité de phase . NiS reste équivalente à celle observée sur des catalyseurs conventionnels.

Ainsi, la littérature montre donc que l'ajout du promoteur augmente significativement l'activité des catalyseurs sulfures. Cependant, il est nécessaire d'adapter la quantité de promoteur ajouté afin d'obtenir un rapport promoteur/métal optimal pour la réaction désirée. D'après les résultats présentés par Yermakov et al. [1984] sur des catalyseurs NiW et NiMo déposés sur silice, un rapport atomique Ni/M (at/at) proche de 0,4 (M = W, Mo) permet d'obtenir une activité catalytique maximale en HDS du thiophène (350°C). En HDS du dibenzothiophène, Halbert et al. [1991] montre que l'activité n'augmente plus pour des phases CoMoS supportées sur alumine qui présentent un rapport atomique Co/Mo situé entre 0,2 et 0,3.

On peut noter que dans le cas d'un catalyseur d'hydrogénation conventionnel, comme un catalyseur CoMoS/Al 2 O 3 , le rapport Co/Mo maximal à partir duquel la vitesse intrinsèque d'HYD du toluène (mol (toluène) /mol (Mo) /h) n'augmente plus se situe vers Co/Mo = 0,3 (at/at). [Gandubert et al., 2008]. Un résultat similaire est obtenu par Marchand et al. [Marchand et al., 2009] pour des phases NiMoS/Al 2 O 3 , avec un rapport maximal Ni/Mo (at/at) situé entre 0.2 et 0.

I.6. Conclusion et stratégie de la thèse

Cette étude bibliographique a mis en avant que l'approche dite de «chimie de surface contrôlée» ou «CSC» est prometteuse pour élaborer de nouveaux catalyseurs d'hydrotraitement plus actifs que les catalyseurs conventionnels. Cette méthode de préparation permet d'améliorer la répartition de la phase métallique sur le support, d'obtenir une quantité plus importante de phase sulfure. De plus cette voie de synthèse entraine une amélioration significative de l'activité catalytique en HDS, aussi bien sur silice, que sur alumine. Le Tableau Dans le cas de la préparation de catalyseurs promus NiW, on pourra envisager d'introduire le précurseur de Ni en co-imprégnation avec le précurseur de W, ou directement sur une phase oxyde de tungstène, ou bien encore directement sur une phase pré-sulfurée. Le dépôt par imprégnation sera privilégié, comme pour la préparation des matériaux non promus.

Part II. Experimental

II.1. Products and materials

All experiments were carried out by using standard Schlenk and glove-box techniques.

Solvents were purified and dried by a solvent purification system (SPS-M-Braun) before being freeze-pumped and stored over 4 Å molecular sieves under argon. Dry ethanol was purchased from Sigma Aldrich, and was also degassed and stored over 4 Å molecular sieves under argon.

[W(OEt) 5 ] 2 (94%), W(OEt) Compressed air was used for both bearing and driving the rotors. Anisotropic dipolar interactions were suppressed by rotating the sample about an axis oriented at 54.74° with respect to the external field, called the Magic Angle Spinning (MAS). In 1 H MAS spectra, the delay between each scans was fixed from 1 to 10 s, to allow for the complete relaxation of the 1 H nuclei. For 13 C CPMAS NMR experiments, a typical cross-polarization (CP) sequence was used to improve the signal/noise ratio: 90° rotation of the 1 H magnetization (impulsion length, 3.8 µs), and then contact between carbon and proton during T c ranging from 1.2 to 1.5 ms, and

Part II 74 finally recording of the spectrum under high-power decoupling. The recycling delay between each scans was fixed to 20 s. 13 C-1 H Heteronuclear Correlation (HETCOR) MAS NMR analyses were performed at ETH Zurich. Typically, more than 1.5k scans were recorded for the HETCOR spectra, using a Decoupling Using Mind Boggling Optimization (DUMBO) NMR sequence [Brown et al., 2004], with 128 increments, a recycling delay of 1 sec, and a contact time between carbon and proton set to 1.5 ms. Chemical shifts are given with the respect to TMS. All chemical shifts are reported in (δ) ppm II.2.b. X-ray photoelectron spectroscopy (XPS)

XPS sampling of the sulphide catalysts was performed in a glove box under argon atmosphere, with controlled oxygen and water level in order to avoid their partial reoxidation.

The samples were crushed and pressed onto an indium foil attached to the sample holder via a double side carbon tape. The sample holder was then moved directly to the introduction chamber of the XPS spectrometer, thanks to the special connection between the glove box and the XPS spectrometer. XPS spectra were recorded on a Kratos Axis Ultra instrument with an Al monochromator source (1486.6 eV) and a hemi-spherical analyzer operating at fixed pass energy of 40 eV. The measurements were made at ambient temperature in steps of 0.05 eV for nickel, 0.1 eV for sulphur and 0.1 eV for tungsten, and at a pressure lower than 1.10 -6 Pa in the sample analysis chamber. Binding energies (BE) of the various elements were referenced to the C 1s level of the contamination carbon at 284.6 eV. The curves were integrated applying a Shirley type baseline for sulphur and tungsten, and linear type baseline for nickel, carbon, oxygen, and aluminium. A Tougaard type baseline was used for silicium. The collected spectra were analyzed by using Vision2 XPS software. Decomposition of the S 2p, W 4f and Ni 2p XPS spectra were performed using the appropriate oxide and sulphide references as supported monometallic catalysts. The methodology, similar to that developed for CoMo [Gandubert et al., 2006;Gandubert et al., 2008] and NiMo [Guichard et al., 2008], has already been described

elsewere [Ben Tayeb et al., 2010] Briefly, the relative atomic concentration C i of the atom i was obtained from the measurement of the corresponding total peak area A i and the use of appropriate sensitivity factor RSF furnished by the constructor.

Experimental

75

To approach the relative atomic surface concentrations, all the atoms detected on the surface were taken into account in Eq. 1.

∑ = = = n i i i i i i i RSF A RSF A C 1 ) / ( / Eq. 1
For one atom, the signal obtained can be decomposed into different contributions relative to various chemical species. The calculation of the respective contribution of each peak area will lead to the knowledge of the relative proportion of each chemical form for a given atom. For example, in the case of W, W 4f photopeak decomposition exhibits 3 contributions attributed to W(VI) oxide (W 4f 7/2 = 36.0 eV, W 4f 5/2 = 38.1 eV), to W(IV) sulphide (W 4f 7/2 = 32.2 eV, W 4f 5/2 = 34.3 eV) [Kim et al., 1996;Reinhoudt et al., 2000;Sun et al., 2001;Zuo et al., 2004] and to W(V) oxisulphide WO x S y (W 4f 7/2 = 33.5 eV, W 4f 5/2 = 35.5 eV) [Hensen et al., 2007]. Note this latter contribution as also been tentatively attributed to WS 3 species [Coulier et al., 2002;Hensen et al., 2007]. The relative amount of WS 2 phase, also called "level of sulphidation" is given by Eq. 2:

100 3 2 2 2 x A A A A WS WO WOxSy WS WS + + = Eq. 2
The sulphidation level is described as the relative amount of W in a WS 2 phase.

Average results found for peculiar binding energies (BE) of W 4f and S 2p photopeaks are summarized as follows: Silica-alumina with a specific area of 229 m²/g was calcined for 6h under air (static conditions), using a ramp of 5°C/min up to 300°C. Then, the system was heated up to 500°C using a ramp of 5°C/min for the solid to be partially dehydroxylated (500°C) under high vacuum

BE (eV) W 4f 7/2 -W(IV) BE (eV) W 4f 7/2 -W(VI) FWHM (eV) W(IV) ∆BE (eV) (W 4f 7/2 W(IV) -S 2p
(5.10 -5 mbar) for ca. 16 h. The system was cooled down to 140°C using a ramp of 10°C/min, and the extrudates were stored in glovebox. After this treatment, the specific area was 225 m²/g. OH densities were measured as previously described for ASA -300 . [Cartes, 2012] [Cartes, 2012] IR (DRIFT): 100 % grafting on isolated SiOH, 2979SiOH, , 2935SiOH, , 2899SiOH, , 2880;;1472, 1447, 1384, 1357 cm -1 . E.A: 5.47 % wt. W.

II.3.a.2. Influence of the W-loading on surface complexes obtained by incipient wetness impregnation of [W(OEt) 5 ] 2

Synthesis of [W(OEt) 5 ] 2 -IWI-0.2/ASA -300 by incipient wetness impregnation. Representative procedure After stirring 0.141 g of [W(OEt) 5 ] 2 in cyclohexane (2 mL) for 10 min, an aliquot of 280 µl of the solution was used to impregnate 0.491 g of ASA -300 extrudates. After 16 h of maturation, the extrudates were dried under high vacuum (5 10 -5 mbar) for 2 h to give an off-white solid, which was stored in the glovebox. IR (DRIFT): 3743, 2982, 2937, 2905, 2877, 1448, 1396, 1387, 1359, 1268, 1258, 1243 cm -1 .

1 H MAS solid state NMR: 1.0 (W-O-CH 2 CH 3 + O ASA -CH 2 CH 3 ), 3.8 (O ASA -CH 2 CH 3 ), 5.0 (W-O-CH 2 CH 3 ). 13 C CPMAS solid state NMR: 15 (W-O-CH 2 CH 3 + O ASA -CH 2 CH 3 ), 59 (O ASA -CH 2 CH 3 ), 76 (W-O-CH 2 CH 3 ).
Synthesis of [W(OEt) 5 ] 2 -IWI-0.5/ASA -300

The material was prepared according to the procedure described above, with 0.871 g of [W(OEt) 5 ] 2 and 9.5 g of ASA -300 . An off-white solid was obtained. IR (DRIFT): 3743, 2981, 2937, Experimental 81 , 2879, 1447, 1396, 1387, 1359, 1268, 1261, 1246 cm -1 . 1 H MAS solid state NMR:

2904

1.0 (W-O-CH 2 CH 3 + O ASA -CH 2 CH 3 ), 3.8 (O ASA -CH 2 CH 3 ), 5.0 (W-O-CH 2 CH 3 ). 13 C CPMAS solid state NMR: 15 (W-O-CH 2 CH 3 + O ASA -CH 2 CH 3 ), 59 (O ASA -CH 2 CH 3 ), 75 (W-O-CH 2 CH 3 ).
E.A: 3.33 % wt. W, e.g. 0.5 (±0.1) W/nm².

Synthesis of [W(OEt) 5 ] 2 -IWI-0.8/ASA -300

The material was prepared according to the procedure described above, with 0.645 g of [W(OEt) 5 ] 2 and 3.945 g of ASA -300 . An off-white solid was obtained. IR (DRIFT): 2978, 2934, 2897, 2877, 2747, 2705, 1469, 1446, 1394, 1387, 1382, 1356, 1268, 1259, 1251 cm -1 . 1 H MAS

solid state NMR: 1.2 (W-O-CH 2 CH 3 + O ASA -CH 2 CH 3 ), 3.8 (O ASA -CH 2 CH 3 ), 5.0 (W-O-CH 2 CH 3 ). 13 C CPMAS solid state NMR: 16 (W-O-CH 2 CH 3 + O ASA -CH 2 CH 3 ), 59 (O ASA -CH 2 CH 3 ), 71 (W-O-CH 2 CH 3 ). E.A: 5.03 % wt. W, e.g. 0.8 (±0.1) W/nm². Synthesis of [W(OEt) 5 ] 2 -IWI-1.7/ASA -300
The material was prepared according to the procedure described above, with 3.359 g of [W(OEt) 5 ] 2 and 10.16 g of ASA -300 . A light brown/yellowish solid was obtained. IR (DRIFT): 2978, 2934, 2897, 2869, 2742, 2700, 1468, 1444, 1394, 1380, 1354, 1246, 1241 cm -1 . The material was prepared according to the procedure described above. A solution (0.50 mL) of a cyclohexane with 0.393 g of [W(OEt) 5 ] 2 was prepared. An aliquot of 0.25 mL of the solution was used to impregnate ca. 0.4 g of ASA -300 . A light brown/yellowish solid was obtained.

1 H MAS solid state NMR: 1.2 (W-O-CH 2 CH 3 + O ASA -CH 2 CH 3 ), 3.8 (O ASA -CH 2 CH 3 ), 5.0 (W-O-CH 2 CH 3 ).
IR (DRIFT): 2972(DRIFT): , 2929(DRIFT): , 2891(DRIFT): , 2869(DRIFT): , 2741(DRIFT): , 2699(DRIFT): , 1733 (w) (w), 1600 (w), 1469 (m), 1445 (m), 1379

(s), 1359 (m) cm -1 . Synthesis of [W(OEt) 5 ] 2 -IWI-3.7/ASA -300
The material was prepared according to the procedure described above, with 3.347 g of [W(OEt) 5 ] 2 and 5.346 g of ASA -300 . A light brown/yellowish solid was obtained. IR: 100% grafting on isolated SiOH. E.A: 21.0 %wt. W, e.g. 3.7 (±0.1) W/nm².

Synthesis of [W(OEt) 5 ] 2 -IWI-4.0/ASA -300

The material was prepared according to the procedure described above. 0.50 mL of the solution was used to impregnate 0.479 g of ASA -300 . A light brown/yellowish solid was obtained.

Part II

82

IR (DRIFT): 2976(DRIFT): , 2931(DRIFT): , 2896(DRIFT): , 2871(DRIFT): , 2741(DRIFT): , 2697(DRIFT): , 1658(DRIFT): (vw), 1608 (vw) (vw). 1468 (m), 1445 (m), 1379 (s), 1351 (m) cm -1 .

Synthesis of [W(OEt) 5 ] 2 -IWI-5.0/ASA -300

The material was prepared according to the procedure described above, with 0.457 g of [W(OEt) 5 ] 2 and 489.3 mg of ASA -300 . A brown/yellowish solid was obtained. IR (DRIFT): 2976, 2931, 2893, 2871, 2741, 2697, 1658 (vw), 1608 (vw), 1468 (m), 1445 (m), 1379 (s), 1352 (m) cm -1 .

II.3.a.3. Investigation of the structure of surface species as a function of W-loading by

using 13 C labelled [W(OEt * ) 5 ] 2 (carbon-13 labelled on the methylene carbon).

Synthesis of 13 C labelled pentaethoxide tungsten (V), referred as [W(OEt * ) 5 ] 2

[W(OEt) 5 ] 2 and 5 equiv. of CH 3

13

CH 2 OH were stirred for 6 h. After evacuation of ethanol under vacuum (10 -2 mbar), the reaction mixture was dried (2 h, 10 -5 mbar), affording a solution containing a white precipitate. After filtration, the solution contained pure [W(OEt * ) 5 ] 2 , 20-30% labelled in position 1. Yield: 86 %. IR (ATR): 2969, 2926, 2892, 2862, 2732 (vw), 2693 (vw), 1737 (vw), 1466, 1441, 1372, 1348, 1275, 1146, 1092 (m), 1054 (s), 1041 (sh), 907, 630, 531

cm -1 . 1 H NMR (CD 2 Cl 2 , 298K): 1.22 (t, W-O-CH 2 CH 3 , J(H-H)=7 Hz), 4.77 (q, W-O-CH 2 CH 3, ,
J(H-H)=7 Hz), 4.53 (q, W-O-13 CH 2 CH 3 , J(H-H)=7 Hz), 5.00 (q, W-O-13 CH 2 CH 3 , J(H-H)=7 Hz),

J( 13 C-H)=144 Hz. 13 C{ { { {1H} } } } NMR (CD 2 Cl 2 , 298K): 18.0 (W-O-CH 2 CH 3 ), 68.0 (W-O-CH 2 CH 3 ).
Synthesis of 13 C labelled [W(OEt * ) 5 ] 2 -IWI-0.2/ASA -300 . Representative procedure for incipient wetness impregnation After stirring 0.159 g of carbon-13 labelled [W(OEt * ) 5 ] 2 in cyclohexane (V sol = 2 mL) for 10 min, an aliquot of 800 µl of the solution was used to impregnate 1.457 g of ASA -300 extrudates.

After 16 h of maturation, the extrudates were dried under high vacuum (5 10 -5 mbar) for 2 h to give an off white solid, which was stored in the glovebox. IR: 3744 (m), 3532 (vbr), 2982, 2937, 2901, 2879, 1471 (vw), 1459 (sh), 1450 (m), 1396 (sh), 1386 (m), 1359

(vw) cm -1 . 1 H MAS solid state NMR: 1.1 (O ASA -CH 2 CH 3 + W-O-CH 2 CH 3 ), 1.7 (SiOH), 3.7 (O ASA -CH 2 CH 3 ) 4.9 (W-O-CH 2 CH 3 ). 13 C MAS solid state NMR: 14 (O ASA -CH 2 CH 3 + W-O-CH 2 CH 3 ), Synthesis of 13 C labelled [W(OEt * ) 5 ] 2 -IWI-0.5/ASA -300
After stirring 0.162 g of carbon-13 labelled [W(OEt * ) 5 ] 2 in cyclohexane (V sol = 1 mL) for 10 min, an aliquot of 430 µl of the solution was used to impregnate 0.801 g of ASA -300 extrudates.

After 16 h of maturation, the extrudates were dried under high vacuum (5 10 -5 mbar) for 2 h to give an off white solid, which was stored in the glovebox. IR: 3744 (w), 3532 (vbr), 2982, 2937, 2901, 2879, 1471 (w), 1459 (sh), 1447 (m), 1396 (sh), 1385 (m), 1358 (vw) cm -1 . 1 H MAS solid state NMR:

1.0 (O ASA -CH 2 CH 3 + W-O-CH 2 CH 3 ), 3.7 (O ASA -CH 2 CH 3 ), 4.9 (W-O-CH 2 CH 3 ). 13 C MAS solid state NMR: 15 (O ASA -CH 2 CH 3 + W-O-CH 2 CH 3 ), 59 (O ASA -CH 2 CH 3 ), 73 (W-O-CH 2 CH 3 ). E.A: 3.49 % wt. W, e.g. 0.5 (±0.1) W/nm². Synthesis of 13 C labelled [W(OEt * ) 5 ] 2 -IWI-0.6/ASA -300
After stirring 0.225 g of carbon-13 labelled [W(OEt * ) 5 ] 2 in cyclohexane (V sol = 1 mL) for 10 min, an aliquot of 460 µl of the solution was used to impregnate 804 mg of ASA -300 extrudates.

After 16 h of maturation, the extrudates were dried under high vacuum (5 10 -5 mbar) for 2 h to give an off white solid, which was stored in the glovebox. IR: 3742 (vw), 3462 (vbr) 2980, 2936, 2900, 2877, 1487 (sh), 1472 (w), 1457 (sh), 1447 (w), 1394 (sh), 1383 (m), 1359 (w) cm -1 . After stirring 0.088 g of carbon-13 labelled [W(OEt * ) 5 ] 2 in cyclohexane (V sol = 370 µL) for 10 min, the solution was used to impregnate 0.602 g of ASA -300 extrudates. After 16 h of maturation, the extrudates were dried under high vacuum (5 10 -5 mbar) for 2 h to give an off white solid, which was stored in the glovebox. IR: 3462 (vbr) 2979, 2936, 2900, 2877, 1472 (w), 1457 (sh), 1447 (w), 1394 (sh), 1383 (m), 1357 (w) cm -1 . 1 H MAS solid state NMR:

1 H MAS solid state NMR: 1.1 (O ASA -CH 2 CH 3 + W-O-CH 2 CH 3 ), 3.8 (O ASA -CH 2 CH 3 ) 5.0 (W-O-CH 2 CH 3 ). 13 C MAS solid state NMR: 16 (O ASA -CH 2 CH 3 + W-O-CH 2 CH 3 ), 59 (O ASA -CH 2 CH 3 ), 73 (W-O-CH 2 CH 3
1.2 (O ASA -CH 2 CH 3 + W-O-CH 2 CH 3 ), 3.8 (O ASA -CH 2 CH 3 ) 5.0 (W-O-CH 2 CH 3 ). 13 C MAS solid state NMR: 16 (O ASA -CH 2 CH 3 + W-O-CH 2 CH 3 ), 59 (O ASA -CH 2 CH 3 ), 72 (W-O-CH 2 CH 3 ). E.A: 4.64 % wt.
W, e.g. 0.7 (±0.1) W/nm².

Synthesis of 13 C labelled [W(OEt * ) 5 ] 2 -IWI-0.9/ASA -300

After stirring 0.315 g of carbon-13 labelled [W(OEt * ) 5 ] 2 in cyclohexane (V sol = 1 mL) for 10 min, an aliquot of 800 µL of the solution was used to impregnate 1.461 g of ASA -300 extrudates.

After 16 h of maturation, the extrudates were dried under high vacuum (5 10 -5 mbar) for 2 h to give an off white solid, which was stored in the glovebox. IR: 3532 (vbr), 2982, 2928, 2901, 2879, 2746, 2698, 1734 (vw) After mixing 0.230 g of carbon-13 labelled [W(OEt * ) 5 ] 2 with cyclohexane (V sol = 360 µL) for 1 min, an aliquot of 330 µL of the solution was used to impregnate 0.578 g of ASA -300 extrudates.

After 16 h of maturation, the extrudates were dried under high vacuum (5 10 -5 mbar) for 2 h to give a light brown/yellowish solid, which was stored in the glovebox. IR (DRIFT) 3545 (vbr), 2973, 2931, 2892, 2869, 2738 (vw), 2700 (vw), 1734 (vw), 1600 (vw), 1482 (sh), 1468, 1445,

1377, 1352 cm -1 . 1 H MAS solid state NMR: 1.2 (O ASA -CH 2 CH 3 + W-O-CH 2 CH 3 ), 3.8 (O ASA -CH 2 CH 3 ), 4.8 (W-O-CH 2 CH 3 ). 13 C MAS solid state NMR: 17 (O ASA -CH 2 CH 3 ), 18 (W-O-CH 2 CH 3 ), 58 (O ASA -CH 2 CH 3 ), 68 & 70 (W-O-CH 2 CH 3 ). Synthesis of 13 C labelled [W(OEt * ) 5 ] 2 -G-0.5/ASA -300 (grafting)
After stirring 0.336 g of carbon-13 labelled [W(OEt * ) 5 ] 2 (0.82 mmol, 1.5 equiv.) with cyclohexane (1.5 mL) for 10 min, the solution was used to impregnate 0.446 g of ASA -300 extrudates (0.54 mmol OH, 1.22 mmol OH/g(ASA)). The mixture was slowly stirred for 16 h and the solid was washed 3 times (30min) with cyclohexane before being dried under high vacuum (5 10 -5 mbar) for 2 h, to give an off white solid, stored in the glovebox. IR: 100 % grafting on isolated SiOH, 2978, 2934, 2898, 2875, 1470, 1447, 1382, 1355 cm -1 . 1 H MAS solid state NMR: After stirring 0.221 g of a mixture of carbon-13 labelled ethanol and non labelled ethanol (50/50 vol/vol) with cyclohexane (V sol = 1 mL) for 10 min, an aliquot of 550 µL of the solution was used to impregnate 1.001 g of ASA -300 . After 16 h of maturation, the extrudates were dried under high vacuum (5 10 -5 mbar) for 16 h to give an off white solid, stored in the glovebox.

1.1 (W-O-CH 2 CH 3 + O ASA -CH 2 CH 3 ), 3.8 (O ASA -CH 2 CH 3 ), 5.0 (W-O-CH 2 CH 3
Subsequent washing with 3 mL of cyclohexane was performed. The solid was dried under high vacuum (5 10 -5 mbar) for 2 h to give an off white solid. 1983,1866,1638

(Si-O-Si) cm -1 Synthesis of 13 C labelled [W(OEt * ) 5 ] 2 -G-0.7/SiO 2-700 (grafting)
After stirring 0.115 g of carbon-13 labelled [W(OEt * ) 5 ] 2 (0.28 mmol, 3.4 equiv.) with cyclohexane (1.5 mL) for 10 min, the solution was used to impregnate 0.308 g of silica powder dehydroxylated at 700ºC (0.08 mmol OH, 0.27 mmol OH/g(SiO 2 )). The mixture was gently stirred for 16 h, and the solid was washed 3 times (30 min) with cyclohexane before being dried under high vacuum (5 10 -5 mbar) for 2 h, to give an off white solid, stored in the glovebox.

IR: 100 % grafting on isolated SiOH, 2978, 2934, 2898, 2875, 1470, 1447, 1382, 1355 cm -1 . γ-alumina (2 g) with a specific surface of 289 m²/g was calcined under air (static conditions) for 16h using a ramp of 5°C/min up to 500°C. Then, air was evacuated for ca. 30 min under high vacuum (5.10 -5 mbar), and the solid was cooled down to 140°C (20°C/min). Afterwards, alumina was stored in the glovebox. Subsequently, 1 g of solid was contact with a vapour of distilled/degassed water, and heated up to 300°C using a ramp of 5°C/min for 30 min. Then, the temperature was increased up to 450°C (5°C/min) and the residual vapour of water was evacuated under high vacuum for 16h at 450°C. Finally, alumina was cooled down to 140°C (20°C/min) and was stored in the glovebox. OH density: between 3.0 and 3.5 OH/nm² according Part II 86 to the literature [Rascon et al., 2011]. IR: 3793 (vw), 3771, 3756, 3730, 3684, 3636, 3588 (w, vbr), 1364 cm -1 Synthesis of 13 C labelled [W( OEt * ) 5 ] 2 -G-0.5/Al 2 O 3-450 (grafting) After stirring 0.419 g of carbon-13 labelled [W(OEt * ) 5 ] 2 (1.02 mmol, 1.5 equiv.) with cyclohexane (1.5 mL) for 10 min, the solution was used to impregnate 0.451 g of Al 2 O 3-450 extrudates (0.69 mmol OH, ca. 1.54 mmol OH/g(Al 2 O 3 )). The reaction mixture was slowly stirred for 16 h and the solid was washed 3 times (30 min) with cyclohexane before being dried under high vacuum (5 10 -5 mbar) for 2 h, to give an off white solid, stored in the glovebox. IR: 2969, 2934, 2898, 2875, 1470, 1447, 1382, 1355 cm -1 . 1 H MAS solid state NMR: 1.1, 4.4. 13 C CPMAS

1 H MAS solid state NMR: 1.0 (W-O-CH 2 CH 3 + O SiO2 -CH 2 CH 3 ), 3.6 (O SiO2 -CH 2 CH 3 ), 4.7 (W-O-CH 2 CH 3 ). 13 C CPMAS solid state NMR: 15 (W-O-CH 2 CH 3 + O SiO2 -CH 2 CH 3 ), 59 (O SiO2 -CH 2 CH 3 ), 72 (W-O-CH 2 CH 3
solid state NMR 18 (W-O-CH 2 CH 3 + O Al2O3 -CH 2 CH 3 ), 60 (O Al2O3 -CH 2 CH 3 ), 72 (W-O-CH 2 CH 3 ).
27 Al MAS NMR: 70 (Al IV ), 39 (Al V ), 11 (Al VI ). E.A: 4.41 % wt. W, e.g. 0.5 (±0.1) W/nm².

Synthesis of Et

* OH/Al 2 O 3-450
After mixing 86 µL of carbon-13 labelled ethanol with cyclohexane (V sol = 275 µL) for 1 min, an aliquot of 180 µL of the solution was used to impregnate 0.225 g of Al 2 O 3-450 extrudates. After 16 h of maturation, the extrudates were dried under high vacuum (5 10 -5 mbar) for 16 h to give an off white solid, Subsequent washing with 3 mL of cyclohexane was performed. The, the solid was dried under high vacuum (5 10 -5 mbar) for 2 h to give an off white solid. IR: 3729, 3707, 3668, 3559 OH group: 61% consumed. 2963, 2929, 2892, 2871, 1491, 1448, 1382 cm -1 .

II.3.d. Preparation of conventional dried and calcined materials

Conventional dried and calcined materials were prepared by incipient wetness impregnation of an aqueous solution of ammonium metatungstate on ASA (co-impregnation) followed by a maturation step of 16 h. Subsequent drying at 120°C gave the sample referred as "dried".

"Calcined" materials were obtained by subsequent calcination under air, at atmospheric pressure, with a flow rate of 1.5 L/g(cat)/h, at 450°C for 2 h.

II.4. Preparation of non-promoted sulphide materials (bulk)

Synthesis of bulk WS 2 [W(OEt) 5 ] 2 (ca. 200 mg) was loaded into a small glass holder, which was placed in a sulphidation cell. After 4 h of sulphidation at atmospheric pressure, at 23°C, with a 15 % mol.

H 2 S/H 2 mixture, the temperature was raised to 150°C (2°C/min). The system was finally cooled down to room temperature (20°C/min) , and evacuated at ca. 1 mbar for 20 min. A brown powder was obtained, and was subsequently treated with a 15 % mol. H 2 S/H 2 mixture at 600°C (using a ramp of 5°C/min) for 6 h. The system was cooled down, and evacuated at ca. 1 mbar for 20 min. The resulting metallic grey powder was stored in the glovebox. XPS: 92 % rel. WS 2 .

II.5. Synthesis of non-promoted sulphide catalysts supported on ASA

Synthesis of WS 2 -ex.[W(OEt) 5 ] 2 -G-0.7/ASA -500 at T sulph. = 350°C. Representative Procedure About 2 g of [W(OEt) 5 ] 2 -G-0.7/ASA -500
were placed in a sulphidation cell under argon (glovebox). The cell was plugged to the sulphidation apparatus, and the gas outlet was purged with argon. Then, a mixture of H 2 S/H 2 (15 % mol . H 2 S, 1 atm) with a flow rate of 2 L/g(cat)/h, was passed onto the catalysts which was heated up to 350°C, using a ramp of 5°C/min. After 2 h at 350°C, the sulphide gas was switched to argon (same flow rate), and the system was cooled down to 250°C (12°C/min). After 2 h at 250°C, the system was cooled down to 120°C (20°C/min). At 120°C, the cell was evacuated for 5 min at ca. 1 mbar and cooled down to room temperature (vide infra). The resulting sulphide material (black solid) was either sealed in ampoules or directly stored in glovebox. XPS: 71 % rel WS 2 Synthesis of WS 2 -ex.W(OEt) 6 -G-0.7/ASA -500 at T sulph. = 350°C

The sample was prepared according to the procedure described above, at a sulphidation temperature of 350°C. XPS:

72 % rel WS 2 Synthesis of WS 2 -ex.[W(O)(OEt) 4 ] 2 -G-0.8/ASA -500 at T sulph. = 350°C
The sample was prepared according to the procedure described above, at a sulphidation temperature of 350°C. XPS: 72 % rel WS 2 Synthesis of WS 2 -ex.[W(OEt) 5 ] 2 -IWI-0.5/ASA -300 at T sulph. = 350°C

The sample was prepared according to the procedure described above, at a sulphidation temperature of 350°C. XPS: 76 % rel WS 2 Part II Synthesis of WS 2 -ex.[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 at T sulph = -25°C About 1 g of [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 was placed in a sulphidation cell under argon (glovebox). The system was cooled down and maintained at -25°C in a cold bath of acetone.

After 30 min, the sulphidation step was started by passing a mixture of H 2 S/H 2 (15% mol. H 2 S) at a flow rate of 2 L/g(cat)/h at atmospheric pressure for 2 h. Then, the gas inlet was switched to argon (same flow rate) for 2 h and allowed to return to room temperature. Finally, the cell was evacuated during 1 hour at ca. 1 mbar, and the light brown solid catalyst was stored inside the glovebox. XPS:

30 % rel WS 2 Synthesis of WS 2 -ex.[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 at T sulph. = 23°C
About 1 to 2 g of [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 were placed in a sulphidation cell under argon (glovebox), at room temperature. The cell was plugged on the sulphidation apparatus, the gas outlet was purged under argon, and the inlet was set to a mixture of H 2 S/H 2 (15 % mol . H 2 S) with a flow rate of 2 L/g(cat)/h (atmospheric pressure), for 2 h. Afterwards, the gas inlet was switched to argon (same flow rate) for 2 h, at the same temperature. Finally, the cell was evacuated during 1 h at ca. 1 mbar and the brown solid was stored inside a glovebox. XPS:

49 % rel WS 2 Synthesis of WS 2 -ex.[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 at T sulph. = 50°C
About 1 to 2 g of [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 was placed in a sulphidation cell under argon (glovebox). The cell was plugged on the sulphidation apparatus, the gas outlet was purged under argon, and the inlet was set to a mixture of H 2 S/H 2 (15 % mol . H 2 S) with a flow rate of 2 L/g(cat)/h (atmospheric pressure). After 2 h at 50°C, the gas inlet was switched to argon (2 L/g(cat)/h) and the reaction conditions kept constant for 2 h. Finally, the cell was evacuated for 1 h at ca. 1 mbar, and the black solid was stored inside a glovebox. XPS: 58 % rel WS 2 Synthesis of WS 2 -ex.[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 at T sulph. = 150°C

The sample was prepared according to the same procedure as WS 2 -ex.[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 (T sulph = 50°C), at a sulphidation temperature of 150°C. XPS: 68 % rel WS 2 .

Synthesis of WS

2 -ex.[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 at T sulph. = 250°C
The sample was prepared according to the same procedure as WS 2 -ex.[W(OEt) 5 ] 2 -G-0.7/ASA -500 (representative one), at a sulphidation temperature of 250°C. XPS: 75 % rel WS 2 .

Synthesis of WS

2 -ex.[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 at T sulph. = 350°C
The sample was prepared according to the representative procedure, at a sulphidation temperature of 350°C. XPS: 85 % rel WS 2 .

Synthesis of WS

2 -ex.[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 at T sulph. = 450°C
The sample was prepared according to the representative procedure, at a sulphidation temperature of 450°C. XPS: 82 % rel WS 2 .

Synthesis of WS 2 -ex.[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 at T sulph. = 600°C

The sample was prepared according to the representative procedure, at a sulphidation temperature of 600°C. XPS: 87 % rel WS 2 Synthesis of sulphide catalysts based on conventional oxide dried or calcined catalyst were prepared according to the representative procedure (from 23°C to 600°C)

II.6. Preparation of nickel-promoted materials

II.6.a. Preparation of conventional dried and calcined oxide materials Conventional dried and calcined materials were prepared by incipient wetness impregnation of an aqueous solution of ammonium metatungstate and nickel nitrate on ASA (coimpregnation) followed by a maturation step of 16 h. Subsequent drying at 120°C gave the sample referred as "dried". "Calcined" materials were obtained by subsequent calcination under air, at atmospheric pressure, with a flow rate of 1.5 L/g(cat)/h, at 450°C for 2 h. II.6.b. Preparation of CSC materials, prior to sulphidation Synthesis of Ni(acac) 2 /ASA -300 Ni(acac) 2 (0.160 g) was stirred in hot toluene (75 to 80°C) for 3 h (2 mL, 0.31 mol/L) to give an homogeneous emerald green solution. ASA -300 (0.910 g) was impregnated with 460 µL of this hot solution under manual stirring. After 16 h of maturation, the solvent was evacuated under high vacuum (5 10 -5 mbar) for 2 h to give light green extrudates, which were stored in the glovebox. IR (DRIFT): 3742 (isolated SiOH, 66 % consumed), 3084, 3006, 2930, 1600, 1581 (sh), 1533, 1517 (sh), 1407 (sh) cm -1 . EA: 0.93 % wt. , e.g. 0.4 (±0.1) Ni/nm².

Part II

90

Synthesis of Ni(1-MeCp) 2 /ASA -300

Ni(1-MeCp) 2 (0.114 g) was stirred for 15 min in cyclohexane (2 mL; 0.26 mol/L) to give a dark green solution. An aliquot of 620 µL of this solution was taken to impregnate 1.20 g of ASA -300 , which turned immediately dark green. After 16 h of maturation, the solvent was evacuated under high vacuum (5 10 -5 mbar) for 2 h to give dark green extrudates, which were stored in the glovebox. IR: 3742 (isolated SiOH,50 % consumed),3113,3088,2934,2872,1511,EA: 1.02 % wt. , e.g. 0.4 (±0.1) Ni/nm².

II.6.b.1. Deposition of nickel precursors onto tungsten surface species

Synthesis of Ni(acac) 2 -IWI-0.21/[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 . Representative procedure Ni(acac) 2 (0.456 g) was stirred for 3 h in hot toluene (75 to 80°C) (5 ml, 0.33 mol/L) to give an emerald green solution. An aliquot (410 µL) of this hot solution was used to impregnate 1.565 g of [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 , which turned green. After 16 h of maturation, the solvent were evacuated under high vacuum (5 10 -5 mbar) for 2 h to give light green extrudates, which were stored in the glovebox. Traces of an off-white product were observed on the glassware. E.A: 10.17 % wt. W, e.g. 1.6 (±0.1) W/nm²; 0.68 % wt. Ni, e.g. Ni/W = 0.21.

Synthesis of Ni

(acac) 2 -IWI-0.44/[W(OEt) 5 ] 2 -IWI-1.7/ASA -300
The sample was prepared according to the same procedure. E.A: 9.52 % wt. W, e.g. 1.5 (±0.1) W/nm²; 1.35 % wt. Ni, e.g. Ni/W = 0.44.

Synthesis of Ni

(acac) 2 -IWI-1.00/[W(OEt) 5 ] 2 -IWI-1.7/ASA -300
The sample was prepared according to the same procedure, with 2 successive impregnations of a toluene solution of Ni(acac) 2 (0.64 mol/L, same target as for Ni/W ≈ 0.4 (at/at)). E.A: 9.26 % wt. W, e.g. 1.5 (±0.1) W/nm²; 2.96 % wt. Ni, e.g. Ni/W = 1.00.

Synthesis of Ni

(1-MeCp) 2 -IWI-0.21/[W(OEt) 5 ] 2 -IWI-1.7/ASA -300
Ni(1-MeCp) 2 (0.166 g) was stirred in 3 mL of cyclohexane for 15 min to give a dark green solution. An aliquot of 780 µL of this solution was slowly added to impregnate 1.50 g of [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 , which turned dark green. After 16 h of maturation, the solvent was evacuated under high vacuum (5 10 -5 mbar) for 2 h to give dark extrudates, which were stored in the glovebox.

Experimental

91 Synthesis of Ni(NO 3 ) 2 -IWI-0.30/[W(OEt) 5 ] 2 -IWI-1.7/ASA -300
Ni(NO 3 ) 2 (0.488 g) was stirred in 5 mL of ethanol for 15 min to give a colourless solution. An aliquot of 600 µL of this solution was slowly added to impregnate 1.49 g of [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 , which turned light green. After 16 h of maturation, the solvent was evacuated under high vacuum (5 10 -5 mbar) for 2 h to give green extrudates, which were stored in the glovebox. E.A: 9.56 % wt. W, e.g. 1.6 (±0.1) W/nm²; 0.92 % wt. Ni, e.g. Ni/W = 0.30. Synthesis of Ni(acac) 2 -0.22/W(POM)-IWI-1.8/ASA Ni(acac) 2 (0.478 g) was stirred for 3 h in hot toluene (75 to 80°C) (5 ml, 0.40 mol/L) to give an emerald green solution. An aliquot (1.2 mL) of this hot solution was used to impregnate 2.95 g of a conventionally prepared ASA supported dried oxide phase (referred as W(POM)-IWI-1.8/ASA, 11.4 % wt. W) The solid turned green. After 16 h of maturation, the solvent was evacuated under high vacuum (5 10 -5 mbar) for 2 h to give light green extrudates. E.A: 11.09 % wt. W, e.g. 1.8 (±0.1) W/nm²; 0.78 % wt. Ni, e.g. Ni/W = 0.22.

II.6.b.2. Deposition of nickel precursors onto tungsten sulphide materials

Synthesis of Ni(acac) 2 -IWI-0.20/WS 2-350°C /ASA -300
Ni(acac) 2 (0.341 g) was stirred for 3 h in hot toluene (75 to 80°C) (5 mL, 0.27 mol/L) to give an emerald green solution. An aliquot (900 µL) of this hot solution was used to impregnate 1.72 g of a dark sulphide material referred as WS 2-350°C /ASA -300 .,Dark extrudates were obtained.

After 16 h of maturation, the solvent was evacuated under high vacuum (5 10 -5 mbar) for 2 h to give a dark solid, stored in the glovebox. E.A: 9.89 % wt. W, e.g. 1.7 (±0.1) W/nm²; 0.66 % wt. Ni, e.g. Ni/W = 0.20. Synthesis of Ni(acac) 2 -IWI-0.24/WS 2-23°C /ASA -300 Ni(acac) 2 (0.345 g) was stirred for 3 h in hot toluene (75 to 80°C) (5 ml, 0.27 mol/L) to give a emerald green solution. An aliquot (800 µL) of this hot solution was used to impregnate 1.575 g of a brown sulphide material, prepared at 23°C (referred as WS 2-23°C /ASA, see preparation on WS 2 -ex.[W(OEt) 5 ] 2 -IWI-1.7/ASA -300 at T sulph. = 23°C). Brown extrudates were obtained. After 16 h of maturation, the solvent was evacuated under high vacuum (5 10 -5 mbar) for 2 h to give a brown solid, stored in the glovebox. Traces of an off-white product were observed on the glassware. E.A: 10.03 % wt. W, e.g. 1.6 (±0.1) W/nm²; 0.79 % wt. Ni, e.g. Ni/W = 0.24.

Part II

92

Synthesis of Ni(acac) 2 -IWI-0.44/WS 2-23°C /ASA -300 Ni(acac) 2 (0.692 g) was stirred for 3 h in hot toluene (75 to 80°C) (5 ml, 0.54 mol/L) to give a emerald green solution. An aliquot (790 µL) of this hot solution was used to impregnate 1.536 g of a brown sulphide material, prepared at 23°C (referred as WS 2-23°C /ASA). Brown extrudates were obtained. After 16 h of maturation, the solvent was evacuated under high vacuum (5 10 -5 mbar) for 2 h to give a brown solid, stored in the glovebox. Traces of an off-white product were observed on the glassware.

Synthesis of Ni(acac) 2 -IWI-0.85/WS 2-23°C /ASA -300
The sample was prepared with 2 successive impregnations of a toluene solution of Ni(acac) 2 (0.54 mol/L). The first one of the two impregnations was performed on 1.58 g of a brown sulphide material, prepared at 23°C (referred as WS 2-23°C /ASA) . E.A: 9.17 % wt. W, e.g. 1.5 (±0.1) W/nm²; 2.49 % wt. Ni, e.g. Ni/W = 0.85.

II.7. Preparation of nickel-promoted sulphide catalysts

Sulphide materials, either prepared via a CSC or a conventional method, were prepared according to the representative procedure, with a sulphidation temperature of 350°C

II.8. Catalytic test

Catalytic activity measurements in toluene hydrogenation (HYD) were carried out in a 16 fixed beds unit reactor Flowrence from Avantium using ca. 450 µl of catalyst. The mass required was calculated from the density of the whole extrudate, unless otherwise stated. Zirconia-based materials are used in the top and the bottom of the reactor in order to correctly set the catalyst bed and fill the void space.

The model feed was composed of dimethyldisulphide (DMDS 5.8 % wt. ) and toluene (20 % wt. ), cyclohexane (74.2 % wt. ) and aniline (0.5 % wt. ). DMDS is decomposed to CH 4 and H 2 S, which maintain the sulphided state of catalyst during test. The hydrogen to feed ratio (H 2 /HC) was 450 NL/L during test and in situ pre-sulphidation step. In order to avoid cracking reactions of catalysts and measure a more accurate value of hydrogenation, the catalysts were tested in the presence of aniline to moderate the acidity [Ben Tayeb et al., 2010]. To this end, aniline was added to the feed and the operating conditions were adapted to allow hydrogenation (and isomerisation) reactions without cracking products formation. The experimental condition was strictly similar for all tests.

Note that the in situ pre-sulphidation of the catalysts was conducted at a liquid hourly space velocity (LHSV) of 4 h -1 with a total pressure of 6 MPa for 2.5 h, during which the temperature increased from 70°C to 350 °C with a ramp of 2 °C/min. Then, the liquid hourly space velocity was turned down to 2 h -1 . Liquid products of the reaction were analyzed by gas chromatography using a DB1 column. Each reactor was analyzed six times over the course of 9 hours (one analysis per reactor per 90 minutes). One strong inconvenient for non-conventional (CSC) catalysts was that in-situ pre-sulphidation causes an important leaching of metal species.

Indeed, the sulphidation step begins around 70°C, when toluene and aniline are still liquid. As toluene, cyclohexane and aniline proved to leach the metal from the surface, the feed, under its liquid state, cleaves "ASA-O-W" bonds before tungsten oxide species being transformed into WS 2 slabs, strongly bonded to the support. Therefore, catalysts were pre-sulphided ex-situ prior to catalytic tests. These sulphide catalysts were loaded into reactors under inert conditions (glovebox) and tested following the same procedure as described earlier: one sulphidation step (liquid phase) and then, the test step. Considering that the sulphidation step of the test modifies the sulphide phase of each catalyst, spent catalysts were recovered after test, quickly stored under argon and analysed by XPS and TEM.

Part III. Preparation of non-promoted ASAsupported W catalysts: impregnation of W(V) and W(VI) alkoxides

Introduction

The aim of this chapter is to evaluate the effect of the structure of different tungsten precursors on the resulting hydrogenating catalysts performances. This is meant to choose a molecular precursor and the detailed characterisation and evaluation of the catalytic performance of the thus-prepared catalyst. In particular, we will look into the effect of the structure of the molecular precursor on the surface species obtained after grafting, and of the resulting sulphide phases obtained after sulphidation on to the catalytic activity. Following the characterisation of tungsten(V) and tungsten(VI) alkoxides molecular precursor by Fourier Transform Infrared (FT-IR) and Nuclear Magnetic Resonance (NMR) spectroscopies, we will describe the preparation and characterisation of materials before and after sulphidation, analysed by IR spectroscopy as well as by X-ray Photoelectron Spectroscopy (XPS), to finish by an evaluation of the catalytic activity.

III.1. Characterisation of molecular complexes of W(V) and W(VI)

The physical properties of metal alkoxides [M(OR) x ] n are strongly influenced by the type of alkyl group R, as well as by the preferential coordination number of the metal. Only a few homoleptic metal alkoxides, e.g. metallo-organic complexes containing identical ligands, have been structurally characterised in the literature. The majority of the complexes which structure were determined usually contain other ligands beside the alkoxy group [Cotton et al., 1985]. The alkoxy ligand RO -can adopt several binding modes to metal and behaves as terminal (Figure 19-a Most of the homoleptic metal alkoxides which are soluble in common organic solvent tend to form oligomers with low degree of oligomerization (e.g. n = 2, 3, or 4) [Bradley, 1958].

Moreover, it has been proposed that for the less bulky alkoxy group, the metal uses the bridging propensity of the ligand to achieve the smallest oligomer compatible, with the metal atoms attaining their preferred coordination number. To minimize the complexity of polynuclear complexes, it is necessary to maximize the number of bridging ligands, by forming face-sharing or edge-sharing polyhedra. Besides, the steric effect of the ligand RO -plays an important role.

By increasing the chain branching or the size of the R-group, steric effects can prevent alkoxybridging mode leading to mononuclear complexes.

In the early 50's, Bradley [Bradley et al., 1953] proposed a theory for metal alkoxides structure based on consideration of molecular weight data, enthalpy and entropy. From this theory, W(OMe) 6 would tend to be monomeric with an octahedral structure, while Nb linked to methoxo groups would be a dimer exhibiting edge-sharing octahedra, as shown on Figure 20. First, we characterised the tungsten precursor (409.15 g/mol) by mass spectrometry (electronic impact, direct introduction). Isotopic peak of W at M/Z = 409.08 confirmed the presence of the complex, as well as several fragment ions formed in the apparatus.

Structural characterisation of tungsten pentaethoxide by X-ray has not been achieved as far as we know. Alkoxides compounds with close molecular formula were, however, crystallized and characterised in the literature. W 2 (µ-OEt) 2 (OEt) 4 Cl 4 [Cotton et al., 1981] as well as W 2 (µ-OMe) 2 (OMe) 8 [START_REF] Bryan | [END_REF] exhibited edge-sharing octahedral structures with bridging ligands. Therefore, we can assume that tungsten pentaethoxide forms a dimer with the formula W 2 (µ-OEt) 2 (OEt) 8 , also denoted [W(OEt) 5 ] 2 , and exhibits two bridging ethoxy ligands (see Figure 21), as previously supposed by Bryan and co-workers. ) term between 917-905 cm -1 and between 1120-1056 cm -1 . Moreover, vibration of "tungsten-oxygen" bond, ν(M-O), were tentatively attributed to IR vibration band at 582 cm -1 and 615 cm -1 . [Reagan and Brubaker, 1970] On the IR spectrum of our product, the strong vibrations between 550 and 520 cm -1 could be in line with a ν(M-O) vibration, as reported for other ethoxo complexes [START_REF] Bradley | Alkoxo and aryloxo derivatives of metals[END_REF].

% transmittance 20 % wavenumber (cm -1 ) 1000 2500 3000 4000

III.1.a.2. Nuclear Magnetic Resonance spectroscopy (NMR)

While tungsten pentaethoxide would be paramagnetic in its monomeric form, W(OEt) 5 , because of the d1 configuration of the metal centre, the absence of EPR signal [Reagan and Brubaker, 1970] and the presence of sharp peak in NMR spectra shows that [W(OEt) 5 ] 2 is diamagnetic [Chisholm et al., 1995]. The spectra obtained by proton NMR, denoted 1 H NMR; and proton decoupled 13 C NMR, denoted 13 C{ 1 H}, are shown in Figure 23. Peaks attribution is summarized in Table 1. The 1 H NMR spectrum (CD 2 Cl 2 , 298K) shows a triplet at δ = 1.22 ppm assigned to W-O-CH 2 CH 3 and a quadruplet at δ = 4.77 ppm assigned to W-O-CH 2 CH 3 as reported in the literature [Reagan and Brubaker, 1970]. 13

δ(CH 3 ) ppm δ(CH 2 ) ppm W-O-CH 2 -CH 3 W-O-CH 2 -CH 3
No XPS could be recorded because the sample was liquid. All data are however consistent with a dimeric structure.

III.1.b. Tungsten hexaethoxide -W(OEt) 6 W(OEt) 6 is also a commercial compound (Alfa Aesar), oxygen and moisture sensitive. Its structure is supposed to be monomeric as the corresponding methoxy complex W(OMe) 6 [Bradley et al., 1977] exhibits a monomeric structure with a W in an octahedral environment (see Figure 24).

Part III

104 2. The 1 H NMR spectrum exhibits resolved multiplets as well as broad peaks. The triplet at δ = 1.22 ppm is assigned to CH 3 groups of ethoxy ligands. A quadruplet at δ = 4.76 ppm is assigned to CH 2 groups of ethoxy ligands [Bradley, 1972]. Then, as we will explain it latter with Figure 31-a, the two broad peaks, at δ = 1.32 ppm and δ = 4.77 ppm are assigned to ethoxy ligands of [W(O)(OEt) 4 ] 2 . The presence of non-negligible amount of this degradation product, already detected by IR, has been confirmed by 13 C{ 1 H} NMR. The 13 C{ 1 H} spectrum (CD 2 Cl 2 , 298K) exhibits 4 peaks, which have been attributed as follows. From the literature, oxo-derivatives of tungsten tend to adopt different nuclearities.

δ = 18.8 ppm (W(OEt) 6 , W-O-CH 2 CH 3 ), δ = 70.1 ppm (W(OEt) 6 , W-O-CH 2 CH 3 ) and δ = 18.2 ppm ([W(O)(OEt) 4 ] 2 , W-O-CH 2 CH 3 ), δ = 72.4 ppm ([W(O)(OEt) 4 ] 2 , W-O-CH 2 CH 3 ).
δ(CH 3 ) ppm δ(CH 2 ) ppm W-O-CH 2 -CH 3 W-O-CH 2 -CH 3 III.1.c. Tungsten oxotetraethoxide -[W(=O)(OEt) 4 ] 2 [W(=O)(OEt) 4 ]
W(O)(OtBu) 4 (thf) has been reported as mononuclear species [Cotton et al., 1985]. Clegg's team [Clegg et al., 1992]

δ(CH 3 ) ppm δ(CH 2 ) ppm W-O-CH 2 -CH 3 W-O-CH 2 -CH 3
No elemental analysis of [W(O)(OEt) 4 ] 2 was performed.

As a conclusion, we showed that commercially available W(OEt) 6 , interesting as a mononuclear species was not pure and contained non-negligible amount of [W(O)(OEt) 4 ] 2 . The oxo-derivative was purer than W(OEt) 6 , and probably exhibited a dimeric structure. Finally, [W(OEt) 5 ] 2 was the purest of tungsten derivatives we analysed.

Part III 110

III.2. Preparation and characterisation of W-supported materials, from W(V) or W(VI) molecular precursors.

Different materials were prepared, by deposition of [W(OEt) 5 ] 2 , W(OEt) 6 and [W(O)(OEt) 4 ] 2 onto amorphous silica-alumina partially dehydroxylated at 300°C or 500°C under vacuum.

Samples impregnations were performed by Incipient Wetness Impregnation (IWI) or by grafting (e.g. stoechiometric impregnation followed by several washing steps). Thermal pretreatments of silica-alumina supports are described in part II, as well as their characterisation.

The three materials prepared by grafting (G) were kindly prepared by M.Cartes at ETH Zürich, and are referred as follows:

-[W(OEt) 5 ] 2 -G-0. Figure 32 shows the IR spectra (4000 cm -1 -1400 cm -1 ) of samples prepared by grafting, e.g. [W(OEt) 5 ] 2 -G-0.7/ASA -500 , W(OEt) 6 -G-0.7/ASA -500 and [W(O)(OEt) 4 ] 2 -G-0.9/ASA -500 . On the spectra, the vibration band attributed to isolated silanols v(OH) i at 3743 cm -1 disappears upon deposition of the precursors. Moreover, apparition of the characteristic features of alkoxy complexes, e.g. ν(CH) and δ(CH) bands, is attributed to the presence of ethoxo ligands, linked to surface tungsten. We can conclude that tungsten complexes are probably grafted on surface hydroxyles.

Preparation of non-promoted ASA-supported W catalysts: impregnation of W(V) and W(VI) alkoxides The first doublet, positioned at the higher BE, is typical of tungsten (VI) species [Wagner, 1979] and represents about 92 % of the total amount of tungsten visible. The second doublet, which principal component is shifted to lower BE, is assigned to partially reduced tungsten species, reduced in-situ upon irradiation by the X-ray beam under the ultra-high vacuum of the apparatus.

In the case of W(OEt) 6 -G-0.7/ASA -500 and [W(O)(OEt) 4 ] 2 -G-0.8/ASA -500 , finding a W(VI) environment is consistent with the oxidation state of the initial precursor. In the case of [W(OEt) 5 ] 2 -based material, one would expect a W 4f photopeak at lower BE. As far as we know, W(V) has never been assigned to a precise BE. Note that Alov et al. and Coulier et al. respectively found BE of ca. 34.4 eV and ca. 33.5 for the W 4f 7/2 component of W(V), respectively in tungsten oxide thin films [Alov, 2005] or in sulphide catalysts [Coulier et al. 2002]. To conclude, we showed that the deposition of the three different precursors led to catalysts with similar IR and XPS spectra. The surface species found on oxide catalysts appeared to be in a W(VI) environment.

Observing a W(VI) environment for [W(OEt

III.3. Characterisation of sulphide catalysts prepared from W(V) or W(VI) precursors

In order to obtain active hydrotreating catalysts, the materials previously impregnated by metallic precursors need to be activated by sulphidation. Sulphidation is the key step to generate the metal sulphides, which represent the active phase in hydrotreating catalysts.

We first tried to carry out the sulphidation of one of the tungsten precursor, to test whether it was possible or not to obtain a 100 % bulk WS 2 . Sulphidation of liquid [W(OEt) 5 ] 2 at 600°C under a mixture of 15 % mol. H 2 S/H 2 (see experimental section part II) gives a grey solid which exhibits ca. 92 (±5) % rel. WS 2 with respect to the surface area of W 4f 7/2 and W 4f 5/2 assigned to W (IV) S 2 . The XPS spectrum (W 4f photopeak) is shown in Figure 34.

Preparation of non-promoted ASA-supported W catalysts: impregnation of W(V) and W(VI) alkoxides 113 Sulphidation of the previous materials, prepared by grafting, was performed at 350°C under a mixture of 15 % mol. H 2 S/H 2 as reported in part II. WS 2 /ASA catalysts were referred as follows:

-WS 2 -ex.[W(OEt) 5 ] 2 -G-0.

III.4. Benchmarking catalytic activities with conventionally prepared catalysts

Tungsten-based catalysts being known for their high activity in aromatic hydrogenation [Stanislaus and Cooper, 1994;Hensen et al., 2007], the catalytic performances of WS 2 /ASA catalysts prepared by deposition of the three different tungsten precursors were tested in hydrogenation of toluene (HYD). The feed was composed of toluene (reactant), cyclohexane (solvent), dimethyldisulphide (sulphiding agent) and aniline. This latter compound is used to inhibit the acidity of the support, and avoid isomerisation of the reactant by the acid sites of the support as explained in the experimental part.

CSC catalysts are compared to conventional WS 2 /ASA catalysts, dried or calcined.

Conventional materials were prepared by IWI of an aqueous solution of ammonium metatungstate, followed by a maturation step of 1 night. Then, after a drying step of 1 night at 120°C, conventional catalysts were referred as "dried". Subsequent calcination under air at 450°C for 2 h gave materials referred as "calcined". These two samples were sulphided at 350°C for 2 h with a 15 % mol . H 2 S/H 2 mixture to give respectively the dried and calcined sulphided catalysts. Note that elemental analyses on these materials showed that they exhibit a W-loading of ca 0.5 W/nm².

Preparation of non-promoted ASA-supported W catalysts: impregnation of W(V) and W(VI) alkoxides

115

The intrinsic rate of hydrogenation (or intrinsic HYD rate), expressed in mol(tol)/mol(W)/h, of these catalysts, depending on their tungsten loading (W/nm²) is shown Figure 36.

Note that the intrinsic HYD rates activities of these previous catalysts are also compared to three similar catalysts, based on CSC materials prepared by IWI of ASA -300 . Catalysts prepared by the CSC method are active and exhibit HYD rates lying between 0.19 and 0.28 mol(tol)/mol(W)/h and only little difference is found for W(V) and W(VI)-based catalysts, whatever the precursor or the support (e.g. ASA -300 or ASA -500 ). Then, although no transmission electron microscopy analyses were undergone on these samples, XPS analyses show that these sulphide phases are, in a first approximation, quite similar (level of sulphidation, intrinsic HYD rates). Besides, conventional catalysts show intrinsic HYD rates (see arrows on

III.5. Conclusion

In this chapter, we investigated the preparation of non-promoted hydrotreating catalysts from tungsten(V) and tungsten(VI) precursors.

We first characterised three tungsten alkoxides, [W(OEt) 5 ] 2 , W(OEt) 6 and [W(O)(OEt) 4 ] 2 , selected as potential precursors for deposition on ASA. We showed that all the metallic complexes exhibits the characteristic features of alkoxide compounds. Then, we deposited these molecules onto amorphous silica-alumina partially dehydroxylated under high vacuum, and characterised these materials. FT-IR and XPS spectroscopy analyses show no significant differences between the catalysts and are consistent with the formation of grafted tungsten alkoxide surface species. Subsequent treatment with 15 % mol. H 2 S/H 2 yielded three sulphide catalysts, which are hardly possible to differentiate according to XPS analyses. Finally, the catalytic test, e.g. hydrogenation of toluene in presence of aniline, shows that all catalysts are active and behave similarly. The comparison with the intrinsic rate of hydrogenation of conventional catalysts reveals that CSC catalysts are as or even more active, given the amount of tungsten loaded on each sample, which is very promising and need to be further studied.

To conclude, we recall that one aim of this PhD work is to study sulphide catalysts, from oxide surface species to WS 2 slabs. To achieve such an investigation, especially via a molecular approach, we need a pure and well-characterized tungsten precursor. Therefore, in view of the readily availability of tungsten pentaethoxide [W(OEt) 5 ] 2 in a pure form, present as a dimeric species, we selected this molecular precursor for the rest of the study. For a greater clarity, this precursor will be denoted [W(OEt) 5 ] 2 in the following chapters.

III.6. References

Introduction

In part III, we have shown that CSC catalysts display equal or higher intrinsic hydrogenation rates than conventional catalysts for similar W-loadings ranging from 0.5 to ca. 0.9 W/nm². The CSC method, which is thus promising to prepare efficient HYD catalysts, will allow us to investigate in details the preparation of CSC samples step by step, from the oxide phase to the sulphide one and its catalytic activity. In this part IV, we will thus focus on the first step of the preparation of catalysts, e.g. the impregnation of the metallo-organic precursor selected in part III : [W(OEt) 5 ] 2 . We will investigate the influence of the tungsten loading on the resulting grafted surface species in oxide materials, prior to sulphidation. All CSC samples will be characterised by IR, NMR and XPS spectroscopies. We will investigate in particular how the metal complex is linked to the surface and which species are preferentially formed, as a function of the tungsten coverage (W/nm²).

Four materials with increasing amount of [W(OEt) 5 ] 2 were prepared by incipient wetness impregnation (IWI) on ASA -300 having a surface of 228 m²/g. They are referred as follows:

-

IV.2. Characterisation by Infrared spectroscopy (IR)

When increasing amounts of [W(OEt) 5 ] 2 are impregnated on ASA partially dehydroxylated at 300°C under high vacuum (10 -5 mbar), the vibration band assigned to isolated silanols [Legrand, 1998, John Wiley & sons Ltd] at 3743 cm -1 increasingly disappears by 61 % and 82 % for 0.2 W/nm² and 0.5 W/nm², respectively and vanishes for loading above 0.8 W/nm². While ASA -300 contains about 3.2 OH/nm² according to chemical titration with CH 3 MgBr (see experimental section), a tungsten loading of 0.8 W/nm² represents ca. 0.3 W/OH. Note that a broad band between 3700 and 3300 cm -1 associated with bonded OH increases when increasing amounts of precursor are impregnated, in agreement with the presence of more residual silanols interacting with surface organic ligands, probably attached to W. Meanwhile, two groups of bands appear in the region 1800 -1450 cm -1 and 3000 -2800 cm -1 , respectively assigned to δ(CH) and ν(CH) vibrations of the aforementioned ethoxy species. Note that a maximum density of 2 W/nm 2 is expected on the basic of the projected surface area of the molecular complex [W(OEt) 5 ] 2 (ca. 1.0 nm²). Overall, the data are consistent with a consumption of isolated silanols (ν(OH) i = 3743 cm -1 ), but not all surface hydroxyls, probably because they Effect of tungsten loading on the nature of surface species obtained after impregnation of [W(OEt) 5 ] 2 on ASA

125

are not all accessible in part because they interact with the complex (presence of shifted OH band interacting via van der Waals interaction with organic ligand. Increasing the tungsten loading does not only increase δ(CH) and ν(CH) vibrations intensity, but also leads to the appearance of two additional groups of vibration bands in the 1740-1580 cm -1 and 1480-1320 cm -1 regions. In the zoomed spectra reported in Figure 39, a broad band is present between 1380 cm -1 and 1420 cm -1 at tungsten loading below 0.5 W/nm².

For 0.8 W/nm² a new band appears at 1382 cm -1 , which is shifted towards lower wavenumbers as found for the δ(CH) of pure [W(OEt) 5 ] 2 , at 1374 cm -1 . These observations indicate that at tungsten loading below 0.5 W/nm² one type of surface species is present, while at higher loading, a second type of species, closely related to unperturbed [W(OEt) 5 ] 2 appears.

In addition, two peaks, not present in the starting compound, also appear at ca. 1736 cm -1 and 1602 cm -1 for tungsten loading above 0.5 W/nm². For a loading of 1.7 W/nm², these two peaks are slightly shifted to 1732 cm -1 and 1600 cm -1 . While their assignment is fully ascertain, one possibility is that the band ca.

IV.3. Characterisation by Solid-State NMR spectroscopy (NMR)

The of two different species, the peak at δ = 1.0 ppm to methyl protons CH 3 , and the peak at δ = 1,8 ppm to remaining silanols [Legrand, 1998, John Wiley & sons Ltd;Brunner et al., 1997].

In addition, the 13 C Cross-Polarisation (CP) MAS solid-state NMR spectrum (see Figure 40, right, green curve) displays three peaks: one at δ = 15 ppm, which corresponds to CH 3 groups and two at δ = 76 ppm and δ = 59 ppm, assigned to two types of OCH 2 groups belonging to different types of ethoxy groups. The former is attributed to ethoxy groups bound to W, while the latter is assigned to ethoxy groups directly bound to the ASA surface.

Effect of tungsten loading on the nature of surface species obtained after impregnation of [W(OEt) 5 ] 2 on ASA 127

Examining the NMR spectra of a series of samples with increasing tungsten loadings is very informative. In the 1 H NMR solid-state spectra (Figure 40-a), increasing the tungsten loading leads to an increase of the intensity of the peak at δ = 5.0 ppm as well as a shift of the peak at δ = 1.0 ppm to δ = 1.2 ppm. Two pairs of peaks are distinguishable and assigned to different types of ethoxy groups: one at {δ = 5 ppm ; δ = 1.2 ppm} and one at {δ = 3.8 ppm ; δ = 1.0 ppm} respectively assigned to ethoxy species linked to W and to ethoxy species adsorbed on the ASA surface and linked to either Si or Al. Similarly, the CPMAS 13 C solid-state NMR spectrum shows that the broad peak at 76 ppm is shifted to 69 ppm at higher loading, for which it increases and sharpens. Meanwhile, the peak at 15 ppm is shifted to 19 ppm.

Furthermore, an additional pair of carbons has a high relative intensity at low loadings at {δ = 59 ppm ; δ = 15 ppm}, whose chemical shifts are similar to this observed for ethoxy species adsorbed on aluminosilicates. [START_REF] Derouane | Effect of tungsten loading on the nature of surface species obtained after impregnation of[END_REF], revealing that such species are preferentially formed at low loadings. In fact, these sharp signals disappear on the 13 C CPMAS spectra, shown in Figure 41 (right). Since the efficiency of cross-polarisation (CP) [Pines et al., 1972], associated with the magnetisation transfer between 1 H and 13 C, is more efficient for strongly bound species (immobile) compared to weakly bound species (physisorbed), it confirms that two types of tungsten species are formed: grafted species on the surface for low tungsten loadings (< 0.7 W/nm², corresponding to a W-bound monolayer) as well as more mobile species, probably physisorbed on top of the grafted ones for higher loadings (> 0.8 W/nm², corresponding to multilayer).

To strengthen the assignment of 1 H and 13 C NMR spectra, 1 H-13 C heteronuclear correlation (HETCOR) NMR experiments were performed.

IV.4. Insights into the characterisation of surface species

IV.4.a. Deposition of ethanol onto SiO 2-700 , Al 2 O 3-450 and ASA -300 .

NMR spectroscopy has revealed that a large amount of surface ethoxides are bound to ASA on the W-containing samples. GC/MS analyses has also shown that less than 0.1 equiv. of EtOH / W is released upon grafting of [W(OEt) 5 ] 2 , independently of the W loading (0.2 -1.7 W/nm²). One possible way to form surface ethoxy species is the reaction of EtOH, released upon grafting [W(OEt) 5 ] 2 with surface silanols. This reaction is discussed further later on (p147). The adsorption of alcohols on alumina has been studied for several years, especially for dehydration reactions, that are catalyzed by alumina at high temperatures [Salomon et al., 1967]. EtOH is reported to be strongly adsorbed on alumina [Greenler et al., 1962], especially on the (100) planes hydroxyles of AlOH when calcined at low temperature, and on pentacoordinated Al 3+ when calcined at temperature higher than 400°C. [Kwak et al., 2011]. Note however that adsorption on Brønsted acid sites (AlOH) or Lewis acid sites (Al 3+ ) is still a matter of debate. [Roy et al, 2012] Therefore, ethanol and/or 13 C labelled ethanol were contacted to Effect of tungsten loading on the nature of surface species obtained after impregnation of [W(OEt) 5 ] 2 on ASA 131 SiO 2-700 , Al 2 O 3-450 and ASA -300 in order to ascertain the proposed reaction pathway and the presence of surface ethoxides.

On SiO 2-700 , which exhibits ca. 0.8 OH/nm², IR spectroscopy analysis (see appendices) vibrations between 1480 cm -1 and 1393 cm -1 . On silica, 100 % of isolated silanols (ν(SiOH) i = 3740 cm -1 ) are consumed, and residual silanols interacting with surface species are present as evidenced by the broad band between 3700 cm -1 and 3300 cm -1 . On alumina, Al IV OH (ν(OH) = 3792 cm -1 ) as well as Al VI OH (ν(OH) = 3770 cm -1 ) totally disappear and (Al VI ) 3 OH (ca. ν(OH) = 3756 cm -1 ) strongly decreases. However a large amount of residual AlOH is still Part IV 134 observed. Note that on ASA, isolated silanols have totally been consumed, and that residual SiOH are revealed by the broad band between 3700 cm -1 and 3300 cm -1 . Mass balance analysis shows ca. 0.9 W/OH (at/at) for the silica material, and 0.2 W/OH (at/at) for alumina and ASA ones, which means that as previously seen for ASA-based materials, surface hydroxyls are not totally consumed, due either to their lower accessibility or to the steric hindrance of the tungsten precursor. exhibits no significant differences of chemical shift with the silica and the alumina ones. Note however that the relative amount of tungsten surface species vs. ethoxy surface species, quantified by integration of the δ(CH 2 ) peak of tungsten surface species (in the 70-74 ppm region), is lower on alumina (37 %) than on silica-alumina (56 %) than on silica (66 %), at ca. the same loading, supporting the aforementioned discussion about EtOH being more easily transferred on alumina or silica-alumina functionalities than on silica's upon grafting. Note however that the signal associated with surface ethoxy on silica is significantly more important than when silica is treated with EtOH, consistent with the assistance of W in the formation of the surface ethoxy species. This species is thus either resulting from the opening of a siloxane bridge either by a grafted surface W species on an adjacent site or by an intramolecular process. First, the 1 H spectrum of ASA -300 was decomposed with a good fit (sdev = 4.93) with a minimal number of sites: three peaks placed at ca. 0.5 ppm, 1.7 ppm and 3.0 ppm (Figure 50).

The first two peaks are assigned to silanols (SiOH) in different environments, and the last one is tentatively ascribed to aluminols (AlOH), by comparison with literature data on aluminosilicate supports [Brunner et al., 1997;Heeribout et al., 1998;Müller et al., 2000]. The peak mainly attributed to AlOH took into account a 1 H { 27 Al} TRAPDOR experiment performed on the ASA -300 sample, in which the peak at ca. 3.0 ppm was partly assigned to protons coupled with aluminium atoms. [Crépeau et al, 2006] Note that the broad band from about 1 ppm to ca. 8 ppm on the ASA -300 spectrum could also be assigned to silanol protons in a variety of hydrogen-bonding environments, on the basis of earlier studies on silica gel. [Bronnimann et al., 1988] Part IV

138

For the NMR spectra of the various [W(OEt) 5 ] 2 -IWI-/ASA -300 materials, besides using the peak of silanols and aluminols described above for ASA -300 , additional peaks were introduced to include the signals associated with ethoxides bound to the ASA surface and these bound to tungsten (see Figure 50). Each decomposition was performed with several constraints: positions were set with a ± 0.1 ppm uncertainty for most of the peaks, and CH 2 /CH 3 ratio for each species was close to 2 / 3. More details are available in the experimental part and appendix A. Part IV

140

The % rel of free OH strongly decreases from 0.2 W/nm² to 0.5 W/nm², and slowly reaches a plateau at higher loading. These results indicate that above W-loading of ca. 0.5 to 0.8 W/nm², no more hydroxyls are consumed as previously observed by IR (see part IV.2) and that additional W species must arise from the adsorption of complex, which interact with the first layer of chemisorbed species. The limited amount of hydroxyls that undergo grafting is probably associated with their accessibility combined with to the large size of precursor, which exhibits a large projected area (ca. 1.0 nm²), which prevents reaction of all OH groups.

IV.4.c.2. Molecular modelling. From the work of Leydier [Leydier, PhD thesis, Paris, 2012] Preliminary quantum molecular modelling of the adsorption of the monomeric tungsten(V) pentamethoxide, W(OMe) 5 , on a model of ASA surface [Chizallet et al., 2009;Chizallet et al., 2010] were previously carried out by density functional theory (DFT) calculations in the PhD thesis of F. Leydier. [2012]. Even if undertaken with a monodentate monomeric complex, this study brings some insights on the interaction of the tungsten molecular precursor with the silica-alumina surface. The calculated reaction energies between a methoxo ligand and various surface hydroxyls vary between -32 and +28 kJ/mol, depending on the type of hydroxyls.

The most favourable exchange energies (-32 kJ/mol) was found for an isolated silanol SiOH (Figure 17-a). On Si-OH---Al pseudo-bridging silanols (Figure 17-b), the energies vary from -22 to -4 kJ/mol. Note that recurrent hydrogen-bondings between a close hydroxyl and one oxygen of the surface complex are observed and that this interaction is stabilizing. More importantly, this computational study shows that W loadings greater than 0.53 W/nm² should lead to disfavoured lateral interactions between methyl groups, which is consistent with the formation of the saturation of the surface at ca. 0. According to the literature, grafting of mononuclear molecular precursors on a support partially dehydroxylated at temperatures lower than 500°C typically yields bis-grafted or trisgrafted metallo-organic complexes. This is, for example, the case for Ti(NEt 2 ) 4 ,

Part IV

146 Ta(=CHtBu)(CH 2 tBu) 3 , V(=NtBu)(CH 2 tBu) 3 , and Cr(CH 2 EMe 3 ) 4 with EMe 3 = tBu or SiMe 3 [Copéret et al., 2003], which form bis-grafted surface species on partially dehydroxylated silica SiO 2-200 , which contains 0.86 mmol of OH.g -1 or 2.8 OH.nm -1 . For ASA -300 , which contains 3.2 OH/nm 2 , a similar behaviour is expected and bis-grafted tungsten centres would be favoured, in particular with dinuclear species, which have a large projected area. Besides, NMR spectra decomposition highlighted ca. First, grafting via (Mec.1) infers the release of 1 equiv. of EtOH per grafted complex. Note also that less than 0.1 equiv. of EtOH is released per W upon grafting and that EtOH does not readily react with ASA in the absence of W. Then, considering the large amount of EtO-ASA, the formation of the surface ethoxy must be assisted by tungsten and originates from EtOH as Part IV

148

shown in (Mec.1.3) and (Mec.1.4) as well as from the reaction of a W-OEt with adjacent M-O-M' bridge as shown in (Mec.2). Water, possibly released upon reaction of EtOH with hydroxyls, can also infer the formation of new hydroxyls, or stay strongly adsorbed on Lewis acid sites. Finally, (Mec. 2) would not lead to a consumption of any surface OH, while (Mec.1) would lead to at least one surface OH consumed by bond formation between the surface and a monografted dinuclear species. Successive steps involving (Mec.1) or (Mec.2) will in fine lead to bis, tris and tetra-grafted tungsten centres as well as numerous surface ethoxy groups. To further illustrate the proposal, (Mec.1.1) and (Mec.1.2) show the formation of a bis-grafted dinuclear species as a 2 nd step of (Mec.1). Note in particular that (Mec.1.1) gives a bis-grafted dinuclear species in which the two tungsten centres are monografted, while (Mec.1.2) gives a bis-grafted dinuclear species in which only one of the two tungsten centres is linked to the surface, in a bipodal mode. Occurrence of these mechanisms before or after (Mec.2) is also possible.

Finally, we can summarize our propositions (Table 5) as follows: For tungsten loading greater than 0.8 (±0.1) W/nm², additional tungsten species results from the adsorption of molecular complexes on top of the aforementioned grafted surface species, which interact more or less strongly via either mu-bridge ethoxide or electrostatic interactions forming additional layers.

Part V. Evolution of catalysts during

sulphidation: from surface species to active WS 2 phases

Introduction

The aim of this chapter is to study the sulphidation and the catalytic properties of materials prepared via the controlled surface chemistry (CSC) method, and previously characterised in part IV. They will be compared to conventional catalysts, whether dried or calcined prior to sulphidation. We will investigate for each system the level of sulphidation, the characteristics of the WS 2 slabs (length, stacking number, and 2D morphology) and the catalytic activity in the hydrogenation of toluene. Part V.1 will focus on the influence of the tungsten loading. Indeed, we have seen in part IV that different surface species were observed when the tungsten loading was modified. It is thus interesting to study the influence of each type of species on the genesis of the WS 2 phase. Then, Part V.2 will investigate the influence of the sulphidation temperature in order to get new insights into the evolution of the properties of the active phase, as for example, the amount of WS 2 formed upon sulphidation

V.1. Influence of the tungsten loading on conventional and CSC catalysts

In this part, we will focus on the influence of the tungsten loading on CSC and A detailed procedure, based on the quantification of residual crystalline compound by XRD [Chung, 1974] is detailed in their paper [Xie and Tang, 1990]. Briefly, the methodology is based on the fact that while no evidence of crystalline phase is detected by XRD when surface species are below a "monolayer" coverage (e.g. close-packed species stuck together), crystalline WO 3 is expected to be detected above such a "monolayer". XRD diffractograms of conventional calcined catalysts with 0.5 W/nm², 1.8 W/nm² and 3. We can see that for tungsten loadings below 1.8 W/nm², no crystalline WO 3 is evidenced, while at 3.7 W/nm², two peaks at ca. 2θ = 24° and 2θ = 34° are assigned to crystalline WO 3 .

Therefore, we assume that for W-loadings ranging from 1.8 W/nm² to 3.7 W/nm², the maximal amount of close-packed species is achieved and that stacking of amorphous WO 3 entities occurs and leads to crystalline WO 3 formation. Our results are in line with literature data where, a "monolayer" coverage of supported WO 3 is reached between 4.1 W/nm² [Yu et al., 2001] and 4.8 W/nm² [Xu et al., 2000] on TiO 2 and between 4.6 W/nm² [van der Vlies, PhD thesis, Zürich, 2002] and 5.4 W/nm² [Xie and Tang, 1990] on γ-Al 2 O 3 . On Silica, only a layer of species that does not correspond to the full coverage of the support was achieved. It is referred as a "submonoloayer" coverage, and is assumed to be ca. 0.5 W/nm², from calculations based on the work of Xie et al. [1990] and Wang et al. [Wang et al., 2003]. Finding a layer of species that Part V 160 covers the full surface or less than the full surface of a support" was tentatively linked by the authors to thermodynamical aspects, related to the influence of the strength of the bond between the monolayer and the surface on the system entropy. Finally, as our ASA support is composed of 70 % wt. Al 2 O 3 , and 30% wt. SiO 2 , this intermediate composition could explain the intermediate threshold between ca. 1.8 and 3.7 W/nm² found for a "(sub)monolayer" coverage of WO 3 on ASA.

Finally, finding a threshold between a so-called "(sub)monolayer" and a multilayer to be 0.8 W/nm² for CSC materials, and between 1.8 and 3.7 W/nm² for conventional samples, is not surprising as the projected area of one stoechiometric unit of WO 3 is ca. 23 A² [Di gregorio et al., 2004], while the projected area of one [W(OEt) 5 ] 2 dimer is ca. 100 A², e.g. 50 A² per W. It means that more WO 3 unit than [W(OEt) 5 ] 2 dimers can be packed together to form a "monolayer" of close packed species, e.g. that a "(sub)monolayer coverage" is reached more quickly on CSC materials than on conventional calcined ones.

For the sake of clarity, all these results about the different oxide species on CSC and conventional materials, depending on the W-loading, are summarized by schematic representations of each material, as shown on the next pages. The sulphidation level of CSC and conventional catalysts was studied by XPS, focusing on the decomposition of their W 4f spectrum. The decomposition procedure applied for the whole set of spectra has already been described earlier [Ben Tayeb et al., 2010] and is available in the experimental section, part II. Figure 61 shows the evolution of the different tungsten phases as well as the S/W atomic ratio in WS 2 slabs, depending on the W loading. On Figure 61-a we can see that at 0.5 W/nm², the CSC catalyst is sulphided at ca. 76 (±5) % rel, WS 2 while dried and calcined catalysts are only sulphided at 51 (±5) % rel. WS 2 and 33 (±5) % rel. WS 2 respectively, which indicates that the CSC catalyst is better sulphided.

Note however that the dried catalyst undergo far better sulphidation (higher % rel. WS 2 ) than the calcined one, as previously described in the literature. [Reinhoudt et al., 1999] These differences can be explained in terms of reactivity of oxide species. Their sulphidation level is expected to depend either on their "W-O" bond dissociative energy, their interaction with the support, e.g. M-O-W linkage (M = Al, Si), or on their reducibility, as sulphidation is a reductive process where W (VI) is reduced into W (IV) . At low W loadings, all catalysts are covered by well-dispersed species, as revealed by the rather identical W/Al atomic ratio shown in Table 6. We recall that for the sake of clarify, examples of CSC and conventional materials' surfaces are illustrated in First, the high level of sulphidation of the CSC materials can be tentatively explained at a more molecular level: "W-OR" bonds in [W(OEt) 5 ] 2 are rather labile and can easily undergo ligand exchange, [Turova, 2002, Kluwer Academic Publishers, London] [ Raybaud and Toulhoat, 2013, Ed. Technip, Paris]. Besides, polyoxometallates species seen on Part V 166 dried materials are reported to develop weak interaction with oxide supports. [Proust et al., 2012] Differences in metal-support interactions can thus partially explain the better level of sulphidation of dried catalysts. To get further insights into the influence of such interactions, we are currently investigating if the limit observed for the sulphidation level of the CSC catalyst is linked to its M-O-W linkages (M = Al, Si), as grafted dimeric surface species illustrated in chapter IV share more than one bond with the surface, bonds which are not supposed to undergo sulphidation.

For tungsten loadings higher than 0.5 W/nm², higher amounts of tungsten are deposited on the surface, which decrease the distance between WO x species on conventional catalysts, as illustrated in Figure 59 WS 2 : this is thus not surprising to find that the highest level of sulphidation of W-supported materials prepared with [W(OEt) 5 ] 2 is lower of equal to 92 (±5) % rel. of the amount of tungsten detected by XPS.

At this point, we have tried to explain the evolution of the % rel WS 2 observed for CSC and conventional catalysts. Then, we investigated the evolution of % rel W(VI), presented in Figure 61-b, as it is strongly linked to the evolution of % rel WS 2 . The % rel W(VI) decreases with increasing tungsten loading for all catalysts. At 0.5 W/nm², in the case of the conventional calcined catalysts, the amount of non-sulphided WO 3 is relatively high, confirming that the amorphous oxide phase is very refractory to sulphidation, especially at low tungsten loadings.

No clear trend could be found for the amount of intermediate phase % rel W(intermed.), as shown in Figure 61-c, with a value rather constant for all catalysts, at about 8 (±5) % rel . Finally, the S/W atomic ratio of WS 2 slabs stays close to {2.2 ; 2.3} in general, with slightly higher values at low loading.

Finally, we investigated the W/Al atomic ratio (seen by XPS) before and after sulphidation. 6 show that oxide materials prepared by the CSC method exhibit a better dispersion of tungsten on the surface, except for 0.5 W/nm². After sulphidation, we can see on Figure 62-d, that the W/Al atomic ratios are rather similar, whatever the preparation method. We see that the difference between the higher and the lower W/Al atomic ratio for a given loading increases when higher amount of tungsten are impregnated. It reveals that the lower the catalysts loading, the closer the way W spreads on the ASA surface in sulphided samples, whatever the preparation method. in Figure 63 as well as related H 2 consumptions values, expressed in ml(H 2 )/g(W), in Table 7.

Note that experiments were run from ca. 36°C to 1000°C, at 5°C/min, followed by 2 h at 1000°C. First of all, in our conditions the ASA support was found to consume little amount of H 2 (ca. 1.4 ml(H 2 )/g ASA in standard conditions of temperature, 273.15 K, and pressure, 100 kPa), which has been subtracted from H 2 consumptions obtained for our catalysts and reported hereafter. For catalysts with W-loading of 0.5 W/nm², two reduction peaks are observed below 1000°C: for conventional catalysts, reduction starts at 785 (±24) °C while for CSC ones, reductions starts at 819 (±25) °C. Reduction of conventional species thus begins slightly before molecular species of the CSC material, which seems to indicate an earlier reducibility of conventional species. However, it has to be balanced against the quantification of the experimental H 2 consumption (from the beginning to the end of the TPR experiment, 313 min) and expected theoretical H 2 consumptions. For estimating the expected theoretical H 2 consumptions, the reduction of W(OEt) 5 (for CSC samples) and WO 3 species (for conventional catalysts) were taken into account, in a first approximation. Note that for conventional dried catalysts, this means that we also assume an O/W ratio close to 3 for the W species being reduced. The related equations are shown below:

EtOH W H OEt W 5 2 5 ) ( 2 5 + → + Eq. 3 O H W H WO 2 2 3 3 3 + → + Eq. 4
The corresponding theoretical values are available in Table 7. For the CSC sample, 83% of the theoretical amount of H 2 needed to complete reduction is consumed, while only 33% of the theoretical value is found for the calcined sample. Finding values which are below the theoretical ones is not surprising as on the TPR pattern in Figure 63, H 2 consumptions are not back to the baseline for the two samples within the time of experiments. Interestingly, more than 2/3 of the CSC surface species are reduced while only 1/3 is reduced for the conventional calcined sample, which indicates that the CSC catalyst is quantitatively more easily reduced, although the reduction temperature starts earlier for conventional catalysts (819°C vs. 785°C).

This result can partially explain the best sulphidation of CSC species for materials with 0.5 W/nm². Besides, H 2 consumptions observed for conventional catalysts are found to be identical.

As surface species on dried samples (W clusters) and on calcined ones (WO 3 patches) are chemically different, we could have expected a different behaviour toward H 2 (and thus a different reducibility). Moreover, note that we don't know the size of the surface species. These sizes, if different, could influence reduction and thus the quantification of H 2 . Therefore, H 2 consumption obtained from TPR experiments cannot explain the XPS results observed on conventional catalysts with 0.5 W/nm² (see part V.1.b).

Then, for tungsten loadings higher than 0.5 W/nm², TPR patterns exhibit two different regions in which reduction peaks are observed for both CSC and conventional materials. Weak reduction peaks are observed at 514°C, 547°C and 554°C respectively for CSC, dried and calcined samples. Then intense peaks are located around 960°C for CSC and dried materials while situated around 979°C for the calcined sample. The precise assignment of these peaks is not obvious, therefore no further interpretation will be made. However, it is noticeable that reduction peaks for CSC species start at lower or similar temperature than for WO x species found on conventional samples. Qualitatively, it would indicate an easier sulphidation of CSC species. Besides, looking at the quantification of H 2 consumed upon reduction, CSC materials still exhibit higher level of reduction (76 % of CSC species reduced, as compared with theoretical values) than conventional materials (66 % for the calcined sample). As for samples with 0.5 W/nm², it means that CSC materials are quantitatively more reduced than conventional ones in similar condition. As mentioned before, these results can thus partially explain the better level of sulphidation observed for CSC sample at 1.7 W/nm². Finally, TPR results found for materials with 0.5 W/nm² and 1.7-1.8 W/nm² are consistent with the observations made from XPS analyses on the sulphidation behaviour of these materials.

First, reducibility of WO x species has been reported to decrease when their dispersion increases [Thomas et al., 1981;Barton et al., 1998;Macht and Iglesia, 2008], due to stronger interactions with the support (Al 2 O 3 , ZrO 2 ). Highly dispersed WO x supported species are more difficult to reduce. This is coherent with the higher H 2 consumption (expressed per g(W)) for higher loading also explaining the lower level of sulphidation of our catalysts for low W-loadings. Moreover, for low W-loadings, the larger difference in reducibility between [W(OEt) 5 ] 2 -based species and conventional ones matched the larger difference of level of sulphidation: 76 (±5) % rel.

vs. 51 (±5) % rel. vs. 33 (±5) % rel. WS 2 respectively for CSC, conventional dried, and calcined samples. For higher W-loadings (as for 1.7-1.8 W/nm²), this difference in reducibility is smaller, which somehow matches the closer % rel. WS 2 values found between our catalysts: 85 (±5) % rel.

vs. 75 (±5) % rel. vs. 49 (±5) % rel. WS 2 respectively for CSC, conventional dried, and calcined samples.

V.1.d. Characterisation by Transmission electron microscopy (Bright field mode)

Transmission Electron Microscopy (TEM) in Bright Field mode was performed to determine the mean length, L, and mean stacking number, N, of WS 2 slabs. The bar graphs obtained for each catalyst were fitted with a log-normal law. Results are shown Figure 64. Bar graphs are available in appendices. For the CSC catalysts, the mean length and stacking number of the WS 2 crystallites are weakly modified by the tungsten loading. In the case of the dried catalysts, only the stacking number increases for increasing amount of tungsten. On the other hand, the length as well the stacking number of the WS 2 slabs of the calcined catalyst increase.

Finally, in the light of the previous results on the sulphidation level of these catalysts, we can say that when increasing the tungsten loading, sulphidation of CSC catalysts has already reached a plateau in terms of % rel WS 2 (ca. 80 ± 5 % rel ) and the mean length and stacking of the WS 2 crystallites (L ≈ 3.7 nm, N ≈ 2.8) does not change. In contrast, conventional catalysts, whose sulphidation is not as simple as for CSC catalysts, behave differently: increasing the tungsten loading has a strong effect on the length and the stacking on the WS 2 slabs, which has already been reported for MoS 2 crystallites [Payen et al. 1989]. Calcined catalysts are the most sensitive to the tungsten loading upon sulphidation.

TEM in bright field mode, although useful to clearly identify WS 2 crystallites, suffers from a loss of information. As only layered W-S sheets oriented with their (001) basal plane along the electron beam direction are detected, numerous slabs are not considered. In addition, the observation of the W-S sheets lying flat on the support surface is not trivial and would require improving the settings of the apparatus. Considering this, we decided to perform Scanning Transmission Electron Microscopy in High Angle Annular Dark Field mode (STEM-HAADF), a technique which allows a direct map of atomic location to be obtained, with intensities which are dependent on the atomic number Z of the observed atoms. sensitive, which makes it really interesting to discriminate W from Al or Si. In this case, the contrast is proportional to the square of the atomic number, making possible and easy to identify tungsten. Contrast analysis makes possible to observe WS 2 slabs, either oriented planar of perpendicular to the surface. As a consequence, it allows the direct detection of their 2D morphology. Investigations of the 2D morphology of MS 2 slabs deposited on carbon, and observed by STEM-HAADF, have already been reported in the literature, especially for MoS 2 crystallites supported on carbon [Carlsson et al., 2006, Brorson et al., 2007, Hanssen et al., 2011]. Tungsten sulphide has also be studied through Scanning Tunnelling Microscopy (STM) on model supports as Au(111) surface [Füchtbauer et al., 2006], or on graphite through STEM-HAADF. [Carlsson et al., 2004;Brorson et al., 2007] Here, we decided to analyse catalysts with low tungsten loading, so as to limit the stacking of the WS 2 sheets. Sulphidation was carried out at 600°C, instead of 350°C, in order to be sure that the slabs were well crystallised. Analyses were performed on WS 2 -supported ASA -300 (ca. 0.8 W/nm²) and SiO 2-300 (ca. 1.0 W/nm²) CSC catalysts, as well as on conventional calcined catalysts WS 2 -supported ASA (ca. 0.5 W/nm²). Calcined catalyst was selected as representative of conventional and industrial catalysts. there is a clear difference between the two catalysts, we have not yet fully understood the origin of such morphology differences which may directly be linked to the preparation method and/or Part V 174 sulphidation conditions. So we first compared the STEM-HAADF results with density functional theory calculations recently undertaken at IFPEN. [Girleanu et al., in preparation] In the same spirit as for MoS 2 systems [Schweiger et al, 2002], the morphology diagram, shown in Figure 66, revealed that the morphology and atomic edge structure depends on the sulfo-reductive conditions. In the sulfo-reductive conditions corresponding to T = 600°C and H 2 S/H 2 with 15 % mol. H 2 S, the chemical potential of sulphur of the gas phase, ∆µ S , is close to -1.03 eV. The thermodynamically stable morphology as given by the Gibbs-Curie-Wulff laws, is a truncated triangle exhibiting ca. 60% M-edge (the ratio of edge lengths being ). This theoretical result is qualitatively in line with the STEM observations on conventional catalyst sulphided in 15 % mol. H 2 S/H 2 ; however it differs for CSC catalyst. Therefore, we suspect that the hexagonal 2D morphology observed for CSC catalysts probably arise from another phenomenon (kinetic limitation) induced by the CSC preparation method. At this stage, it has not been possible to pin point the origin of the formation of more hexagonal like slabs via the CSC method. However, to check if this phenomenon can be overcome by the sulphidation procedure, we performed a sulphidation of the same CSC catalyst during a longer period of time (30 h) under H 2 S/H 2 at 600°C (5 steps of 6 hours, for details see experimental section). STEM-HAADF pictures of this sample revealed large slabs, highly stacked, which made it difficult to find isolated planar ones.

The main shape of the slabs resembles more the truncated triangle in closer agreement with the theoretical prediction (see Figure 65-c). In addition, a third sulphidation procedure was tested at T = 600°C under pure H 2 S (during 2 h): it reveals a similar truncated triangular shape (see Figure 65-d), as predicted by DFT calculations for high partial pressure of H 2 S. V.1.f. Characterisation by Carbon monoxide adsorption at low temperature (77K), monitored by IR spectroscopy -IR(CO) CO adsorption at low temperature, monitored by IR spectroscopy, is widely used to characterise the sulphide MoS 2 phase. [Bachelor et al, 1984;Peril, 1982;Müller et al., 1993;Travert et al., 2001;Travert et al., 2006] CO behaves as a probe molecule, highlighting acidity of both the support and the active phase. Usually, CO is first adsorbed on the sulphide phase, but due to the low amount of tungsten and the high dispersion of WS 2 slabs on the surface, numerous competitive adsorption sites on the support for carbon monoxide exist.

Figure 67-a shows the IR(CO) spectra, normalised by the amount of W in the samples, and not baseline corrected, of CSC, conventional dried and calcined catalysts, with ca. 1.7 W/nm², and a sulphidation temperature of 350°C (H 2 S/H 2 , 15 % mol. H 2 S). Note that only spectra collected at saturation of the sulphide phase with carbon monoxide are shown (see experimental part for more information).

Part V 176

Similarly, Figure 67-b shows the IR(CO) spectra, normalised by the amount of W in the samples, and not baseline corrected, of CSC catalysts with increasing W-loadings (from 0.5 to 1.7 W/nm²), where they are compared to the IR(CO) spectrum of the calcined sample, prepared with 0.5 W/nm². Note that these samples underwent sulphidation at 600°C (H 2 S/H 2 , 15 % mol. H 2 S) instead of 350°C. Sulphidation at this temperature was realised to get a well formed WS 2 phase, as sulphidation of samples with low W-loadings at 350°C (see part V.1.2) proved to give low relative amounts of WS 2 .,Besides, it was the opportunity to analyse two samples previously studied by STEM-HAADF, e.g. the CSC catalyst with 0.8 W/nm² and the conventional calcined one with 0.5 W/nm², in order to observe if the IR(CO) signal was different for 2D morphologies that are respectively hexagonal-like or triangular-like. As for Figure 67-a On Figure 67-a, CSC catalysts exhibit 3 bands at ν(CO) = 2068 cm -1 , ν(CO) = 2121 cm -1 and ν(CO) = 2160 cm -1 . The two first ones are assigned to CO adsorbed on WS 2 edge sites according to previous works. [Zuo et al., 2004], while the last one is attributed to CO mainly adsorbed Brønsted acid sites of the catalysts. By analogy with IR(CO) data on MoS 2 , the two bands attributed to CO adsorbed on WS 2 edge sites are assumed to be assigned to CO interacting with W-edge (2121 cm -1 ) and S-edge (2068 cm -1 ) sites respectively. [Travert et al, 2001;Travert et al., 2006]. The ν(CO) vibration band at 2121 cm -1 exhibit very low intensity on the dried catalyst and is totally absent in the calcined one. Moreover, the ν(CO) vibration band at 2068 cm -1 is not visible on the two conventional catalysts.

We are currently investigating what could explain such differences between the catalysts.

Several hypotheses can be formulated. Looking at the two major bands, tentatively attributed to CO interacting with W-edge sites and S-edge sites, we could propose that a specific 2D-morphology would be responsible for these signals. Besides, the FWHM of the band at ν = 2121 cm -1 , surprisingly very sharp, could highlight very well crystallised edges, on which CO could easily be adsorbed on one type of site, in only one fashion, linear or bent. Conventional catalysts, on which slabs would have more defects on their edges, would exhibit a larger distribution of adsorption sites, shown by a large signal in IR(CO), decreasing dramatically their intensity.

Data collected from integration of the IR(CO) spectra between ca. 2140 cm -1 and 2050 cm -1 , and normalised by the amount of sulphide phase WS 2 , are reported in Table 8, as expressed in a.u/cm/mol(W)* where a.u stands for absorbance units and where mol(W)* stands for mole of tungsten engaged in the sulphide phase, in the sample. a Calculated with the amount of CO adsorbed at saturation of the sulphide phase, and the mass of the pellet

W/nm²

CSC

The amount of CO interacting with the sulphide phase increases with the W-loading of CSC catalysts, from 1.0 to 5.0 a.u/cm/mol(W)*. This result means that for CSC samples, when increasing amount of W are deposited and sulphided (600°C), either interactions of CO on W edge sites are stronger, or more edge sites are readily available for CO interaction. Besides, the value found for the conventional catalyst prepared with 0.5 W/nm² is 2.5 times higher than that of its CSC counterpart, which is surprising. This observation could be linked, as aforementioned, to the presence of more edge sites or stronger interactions of CO with edges of WS 2 slabs for the conventional calcined sample.

V.1.g. Catalytic results and discussion

Tungsten-based catalysts being known for their high activity in aromatic hydrogenation [Stanislaus and Cooper, 1994;Hensen et al., 2007], the catalytic performances of the catalysts were tested in hydrogenation of toluene. The feed was composed of toluene (reactant), cyclohexane (solvent), dimethyldisulphide (sulphiding agent) and aniline. This latter compound is used to inhibit the acidity of the support, and avoid isomerisation of the reactant by the acid sites of the support. However, we considered, in a first approximation, that this so-called HYD rate r i ' was representative of the catalysts at their steady state. Moreover, as it was not possible to analyse all the spent catalysts, we only performed XPS measurements on specific ones, mainly exhibiting low sulphidation level before test. We found that:

-conventional dried and calcined catalysts with 0. In Figure 68-b, the HYD intrinsic rate of CSC and conventional catalysts is very similar to the previous one described in Figure 68-a. Indeed, the amount of sulphide phase is supposed not to change for most of the catalysts. On the whole, the main results is that the HYD intrinsic rate of the CSC catalyst is ca. 0.33 mol(tol)/mol(W)*/h, which is about 2.2 times higher than the one observed for the conventional calcined catalyst.

Then, we used the mean length and mean stacking number to refine our interpretation of the catalytic activity. For conventional catalysts, we have observed that increasing the tungsten loading led to an increase of the stacking and/or the length of the WS 2 slabs. This last phenomenon causes a decrease of the number of atoms on the edges of the slabs, by increasing the number of atoms belonging to the basal planes. As a consequence, the amount of active sites (which are supposed to be on the edges) decreases: this could be at the origin of the decrease of HYD rates. In the case of the CSC catalysts however, there is no direct explanation justifying the presence of an optimum. Therefore we decided to renormalize the activity by considering the geometrical model of WS 2 slabs initially proposed by Kasztelan et al.

[ Kasztelan et al, 1984] This will in particular help us to calculate the number of atoms on the edges.

Part V 182

For a given slab length, the 2D morphology of a crystallite is defined by two parameters, n M and n S , standing respectively for the number of M-edge and S-edge atoms, as illustrated in Figure 69.

L n n W W d S M = + × - ) ( ) ( Eq. 6
in which d(W -W) ≈ 0.32 nm according to the WS 2 structure.

Moreover, we decided to use the following hypotheses: Evolution of catalysts during sulphidation: from surface species to active WS 2 phases

183

(1) M-edge and S-edge sites are HYD active. Indeed, Gandubert et al [Gandubert et al., 2008] assign the hydrogenating activity (toluene hydrogenation) of their CoMoS/Al 2 O 3 catalysts to active sites located on M-edge of crystallites. M-edge sites' HYD activity was also proposed by Moses et al., from their DFT calculations on thiophene hydrogenation by MoS 2 as part of the thiophene HDS reaction. [Moses et al., 2007]. However, involvement of S-edge sites cannot be fully ruled out. Therefore, we also decided to include them as HYD active sites.

(2) corners are also considered as HYD active (their reactivity being not well understood)

(3) every WS 2 slab, on the catalyst surface, can be described by only one geometrical model ( 4) in a first approximation, hexagonal model were chosen for CSC catalyst, and truncated triangle model for conventional catalysts, independently of the W loadings.

However, note that we do not know the 2D morphology of WS 2 slabs present on spent catalysts, after test. This morphology could be either more triangular or more hexagonal, and could thus influence the results of our activity normalisation.

Then we used the geometrical model, as it was done previously by Gandubert et al, [Gandubert, PhD thesis, Lille, 2006] to calculate the number of edge sites (W-edge and S-edge atoms as well as corners sites), relative to the total number of atoms in one slabs. We considered that this amount of edge sites was responsible for the observed HYD rate. Table 10 summarizes some of the compromises found for the geometrical parameters of each catalyst, depending on the tungsten loading. Best comprises are denoted in bold. Conventional dried catalysts exhibit a quasi constant TOF at ca. 0.82 (±0.13) mol(tol)/mol(site)/h, whatever the tungsten loading. For the calcined samples, the TOF decreases from ca. 0.55 (±0.09) to 0.35 (±0.06) mol(tol)/mol(site)/h when the W loading increases, as seen before on Figure 68-b. At low as at high W content, TOF of CSC and dried catalysts are similar but in particular, TOF of CSC materials reaches a maximum at ca. 1.16 ± 0.19 mol(tol)/mol(site)/h for a W-loading of 1.7 W/nm². This means that the nature of active sites on CSC samples are different for this loading, as it was highlighted by IR(CO) analyses for samples prepared at 350°C.

Part V 184

We performed similar catalytic tests on CSC and conventional calcined samples sulphided at 600°C before test, and exhibiting between 0.5 W/nm² and 1.7-1.8 W/nm². It was the opportunity to study if any difference of activity was observed for the samples on which hexagonal (CSC) or truncated-triangular (conventional) slabs were directly observed by STEM-HAADF before test. Intrinsic HYD rate r i expressed in mol(tol)/mol(W)/h is shown in Afterwards, we normalised the intrinsic HYD rate by mole of tungsten sulphided, as previously done for catalysts prepared at 350°C. To do so, XPS analyses were performed prior to catalytic tests, and revealed that the level of sulphidation was lying between 78 and 87 (±5) % rel. WS 2 for CSC samples while it was ranging from 81 to 82 (±5) % rel. WS 2 for calcined ones, depending on the W-loading. Spent catalysts did not underwent XPS analyses, but as the amount of WS 2 was rather high for each catalyst before the catalytic test, we supposed that the aforementioned % rel. WS 2 values could be used to normalise the intrinsic HYD rates, in a first approximation. Results are depicted in Figure 71-b. Intrinsic HYD rates follow the same evolution as before normalisation by the amount of WS 2 , which is not surprising considering the similar % rel. WS 2 observed, and finally does not give more information than Figure 71-a.

Then, we used the 2D geometrical model to calculate the TOF of these catalysts sulphided at 600°C. The parameters of the 2D models are available in Table 11. Conv. calc.

CSC

First, there is a significant difference of slab length L between CSC and conventional calcined catalysts. For the CSC catalyst, while the mean value is similar for 0.5 W/nm² and 0.8 W/nm² with ca. 3,4 nm (34 Å), it strongly increases to 5.1 nm², highlighting a strong sintering effect. The low values are probably due to grafted surface species which exhibit low mobility upon formation of WS 2 slabs during sulphidation. The highest one found for the 1.7 W/nm² loading probably comes for aggregation of more W centres during sulphidation, due to more mobile species belonging to the layers loosely bonded onto the grafted one. For the calcined sample, the mean slab length is similar with ca. 3.9 nm. It is tentatively assigned to the strong interaction of the amorphous WO 3 phase with the surface, which leads to a reduced mobility of W species upon sulphidation.

Second, this difference of slabs length leads to different amount of edge sites on slabs' edges. For CSC catalysts, when increasing the slab length, the relative percentage of edge site decreases, from 32.6 % to 22 % of the number of W atoms in one slab. .For the calcined material, about 28.5 % of edge sites is calculated. These values were used to calculate the TOF.

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The TOF, expressed in mol(tol)/mol(site)/h, is shown in Figure 72. The TOF of CSC and conventional calcined catalysts slightly decreases, and no more maximum is observed for the CSC sample with a W-loading 1.7 W/nm², compared to its CSC counterpart sulphided at 350°C. Then, the TOF of conventional catalysts is lower than the one of CSC samples, as previously seen when these materials were sulphided at 350°C.

We tried to refine our interpretation of catalytic results using results obtained by IR(CO)

analyses. What is surprising is that quantification results, reported in Table 8 and Table 9, show different amounts of CO interacting with tungsten edge sites, which cannot be directly correlated to the TOF. For catalysts with 0.5 W/nm², sulphided at 600°C, the conventional calcined sample shows 2.9 times more CO interacting with sulphided tungsten edge atoms than its CSC counterpart, while its TOF is ca. 1.6 times lower (normalisation of values found in Table 9 by the corresponding %edge sites of Table 11). Similarly, IR(CO) analyses on catalysts with 1.7 W/nm², and sulphided at 350°C (see Table 8) reveal that much more CO interacts with edge sites on the CSC sample than on conventional ones. Even if the CSC sample shows a higher TOF, it does not reflect the differences observed in IR(CO) between the dried and the calcined catalysts.

V.1.h. Conclusion on the influence of the tungsten loading on the genesis and activity of the active phase of WS 2 /ASA catalysts

To conclude, we prepared well-characterised WS 2 -supported ASA catalysts, especially by varying the amount of W deposited. We managed to understand their HYD activity at the molecular level thanks to their sulphidation level obtained by XPS, and with the characteristics of their WS 2 slabs revealed by TEM, geometrical models and IR(CO) analyses. The results of our investigations can be summarized as follows:

(1) The CSC method allows the preparation of well-sulphided catalysts, exhibiting level of sulphidation ranging from 76 to 85 (± 5) % rel. WS 2 as from 0.5 W/nm² to 3.7 W/nm².

These catalysts exhibit higher or similar level of sulphidation than their conventional counterparts. The differences of sulphidation level are partially explained by the reducibility of their oxide surface species, as shown by TPR experiments.

(2) When sulphided at 350°C (15 % mol. H 2 S/H 2 ), the intrinsic rate of hydrogenation in toluene hydrogenation in presence of aniline is higher for CSC catalysts than for conventional ones, especially compared to their calcined counterparts. The same observation is made when CSC and calcined materials are sulphided at 600°C.

(3) With the help of STEM-HAADF analyses, TEM data, and 2D geometrical model of WS 2 slabs, refinement of catalytic activities allowed the expression of the TOF of our catalysts. The TOF of CSC materials is found to be higher than the conventional ones'.

(4) Geometrical models were based on the average 2D geometry of WS 2 slabs as observed from STEM HAADF analyses and DFT calculations. In this regard, we report for the first time the average 2D-morphology of WS 2 slabs of catalysts supported on industrial support (amorphous silica-alumina or silica): catalysts prepared using conventional precursors exhibits rather truncated triangular slabs. The origin of the formation of more hexagonal like ones via the CSC preparation method has not been ruled out yet.

(5) IR(CO) analyses performed on catalysts sulphided at 350°C or 600°C reveal that CO interacts with edge site of WS 2 slabs in a different fashion for CSC and for conventional catalysts. Noteworthy is the observation of a narrow vibration band at ν(CO) ≈ 2124 cm -1 , assumed to be assigned to CO adsorbed on W-edge atoms. This narrow band, which is not visible on conventional samples sulphided at 350°C, seems to be observed only for catalysts with high level of sulphidation. We were not able to find a Part V 190 simple link between the quantity of CO interacting with the WS 2 phase of our catalysts and their TOF.

As a consequence, we propose that the higher TOF of CSC catalyst can be attributed to two possible effects. On the one hand, it develops specific nature of edge active sites or specific distribution of edge active sites during catalytic tests. This effect cannot be revealed by IR(CO)

but is revealed by STEM highlighting the specific hexagonal morphology before test. This result may imply that the distribution of S-edge/W-edge might also be different within each crystallite during test, thus leading to different TOF. With that respect, this would also mean that S-edge could play a role during toluene hydrogenation. On the other hand, we cannot rule out that different support effects may influence the reactivity itself: this support effect could be inherited from the CSC preparation method itself.

In order to further understand the formation and the reactivity of tungsten sulphide phases, we decided to investigate the influence of the sulphidation temperature, which has been tackled at the end of this part V.1.

V.2. Influence of the sulphidation temperature on CSC and conventional catalysts

In part V.1, we showed that the highest HYD rate was obtained for the CSC catalyst, prepared around 1.7 W/nm². Therefore, we decided to focus on CSC and conventional catalysts prepared at ca. 1.7-1.8 W/nm² (e.g. ranging from 11 to 13 % wt. W), and investigate how the sulphidation temperature influences their properties and their catalytic activity in toluene hydrogenation. Part V.2 is thus dedicated to the characterisation of sulphide phases by either XPS, TEM, STEM-HAADF and/or IR(CO) analyses for various sulphidation temperatures ranging from -25°C to 600°C. We will present the intrinsic rate of hydrogenation of our catalysts, and refine catalytic results through the calculation of Turn-Over Frequencies thanks to geometrical models of WS 2 slabs. Parallel with these refinements, influence of peculiar active sites/species (such as CUS or sulfhydryl species M-SH) on observed TOFs will be discussed.

V.2.a. Characterisation by X-ray photoelectron spectroscopy (XPS)

The sulphidation level of CSC and conventional catalysts was studied by decomposition of catalysts calcined at 500°C [Breysse et al., 1988]. In their study, the authors found that the level of sulphidation exhibit an inflexion point located around 300°C, which is close to the inflexion point (see Figure 74) found for our calcined sample at about 350°C. Besides, in order to investigate the support effect between ASA and alumina, we compared the level of sulphidation of our conventional dried sample with another dried one, prepared on γ-Al 2 O 3 (1.8 W/nm² also).

The latter shows a level of sulphidation of ca. 10 % rel. WS 2 when sulphided at in similar conditions (350°C, 2 h, 15 % mol. H 2 S/H 2 ) which is more than 7 times lower than the dried catalyst prepared on ASA. The higher level of sulphidation observed on the dried material supported on ASA can be explained by the easier sulphidation of samples prepared on the ASA support developing weaker "support -oxide phase" interactions than alumina.

Moreover, with the use of [W(OEt) 5 ] 2 as W precursor, the S-shaped curve representing the level of sulphidation of CSC catalysts is strongly shifted to lower temperatures, with an inflexion point located at around -25°C. Indeed, we could surprisingly sulphide our CSC materials at room temperature, where about 50 % rel WS 2 is reached. We were also able to synthesise a WS 2 phase at -25°C, which is as far as we know the first time that W-based catalysts are reported to exhibit tungsten sulphide below 0°C. In the case of conventional catalysts, the first entities of WS 2 appear at ca. 150°C but sulphidation begins earlier, with the apparition of a partially sulphided phase (intermediate phase) denoted WO x S y . CSC catalysts, however, exhibit sulphidation level far above the ones ever observed for conventional catalysts at this temperature.

In a symmetric way, Figure 75-a shows that for CSC catalysts, the amount of nonsulphided W(VI) phase is lower than for conventional ones, as from sulphidation at -25°C. Then the amount of the oxide phase slowly decreases until 150°C. At this temperature, the W(VI) phase of conventional catalysts begins to decrease, more rapidly for dried catalysts than for their calcined counterparts. Finally, quasi complete conversion of the oxide phase is achieved after sulphidation at 600°C, with 9 ± 2 % rel W(VI) remaining. oxysulphide species MO x S y [Hensen et al., 2007;Payen et al., 1988;van Der Vlies et al., 2002a;Rochet, PhD thesis, Paris, 2011], or via MS 3 [Hensen et al., 2007;Payen et al., 1988;Rochet, PhD thesis, Paris, 2011;Sun et al., 2001] -the reduction of tungsten from a +VI to a +V oxidation state, concomitant with the formation of an intermediate phase where sulphur is slowly incorporated in the oxide phase -the transformation of this partially sulphided oxysulphide phases into WS 2 .

Note however that due to their high reactivity, oxide species obtained with the CSC method undergo sulphidation at lower temperatures than conventional species. Furthermore, they all exhibit a ratio close to 2.2 when the sulphidation temperature reaches 350°C. These results indicate that for temperatures lower than 350°C, the sulphide phase is not composed of WS 2 slabs with a 1:2 stoichiometry. Different hypotheses could explain such a stoichiometry. First, the 2D morphology of WS 2 slabs, for a given cluster size (e.g. number of M-Part V 196 edge atoms), influences the S/W atomic ratio and can lead to excess or lack of sulphur atoms.

For example, Schweiger et al. [2002] have shown that for triangular shaped MoS 2 slabs exhibiting 10 Mo atoms on edges, the S/Mo atomic ratio on 100 %S Mo-edge was 2.73, an increases to 3.60 for slabs with 4 Mo-edge atoms. Second, we could expect a decrease of the sulphur coverage on slabs' edges when increasing the temperature. Last but not least, WS 2 slabs genesis could be achieved through the formation of tungsten species supersaturated with sulphur, such as WS 3 , as discussed just above. Then, to get further insights into the understanding of the sulphidation of our catalysts, we tried to investigate the decomposition of S 2p spectra of CSC catalysts, but we were not able to find significant results.

Finally, the overall coverages of tungsten on the support's surface are evaluated by XPS.

The W/Al and W/Si atomic ratios shown in Figure 76, highlight that there is no significant difference between the catalysts, whatever the sulphidation temperature. These TEM micrographs obviously reveal the growth of WS 2 layers as a function of sulphidation temperature. On TEM micrographs, no WS 2 slabs are observed on the catalyst prepared at -25°C while nanosized spot-like entities (1 nm to 2 nm) are visible. Note that the formation of nanosized particles was reported in the literature for NiW, NiMo and CoMo samples supported on alumina or silica. They were assigned to non-crystalline W or Mo (oxy)sulphide entities, barely visible in samples sulphided at higher temperatures like 600°C. [Reinhoudt et al., 1998;Kooyman et al., 2001;Okamoto et al., 2009] Then, mean slabs length and mean stacking number obtained from picture analysis are summarized in For CSC catalysts and conventional dried catalysts, the mean length of the WS 2 crystallites increases when the sulphidation temperature increases. As shown in Table 12 and in Figure 4 between 350°C and 600°C, it respectively varies from ca. 3.8 nm to 5.1 nm for the CSC catalyst, and from 3.7 nm to 4.4 nm for its conventional counterpart. In the case of the calcined catalysts, there are no significant changes: L ≈ 4.0 nm. For the stacking number, CSC and conventional dried catalysts exhibit the same behaviour, with a mean stacking between 3.1 and 3.6. As before, the calcined catalyst does not appear to be sensitive to the sintering effect, as N is constant at ca 2.7. This weaker sintering effect observed for the latter sample (calcined) could arise from stronger interactions between oxide surface species and the ASA support, decreasing the mobility of tungsten atoms and thus preventing nucleation of stacked WS 2 slabs.

For sulphidation temperature lower than 350°C, only CSC catalysts have been analysed. From 23°C to 150°C, the mean length is barely changed with around 3.2 nm, as for the mean stacking number which ranges from 2.6 to 2.4. In the literature, Glasson [Glasson, PhD thesis, Lyon, 1999] and Baubet [Baubet, PhD thesis, Lyon, 2013], who studied calcined (Co)MoS 2 -supported catalysts, showed that the mean length of MoS 2 slabs increases when the sulphidation temperature increases. Concomitantly, they observed that the stacking number barely increases, or could even be stabilised at around 400°C. Their results are thus consistent with ours. Note however that we only considered catalysts with tungsten loading of ca. 1.7-1.8 W/nm² (e.g. ca. 11-12 % wt. W) and catalysts with different tungsten amounts can exhibit WS 2 slabs with different behaviours. In part V.1.c) we showed that for catalyst sulphided at 600°C, different morphologies could be obtained depending on the preparation method. The CSC method gave rather hexagonal WS 2 slabs, while the conventional method allowed the preparation of truncated triangular ones.

However, as sulphidation at 600°C is never used in industrial processes, and that the main part of our study deals with sulphidation and catalytic test performed at 350°C, we carried out STEM-HAADF analyses on samples sulphided at 350°C. As before, we chose a calcined catalyst, exhibiting ca. 0.5 W/nm², and a CSC one, loaded with ca. 0.8 W/nm². Figure 79 represents STEM-HAADF micrographs of catalysts sulphided at 350°C and 600°C.

At 350°C, we cannot distinguish a clear morphology, whatever the preparation method. For the CSC catalyst, we can see atomically resolved WS 2 slabs, but stacking effect and difficulties to identify an isolated slab made the 2D shape elucidation almost impossible. Moreover, as in TEM micrographs, STEM-HAADF pictures highlight the presence of nanosized spot-like entities (arrows, on the micrographs), dispersed on the surface. These small entities are much more visible on the conventional catalyst, where it was hard to distinguish WS 2 slabs lying flat on the surface.

Part V At 600°C, hexagonal slabs for the CSC catalyst are formed, whereas a truncated triangular ones for the calcined catalyst. There are still a few nanosized dots on the CSC catalyst surface, not much as before. However, there are far less of these particles on the calcined one, compared with the sulphidation at 350°C.

These analyses have shown that it was difficult to distinguish the 2D morphology of the WS 2 slabs when catalysts are sulphided at 350°C. This is mainly due to the difficulties to find isolated slabs, lying flat on the surface, and not to a low sulphidation level, as slabs "edgeoriented" are visible by STEM and TEM BF. In addition, well-formed slabs exhibiting clear 2D morphology are expected for WS 2 with high degree of crystallinity, supposedly obtained for high sulphidation temperatures (600°C and above). On this purpose, crystallinity of WS 2 slabs is difficult to evaluate. XRD analyses could be performed, but they would only focus on the difference of full width at half height (FWHH) of the stacking peak (2θ ≈ 14°) of WS 2 , which can suffer from a lack of precision because of the low stacking number of WS 2 slabs observed on our catalysts (3 to 4). Besides, crystalline compounds usually exhibit XPS photopeaks with small FWHH while poorly crystalline ones show broader peaks. As a reference, our assynthesised WS 2 sample prepared by sulphidation of [W(OEt) 5 ] 2 at 600°C (H 2 S/H 2 15 % mol. H 2 S) exhibits a W 4f photopeak where the W4f 7/2 contribution of W(IV) reveals a FWHH of around 0.82 eV. For the WS 2 /ASA catalysts, the main contribution assigned to W(IV) in the W 4f photopeak, e.g. W 4f 7/2 , is ca. 1.53 eV when the materials were sulphided at 23°C and is ca.

1.05 eV when the materials were prepared at 600°C. As the FWHH decreases and gets closer to the value found for pure WS 2 , we suppose that a better crystallinity of the sulphide phase is reached when sulphided at high temperatures.

Moreover, as the contrast of STEM-HAADF pictures is sensitive to the atomic number, the intense white spot-like entities are attributed to W atoms probably assembled in clusters of different sizes. However, we were not able to figure out if these clusters were the fingerprints of tungsten oxide, and/or partially or fully sulphided tungsten atoms. Moreover, although CSC catalysts have the same level of sulphidation, it is not supposed to influence that much parallel with the sulphidation temperature, the level of sulphidation could influence the presence of these nanosized spot-like entities Evolution of catalysts during sulphidation: from surface species to active WS 2 phases 201 23°C, the catalyst exhibits a broad band between 2170 cm -1 and 2080 cm -1 , attributed to CO interacting with a partially sulphided phase. Indeed, ν(CO) vibration of carbon monoxide interacting with W atoms exhibiting oxidation states lower than +VI are reported between 2198 cm -1 and 2154 cm -1 [Yan et al., 1991]. For sulphidation at 350°C, similar features are present, as well as two additional bands: a rather sharp one, positioned at ν(CO) = 2121 cm -1 , Part V

202

and a very weak one, close to 2068 cm -1 . The sharp band is attributed to a ν(CO) vibration band, assumed to be assigned to CO adsorbed on W-edge atoms, as already discussed in part V.1, while the weak one is attributed to a ν(CO) vibration band, tentatively assigned to CO interacting with S-edge atoms. Presence of the narrow band at ν(CO) = 2121 cm -1 for sulphidation at 350°C is due to a better sulphidation of the sample compared to the one prepared at 23°C, probably leading to a reduced distribution of adsorption sites for CO. Then, sulphidation at 600°C gives a sharp band at ca. 2124 cm -1 , more intense than the one observed for sulphidation at 350°C. Quantitative bands' integration reported in Table 13, reveals that increasing the sulphidation temperature of the materials leads to a higher amount of CO interacting with the sulphide phase. Normalisation of the CO quantification by the amount of sulphide phase leads Evolution of catalysts during sulphidation: from surface species to active WS 2 phases 203 to values spread from 3.2 to 4.7 a.u/cm/mol(W)* where mol(W)* stands for the amount of tungsten (mol) incorporated in the sulphide phase.

Finally, IR(CO) analyses show that sulphidation at low temperatures leads to partially sulphided phases, where tungsten is no more in a +VI oxidation state. Increasing the temperature gives rise to particular sites, with which CO interacts in a peculiar fashion. It leads to a sharp signal at around 2124 ± 3 cm -1 , assigned to a narrow distribution of either strong or abundant sites. In the case of the vibration attributed to the interaction between CO and S-edge atoms, the low intensity of the vibration band prevents an accurate quantification from being performed. Moreover, the blue shift observed for the CO stretching vibration, from 2068 cm -1 to 2076 cm -1 between 350°C and 600°C, could indicate that the interaction between CO and W atoms is stronger when sulphidation is carried out at 350°C, which probably comes from CO interacting with WS 2 slabs which are smaller, or which possibly exhibit a lower amount of adsorption sites. a Calculated with the amount of CO adsorbed at saturation of the sulphide phase, and the mass of the pellet

V.2.e. Catalytic results and Discussion

We performed catalytic tests on CSC and conventional catalysts sulphided between 23°C and 600°C. Note that the test, previously described in part V.1) is undertaken at 350°C, increasing the % rel WS 2 of catalysts sulphided ex-situ at temperatures lower than 350°C: the active phase will thus be different from the one we analysed. As a consequence, some spent catalysts were analysed by XPS to get insights into the WS 2 phase which has really catalysed the hydrogenation reaction. Using the same approach as part V.1), we first calculated the HYD rate of catalysts normalised by mole of tungsten in the sample: r i . , which is shown in On the whole range of sulphidation temperature, CSC catalysts exhibit higher HYD rates than conventional ones. The HYD rate slowly decreases for temperatures higher than 250°C, no matter what the preparation method. It indicates that sulphidation between 250°C and 350°C is sufficient to provide the best catalytic activity achievable.

To get further insights into the influence of the level of sulphidation of catalysts, we took into account the % rel . WS 2 of spent catalysts. Note that as it was not possible to analyse all the spent catalysts, we only performed XPS measurements on specific ones, exhibiting low sulphidation level before test. We found that:

-CSC and conventional dried catalysts, pre-sulphided at 23°C, previously exhibiting from 50 to 0 % rel. WS 2 , reveal 84 (±5) % rel. WS 2 after test -the conventional calcined catalyst, pre-sulphided at 23°C, previously exhibiting no WS 2 phase detected by XPS, exhibits 80 (±5) % rel. WS 2 after test -as previously reported in part V.1, the calcined catalyst pre-sulphided at 350°C reveals 78 (±5) % rel. WS 2 after test Therefore, we assumed that CSC, dried and calcined spent catalysts display similar average levels of sulphidation after test. Moreover, note that catalysts sulphided at temperatures lower than 250°C where not submitted to a post treatment under argon at 250°C, as post treatment at temperature higher than the pre-sulphidation one could modify the sulphide phase of catalyst.

Evolution of catalysts during sulphidation: from surface species to active WS 2 phases 205 Finally, the combination of measured % rel. WS 2 and estimated ones were used to calculate the HYD rate r i ', expressed in mol(tol)/mol(W)*/h, as shown in Figure 82. As before normalisation by the % rel. WS 2 , CSC catalysts exhibit higher HYD rates than conventional ones on the whole range of sulphidation temperature. The HYD rate increases for sulphidation between 23°C and 250°C, and slowly decreases for higher temperatures, no matter what the preparation method. Between 23°C and 250°C, we already demonstrated that there was a deep transformation of the sulphide phase, especially around 250°C -350°C, which probably explains why the HYD rate increases with the sulphidation temperature. Then for sulphidation temperatures higher than 350°C, the catalytic properties during the reaction were assumed to be stable, because the reaction temperature was equal or lower than that used for the catalyst pre-sulphidation, before test. Therefore, the decreases of activity observed for CSC as well as conventional catalysts is probably attributed to a sintering effect, more important for CSC and dried ones as their HYD rates decrease more rapidly than the calcined ones. This qualitative explanation is consistent with TEM data, reported in part V.2.b) where CSC and conventional dried catalysts exhibited longer WS 2 slabs, with higher stacking numbers Part V 206 compared to calcined ones, probably due to stronger interactions between the ASA support and amorphous WO 3 species observed on the calcined sample.

In order to take into account this sintering effect, we used the geometrical models presented part V.1.d) to normalise the HYD rate by the number of active edge sites. We calculated models for catalyst sulphided between 350°C and 600°C, using the same hypothesis as before. Note that the slabs length used for the calculation is the length measured for catalysts before test, as TEM measurements have not been run on spent catalysts so far. The best compromises found for geometrical models are presented Table 14, in bold letters. Looking at Table 14 for CSC materials, increasing the slabs length from 3.8 nm (38 Å) to 5.1 nm divides the amount of active sites by ca. 1.3 for a hexagonal geometrical model. It directly highlights the loss of active sites due to the sintering effect of WS 2 slabs. For the conventional samples, represented by truncated triangles, the amount of active sites is divided by ca. 1.1 for the dried catalyst while it does not change for the conventional calcined one.

Finally, CSC materials tend to exhibit less active sites than conventional ones when sulphided at temperatures higher than 350°C.

The corresponding TOFs (r i "), expressed in mol(tol)/mol(site)/h are shown On Figure 83, we can see that for each catalyst, the HYD rate r i " is rather constant whatever the sulphidation temperature, considering that W atoms on W-edge, S-edge and corner sites are hydrogenation active sites. It means that normalisation of the intrinsic HYD rates by the amount of active sites, calculated with geometrical models, reveals an average TOF for each catalyst. In this case, TOFs of conventional catalysts are still lower than the CSC ones. Supposing that the 2D morphology of CSC catalysts could be more triangular shaped (as truncated triangular slabs reflect the most thermodynamically stable geometry from DFT calculations -see part V.1.e), we tried to calculate similar TOF by using truncated triangular shapes for CSC samples. Results were found to be barely different from the ones discussed just above. Finally, it highlights that, as for catalysts prepared at different tungsten loadings and sulphided at 350°C (H 2 S/H 2 ), another parameter influencing hydrogenation reactions has to be at stake.

One first parameter could be the stacking number, which has been set to 1 in our model.

Figure 78 shows that between 350°C and 600°C, calcined catalysts are less stacked (2.7 -2.9) than CSC (3.1 -3.5) and dried ones (3.0 -3.6). We can thus wonder if each layer of the stacked crystallites exhibits the same HYD activity. In this spirit, several studies have reported structureactivity relationships for sulphide catalysts. [START_REF] Massoth | Proceedings of the Fourth International Conference on the Chemistry and Uses of Molybdenum[END_REF] concluded that, for Mo/Al 2 O 3 catalysts, all the edge planes of the clusters are HYD active.

With their geometrical model, Kasztelan et al. [Kasztelan et al., 1984] concluded that HYD are Part V 208 performed at the edge planes of MoS 2 . Later on, Daage and Chianelli [Daage and Chianelli, 1994] proposed the so-called "rim-edge" model (see Figure 84) in which HYD is catalyzed exclusively on the top and bottom of edge planes, called rim sites. If we try to draw a parallel with our catalytic results on toluene HYD, and in the spirit of Daage model, WS 2 slabs highly dispersed on the surface, and exhibiting low stacking number

(1 or 2) would be more efficient HYD catalysts, as they would maximize their number of rim sites.

Note that the same reasoning applies to "brim sites" proposed by Topsøe et al. [Topsøe et al., 2005], located on the top of monolayered sulphide slabs. However, our results do not match the Daage model as the more hydrogenating catalysts also exhibit the more stacked WS 2 slabs, especially at high sulphidation temperatures. One explanation could be that Daage's model, established for HDS and HYD reaction of dibenzothiophene, is not suitable to describe hydrogenation of toluene. Besides, from TEM experiments and catalytic results, stacking does not seem to influence the toluene HYD for catalysts exhibiting stacking number between ca. 2.7 and 3.6.

Besides, a study of Sakashita et al. [Sakashita et al., 2001] reveals that surface orientation of the support promotes peculiar reactions: MoS 2 crystallites would show higher HYD rates when located on spherical-like alumina exhibiting {111} and {100} planes compared to crystallites located on {100} planes of plate-like alumina planes [Sakashita et al., 2001].

Nevertheless, the support used in our study, which is composed of alumina platelets and amorphous silica, is supposed to be stable in the range of temperature we used, and alumina crystallites are not expected to change, therefore not influencing the catalytic activity.

IR(CO) analyses performed on CSC catalysts sulphided at 350°C and 600°C showed that CO was interacting with a large distribution of adsorption sites (on W-edge) at 350°C, and with a narrower one at 600°C: these highly reactive sites probably being the so-called CUS. However, Evolution of catalysts during sulphidation: from surface species to active WS 2 phases 209 as the TOF does not seem to be different for these two temperatures, we could suppose that there is little influence of the different adsorption sites, and that CO adsorption has only allowed us to quantify the amount of WS 2 phase.

Then, another parameter can be taken into account to improve our understanding of the catalytic results, which is the presence on sulfhydryl species MSH on WS 2 slabs edges. Indeed, sulfhydryl species, present on slabs edges, take part into the HYD mechanism of toluene, as described by Gandubert et al. [2008] and Guernalec et al. [Guernalec et al, 2004]. From DFT calculations performed at IFPEn (see part V.1.e), WS 2 crystallites modelled in conditions close to our sulphidation conditions (calculations performed at 600°C) revealed that M-edges exhibit a sulphur coverage of 50 %, while S-edges exhibit a sulphur coverage of 87.5 %. Considering in a first approximation that WS 2 and MoS 2 crystallites behave similarly, MSH species could be stabilised either on W-edge of S-edge. Indeed, Prodhomme et al [Prodhomme et al. 2011] have evidenced by DFT calculations, that for MoS 2 slabs, Mo-edge with 37 %S exhibiting sulphur vacancy (e.g. CUS) as well as Mo-edge with 50 %S and 50 %H can be stabilized in relevant HDS conditions. The presence of these two types of sites is expected to favour HDS reactions, as CUS represents readily adsorption sites for sulphided molecule, which can undergo hydrogenation thanks to available H ad-atoms diffusing from neighbouring MSH species. Note that the authors reported that even is the presence of CUS is scarce on Mo-edge, they are abundant on S-edge, which might thus play an important role in hydrodesulphurization reactions.

For toluene hydrogenation in particular, Gandubert et al. [2008] have shown that for CoMoS phases, the promoted M-edge with CoMo mixed site provides a stable configuration for toluene adsorption. The stabilisation of adjacent MSH and MH species on the same edge offers a favourable situation for subsequent hydrogenation of toluene, as proposed in the kinetic modelling of Guernalec et al. [Guernalec et al., 2004;Guernalec et al., 2006] With this in mind, the higher activity of CSC catalysts could be tentatively attributed to the hexagonal shape of their crystallites (observed by STEM-HAADF), leading to a more favourable edge structural environment for toluene activation and H 2 activation into MSH and MH species.

Characterisation of such MSH species has already been reported by different authors through analyses of MoS 2 phases by inelastic neutron scattering [Sundberg et al., 1991] Raman spectroscopy [Polz et al., 1989] or IR spectroscopy [Burrow et al., 1989], and correlated with DFT calculations [Prodhomme et al., 2011]. Lauritsen et al. also reports the characterisation of MSH species by STM studies on MoS 2 phases [Lauritsen et al., 2004;Lauritsen et al., 2006].

Therefore, performing Raman or IR spectroscopy analyses on catalysts should enable to observe such MSH species on WS 2 phases prepared in this PhD thesis. As another further Part V 210 perspective to this work, quantifying the amount of sulphur on slabs edge by TPR experiments of WS 2 samples is possible [Raybaud and Toulhoat, 2013, Ed. Technip, Paris]. Breysse et al.

[ Breysse et al., 2002] have summarized the main results found on TPR experiments of sulphide catalysts and they found three peculiar reduction regions on TPR spectra, among which the first one was around 200°C ; the second one between 400°C and 600°C and the last one around 900°C. The two former ones were assigned to sulphur atoms on slabs edges, while the last one was assigned to the total reduction of the sulphide phase. Beside, different groups [Dinter et al., 2009;Afanasiev et al., 2010] proposed that the first peak was caused by reduction of sulphur species (S 2 2-

) on the M-edge particularly. Regarding these results, TPR experiments performed on our catalysts could probably allow to quantify the amount of sulphur on W-edge as a function of the preparation method. Along with the calculation of the theoretical amount of sulphur atom on W-edge with our geometrical model, it could probably bring complementary insights into the understanding of the sulphur coverage of W-edge, and thus the understanding of the catalytic activity.

V.2.f. Conclusion on the influence of the sulphidation temperature on the genesis and activity of the active phase of WS 2 /ASA catalysts We can summarize our previous findings as follows:

(1) CSC catalysts undergo sulphidation at lower temperatures than conventional ones, due to their high reactivity, already discussed in part V.1. XPS analyses showed that when sulphided at room temperature (which has never reported before, to the best of our knowledge), CSC catalysts exhibit ca. 50 % rel WS 2 when conventional ones show no evidence of WS 2 phase.

(2) IR(CO) analyses showed that for CSC materials sulphided at 23°C, CO was interacting with (oxy)sulphides at wavenumbers higher than expected for well crystallised WS 2 . Sulphidation at 600°C totally removes these (oxy)sulphide species. Concomitantly with that, CO was shown to interact with peculiar adsorption sites at ν(CO) = 2124 ±3 cm -1 , tentatively assigned to W-edge sites, probably being the so-called CUS.

(3) Catalytic activity measurements, together with geometrical model calculations showed that sintering effect at high sulphidation temperature was playing a role in the different HYD TOF observed. W-edge, S-edge and corner sites were taken into account as HYD active sites but another parameter had to be critical to fully explain data collected.

Although we have not been able to quantitatively explain the origin of the better TOF of

Part VI. Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel

Introduction

In the previous chapters, we have shown that the CSC approach was suitable to prepare non-promoted WS 2 /ASA catalysts exhibiting higher activities than their conventional homologues in hydrogenation of toluene. However, it is well known that non-promoted catalysts are much less efficient than the promoted ones, which typically exhibit higher hydrogenation (HYD) activities by about one order of magnitude. We therefore investigated the preparation of NiWS/ASA catalysts (promoted catalysts) by a CSC method, and compared them to conventional ones.

In part V, we revealed that CSC catalysts prepared by incipient wetness impregnation of [W(OEt) 5 ] 2 onto ASA with 1.7 W/nm² exhibited the highest Turn-Over Frequency (TOF). Then previous studies on NiWS/ASA catalysts realised at IFPEn had previously shown that the highest intrinsic rate of hydrogenation was obtained for Ni/W atomic ratio between 0.2 and 0.3.

Therefore, the study will focus first on the preparation of Ni-promoted catalysts via CSC with 1.7 W/nm² and an atomic ratio Ni/W of ca. 0.2 (at/at).

We investigated via CSC the preparation of NiW catalysts by co-impregnation of tungsten and nickel precursors, in a way similar to what is used for the preparation of conventional NiW oxide phases. However, due to the difficulties to find an appropriate solvent for impregnation of both [W(OEt) 5 ] 2 and nickel precursors (Ni-bis-acetylacetonato, Ni(acac) 2 , or

Ni-bis-1-methylcyclopentadienyl, Ni(1-MeCp) 2 , or Ni nitrate, Ni(NO 3 ) 2 ), a successive impregnation approach, with first, an impregnation of tungsten, and then the nickel precursors, was chosen (see Figure 85).

As in the literature, previous studies [Okamoto et al., 2005, Okamoto et al., 2009, Maugé et al., 1989;Maugé et al., 1992] had reported the preparation of enhanced HDT catalysts by deposition of the precursor onto a pre-sulphided phases, we decided to investigate the deposition of nickel onto a sulphide phase prepared at 350°C (2 h, 15 % mol. H 2 S/H 2 , see The IR spectrum reveals a partial disappearance of isolated silanols (ν(OH) = 3742 cm -1 , ca. 50 % consumed) and the appearance of vibration bands between 3113 and 3088 cm -1 , between 2934 and 2872 cm -1 as well as between 1511 and 1383 cm -1 are respectively assigned to ν(C sp2 H) and ν(C sp3 H) stretching vibrations, and δ(CH) vibration of methylcyclopentadienyl rings of the nickel precursor. Ni(1-MeCp) 2 is thus not very reactive towards the OH groups of ASA -300.

As Ni(1-MeCp) 2 is air sensitive, not very stable, even when stored in a glovebox, and not very reactive towards surface hydroxyl functionalities, we investigated the use of another

Ni precursor, which contains the more reactive anionic acetyl acetonate ligands, namely (bisacetylacetonato)nickel, Ni(acac) 2 In that case, the corresponding samples have been characterised in much more details as described below.

VII.1.a.2. (bis-acetylacetonato) nickel -Ni(acac) 2 -based materials

Ni(acac) 2 (Figure 88) had to be solubilised in hot toluene before impregnation on ASA -300 ;

a solid with ca. 0.9 % pds. Ni (about 0.4 Ni/nm²) was obtained.

Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 223 The IR spectrum of the supported nickel sample, which is shown in Figure 89, exhibits the same features as Ni(acac) 2 /α-Al 2 O 3 prepared by Molina et al. [Molina et al., 1999] The ν(C=C)

stretching vibration at ca. 1533 cm -1 is in particular attributed by the authors to Hacac species (C 4 H 8 O 2 ), released from Ni(acac) 2 upon reaction with the alumina surface and subsequently interacting with surface Lewis acid site. Besides, note the partial consumption of isolated silanols (ν(OH) = 3742 cm -1 , 66 % consumed), resulting from the grafting of the nickel precursor. ν(CO), ν(C=C) and δ(CH) vibrations bands belonging to nickel species are respectively visible at ca. 1600 cm -1 and 1517 cm -1 as well as 1407 cm-1 (reference spectrum: Ni(acac) 2 /ASA -300 , see Figure 90-a)

ν(CO) = 1533 cm -1 and ν(CO) = 1581 cm -1 are tentatively assigned to Hacac species, interacting with surface Al 3+ . [Molina et al., 1999] Note that the previous IR vibration bands were attributed on the basis of IR analyses of the corresponding samples resulting from the impregnation of [W(OEt) 5 ] 2 (see part IV for details)

and Ni(acac) 2 separately onto ASA. Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 225 GC/MS analyses of the liquid phase after impregnation reveal the presence of ethanol and diethylether, while acetyl acetone is not detected. Adsorption of acetyl acetone on the support is also consistent with the work of Salinier et al. [Salinier et al., 2009] in which grafting of Zr(acac) 4 on silica quantitatively yielded a well-defined monopodal species (≡SiO)Zr(acac) 3 with Hacac ligands strongly adsorbed on the silica support.

In the same spirit as in part IV, where supported surface W-species' structure was investigated, the structure of Ni and W surface species of the aforementioned supported NiW material is (shortly) discussed. While the reactivity of Ni(acac) 2 toward supported surface alkoxide species is unknown, its reaction with titanium alkoxo molecular complexes such as Ti(OEt) 4 in toluene is reported to give a Ni 2 Ti 2 (acac) 4 (OEt) 8 solid, which crystal structure (XRD) revealed Ti and Ni atoms linked by µ-bridge ethoxy ligands (M-(OEt)-M', with M = Ti, Ni; M' = Ti, Ni). [Kessler et al., 2006] If transposable to tungsten alkoxide complexes, this result would suggest the formation of a compound which formula would be Ni 2 W 2 (acac) 4 (OEt) 8 , and which structure, inspired from the work of Kessler et al., is In this part, we show the characterisation of sulphided samples, initially prepared by successive impregnation of first, the W precursor, and then, the Ni one. XPS analyses were run to investigate the level of sulphidation (% rel. WS 2 ) as well as the relative percentage of each nickel phases, e.g. the NiS phase, the NiO x phase where Ni is strongly interacting with the ASA support, and finally the mixed phase "NiWS" (% rel. NiWS), also referred as the promotion degree of the sulphide phase. To evaluate the influence of the CSC method, CSC NiWS phases will be compared to these prepared by conventional approaches.

Conventional dried materials were prepared following the general procedure, e.g. incipient wetness impregnation of an aqueous solution of ammonium metatungstate and nickel nitrate on ASA (co-impregnation), followed by a maturation step of 16 h, with subsequent drying at 120°C. Calcined materials were obtained by calcination of the aforementioned dried samples under air, at 450°C for 2 hours. These samples were sulphided at 350°C for 2 h, under a 15 % mol. H 2 S/H 2 mixture.

CSC materials were prepared by impregnation of Ni precursors (Ni(1-MeCp) 2 , Ni(acac) 2 or Ni(NO 3 ) 2 onto [W(OEt) 5 ] 2 -IWI-1.7/ASA, and were dried under vacuum (10 -5 mbar, 2 h). Then, they were sulphided at 350°C for 2 h, under a 15 % mol. H 2 S/H 2 mixture.

Note also the preparation of an additional sample by deposition of Ni(acac) 2 onto a conventional catalysts (dried, non-calcined sample referred to as "acac/W(POM)/ASA" where POM stands for polyoxometallate) to investigate the effect of supported W-species (used as support) on the characteristics of the sulphide phase after sulphidation under similar conditions. For all the catalysts, prepared either by the CSC or conventional methods, tungsten and nickel coverages are calculated on the basis of the support surface area, which is ca. 228 m²/g. 15. Note that decomposition of Ni 2p photopeaks has already been reported in previous studies [Guichard et al., 2008]. An example of Ni 2p decomposition is shown in Figure 92. The improved incorporation of Ni in a mixed phase "NiWS" when using Ni(acac) 2 can be tentatively explained by the presence of well-dispersed Ni and W species on the surface, promoting an intimate contact between Ni atoms with W ones.

For conventional catalysts, the same trend as for non-promoted conventional ones is found:

dried catalysts show higher level of sulphidation (% rel. WS 2 ) and exhibit lower amount of W(VI) phase than their calcined counterparts, while their tungsten surface coverage of tungsten, detected by XPS, is similar. However, the amounts of NiWS site/nm² are not really affected by calcination of the sample, with 0.26 (± 0.04) NiWS site/nm² and 0.23 (± 0.04) NiWS site/nm² for the dried and the calcined samples respectively. A similar trend is observed for the nickel-totungsten ratio in tungsten sulphide slabs: (Ni/W) slab = 0.30 (± 0.03) for calcined and dried catalysts.

Note that the sample prepared by deposition of Ni(acac) 2 onto a conventionally prepared oxide phase (dried sample, earlier referred as W(POM)) exhibit a level of sulphidation close to that of CSC samples, but its promotion degree (% rel. NiWS) is extremely low: the NiWS phase is thus barely present on this sample, in favour of the formation of a undesirable NiS phase.

Comparison of CSC and conventional catalyst show that their sulphide phase is similar in 16, reveal that the mean length of sulphide slabs (L) and their mean stacking number (N) is similar whatever the preparation method used, with L ≈ {3.6 -3.7} nm and N ≈ 3.1. These results are similar to non-promoted WS 2 /ASA catalysts ones (see part V.1).

Part VI 230 In the same spirit as in part V.1.e for unpromoted WS 2 phases, DFT calculations were carried out to understand this phenomenon [Girleanu et al., in preparation]. Considering the Ni-promoted WS 2 nanocrystallite, a combined effect of the promoter and the sulphur coverage on the edge energy is expected. As observed for the Ni promoted MoS 2 system [Schweiger et al., 2002] Ni reveals peculiar effect on WS 2 : the edge energy of the Ni promoted edges is significantly lower than the non-promoted one (Figure 94). This energy gain is induced by the substitution of some W atoms by Ni atoms at the edges as illustrated in Figure 95. This effect obviously depends on the type of edge: the S-edge energy decreases more significantly than the W-edge energy. For ∆µ S = -1.03 eV which corresponds to the sulphidation conditions used here (15 % mol. H 2 S/H 2 mixture and T = 600°C), the decoration of the W-edge by Ni is less favoured than the S-edge: Figure 95 shows that the S-edge exhibits a Ni/W edge ratio close to 1/2 whereas it is close to 1/3 on the W-edge. This also implies that the EXAFS data reported on NiWS catalyst supported either on carbon [Louwers et al., 1993] or on silica-alumina. [van der Meer et al., 2004;Kelly et al., 2009] Moreover, as discussed by Kelly et al. [2009] the coordination number of Ni-atoms is found to be close to 4 with either a tetrahedral environment on the S-edge or a square planar one on the M-edge and on the S-edge depending on the chemical potential value (Figure 95). Similar Ni environment have been reported for NiWS [Sun et al., 2004] and for NiMoS system. [Schweiger et al., 2002[START_REF] Raybaud | [END_REF] It can be added that according to Figure 95, different sulphidation conditions (higher chemical potential of sulphur, of about -0.50 eV), also lead to a similar morphological trend with a higher Ni/W ratio at both edges. Note that the initial W-loading was 1.7 W/nm², but elemental analyses on the final materials revealed W-loading going from 1.6 to 1.5 W/nm² respectively. These lower % wt. W amounts are attributed to the leaching of tungsten species during impregnation (extraction by toluene), even if performed with only a slight excess of solution with respect to pore volume. Indeed, we showed in part IV that at 1.7 W/nm², the CSC catalyst is covered by a multilayer of surface species e.g. a layer of species grafted on the surface; the additional layers are likely loosely bonded species, and can therefore be removed by additional step involving solvents.

Part VI

236

VI.1.f.1. Characterisation by X-ray photoelectron spectroscopy (XPS)

The aforementioned catalysts underwent sulphidation at 350°C for 2 h, under a mixture of H 2 S/H 2 (15 % mol. H 2 S), to give the 3 NiWS/ASA catalysts referred as:

-NiWS ex. acac-IWI-0.2/[W(OEt) 5 ] 2 -1.6/ASA -300 with 1.6 W/nm² and Ni/W = 0.21 -NiWS ex. acac-IWI-0.4/[W(OEt) 5 ] 2 -1.5/ASA -300 with 1.5 W/nm² and Ni/W = 0.44 -NiWS ex. acac-IWI-1.0/[W(OEt) 5 ] 2 -1.5/ASA -300 with 1.5 W/nm² and Ni/W = 1.00

The catalysts were analysed by XPS. Data are summarized in Table 18. Note that independently of the Ni/W atomic ratio, the level of sulphidation is ca. 69 ± 2 % rel. WS 2 . The relative amount of W(VI) phase and partially sulphided phase (Wintermed.) as well as the tungsten coverage on the surface is more or less constant. between Ni/W atomic ratios of ca. 0.6 to 0.7. These results are found to be similar to the ones reported for NiWS/ASA catalysts when prepared with higher W (thus Ni) content, e.g. 23-25 % wt.

W [Raybaud and Toulhoat, 2013, Ed. Technip, Paris, p255]. Besides, the effective content of NiO x linearly increases. Finally, quantification of NiWS site/nm² (see

VI.2. Impregnation of Ni-precursors onto a WS 2 phase, prepared at 350°C

In this part, we focus our study on the deposition of Ni(acac) 2 and Ni(1-MeCp) 2 directly on sulphided tungsten materials. This preparation method has already been described in the literature for different metals and different sulphide materials. For example, Co(acac) 2 was impregnated on MoS 2 /Al 2 O 3 catalyst [Roukoss et al., CRC 2009], and Ni(C 3 H 5 ) 4 was impregnated on WS 2 /SiO 2 [Yermakov et al., 1984, while Co(CO) 3 NO was deposited on MoS 2 catalysts supported on SiO 2 by chemical vapour deposition [Okamoto et al., 2005, Okamoto et al., 2009] or Al 2 O 3 [Maugé et al., 1989;Maugé et al., 1992]. Note that catalysts prepared with this preparation method have revealed improved catalytic activities in thiophene hydrodesulphurization compared to conventional deposition procedures using co-impregnation of aqueous solution containing cobalt (nickel) salt alongside with tungsten (molybdenum) -NiWS ex. MeCp-IWI-0.2/WS 2_350°C -1.7/ASA -300 with 1.7 W/nm² and Ni/W = 0.20 -NiWS ex. acac-IWI-0.2/WS 2_350°C -1.7/ASA -300 with 1.7 W/nm² and Ni/W = 0.20 Note that 0.2 refers to the Ni/W atomic ratio, and 1.7 refers to the W-loading, as stated in the previous chapters. On these samples the tungsten content is based on elemental analyses, while the nickel content used for calculations is based on the amount of precursor weighted in the impregnation solution, as no Ni elemental analyses have been obtained so far.

The catalyst prepared with Ni(acac) 2 has been studied by IR spectroscopy (transmission), before and after impregnation, as well as after subsequent sulphidation at 350°C. Besides, note that these two samples were analysed after dilution in low specific surface area α-alumina (< 10 m²/g) to improve the analysis quality (higher IR transparency of the sample pellet) without significantly adding surface OH groups. For reference, Figure 98-a shows the spectrum of the WS 2_350°C /ASA catalyst, used as a support for the impregnation. Very low intensity ν(CH)

vibrations between 2988 cm -1 and 2886 cm -1 as well as δ(CH) vibrations around 1448 cm -1 and 1400 cm -1 , tentatively attributed to traces of remaining tungsten surface species or remaining surface ethoxides. Traces of isolated silanols (ν(OH) = 3743 cm -1 ) are visible, as well as physisorbed H 2 O which probably comes from sample pollution before analysis. After impregnation, the IR spectrum, shown in Figure 98-b, exhibits the typical features of pure Ni(acac) 2 with ν(C=C) at 1520 cm -1 , ν(C=O) at 1607 cm -1 and 1595 cm -1 and δ(CH) between

Part VI 240 1406 cm -1 and 1367 cm -1 . In addition, the ν(C=O) at 1533 cm -1 is attributed to Hacac in interaction with the surface. As discussed before, traces of isolated silanols are observed. We can thus say that after deposition of Ni(acac) 2 on WS 2 /ASA, IR spectroscopy reveals that the nickel molecular precursor is in interaction with the ASA surface, but no feature of any direct interaction with WS 2 has been observed. After subsequent sulphidation, the IR spectrum, shown in Figure 98-c, illustrates that the ν(OH) vibration of isolated silanols are slightly more intense.

Presence of small amount of these hydroxyls upon sulphidation reveals that if there are

VI.2.c. Characterisation by Transmission electron microscopy (TEM)

TEM experiments have only been performed on the sample prepared with Ni(acac) 2 . The analysis reveals that the mean slabs length is ca. 4.0 nm and that the mean stacking number is ca. 3.4. These values are slightly higher than the ones found for the catalysts previously analysed (see Table 16 andTable 19).

As explained in part VI.1.d, the edge energy of the Ni promoted edges is significantly lower than the non-promoted ones, which should stabilise edges with less edge atoms, e.g. leading to smaller slabs. This effect should preferentially occur if Ni and W precursors are added simultaneously such as during co-impregnation and if they undergo sulphidation simultaneously.

However, NiWS catalysts analysed in this part were prepared by deposition of Ni onto a preformed WS 2 phase (350°C, 2 h, 15 %mol. H 2 S/H 2 ). Without the promoter, crystallites of the preformed WS 2 phase exhibit a longer mean slabs length. We suspect that the subsequent deposition of Ni followed by sulphidation at 350°C (2 h, 15 % mol. H 2 S/H 2 ) does not influence the length of WS 2 crystallites, which have been settled down at the pre-sulphidation step of the W precursor.

Then, observing longer and more stacked slabs after several sulphidations can possibly indicate that only one ex-situ sulphidation of 2 h at 350°C with a 15 % mol. H 2 S/H 2 mixture is not sufficient to stabilize the slabs length and stacking. This assumption would suggest that any interpretation of catalytic activity using the slabs length and stacking number obtained on fresh catalysts has to be taken cautiously. Indeed, it would be more accurate to perform XPS and TEM analyses on spent catalysts, and interpret data to get the amount of sulphided and promoted phase, as well as mean length and stacking number of slabs. In our study of NiWS/ASA catalysts with W-loadings between 1.7 and 1.8 W/nm², XPS analyses were performed on spent catalysts but no exhaustive TEM analyses were conducted. However, TEM analyses of fresh and spent NiWS/ASA catalysts prepared by CSC or conventional methods, and which contain ca. 3.5 W/nm², with Ni/W = 0.2 (at/at), revealed that the slabs length and stacking number observed on spent catalysts were little higher than on fresh ones. In particular, length and stacking number of slabs showed to be less than 10 % higher on spent catalysts, compared to fresh ones. Therefore, we decided not to perform TEM analyses on spent catalysts, assuming that less than 10 % of variation was lying within the uncertainty of the analyses.

Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel

243

VI.3. Impregnation of a Ni-precursor onto a WS 2 phase, prepared at 23°C: study of the influence of the Ni content

In this part, we try to control the morphology and in particular, the length of the WS 2 crystallites by taking advantage of a low sulphidation temperature used on CSC catalyst.

Previously, we have shown that sulphidation of 23°C (part V.2) enabled to trigger off little sulphided particles which size was lower or equal to 3.2 nm on CSC catalysts (at least for the corresponding amount of pre-sulphided WS 2 crystallites). We decided to incorporate nickel at this stage, in order to block the growth of future WS 2 slabs using the edge stabilisation provided by Ni addition on WS 2 crystallite edge (as quantified by DFT).

We study the influence of the Ni loading of catalysts prepared by deposition of Ni(acac) 2 onto a sulphided material, prepared at 23°C (2 h, 15 % mol. H 2 S/H 2 ). Indeed, we showed in part V that sulphidation of the CSC material [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 , at room temperature in these conditions gives a WS 2 /ASA catalyst which exhibits ca. 50 % rel. WS 2 , with small WS 2 crystallites of about 3.2 nm along with several nanosized spot-like entities (1 nm to 2 nm). Via deposition of nickel onto such a material, we suppose that we could obtain:

smaller sulphide slabs compared to the previously analysed NiWS catalysts. Indeed, promoted catalysts are known to be covered by smaller slabs than their unpromoted counterparts [Baubet, PhD thesis, Lyon, 2013]. This is due to a "promoter effect" which reduces the size of MS 2 crystallites (M = Mo, W) by diminishing their edge energy. We thus tried to deposit Ni on the small slabs and nanosized entities found on the WS 2 /ASA catalyst sulphided at 23°C to prepared promoted slabs for which growth would be somehow limited by the promoter, even at low Ni/W atomic ratio, as illustrated in

a better promotion of the sulphide phase, as sulphidation of tungsten at 23°C is incomplete. Indeed, sulphide species (WO x S y or WS 2 ) are supposed not to be well organized (few WS 2 slabs visible, presence of nanosized spot-like entities) or crystallised, and Ni could also be incorporated in the WS 2 matrix more easily.

alkoxides species (see Table 15). It indicates that W is slightly more dispersed on the ASA surface for these catalysts, which probably originates from the high tungsten coverage of the surface, observed on supported alkoxides materials, in part V.1.b. The well-dispersed tungsten phase, which is not sulphided after pre-sulphidation at 23°C (ca. 40 % rel. from XPS analyses in part V.2.a), can thus gently spread over the ASA surface upon the second sulphidation step (subsequently performed after Ni addition). Note that one objective of this study is to identify if adding nickel on pre-formed small WS 2 crystallites could limit their growth upon sulphidation. The starting WS 2_23°C -1.7/ASA -300 material used as "support" exhibits slabs length of ca. Part VI

248

VI.4. Characterisation of spent catalysts

In order to interpret the catalytic results, it is more accurate to use data collected from analyses of spent catalysts, especially XPS ones. Therefore, XPS analyses was carried out on catalysts recovered after toluene hydrogenation in the presence of aniline (vide infra, part VII.5).

This part only discusses the characterisation of the sulphide phase. XPS data were obtained by decomposition of W 4f and Ni 2p photopeaks. The results are summarized in 23). Note however that we used TEM results obtained on fresh samples, as we previously assume that mean slabs length and stacking number are, in a first approximation, not significantly changed by the test.

First, preliminary tests were performed to evaluate the catalytic potential of five catalysts:

(1) a CSC catalyst prepared by deposition of Ni(acac) 2 onto [W(OEt) 5 ] 2 /ASA: 1.7 W/nm², e.g. 12.9 % wt. WO 3 and Ni/W = 0.21 at/at, e.g. 0.9 % wt. NiO

(2) a conventional dried catalyst with 1. First, the less active NiWS/ASA catalyst, prepared by deposition of Ni(acac) 2 on a conventional dried tungsten phase [W (POM) ], is 1.6 times more hydrogenating than the nonpromoted WS 2 /ASA sample (0.10 vs. 0.06 g(tol)/g(cat)/h), which highlights the crucial role of the promoter to improve hydrogenation reactions, as described for various transition metal sulphide by the volcano curve of Guernalec et al., correlating sulphur-metal bond energies and intrinsic catalytic activities in toluene hydrogenation. [Guernalec et al., 2006;Guernalec et al., 2011] No significant difference is observed between sulphide materials prepare by deposition of Ni(acac) 2 , Ni(1-MeCp) 2 and Ni(NO 3 ) 2 on supported alkoxide species (CSC): they are the most active samples, with about 0.21 (±0.01) g(tol)/g(cat)/h. Moreover, the comparison between conventional and CSC catalysts reveals that the three aforementioned CSC samples are at least 30 % more active than conventional samples. These latter are, however, more active than the sample prepared by deposition of Ni(acac) 2 on conventional dried tungsten phase denoted W (POM) . In addition, note that compared to the calcined sample, the slightly higher activity found of the dried sample is not really significant.

The HYD activity of CSC samples thus seems not to depend on the nickel precursor, when deposited on supported alkoxides species. However, it is important to stress that deposition of NiWS, as revealed by XPS on spent catalysts. In particular, when catalysts are prepared by deposition of Ni(acac) 2 onto a conventional tungsten oxide phase (dried), e.g. W (POM) /ASA, their intrinsic HYD rate is two times lower than when prepared by deposition of a Ni-precursor on supported tungsten alkoxide species, which is correlated with the lower amount of NiWS sites observed on the former sample: 0.10 site/nm² vs. 0.22 site/nm². However, intrinsic HYD rates of the best CSC samples are ca. 30% higher than that of conventionally prepared catalysts, while they reveal similar amount of NiWS sites (0.21 to 0.25 (±0.4) NiWS site/nm²): as a consequence, another parameter such as the (Ni/W) slab ratio must influence the activity and the nature of active site(s). This ratio is slightly higher for CSC samples (between 0.26 and 0.32) than for conventional ones (0.23 to 0.27), which signifies that more Ni atoms have substituted W ones, and probably have formed more mixed sites on edges (Ni in close vicinity to W at the edge).

Note also that the slabs length also plays a role, especially in the 2D morphology of crystallites and in the repartition of mixed sites on edges, which will be discussed later on in the discussion (part VI.6), together with the influence of the (Ni/W) slab parameter. Deposition of a nickel precursor onto a sulphide material, prepared at 350°C or 23°C, allows the synthesis of catalysts exhibiting different activities. Indeed, the catalyst prepared with a material sulphided at 23°C (referred as ex. acac/WS 2-23°C ) converts 1.8 times more toluene than its CSC counterpart obtained on a sulphide phase prepared at 350°C (denoted ex. acac/WS 2-350°C ). Besides, no significant activity difference is found between the catalysts for Part VI 258 which the nickel is impregnated directly onto CSC surface alkoxide species (ex. acac/[W(OEt) 5 ] 2 ), or onto a CSC sulphide phase, prepared à 23°C: they convert between 0.20 and 0.21 (±0.01) g(tol)/g(cat)/h, which is more than 30 % higher than conventionally prepared samples. Then, we investigated the influence of the preparation method on the intrinsic HYD rate of these catalysts (see Figure 109). Conclusions are similar to the ones previously found for the weight flow rate of toluene converted. The most important is that preparation of a CSC samples by deposition of Ni(acac) 2 onto a sulphide material prepared at 23°C, subsequently followed by a sulphidation at 350°C, gives a NiWS/ASA catalyst exhibiting an intrinsic HYD rate as high as the one observed for sample prepared by impregnation of the Ni-precursor directly onto supported alkoxide species, which is higher than that of conventionally prepared samples.

These results will be discussed later on, in part VI. Then, the intrinsic HYD rate of NiWS/ASA catalysts (1.5 to 1.6 W/nm²) was investigated as a function of their Ni content. They were prepared by deposition of Ni-precursors either on supported alkoxide species, or on a sulphide material previously prepared at 23°C for 2 h with a 15 % mol. H 2 S/H 2 mixture. Figure 110 reveals that for these samples, the ones prepared on supported surface alkoxide W-species (ex. acac/[W(OEt) 5 ] 2 ) exhibit an intrinsic HYD rate which decreases for Ni/W atomic ratio higher than 0.44: from 3.77 to 1.49 mol(tol)/mol(W)/h. This trend is found to be similar to the one observed for conventional calcined NiWS/ASA (4.3 W/nm²) exhibiting increasing amount of Ni [Raybaud and Toulhoat, 2013, Ed. Technip, Paris, p255].

However, the Ni/W atomic ratio after which the intrinsic HYD rate of these conventional catalysts decreases is lower, at about 0.30 (at/at). On the contrary, catalytic results found for catalysts prepared onto a sulphide phase prepared at 23°C (ex. acac/WS 2_23°C ) follow a different trend:

Part VI 260 increasing the amount of nickel slightly increases the intrinsic HYD rate which seems to reach a plateau between 3.9 and 4.0 mol(tol)/mol(W)/h. Finally, as the experimental error is close to 0.5 for the most active materials, we can assume that the highest intrinsic rate of HYD achievable for catalysts with ca. 1.6 (± 0.1) W/nm² lies between 3.7 and 4.0 mole of toluene converted per mole of tungsten per hour. For catalysts with greater W-loading, this intrinsic rate is lowered to ca. 1.5 mol(tol)/mol(W)/h.

L L     - - promoted edge S edge W L L     - - -1.03 1.63 1.12
The morphology diagram of NiWS crystallites obtained by DFT modelling is shown in

264

Note that no STEM HAADF experiments were performed on CSC catalysts, contrary to conventional calcined ones. As a consequence, we assume that the 2D morphology of CSC NiWS crystallites is similar to that of conventional samples. Note that this hypothesis, about crystallites observed on CSC samples following DFT calculations, has not been taken into account for non-promoted samples. Indeed, STEM-HAADF pictures revealed that crystallites observed on non-promoted CSC WS 2 /ASA catalysts were much more hexagonal shaped that predicted, while the 2D morphology of WS 2 slabs observed on conventionally prepared samples matched the predictions.

Besides, Figure 112 also shows the stability domain of 3 relevant NiWS crystallite structures, while only one structure is expected to be stabilized in our experimental conditions (T = 350°C, p(H 2 S)/p(H 2 ) ≈ 15 % mol.

∆µ S = -1.03 eV). However, as boundaries between each structure are rather close (-0.92 eV and -0.85 eV) and assuming a slight fluctuation in sulphiding conditions ∆µ S = -1.03 eV, we assume that the 3 structures can probably be stabilized. [ Krebs et al., 2008;Krebs et al., 2009].

Then, in order to investigate how Ni atoms decorate WS 2 slabs, e.g. in which extent Ni atoms can replace W ones on edges (either W-edge or S-edge), we calculated, with the help of geometrical models, the nickel-to-tungsten substitution ratio (atomic) on crystallites edges Part VI 266 and corners, denoted X subst. . This parameter refers to the amount of nickel atoms which have substituted W ones on edges and/or corners. It is calculated with the following equation inspired from previous works of the literature [Marchand et al., 2009;Baubet, PhD thesis, Lyon, 2013;Gandubert, PhD thesis, Lille, 2006] 3) by a conventional method, samples being dried or calcined First, we studied the theoretical (Ni/W) slab parameter in order to find for which value every W atoms on edges would be substituted by Ni ones. In other words, we focused on the highest (Ni/W) slab for which the atomic Ni-to-W substitution ratio on edges and corners (X subst ) is 100 %.

Calculations are summarized in appendix F (Table F where %Ni W-edge and %Ni S-edge stand for the relative% of Ni on W-edge and S-edge respectively, and where (number of M atoms) W-edge and (number of M atoms) S-edge stand for the number on metal atoms on W-edge and S-edge respectively.

(2) to calculate the number of W atoms not substituted by Ni ones: where (number of W atoms) total stands for the total number of tungsten atoms in a crystallite, and where (number of M atoms) total stands for the total number of metal atoms in a crystallite.

Note that considering the presence of one Ni atom on each corner of the 3 relevant NiWS crystallites, we assume, in a first approximation, that in each case, corner atoms are Ni atoms.

The total amount of Ni atoms is thus Ni edges+corners = Ni edges + 6.

(3) to calculate the (Ni/W) slab_theo atomic ratio: where Ni edges+corners and (number of W atoms) total are as described above.

(4) to calculate the theoretical atomic Ni-to-W substitution ratio on edges and corners, X subst_theo : where Ni edge is as described above, and where (number of M atoms) edge+corners stands for the number of metal atoms on edges and corners of a crystallite.

Results of our calculations are summarized in Table 25. et al. [2008] for CoMoS phases. In addition, as for all NiWS/ASA samples the amount of edge sites is relatively close (from 26.6 % to 32.6 % of the total number of atoms in a crystallite, given its length) the influence of the location of mixed sites (on W-edge or S-edge) is assumed not to be significant. HYD reactions are supposed to depend on the existence of activated intermediates generated on both edges: H atoms (hydride or sulfhydryls) and adsorbed toluene or toluene hydrogenated derivatives. This synergy effect between the two edges was also underlined for non promoted WS 2 systems investigated in Part V. Note finally that as far as we know, probing the strength of mixed sites located on edge, or corners, is barely possible.

Finally, a compromise of all our results lead to an optimal nickel-to-tungsten atomic ratio in crystallites (Ni/W) slab belonging to the interval { { { {0.23 -0.32} } } }. This final result means that catalysts prepared with an experimental Ni/W atomic ratio between 0.20 and 0.30 (at/at) provide NiWS phases with optimised Ni-promoted crystallites, which is supported by previous work of the literature [Raybaud and Toulhoat, 2013, Ed. Technip, Paris, p255] Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 277 (at/at), which would lead to intermediate Ni decoration of W-edge and S-edge, and thus to the presence of mixed sites providing the expected HYD activity. However, the balance between the amount of NiWS sites and their strength (intrinsic HYD rate) is supposed not to be as optimal as that of CSC samples, which exhibit similar (Ni/W) slab values but higher intrinsic HYD rates. Note that all these interpretations do not take into account the slabs stacking, which is, however, not supposed to have a significant influence as TEM analyses reveal only slight differences between the samples.

Part VI

278

VI.7. Conclusion

The aim of this part was to study NiWS/ASA catalysts prepared by a molecular approach, with different Ni-precursors and different impregnation strategies. Through XPS and TEM analyses on catalysts before and after catalytic tests, as well as with the help of 2D geometrical models and DFT modelling, we demonstrated that:

(1) the HYD activity of NiWS/ASA catalysts is linked to the presence of mixed sites (Ni atoms in close vicinity to W ones, at the edge)

(2) the strength (intrinsic HYD rate) of these mixed sites is higher when they are isolated on crystallites edges. This strength decreases when the Ni content on edges increases.

(3) finding the right balance between the amount of NiWS sites and their strength is the key parameter to reach high intrinsic HYD rates. This balance is strongly correlated with the Ni repartition on W-edge and S-edge.

We investigated the influence of different Ni-precursors on the level of sulphidation as well as the amount of active phase formed on NiWS samples, concomitantly with the consequences on their HYD activity. We found strong similarities between conventional NiWS/ASA samples (prepared by co-impregnation of ammonium metatungstate and nickel nitrate) and CSC material obtained by impregnation of bis-acetylacetonato nickel (Ni(acac) 2 ) or nickel nitrate on supported surface alkoxide W-species. The activity of CSC samples in toluene hydrogenation were found to be ca. 30 % higher, which is tentatively assigned to the reactivity of CSC tungsten surface species toward Ni precursors upon deposition. This increase of activity can be related to a more intimate contact between Ni and W atoms, which promotes the formation of NiWS crystallites with an optimal balance between the amount and the strength of active sites.

The influence of the preparation method was also investigated by impregnation of Ni-precursors on ASA-supported alkoxide species or on a CSC sulphide material (prepared at either 350°C or 23°C). Deposition of nickel onto supported surface alkoxide tungsten species or sulphide ones prepared at 23°C (2 h, 15 % mol. H 2 S/H 2 ) leads to high intrinsic HYD activities, correlated with the optimal balance observed between the presence of mixed sites and their strength. More interestingly, we propose that impregnation of the nickel precursor on supported surface alkoxide W-species is in favour of the formation of NiWS crystallites exhibiting highly Ni-decorated edges (either 100 %Ni on W-edge and 50 or 100 %Ni on S-edge), while impregnation of the nickel precursor on a sulphide material prepared at 350°C (same sulphiding Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 279 conditions) leads to crystallites' structure partially decorated, with 25% Ni on W-edge and 50 %Ni on S-edge, less optimal for HYD reactions.

The study of the influence of the Ni content reveals an optimal promoter-to-tungsten ratio in crystallites (Ni/W) slab located in between 0.23 and 0.32 (at/at). This ratio, experimentally found by XPS analyses of spent catalysts, is achieved when samples are initially prepared with experimental Ni/W atomic ratio in between 0.20 and 0.30.

Finally, the preparation of NiWS/ASA catalysts via a molecular approach is found to be very promising from an industrial point of view. CSC samples are at least more than 50 % more active than their industrial NiWS/ASA counterpart, while they exhibit at least 2 times less W atoms. (2) For tungsten loading greater than 0.8 (±0.1) W/nm², the additional tungsten species are adsorbed more or less strongly on top of the grafted W surface species via either µ-bridge ethoxide or electrostatic interactions, making an overlayer of W molecular species according to detailed NMR and IR spectroscopic analysis (see Figure 121). At 0.5 W/nm² in particular, CSC samples undergo sulphidation in a larger extent than their conventional counterparts (76 % rel . WS 2 vs. 33 % rel WS 2 for the calcined sample). While their surface coverages are similar in terms of W/Al atomic ratios and therefore cannot explain the differences between the various preparation methods, it is likely that their reducibility/sulphidation depends strongly on the strength and the nature of the interaction between W and its ligands (supports vs. O-network in HPA, vs. O-network in an oxide layer), making a larger difference between the conventional calcined oxide phases and supported alkoxide species. In addition, the higher levels of sulphidation observed for greater W-loadings (up to 85 % rel. WS 2 for CSC samples with a W content greater than 0.5 W/nm²) is assigned to:

(1) the greater proximity between surface W sites, which could facilitate sulphidation through an easier migration of surface species and (2) to the presence of weakly adsorbed and more mobile W species in the multilayer of the CSC samples. Note also that the enhanced reactivity of these CSC surface species towards sulphidation probably originates from their similarities to the starting molecular complex, which is readily converted in bulk WS 2 under similar conditions.

On the contrary, for conventional materials and specifically in the case on the calcined one, formation of stacked species is concomitant with the appearance of crystalline WO 3 , an oxide phase known to be refractory to sulphidation, thus explaining the lower level of sulphidation of calcined samples.

The stronger modification of mean slabs length and stacking number occurs for sulphide phases originating from calcined materials as revealed by TEM: mean slab length and mean stacking number increase when greater amounts of tungsten are used. Noteworthy, STEM-HAADF experiments show for the first time clear evidence that the 2D morphology of WS 2 slabs on conventional non-promoted catalysts supported on oxide (ASA, as a relevant industrial support) is close to a truncated triangle, for sulphidation carried out at 600°C

(2 h, 15 % mol. H 2 S/H 2 ). , close to ca. 1.6. [Girleanu et al., in preparation] Part VII

288

In the case of CSC catalysts (600°C for 2 h, H 2 S/H 2 15 % mol. H 2 S), the 2D morphology is more hexagonal (Figure 123-b). While the origin of this peculiar morphology is not clear yet, one hypothesis is that the CSC method induces the formation and the stabilisation of a kinetic form of WS 2 slabs, with a less triangular shaped 2D morphology than the thermodynamically stable one found for calcined samples.

Catalytic activity in toluene hydrogenation have also been evaluated by taking into account the amount of sulphide phase detected by XPS analyses on spent catalysts, in order to express activity per surface (active) sites. With the help of TEM data, DFT calculations and geometrical models, Turn-Over Frequencies (TOF) can be evaluated and expressed in mole of toluene converted per mole of tungsten on edge and corners per hour, assuming that W atoms on W-edge, S-edge and corners are active hydrogenation sites. CSC materials are typically more active than conventional ones, especially for a W-loading of 1.7 W/nm². Even if not totally understood, TOF differences likely originate from different amounts of active sites such as the so-called CUS (Coordinatively Unsaturated Sites), but it can also results from the presence of different type of active sites. In fact, IR(CO) analyses (recorded a low temperature, ca. 77K), are consistent with the presence of different sulphide phases on CSC and conventional sulphide samples, when sulphidation is performed at 350°C: CO strongly interacts with the sulphide phase of CSC samples, while much lower or even no interaction is observed for conventional materials. Noteworthy, this strong interaction of CO with WS 2 is highlighted by a sharp band at ν(CO) = 2121 ±3 cm -1 , tentatively attributed to a CO interaction with W-edge of WS 2 crystallites. However, further work is necessary to ascertain the IR signature of CO interacting with a WS 2 sulphide phase and quantify the amount of CO interacting with the surface sites.

Another important parameter has been to study the effect of the sulphidation temperatures in order to obtain more information about the genesis of the sulphide phase, With the most promising systems (W-loading close to 1.7 W/nm²), XPS has shown that the level of sulphidation follows an S-shaped curve as a function of the sulphidation temperature for all samples (see Figure 124). The inflection point, however, depends greatly on the preparation methods.

Decomposition process:

First, hydroxyles amplitudes were put at their maximum so as to maximize their quantity, especially for SiOH at ca. δ = 1.7 ppm. Then the others peaks were placed at their given chemical shift with an arbitrary width. At this point, only peak width and amplitude were allowed to be modified by the software. Positions were manually set at ± 0.1 ppm. After a first calculation by the software, width and amplitude were adjusted manually in order to respect the ratio CH 2 / CH 3 which should be close to 2 / 3. A tolerance of 10% was applied for this constraint.

A similar constraint was applied to methylene and methyl protons assigned to each surface species, e.g. surface ethoxides and tungsten surface species. Little by little, the number of degree of freedom was diminished and calculations were run until reaching the 2 / 3 ratio expected.

Results obtained after 1 H NMR spectra decomposition by dmfit (peak position, peak width) are available in the following table: CH3 -CH2-O-ASA 1.0 0.9 0.9 0.9 0.9 0.9 0.9 1.0 0.9 +/-0.1 In the model, integration of each peak was given in %.

CH3

Calculation of the number of ethoxy ligand still linked to a W centre was deduced from the number of surface ethoxides. The number of surface ethoxides was calculated as follow:

where, if we take the example of the material with 0.2 W/nm², which data are available above:

-N(ethoxy) stands for the amount of ethoxides, bound to the surface a Calculated from the number of W atoms on W-edge, relative to the total number of W atoms on edges (W-edge + S-edge)

-(CH
b Calculated from the number of W atoms on W-edge, S-edge and corners, relative to the total number of W atoms in one slab. a Calculated from the number of W atoms on W-edge, relative to the total number of W atoms on edges (W-edge + S-edge) b Calculated from the number of W atoms on W-edge, S-edge and corners, relative to the total number of W atoms in one slab.

Conv. dried ex. acac/WS 2_350°C Résumé L'enjeu de cette thèse réside dans la compréhension et l'amélioration de la sulfuration de catalyseurs à base de W. Elle a pour objectif la rationalisation des différentes étapes de préparation de catalyseurs d'hydrotraitement de type NiWS depuis la préparation jusqu'au test catalytique par une approche moléculaire (appelée «chimie de surface contrôlée» ou CSC), ce qui permet de proposer de nouvelles voies pour lever le verrou majeur, lié à la mauvaise sulfuration du W. Au coeur de cette approche se situe l'utilisation d'une méthode de préparation originale, ayant recours à des composés moléculaires métallo-organiques bien-définis comme précurseurs de la phase sulfurée WS 2 , combinée à une analyse poussée par spectroscopies multiples (IR, RMN, XPS) et chimie computationnelle.

La famille des alcoxydes de tungstène a été sélectionnée ; les précurseurs mono ou dinucléaires tels que W(OEt) 6 , [W(=O)(OEt) 4 ] 2 ou [W(OEt) 5 ] 2 ont été greffés sur silice-alumine partiellement deshydroxylée, et leur conversion en phase sulfure a montré que le type de précurseurs moléculaires influençaient peu les propriétés des catalyseurs non promus (WS 2 /ASA), en termes de taux de sulfuration (déterminé par XPS) ou d'activité catalytique, en hydrogénation du toluène en présence d'aniline. Le composé [W(OEt) 5 ] 2 a ensuite été sélectionné pour approfondir l'étude des catalyseurs préparés par CSC.

L'approche visant à améliorer la compréhension des différentes espèces de surface formées a été réalisée par l'étude des matériaux avant et après sulfuration. L'augmentation de la quantité de W déposé sur les matériaux CSC a permis de révéler la formation de (1) une couche d'espèces greffées sur la surface de silice-alumine, puis (2) de couches successives, formées d'espèces plus mobiles. L'étude portant sur la sulfuration de ces matériaux en fonction de leur teneur en W, et de la température de sulfuration, a permis de les comparer aux catalyseurs sulfurés dits «conventionnels». Cette étude approfondie a mis en évidence une amélioration de la sulfuration du W pour les matériaux CSC aux températures habituellement utilisées (350°C). La vitesse intrinsèque d'hydrogénation des catalyseurs CSC, jusqu'à deux fois supérieure à celle des catalyseurs conventionnels, a en partie été expliquée par un meilleur taux de sulfuration, et par la morphologie 2D des feuillets WS 2 (STEM-HAADF), de forme triangulaire tronquée, dans le cas d'un catalyseur conventionnel.

Finalement, ayant démontré que l'emploi d'espèces moléculaires mono et binucléaires permettait d'améliorer les catalyseurs non promus par rapport à l'approche conventionnelle utilisant des clusters polyanioniques, les catalyseurs promus de type NiW/ASA ont été étudiés. Différents précurseurs ont été utilisés (par exemple Ni(acac) 2 ) ainsi que différentes méthodes de dépôt (dépôt du nickel sur un matériau sulfuré, ou non) et quantités de nickel. Ces travaux ont permis d'estimer l'influence de ces paramètres sur la sulfurabilité du W et du Ni, ainsi que sur l'activité catalytique des catalyseurs, et montrer que l'emploi d'une approche moléculaire dans la préparation des phases NiWS supportées permet d'améliorer la promotion des feuillets sulfures par le nickel, mais aussi d'accéder à des catalyseurs pouvant avoir des vitesses intrinsèques d'hydrogénation quatre fois supérieures celles de catalyseurs conventionnelles de référence. Ces résultats catalytiques sont très probablement liés à une balance optimisée entre «nature» et «quantité» de sites actifs mixtes Ni-W. Cela démontre l'intérêt d'une approche moléculaire pour la préparation de catalyseurs d'hydrotraitement plus performants.

  moléculaire de catalyseurs d'hydrotraitement préparés à partir de précurseurs métallo-organiques

I. 3 .I. 7 .

 37 des matières ..................................................................................................................21 I.1. Généralités sur les procédés d'hydrotraitement.............................................................23 I.2. Les catalyseurs d'hydrotraitement couramment utilisés ...............................................25 La phase sulfure ................................................................................................................26 I.3.a. Généralités et modèle(s) issu(s) de la littérature .......................................................26 I.3.b. Morphologie 2D de la phase sulfure .........................................................................28 I.3.c. Généralités sur l'activité des catalyseurs en HDS et HYD .........................................31 I.4. Préparation conventionnelle et activation des catalyseurs sulfures ............................33 I.4.a. Préparation des phases oxydes supportées non promues ........................................33 I.4.b. Préparation des phases oxydes supportées promues ..............................................34 I.4.c. Activation des catalyseurs ........................................................................................35 I.5. Apport de la Chimie de Surface Contrôlée (CSC) : catalyseurs préparés par voie non conventionnelle .......................................................................................................................37 I.5.a. Caractérisation et préparation des supports .............................................................39 I.5.b. Utilisation de la méthode CSC (ou COMS) pour la préparation de catalyseurs ayant des sites actifs bien définis : généralités. ...........................................................................46 I.5.c. Catalyseurs d'hydrotraitement non promus, préparés par voie CSC .........................49 I.5.d. Catalyseurs d'hydrotraitement promus, préparés par voie CSC ................................52 I.6. Conclusion et stratégie de la thèse .................................................................................56 Références bibliographiques ...........................................................................................61 Etude bibliographique 23

Figure 1 :

 1 Figure 1 : schéma simplifié d'une raffinerie [energie.sia-partners.com]

  Ils permettent d'éviter la formation de gommes (hydrogénation des oléfines), d'améliorer les propriétés des gazoles (amélioration de l'indice de cétane) ou d'hydrogéner des coupes lourdes (hydrogénation des aromatiques) avant hydrocraquage. La réaction d'hydrogénation des aromatiques est thermodynamiquement favorisée à haute pression d'hydrogène et faibles températures, mais cinétiquement favorisée à hautes températures. Pour réaliser ces réactions, des conditions opératoires présentant entre 30 et 150 bar d'H 2 et une température comprise entre 340°C et 410°C représentent un bon compromis.[Raybaud and Toulhoat, 2013, Ed. Technip, Paris]

26 Figure 2 :

 262 Figure 2: Cours du ferrotungstène (orange) et de l'oxyde de molybdène (gris) entre Novembre 2005 et Avril 2013. [infomine.com]

Figure 3 :

 3 Figure 3: Schéma de principe de la transformation d'une phase oxyde en phase sulfure

Ni 3 S

 3 Figure 4 : Représentation schématique des différentes espèces de surface d'un catalyseur CoMo/Al 2 O 3 . En violet, Mo; en vert, Co, en jaune, S. [Raybaud and Toulhoat, 2013, Ed. Technip, Paris]

  Figure 5 : Représentation schématique d'un feuillet MS 2 hexagonal ou triangulaire. Bleu : W ou Mo; jaune : S

  ont aussi montré que la variation de p(H 2 S)/p(H 2 ) aurait peu d'influence sur la stabilité des faces latérales Mo-edge et S-edge : la morphologie des cristallites MoS 2 d'un catalyseur promu resterait proche d'une structure hexagonale, quelle que soient les conditions sulfo-feuillets sulfures hexagonales, triangulaires ou triangulaires tronquées (hexagonales déformées) ont donc été à la fois décrites par calculs DFT, et observées par STM. Parallèlement aux études de catalyseurs par STM, la morphologie 2D des cristallites MS 2 (M = Mo, W) a aussi été observée par MET. Cette technique, utilisée en mode transmission en champ clair (MET-BF pour bright field) permet de connaitre la longueur moyenne et l'empilement moyen des feuillets. Cependant, elle ne permet de visualiser que les cristallites positionnées parallèlement par rapport au faisceau d'électrons incidents. Le mode de détection en champ sombre (ou STEM-HAADF pour scanning transmission electron microscopy in high angle annular dark field) permet quant à lui d'observer les feuillets positionnés perpendiculairement à la direction des électrons incidents, mais aussi d'observer des feuillets « à plat », ce qui permet donc d'évaluer la morphologie 2D des feuillets, s'ils sont peu empilés.

  ont réalisé des clichés STEM-HAADF de catalyseurs promus et non-promus (WS 2 , MoS 2 , NiWS et Co(Ni)MoS), déposés sur graphite (C). Ils retrouvent les variations de morphologies dues à l'influence du promoteur, précédemment décrites grâce aux travaux STM et aux calculs DFT. La Figure 6 montre que l'ajout du promoteur, sur un catalyseur MoS 2 /C dont les cristallites sont triangulaires ou triangulaires tronquées, entraine un changement morphologique vers une structure hexagonale déformée.

Figure 6 :

 6 Figure 6 : Clichés STEM-HAADF [Carlsson et al., 2006] et STM [Lauritsen and Besenbacher, 2006] de catalyseurs déposés sur graphite; a-b) MoS 2 , c) NiMoS, d) CoMoS.

  expérimentaux de STM et STEM-HAADF relativise les résultats obtenus. En effet, les études ont été majoritairement effectuées sur des catalyseurs supportés sur des surfaces d'or ou de graphite, reconnues pour leurs plus faibles interactions « support -phase métallique ». L'étude de la morphologie 2D des feuillets sulfures présents sur des catalyseurs supportés sur support oxyde (silice, silice-alumine ou alumine) représente donc un réel intérêt à la vue du fait que ces matériaux sont communément employés dans l'industrie, et développent de plus fortes interactions avec les phases oxydes. I.3.c. Généralités sur l'activité des catalyseurs en HDS et HYD Les performances catalytiques des catalyseurs non promus, en particulier leurs activités (i.e. leur capacité à convertir des réactifs ciblés) sont faibles et l'ajout d'un promoteur permet d'améliorer d'un facteur ca. 10 leur activité en HDS et HYD. Cela traduit l'effet de synergie entre le promoteur (cobalt ou nickel) et la phase MoS 2 ou WS 2 . Les travaux expérimentaux de

Figure 7 )

 7 qui montre que l'activité d'un catalyseur dépend de l'énergie de liaison « métal -soufre » E M- S , et qu'il existe un optimum d'énergie à environ 130 kJ.mol -1 . L'ajout du promoteur permet de diminuer l'énergie de la liaison «métal -soufre» pour les catalyseurs NiMoS, d'environ 25 kJ.mol -1 par rapport à l'énergie plus élevée d'un catalyseur MoS 2 . De même, l'ajout de Co permet de diminuer d'environ 30 kJ.mol -1 cette même énergie pour les catalyseurs CoMoS. Cependant, la plupart des travaux de la littérature montre que l'activité HDS des CoWS est très faible par rapport aux CoMoS, alors que leur énergie E M-S diffère de moins de 5 kJ.mol -1 . Ce faible effet du promoteur dans le cas du tungstène pourrait provenir des difficultés rencontrées pour former une phase mixte «Co-W-S» lors de la sulfuration. Un effet de synergie a été en revanche trouvé dans les catalyseurs W promus au Ni (NiWS). Dans ce cas, l'énergie E M-S pour un catalyseur NiWS est très proche de celle d'une phase NiMoS, située au sommet de cette courbe en volcan.

Figure 7 :

 7 Figure 7 : Activité catalytique de différentes phases sulfures en HDS du dibenzothiophène, en fonction de l'énergie de liaison «métal-soufre» E M-S [Pecoraro and Chianelli, 1981; Toulhoat and Raybaud, 1999]

  d'une solution d'heptamolybdate d'ammonium, mis en évidence par Carrier et al. [Carrier et al., des catalyseurs est réalisée lors de la sulfuration de la phase oxyde en phase sulfure, précédemment décrite partie I.3.a., durant laquelle le métal est réduit d'un degré d'oxydation +VI à un degré d'oxydation +IV, parallèlement à une réorganisation des espèces de surface (agglomération des atomes de tungstène pour former les feuillets WS 2 ).

  La préparation de catalyseurs à base de Mo et W peut être réalisée en remplaçant les précurseurs conventionnels par des complexes métallo-organiques. Un complexe métalloorganique est formé d'un métal entouré de ligands dont la nature (anionique : alkoxo (OR), amino (NR 2 ) mais aussi halogéno : Cl, Br ou neutre : alcools, amines, éthers…) et le mode de coordination (mono or multidentate) peuvent varier; ce qui détermine son degré d'oxydation et sa géométrie. Les complexes peuvent se présenter sous forme de monomères ou d'oligomères par l'intermédiaire de ligands pontants. Cette grande diversité de complexes métalliques permet d'avoir accès à des espèces aux propriétés physico-chimiques très différentes. On peut citer par exemple la tension de vapeur des composés, plus ou moins élevée suivant le type de ligands entourant le métal. Par ailleurs, les complexes métallo-organiques sont très souvent des espèces sensibles à l'air et à l'humidité, et doivent donc être manipulés en milieu inerte (atmosphère d'azote, argon ou hélium). Enfin, le dépôt de ces précurseurs peut être réalisé par plusieurs méthodes distinctes parmi lesquelles on retrouve l'imprégnation dans un solvant, ou le dépôt chimique en phase vapeur (ou CVD pour Chemical Vapour Deposition). L'imprégnation à sec est réalisée suivant la même méthode que celle utilisée pour déposer les précurseurs conventionnels. Le complexe moléculaire est préalablement dissout dans un solvant et un volume de cette solution, identique au volume poreux du support, est ensuite imprégné sur le support. Par la suite, le catalyseur est séché, puis conditionné en boite à gants. Le dépôt en phase vapeur est réalisé pour des composés dont la tension de vapeur est élevée. Ils sont aisément sublimables et peuvent donc être déposés sous phase vapeur sur le Partie I support. Il existe de nombreuses méthodes de dépôt par voie CVD, les plus classiques étant le dépôt sous flux ou le dépôt en ampoule scellée. Le dépôt sous flux est généralement réalisé en lit fluidisé. Le précurseur, sous phase vapeur, est entrainé par un gaz vecteur et traverse un lit d'extrudés chauffés durant la durée de la manipulation. Le dépôt en ampoule scellée réunit quant à lui le précurseur et le support au sein d'un même contenant. Ces solides sont scellés dans une ampoule, sous vide partiel (quelques mbar de gaz neutre), et cette ampoule est chauffée durant un temps défini pour provoquer la sublimation du complexe et son dépôt sur le support.

Figure 8 :

 8 Figure 8 : Schéma d'un métal M greffé sur une surface.

Figure 9 :

 9 Figure 9: Différents hydroxyles de surface présents sur silice

  et celui-ci diminue de manière exponentielle avec la température à partir de 200°C (voir Figure10). Par exemple, le taux d'hydroxylation de la surface est de 2,1, 1,4 et 0,8 OH/nm² après un traitement sous vide à 300, 500 et 700°C, respectivement. A 700°C, la surface comporte principalement des silanols isolés (> 90% et quelques silanols géminaux, ca. 5-10%) et des ponts siloxanes. Au-delà, la deshydroxylation s'accompagne d'une perte de surface spécifique, notamment pour une silice de flamme type Aerosil®, provenant de l'agrégation de particules.[Rascon et al., 2011] Enfin, à des températures supérieures à 1200°C, la silice cristallise et ne comporte plus que des ponts siloxanes.

Figure 10 :

 10 Figure 10 : Effet du prétraitement en température d'une silice sur le taux d'hydroxylation θ OH.Adapté de la ref.[Rascon et al., 2011]

  Figure 11 : a) Spectre infrarouge d'une alumine-γ γ γ γ deshydroxylée à 500°C sous vide (≈10 -5 mbar). Adapté de la ref. [Rascon et al., 2011]. b) Effet du prétraitement en température d'une alumine-γ γ γ γ sur le taux d'hydroxylation θ θ θ θ OH mesuré par titration avec CH 3 MgBr (•) ou intégration des bande OH du spectre IR (○). Adapté de la ref. [Wischert et al., 2011]

Figure 12 :

 12 Figure 12.

Figure

  Figure 13 : Spectres FT-IR (transm.) d'une silice-alumine, prétraitée sous vide secondaire (10 -5

Figure 14 :

 14 Figure 14 : Espèces de surface formées lors du greffage de Ta(=CHtBu)(CH 2 tBu) 3 sur SiO 2-700 ou SiO 2-300 .

Figure 15 :

 15 Figure 15 : Espèce de surface formée lors du dépôt de l'oxotriisopropoxyde de vanadium, sur silice.

  Figure 16 : A gauche : différentes voies de préparation de catalyseurs COMS sulfurés, à partir de W(C 4 H 7 ) 4 sur SiO 2 -A droite : activité catalytique en HDS du thiophène des catalyseurs préparés suivant les différentes voie présentées. Le catalyseur 5 représente un catalyseur dit conventionnel, préparé à partir de (NH 4 ) 2 WO 4 . α représente le degré de conversion du thiophène.

  ont déposé du cobalt tricarbonyle nitrosyle, ou Co(CO) 3 NO, par voie CVD directement sur un catalyseur sulfuré. Dans leur étude, Okamoto et al. [2009] ont tenté de mettre en évidence l'influence de la température de sulfuration des catalyseurs CoMoS et CoWS en HDS du thiophène. A cette température, et pour une sulfuration à P atm avec un rapport H 2 S/H 2 de 0.1, l'existence de deux types de phases mixtes Co-M-S (M = W, Mo) a été discutée. Pour des catalyseurs supportés sur silice, une phase dite de « type I » serait formée à Etude bibliographique 53 partir de 400°C tandis qu'une phase de type « type II » apparaîtrait à partir de 600°C. Toutefois, la notion de « type I » et « type II » demeure très vague, et ne se caractérise que très empiriquement par une meilleure activité hydrodésulfurante d'un type par rapport à l'autre. D'après Okamoto, la phase CoMoS de « type II » serait formée lorsque le promoteur est déposé sur une phase métallique parfaitement sulfurée. Les auteurs ont aussi mis en avant que l'influence des interactions «MoS 2 -O-support» sur l'état électronique des feuillets MoS 2 conditionne l'état électronique des sites Co-Mo-S de bord, et ainsi, leur activité intrinsèque. La vitesse intrinsèque de conversion du thiophène des CoMoS « type I » serait deux fois plus importante que celle des «type I». De plus, les auteurs ont démontré que les Co-W-S dits de « type II » étaient 1,6 fois plus actifs que les Co-Mo-S en HDS du thiophène. Néanmoins, cela donne peu d'information sur la nature exacte des phases dites de « type II ».

  a montré que l'emploi de Co(CO) 3 NO permettait de multiplier par 2 l'activité HDS d'un catalyseur promu CoMo/Al 2 O 3 préparé par voie CSC, mais n'en modifiait par l'activité hydrogénante. Cela illustre le fait que les réactions d'hydrogénation et d'hydrodésulfuration ne mettent pas en jeu les mêmes sites actifs. Cette observation est cohérente avec les travaux de Moses et al. [2007] et Gandubert et al. [2008] abordés partie I.3.c. Enfin, il convient de mentionner l'emploi combiné de Metal-Organic framework (MOF) et de carbonyles (Mo(CO) 6 , Cr(CO) 6 ) pour la préparation de catalyseurs promus non supportés. [Laribi et al., 2012] Brièvement, le promoteur est contenu dans la charpente du MOF, comme pour [Ni 2 (dhtp)] (H 4 dhpt = acide 2,5-dihydroxyterephthalique). Le précurseur de Mo ou Cr est déposé par sublimation dans les pores du MOF, pour donner des espèces du type M(CO) 3 , en interaction avec les cycles aromatiques de la charpente du support. La sulfuration du matériau dégrade le MOF pour donner un catalyseur massique du type NiMS (M = Cr, Mo) pour lequel seul le catalyseur préparé avec la combinaison Ni+Mo est actif. L'activité intrinsèque du NiMoS massique ex-MOF est 10 fois plus importante que celle d'un NiMoS massique conventionnel en HDS du dibenzothiophène, et 8 fois plus élevée en hydrogénation du naphtalène. Néanmoins, cette méthode de préparation doit être améliorée car les performances des catalyseurs ex-MOF restent inférieures de moitié à celle d'un NiMoS/Al 2 O 3 conventionnel.

55 Figure 17 :

 5517 Figure 17 : Activité intrinsèque en HDS du thiophène à 350°C, de catalyseurs NiW et NiMo déposés sur silice ou alumine, en fonction de leur méthode de préparation (d'après Yermakov et al.[1984])

  3. De précédents travaux réalisés à IFPEn ont quand à eux montré que pour des catalyseurs conventionnels NiWS/ASA, le rapport optimal Ni/W (at/at) était situé entre 0,2 et 0,3. [Raybaud and Toulhoat, 2013, Ed. Technip, Paris] L'influence du support et du promoteur ne semblent Partie I 56 donc pas être significatifs sur la valeur de cet optimum promoteur/métal (ou P/M, avec P = Ni, Co et M = W, Mo).

Figure 18 :

 18 Figure 18 : Liste de différents précurseurs métallo-organiques de W, présélectionnés pour être déposés sur ASA.

13C

  CPMAS solid state NMR: 19 (W-O-CH 2 CH 3 + O ASA -CH 2 CH 3 ), 59 (O ASA -CH 2 CH 3 ), 69 (W-O-CH 2 CH 3 ). E.A: 10,89 % wt. W, e.g. 1.7 (±0.1) W/nm². Synthesis of [W(OEt) 5 ] 2 -IWI-3.0/ASA -300

1H

  MAS solid state NMR: 1.3, 4.0. 13 C CPMAS solid state NMR: 18 (O Al2O3 -CH 2 CH 3 ), 58 (O Al2O3 -CH 2 CH 3 ). 27 Al MAS NMR: 70 (Al IV ), 39 (Al V ), 11 (Al VI ).

:

  Figure 19 : binding modes of alkoxy ligands

Figure 20 :

 20 Figure 20: structural types adopted by W(OMe) 6 and [Nb(OMe) 5 ] 2 from Bradley's theory

Figure 21 :

 21 Figure 21: Structure of [W(OEt) 5 ] 2

Figure 22 :

 22 Figure 22: IR spectrum (ATR) of commercial [W(OEt) 5 ] 2

  Figure 23: NMR spectra (298K, CDCl 2 ) of commercial [W(OEt) 5 ] 2 : a) 1 H spectrum, and b) 13 C{ { { { 1 H} } } } spectrum.

Figure 24 :Figure 25 :AbsorbanceFigure 26 :

 242526 Figure 24: supposed structure of W(OEt) 6

Figure 27 :

 27 Figure 27: NMR spectra (298K, CDCl 2 ) of commercial W(OEt) 6 : a) 1 H spectrum, and b) 13 C{ { { { 1 H} } } }

  2 was kindly provided by M.Cartes (synthesized during her post doctoral position at ETH Zürich) as part of our on-going collaboration. The oxo-derivative synthesis is available in the experimental section (part II).

  synthesised and characterised various oxo-alkoxides with formula W(O)(OR) 4 (R = Me, Et). X-ray characterisation of W 2 (O) 2 (µ-OMe) 2 (OMe) 6 has shown that this compound was a dimeric molecule, adopting a distorted edge-shared bi-octahedral structure Preparation of non-promoted ASA-supported W catalysts: impregnation of W(V) and W(VI) alkoxides 107 featuring terminal oxo ligand trans to the bridged-methoxo group. According to the work of Clegg, [W(O)(OEt) 4 ] 2 can adopt a bi-octahedral geometry as depicted in Figure 28.

Figure 28 :Figure 29 :Figure 30 :Figure 31 :

 28293031 Figure 28: proposed structure of [W(O)(OEt) 4 ] 2 by Clegg and co-workers [Clegg et al., 1992]

  Figure 32: IR spectra (DRIFT) of a) amorphous silica alumina -ASA -500 ; and W-based materials supported on ASA -500 , prepared with b) [W(OEt) 5 ] 2 , c) W(OEt) 6 , and d) [W(O)(OEt) 4 ] 2 .

Figure 33 :

 33 photopeak W 4f 7/2 to values typically found for W(VI) species.

Figure 34 :

 34 Figure 34: XPS spectra. W 4f photopeak of bulk WS 2 prepared by sulphidation of [W(OEt) 5 ] 2 (details available in experimental section). Calibrated vs. C 1s at 284.6 eV.

Figure 35 :

 35 Figure 35: : XPS spectra normalised. W 4f contribution of sulphide catalysts supported on ASA - 500 , and prepared with [W(OEt) 5 ] 2 (red), W(OEt) 6 (green), and [W(O)(OEt) 4 ] 2 (blue). Calibrated vs. carbon C 1s at 284.6 eV. Right: decomposition of W 4f photopeak of [W(OEt) 5 ] 2 based catalyst.

Figure 36 :

 36 Figure 36: Intrinsic rate of hydrogenation [mol(tol)/mol(W)/h] of catalysts prepared by incipient wetness impregnation (square ) or grafting (diamonds ). Precursors used are W(OEt) 6 (green), W(O)(OEt) 4 (black) and [W(OEt) 5 ] 2 (pink)

Figure 36 )

 36 Figure36) between 0.15 and 0.19 mol(tol)/mol(W)/h, which is similar or lower than the intrinsic HYD rates observed for CSC WS 2 /ASA catalysts. Therefore, these results indicate that the catalysts originating from sulphidation of materials prepared by deposition of a molecular precursor of tungsten on ASA are as active as or even more active than their conventional counterparts, and are thus promising samples.

  Alov, N.V., Journal of Analytical Chemistry (2005), 60, 5, 431-435 Bradley, D.C.; Mehrotra, R.C.; Swanwick, J.D. and Wardlaw, W., Journal of the Chemical Society (1953), 2025-2030 Bradley, D.C., Nature, London (1958), 182, 1211 Bradley, D.C. International review of science (1972), 5, series I, 65-91, Editions Butterworths, London Part IV. Effect of tungsten loading on the nature of surface species obtained after impregnation of [W(OEt) 5 ] 2 on ASA Outline (part IV) Outline (part IV) ..................................................................................................................... Introduction ........................................................................................................................... IV.1. Characterisation of CSC materials by X-ray photoelectron spectroscopy (XPS)..... IV.2. Characterisation by Infrared spectroscopy (IR) ......................................................... IV.3. Characterisation by Solid-State NMR spectroscopy (NMR) ....................................... IV.4. Insights into the characterisation of surface species ................................................ IV.4.a. Deposition of ethanol onto SiO 2-700 , Al 2 O 3-450 and ASA -300 . .................................... IV.4.b. Location of W-containing species ......................................................................... IV.4.c. Detailed structure of W-containing species ........................................................... IV.5. Discussion. ................................................................................................................... IV.5.a. Surface species for coverage below ca. 0.8 (± 0.1) W/nm² ................................... IV.5.b. Surface species for coverage above ca. 0.8 (± 0.1) W/nm² .................................. IV.6. Conclusion .................................................................................................................... IV.7. References ....................................................................................................................

Figure 37 :

 37 Figure 37: XPS spectra of [W(OEt) 5 ] 2 -IWI-/ASA -300 catalysts exhibiting 0.5 W/nm², 0.8 W/nm² and 1.7 W/nm². Calibrated vs. C 1s at 284.6 eV.

Figure 38 :

 38 Figure 38: IR spectra. (DRIFT) a) ASA -300 and [W(OEt) 5 ] 2 -IWI-/ASA -300 catalysts: b) 0.2 W/nm²; c) 0.5 W/nm²; d) 0.8 W/nm² and e) 1.7 W/nm². Pure [W(OEt) 5 ] 2 (ATR) is added as reference, f).

Figure 39 :

 39 Figure 39: Expanded scale IR spectra of a) ASA -300 and [W(OEt) 5 ] 2 -IWI-/ASA -300 catalysts: b) 0.2 W/nm²; c) 0.5 W/nm² and d) 0.8 W/nm². Pure [W(OEt) 5 ] 2 is added as reference, e).

  1 H Magic Angle Spinning (MAS) solid-state NMR spectrum of [W(OEt) 5 ] 2 -IWI-0.2/ASA 300 , prepared with ca. 0.2 W/nm² (shown Figure 40, left, green curve), displays four peaks: these at δ = 5.0 ppm and δ = 3.8 ppm are tentatively attributed to methylene protons CH 2

  Figure 40: Solid state NMR spectra. 1 H MAS spectra (left) and 13 C CPMAS spectra (right) of [W(OEt) 5 ] 2 /ASA -300 catalysts exhibiting increasing W/nm². Asterisks denote impurities.

  Figure 41: 13 C MAS (left) and CPMAS (right) solid-state NMR spectra of 13 C labelled catalysts supported on ASA, with increasing W/nm². a W loading to be confirmed by elemental analysis.

  Figure 42: 1D 13 C CPMAS solid state NMR spectrum (x-axis), 1D 1 H MAS spectrum (y-axis) and

  highlights that ca. 50 % of isolated SiOH are consumed, and shows the characteristic features of ethoxy groups: ν(CH) vibrations between 2983 cm -1 and 2881 cm -1 , as well as δ(CH) vibrations between 1480 cm -1 and 1393 cm -1 . Besides, 1 H MAS solid state NMR spectrum, shown in Figure43, reveals four peaks: three are tentatively attributed to adsorbed EtOH (δ(CH 2 ) = 3.7 ppm, δ(CH 3 ) = 1.0 ppm, δ(OH) = 2.6 ppm) and one to remaining silanols of SiO 2 (δ(OH) ca. 1.7 ppm), according to their chemical shift in solution or to literature data[Legrand, 1998, John Wiley & sons Ltd]. The 13 C CPMAS NMR spectrum shows two peaks of very low intensity, at 59 ppm and 17 ppm, respectively attributed to CH 2 groups and CH 3 groups of chemisorbed ethoxy groups. These analyses reveal that only a low amount of EtOH is grafted on the silica surface: the major part of ethanol is only physisorbed.Ethanol was then contacted onto Al 2 O 3-450 , which exhibits ca. 3.0 -3.5 OH/nm²[Rascon et al., 2011]. After impregnation and subsequent washing, Et * OH/Al 2 O 3-450 was analyzed by IR and solid-state NMR. The IR spectra (see appendices) show that ca. 61 % of OH are consumed, and shows the characteristic features of ethoxy groups: ν(CH) vibrations between 2967 cm -1 and 2869 cm -1 , as well as δ(CH) vibrations between 1490 cm -1 and 1383 cm -1 . Moreover, 1 H MAS solid-state NMR spectrum (Figure43) displays one broad peak at δ = 1.3 ppm and one very broad peak at δ = 3.7 ppm, respectively attributed to CH 3 and CH 2 groups of the ethoxy species strongly adsorbed on alumina. In addition, the 13 C CPMAS solidstate NMR spectrum exhibits two peaks at δ = 18 ppm and δ = 58 ppm, associated to the CH 3 and CH 2 groups of the aforementioned ethoxy species. Moreover, 27 Al CPMAS solid state NMR shows that a peak of low intensity, tentatively attributed to Al V species, is visible on the spectrum of the Et * OH/Al 2 O 3-450 material which is not observed on pure Al 2 O (see appendices). This result indicate that a restructuration of the surface of alumina, possibly via opening of Al-O-Al bridge or the conversion of surface Al IV into Al V species through the formation of an additional bond with a surface ethoxide. Overall, the reaction of ethanol on alumina leads to strongly adsorbed, probably chemisorbed ethoxy species. Besides, note that traces of ethanol and diethylether (CH 3 CH 2 -O-CH 2 CH 3 ) were observed in the liquid phase after washing the material (GC/MS analysis), consistent with the fact that: (1) not 100 % of EtOH molecules react with the surface, as observed by IR spectroscopy, (2) EtOH reacts to yield diethylether and water[DeWilde et al., 2013].EtOH was also contacted onto ASA -300 , which exhibits 3.2 OH/nm². First, the aforementioned material was studied directly after impregnation, without any washing step. In Part IV 132 this case, weakly held and strongly adsorbed EtOH molecules could be observed. The IR spectrum of Et*OH/ASA -300 (see appendices) highlights characteristic features of ethoxy groups: ν(CH) vibrations between 2983 cm -1 and 2881 cm -1 , as well as δ(CH) vibrations between 1480 cm -1 and 1393 cm -1 . Note in particular, the partial consumption of isolated SiOH (35%), and the absence of clear δ(OH) vibration of water expected at ca. 1630 cm -1 . The 1 H MAS solid state NMR spectrum (Figure43) displays three sharp peaks at δ = 1.0 and 3.7 ppm associated to the CH 3 and CH 2 of the ethoxy species strongly adsorbed on ASA, along with a signal at 1.7 ppm attributed to surface silanols. A broad signal is also observed at ca. 2.5 ppm, which could be assigned to AlOH and other hydroxyls of ASA, or to OH group of adsorbed ethanol/water. On the 13 C MAS solid-state NMR spectrum (see Figure 44), two peaks at δ = 14 ppm and δ = 58 ppm are observed and respectively assigned to CH 3 and CH 2 of [ASA-O-CH 2 CH 3 ] surface species.

  Figure 43: 1 H MAS solid-state NMR spectra of EtOH/SiO 2-700 , Et * * * * OH/Al 2 O 3-450 and Et * * * * OH/ASA -300

  Figure 45: IR spectra (transm.) of SiO 2-700 , Al 2 O 3-450 and ASA -300 and corresponding 13 C labelled

  Figure 46: 13 C CPMAS Solid-state NMR spectra of 13 C labelled materials prepared on SiO 2-700 (red),

  Figure 47: 29 Si MAS solid-state NMR of SiO 2-700 and [W(OEt * * * * ) 5 ] 2 -G-0.7/SiO 2-700

Figure 51 :

 51 Figure 50: 1 H MAS solid state NMR spectra decomposed with dmfit software [Massiot et al. 2002]. Top: ASA -300 spectrum. Bottom: Catalyst [W(OEt) 5 ] 2 -IWI-0.2/ASA -300 (ca. 0.2 W/nm²). Hydroxyls in green, methylene and methyl protons belonging to ethoxides bound to the ASA surface in purple, methylene and methyl protons bound to W in blue.

142 -

 142 Figure 53: a) b) 3D molecular views of a tungsten surface species [ASA-O-W(OMe) 4 ] resulting from the adsorption of W(OMe) 5 on a ASA surface. Two optimal structures obtained by DFT calculations: a) on isolated silanol (SiOH), b) on a Si-OH---Al pseudo-bridging silanol with H-bond. c) Top view of the [ASA-O-W(OMe) 4 ] system corresponding to a coverage of 0.53 W/nm 2 Adapted from [Leydier, PhD thesis, Paris, 2012]

  At this point, four families of surface species can be proposed: monografted dinuclear species for structure I to IV, bis-grafted dinuclear species for structure V to IX, tris-grafted dinuclear species for structure X to XIII and finally, tetra-grafted dinuclear ones for structure XIV to XVIII.

Figure 54 :

 54 Figure 54: Different mechanisms proposed for reaction between [W(OEt) 5 ] 2 and ASA -300 surface functionalities. M and M' stand for Al or Si atoms.

  bonds W-O ASA bond per W centre YES YES As shown in Table 5, grafting of [W(OEt) 5 ] 2 cannot involve a single mechanism but likely several ones, by direct reaction with hydroxyl groups, and M-O-M' bridge opening (M = Al, Si; M' = Al, Si). One ideal grafting pathway would involve the reaction of the dinuclear W molecular species with two M-OH and two adjacent M-O-M' bridge. It would lead to a tetragrafted W dimer with the concomitant formation of four EtO-ASA surface species (as illustrated by structure XIV to XVIII). Effect of tungsten loading on the nature of surface species obtained after impregnation of [W(OEt) 5 ] 2 on ASA 149 IV.5.b. Surface species for coverage above ca. 0.8 (± 0.1) W/nm² For tungsten loadings greater than ca. 0.8 (± 0.1) W/nm², additional tungsten species are present; they are not directly grafted on the oxide surface, but are adsorbed on previously grafted surface species (multilayer formation); the additional layer of precursors probably interacts with the grafted species via W-O(Et)-W bridges or weaker electrostatic interaction. In fact, additional washing with cyclohexane of the material decreases the loading from 1.7 to 1.4 W/nm². Higher coverage/loading probably leads to the formation of additional layers, more loosely bonded (physisorbed). This is consistent with an increase of the number of EtO ligand bound to W from 3.5 to 4.3 (±0.5) at loading greater than 0.8 W/nm 2 , a value closer to the theoretical number of 5 ligands / W expected in [W(OEt) 5 ] 2 . In addition, at higher loadings, the new observed species are more mobile according to NMR (sharper signals) and closer to the molecular precursor according to both IR and NMR. Finally, when increasing the amount of [W(OEt) 5 ] 2 are deposited, multilayer of tungsten species are formed, with concomitant structural changes. W-O(Et)-W bridges as well as hydrogen bonds are supposed to play a role in the stabilisation of the multilayer, more or less strongly bound to the grafted layer of species. One possible sketch of the multilayer is represented in Figure 55, which highlights strong interactions (W-O(Et)-W bridges) between tungsten species, as well as weaker ones (dotted arrows), like electrostatic interactions.

Figure 55 :

 55 Figure 55: Schematic representation of surface species for high tungsten loadings, where M and M' stand for either Si or Al atoms, and black arrows indicate electrostatic interactions.

  Figure 57: XRD pattern of pristine ASA and conventional calcined catalysts supported on ASA, with increasing W-loadings. α α α α-Al 2 O 3 was added to conventional materials for quantification purpose. * * * * indicates diffraction peaks coming from tungsten impurities deposited on of the X-ray tube Cu.

  Evolution of catalysts during sulphidation: from surface species to active WS 2 phases 161 CSC materials are represented in Figure58, where tungsten dinuclear species are illustrated by rectangles. In light pink are represented the tungsten species grafted on the ASA surface, as previously detailed in part IV. Besides, loosely bonded species, forming additional layers deposited onto the grafted one, are shown in pink. The left part of the figure shows a representation of a side view, while the right part shows a representation of a top view. The former one allows a better understanding of the stacking of the different species, while the latter highlights how the species are dispersed on the surface, on a square of 10 nm long. Note that for more chemical representations, the reader is asked to come back to part IV.

Figure 58 :Figure 59 .Figure 59 :

 585959 Figure 58: Schematic representation of the surface of CSC materials as a function of the W-loading. Materials were obtained by deposition of [W(OEt) 5 ] 2 onto ASA -300 .

Figure

  Figure 60: Schematic representation of the surface of conventional calcined materials as a function of the W-loading. Materials were obtained by calcination of a dried material at 450°C, with air, for 2 h

  Figure 61: XPS data of CSC and conventional catalysts (dried or calcined) depending on tungsten loading. a) Sulphidation level. b) Relative percentage of non-sulphided W(VI) phase. c) Relative percentage of partially sulphided W(intermed.) phase. d) S/W atomic ratio*, calculated from peak area of W(IV) on W 4f spectra and S(-II) on S 2p spectra.

Figure 58 to

 58 Figure 58 to Figure 60.

Figure 62 -

 62 Figure 62-a, shows that this quantity which represents the coverage on the support by tungsten species is lowered upon sulphidation of CSC catalysts. It indicates that sulphidation causes aggregation of the well-dispersed W species (grafted as a monolayer or forming multilayer),

  Figure 62: W/Al atomic ratios (x100), obtained from XPS analyses. Comparison between oxide and sulphide materials prepared by a) CSC, b) Conventional dried, and c) Conventional calcined methods. Comparison between sulphided catalysts is depicted in d).V.1.c. Characterisation by Temperature-programmed reduction (TPR)

  Figure 63: TPR patterns of oxide materials with a) 0.5 W/nm² or b) 1.7-1.8 W/nm². CSC in pink, conventional dried in blue, and conventional calcined catalysts in light blue.

Figure 64 :

 64 Figure 64: Mean length distribution (a) and mean stacking layer distribution (b) of WS 2 crystallites on WS 2 /ASA-300 catalysts when increasing the W loading. Fittings by a Log Normal law.

Figure 65 :

 65 Figure 65: HR STEM-HAADF micrographs of WS 2 /ASA catalysts: a) conventional calcined catalyst (0.5 W/nm²). b) CSC catalyst (0.8 W/nm²). Sulphidations of a) and b) were carried out at 600°C, for 2 h, H 2 S/H 2 mixture with 15 % mol. H 2 S. c) CSC catalyst (0.8 W/nm²) sulphided at 600°C for 5x6 h, H 2 S/H 2 mixture with 15 % mol. H 2 S. d) CSC catalyst (0.5 W/nm²) sulphided at 600°C, 2h, 100% H 2 S. e) HR STEM-HAADF micrographs of a CSC WS 2 /SiO 2-300 (1.0 W/nm²), sulphided at 600°C, for 2 h, H 2 S/H 2 mixture with 15 % mol. H 2 S.

  where H 2 S is used as the sole sulfo-reductive agent, the chemical potential of sulphur in the gas phase is close to 0 and the equilibrium morphology should exhibit a higher proportion of W-edge ca. 71% (

Figure 66 :

 66 Figure 66: a) Morphology diagram for the WS 2 crystallites as a function of the sulphur chemical potential and the pressure of H 2 S, p(H 2 S)/p(H 2 ), at T = 600°C, after reference [Girleanu et al, in preparation]. The proportion of W-edge is given by the blue broken line. The S-edge composition in sulphur is reported above the blue line, and the W-edge composition in sulphur is below this line. Sulphur content at the edge is also indicated above. b) Atomic structure of the S-edge and Wedge for the conditions T=600°C and p(H 2 S)/p(H 2 )=15% .

Figure 67 :

 67 Figure 67: IR(CO) spectra (CO adsorption at 77 K) at saturation of the sulphide phase, resulting from introduction of small doses of CO. Spectra are not baseline corrected, and normalised by the amount of W in the samples. Left) CSC, conventional dried and calcined catalysts sulphided for 2 h (15 % mol. H 2 S/H 2 ) at 350°C. Tungsten loading: 1.7 W/nm². Right) CSC and conventional calcined catalysts, sulphided at 600°C, in the same sulphidation conditions. CSC catalysts were loaded with 1.7 W/nm², 0.8 W/nm² and 0.5 W/nm². Conventional calcined catalyst was loaded with 0.5 W/nm².

Figure 68 -

 68 Figure 68-a, shows the intrinsic rate of hydrogenation (HYD), r i , expressed in mole of toluene converted per mole of tungsten per hour, denoted mol(tol)/mol(W)/h, where mol(W)stands for the amount tungsten (in mol) in the sample, calculated from elemental analyses. All these catalysts were sulphided at 350°C (15 % mol. H 2 S/H 2 ). First, CSC catalysts exhibit a higher intrinsic rate of HYD than conventional catalysts and calcined catalysts are the less active ones.

Figure 68 :

 68 Figure 68: Intrinsic rate of HYD of CSC and conventional catalysts, sulphided at 350°C for 2h with 15 % mol. H 2 S/H 2 ). a) expressed in mol(tol)/mol(W)/h, where mol(W) is calculated from elemental analyses. b) expressed in mol(tol)/mol(W)*/h, where * stands for mole of W incorporated in a WS 2 phase, calculated using "mol(W)" and the % rel WS 2 of spent catalysts (XPS). In b), filled symbols correspond to spent catalysts which underwent XPS analyses. Empty ones correspond to catalysts which % rel. WS 2 after test has been supposed.

Figure 69 :

 69 Figure 69: 2D morphology of a WS 2 crystallites defined by the number of W atoms on W-edge (nM) and S-edge (nS). Green balls: tungsten. Yellow balls: sulphur.

Figure 70 Figure 70 :

 7070 Figure70shows the intrinsic rate of HYD, expressed in mol(tol)/mol(site)/h, where site stands for "edge sites" (active sites) relative to the total number of atoms in one slab. In other words, this can be considered as a Turnover Frequency (TOF), where the time unit is one hour.

Figure 71 -Figure 71 :

 7171 Figure71-a. CSC catalysts prepared at 600°C (15 % mol. H 2 S/H 2 ) exhibit a HYD rate at least 1.6 times higher than the conventional calcined samples, whatever the W-loading. Moreover,

Figure 72 :

 72 Figure 72: Intrinsic rate of HYD expressed as a TOF, in mol(tol)/mol(site)/h for catalysts sulphided at 600°C for 2 h, 15 % mol. H 2 S/H 2 . Site stands for active sites, calculated as the number of edge sites (W-edge and S-edge sites and corners) relative to the total number of atoms in one slab.

Figure 74 :

 74 Figure 73: XPS spectra. W 4f photopeak of a) bulk WS 2 coming from sulphidation of [W(OEt) 5 ] 2 , b) CSC, c) dried and d) calcined WS 2 /ASA catalyst sulphided at 23°C, 2h, 15 % mol. H 2 S/H 2

Figure 75 :

 75 Figure 75: XPS data of CSC and conventional (dried or calcined) catalysts sulphided at different temperatures between 23°C and 600°C (2h, 15 % mol. H 2 S/H 2 ) a) Relative percentage of nonsulphided W(VI) phase. b) Relative percentage of partially sulphided W(intermed.) phase. c) S/W atomic ratio "in WS 2 slabs" calculated from peak area of W(IV) on W 4f spectra and S(-II) on S 2p spectra.

Figure 75 -

 75 Figure75-c exhibits the S/W atomic ratio in WS 2 slabs, calculated, in a first approximation, by dividing the relative amount of S(-II) by W(IV) species, respectively obtained from S 2p and W 4f photopeaks decompositions. When the sulphidation temperature increases, this ratio decreases from ca. 4.0 to 2.2 for conventional catalysts, and from 2.7 to 2.2 for CSC catalysts.

Figure 76 :Figure

 76 Figure 76: W/Al and W/Si atomic ratios (x100), collected from XPS analyses

Figure 78 :

 78 Figure 78: mean length distribution (a) and mean stacking layer distribution (b) of WS 2 crystallites on WS 2 /ASA catalysts when increasing the sulphidation temperature. Tungsten loading: ca. 1.7 -1.8 W/nm².

Figure 79 :

 79 Figure 79: STEM-HAADF micrographs of CSC and conventional dried catalysts sulphided at 350°C and 600°C (H 2 S/H 2 ). Arrows indicate nanosized spot-like entities, supposed to be partially sulphided species (see in the text).

Figure 80 :

 80 Figure 80: IR(CO) spectra (adsorption at 77 K) of CSC catalysts sulphided at 23°C, 350°C and 600°C, at saturation of the sulphide phase, resulting from introduction of small doses of CO. Spectra are not baseline corrected, and normalised by the amount of W in the samples. Samples were submitted to subsequent post-treatment under argon at 250°C after sulphidation, and before CO adsorption. Tungsten loading: ca. 1.7 W/nm².

Figure 81 :

 81 Figure 81: Intrinsic rate of HYD -r i -of CSC and conventional catalysts sulphided between 23°C and 600°C (ex-situ sulphidation, 15 % mol. H 2 S/H 2 , before test). r i is expressed in mol(tol)/mol(W)/h, where mol(W) stands for the amount of W (in mol) in the sample

Figure 82 :

 82 Figure 82: Intrinsic rate of HYD -r i '-of CSC and conventional catalysts sulphided between 23°C and 600°C (ex-situ sulphidation, 15 % mol. H 2 S/H 2 , before test). r i ' is expressed in mol(tol)/mol(W)*/h, where mol(W)* stand for W engaged in a WS 2 phase, calculated using "mol(W)" (elemental analyses) and the % rel WS 2 of spent catalysts (XPS). Arrow indicates the temperature at which the test is run: 350°C. Tungsten loading: ca. 1.7-1.8 W/nm². Filled symbols correspond to spent catalysts which underwent XPS analyses. Empty ones correspond to catalysts which % rel. WS 2 after test has been assumed to be similar to catalysts sulphided at 23°C.

Figure 83 .Figure 83 :

 8383 Figure 83: TOF-(r i ") of CSC and conventional catalysts sulphided between 350°C and 600°C (exsitu sulphidation, 2h 15 % mol. H 2 S/H 2 , before test). Expressed in mol(tol)/mol(site)/h, where mol(site) stands for the amount of active sites, calculated from the number of tungsten atoms on W-edge, S-edge and corners, relative to the total number of atoms in one slab. Tungsten loading: ca. 1.7-1.8 W/nm².

Figure 84 :

 84 Figure84: rim-edge model, proposed byDaage and Chianelli [1994]

FigureFigure 87 :

 87 Figure 85).Additionally, we investigated the control of the morphology of WS 2 slabs in NiWS catalysts.Indeed, the presence of a promoter (Ni, Co) on crystallites edges is known to promotes their stabilisation and thus to decrease their length. It partly explains why promoted samples usually exhibit smaller slabs than non-promoted ones. As we revealed in part V that sulphidation of nonpromoted [W(OEt) 5 ] 2 -based samples, at 23°C (15 % mol . H 2 S/H 2 ), gave small WS 2 slabs(3.2 nm) and numerous nanosized spot-like particles (1 to 2 nm), deposition of nickel on these entities would probably prevent their growth upon additional sulphidation. NiWS samples with smaller

Figure 88 :

 88 Figure 88: (bis-acetylacetonato) nickel (II) precursor

Figure 89 :

 89 Figure 89: IR spectra (DRIFT) of a) ASA -300 and b) Ni(acac) 2 /ASA -300

  Figure 90: IR spectra of a) Ni(acac) 2 /ASA -300 , b) [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 and c) Ni(acac) 2 deposited onto [W(OEt) 5 ] 2 -IWI-1.7/ASA -300

  Figure 91: Proposition of structure for a) Ni 2 W 2 (acac) 4 (OEt) 8 ; Surface species containing W and Ni: b) in case of several surrounding surface alkoxide W-species, with acac ligands on Ni or W; c) in case of more isolated surface alkoxide species.

  Tungsten loadings and experimental Ni/W atomic ratio are obtained from elemental analyses, unless otherwise stated. The whole set of NiW supported materials thus underwent sulphidation at 350°C for 2 h, under a 15 % mol. H 2 S/H 2 mixture. Catalysts are referred as follows: -NiWS ex. MeCp-IWI-0.2/[W(OEt) 5 ] 2 -1.6/ASA -300 with 1.6 (±0.1) W/nm² and Ni/W ≈ 0.21 -NiWS ex. acac-IWI-0.2/[W(OEt) 5 ] 2 -1.6/ASA -300 with 1.6 (±0.1) W/nm² and Ni/W = 0.21 -NiWS ex. NO 3 -IWI-0.3/[W(OEt) 5 ] 2 -1.5/ASA -300 with 1.5 (±0.1) W/nm² and Ni/W = 0.30 Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 227 -NiWS / ASA ex conventional dried, with 1.8 (±0.1) W/nm² and Ni/W = 0.22 -NiWS / ASA ex conventional calcined, with 1.8 (±0.1) W/nm² and Ni/W = 0.22 -NiWS ex. acac-IWI-0.2/W(POM)-1.8/ASA, with 1.8 (±0.1) W/nm² and Ni/W = 0.22 Data obtained by decomposition of the W 4f, and Ni 2p photopeaks are summarized in Table

Figure 92 :

 92 Figure 92: XPS spectrum. Ni 2p photopeak decomposition with 3 contributions: NiWS, NiS and Ni interacting with ASA, also referred as NiO x . Additional peaks are satellites of the different Ni 2p 3/2 and Ni 2p 1/2 contributions. Calibration vs. C 1s at 284.6 eV.

  terms of sulphidation (close % rel. WS 2 , W/Al atomic ratio), except for the calcined sample, which undergo sulphidation in a lesser extent. While incorporation of nickel into the WS 2 phase (NiWS site.nm²) is rather similar for conventional catalysts and CSC ones prepared from Ni(acac) 2 , and Ni(NO 3 ) 2 , the sample prepared with Ni(1-MeCp) 2 reveals a lower amount of NiWS sites. Besides, deposition of Ni(acac) 2 onto W(POM) is finally the preparation which leads to the lower amount of NiWS sites. VI.1.c. Characterisation of NiWS sulphide phases by Transmission electron microscopy (TEM) TEM analyses were also performed to evaluate the average length and stacking number of WS 2 crystallites of NiWS catalyst. Analyses were performed on catalysts prepared by CSC (Ni(acac) 2 based sample only) or conventional approaches. The results, summarized in Table

Figure 93 :

 93 Figure 93: STEM-HAADF micrograph of a Ni-promoted WS 2 slabs, supported on ASA. Catalyst: NiWS/ASA with 0.5 W/nm², Ni/W ≈ 0.2 (at/at), prepared by a conventional method, calcined, and sulphided ex-situ at 600°c for 2 h under a mixture of H 2 S/H 2 . [from Girleanu et al., in preparation].

Figure 94 :Figure 95 :

 9495 Figure 94: Evolution of the energy of the W-edge and S-edge as a function of the chemical potential of Sulphur in the experimental conditions. The vertical bars correspond to the three sulphiding conditions discussed in the main text (including our experimental ones). The dashed region represents the segregation domain of Ni

  ) a Integration is calculated with the total amount of CO adsorbed at saturation of the sulphide phase, and the mass of the pellet VI.1.f. Influence of the Ni content on properties of NiWS phases: the case of Ni(acac) 2 /[W(OEt) 5 ] 2 /ASA sulphide samples As previous characterisations of NiWS/ASA catalysts revealed that the CSC ones prepared with Ni(acac) 2 exhibited the highest amount of NiWS site/nm², and that preliminary catalytic tests revealed they were highly active, we decided to study the influence of the Ni/W atomic ratio on the promotion of the sulphide slabs using this Ni precursor. Therefore, we prepared 3 catalysts with increasing Ni content, e.g. increasing experimental Ni/W atomic ratios, by deposition of Ni(acac) 2 onto a CSC material: [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 . Catalysts are referred as follows: -NiW ex. acac-IWI-0.2/[W(OEt) 5 ] 2 -1.6/ASA -300 with 1.6 W/nm² and Ni/W = 0.21 -NiW ex. acac-IWI-0.4/[W(OEt) 5 ] 2 -1.5/ASA -300 with 1.5 W/nm² and Ni/W = 0.44 -NiW ex. acac-IWI-1.0/[W(OEt) 5 ] 2 -1.5/ASA -300 with 1.5 W/nm² and Ni/W = 1.00

Figure 97

 97 Figure 97 shows the evolution of the effective content of Ni (% wt. ) in NiWS, NiS and NiO x phases, where NiO x stands for Ni strongly interacting with ASA, as a function of the experimental Ni/W ratio. The formation of NiS develops almost linearly when increasing the Ni/W ratio, while the amount of NiWS phase starts by increasing before reaching a plateau

Figure 97 :

 97 Figure 97: XPS data. Effective content of Ni in the different Ni phases: mixed phase NiWS, NiS and Ni strongly interacting with ASA (referred as NiO x ). NiWS/ASA catalysts prepared by deposition of Ni(acac) 2 onto [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 with W-loadings between 1.5 W/nm² and 1.6 W/nm², and Ni/W atomic ratio between 0.21 and 1.00. Sulphidations ex-situ were carried out at 350°C for 2 h, under a mixture of H 2 S/H 2 (15 % mol. H 2 S).

  Figure 98: IR spectra of a) WS 2_350°C -1.7/ASA -300 , b) Ni(acac) 2 deposited onto WS 2_350°C -1.7/ASA -300 , c) NiWS ex.acac-IWI-0.2/WS 2 -350°C -1.7/ASA -300 and d) Ni(acac) 2 /ASA -300 as a reference spectrum.

a

  Figure100shows the evolution of the effective Ni content in NiWS, NiS and NiO x phases.The formation of NiS and NiOx (Ni strongly interacting with the ASA support) phases develop almost linearly when increasing the experimental Ni/W ratio. On the contrary, when increasing this Ni/W atomic ratio, the amount of NiWS phase increases before reaching a maximum for an experimental Ni/W atomic ratio of 0.4 -0.5, and then decreases. Then the quantification of NiWS site/nm² reveals that the catalyst prepared with Ni/W = 0.44 exhibits the highest amount of NiWS site/nm², estimated to be 0.30 NiWS site/nm². The (Ni/W) slab follows the same trends as the amount of NiWS sites: when increasing the Ni/W atomic ratio, (Ni/W) slab increases from 0.27 to 0.41 and then decreases until reaching ca. 0.16. Finding a decrease of the amount of the NiWS phase at high Ni content can be tentatively explain as follows: when deposited on a sulphide phase, whatever the pre-sulphidation temperature, the Ni precursor hardly react with the sulphide phase, and is poorly dispersed on the surface; subsequent sulphidation promotes the incorporation of Ni in a mixed phase "NiWS", concomitantly with the formation of non

  Figure 101: Mean length distribution (a) and mean slabs stacking layer distribution (b) of WS 2 crystallites of NiWS/ASA catalysts prepared by deposition of Ni(acac) 2 onto WS 2_23°C -1.7/ASA -300 pre-sulphided at 23°C.with W-loadings between 1.5 W/nm² and 1.6 W/nm², and Ni/W atomic ratio of 0.24, 0.44 and 0.85. Sulphidations ex-situ were carried out at 350°C for 2 h, under a mixture of H 2 S/H 2 .

  ) 2 on a pre-formed conventional dried oxide phase (W (POM) ) do not enhance the activity, which highlight the strong role of the tungsten surface species (dispersion on the surface and reactivity toward Ni-precursors) on which promoters are deposited when samples are prepared by successive impregnation.The intrinsic HYD rate of the previous catalysts is depicted in Figure107. Results are similar to the previous ones found for the weight flow rate of toluene converted. The CSC method allows the preparation of samples exhibiting the highest intrinsic HYD rates (ranging from 3.51 to 3.77 (±0.49) mol(tol)/mol(W)/h), probably due to their high amount of mixed phase

Figure 107 :

 107 Figure 107: Intrinsic HYD rate of different (Ni)WS 2 /ASA catalysts, expressed in mol(tol)/mol(W)/h. NiWS/ASA samples prepared with either Ni(acac) 2 , Ni(1-MeCp) 2 or Ni(NO 3 ) 2 . CSC samples are compared with conventional dried and calcined ones. W-loading ranging from 1.5 to 1.8 W/nm². Ni/W (at/at) ranging from 0.21 to 0.30. Sulphidations ex-situ were carried out at 350°C, for 2 h, in a 15 % mol. H 2 S/H 2 mixture prior to HYD tests

Figure 109 :

 109 Figure 109: Intrinsic HYD rate [mol(tol)/mol(W)/h] of different Ni promoted catalysts, prepared with either Ni(acac) 2 deposited onto supported tungsten alkoxide species, or deposited onto sulphide phases prepared at either 350°C or 23°C (2 h , 15 % mol. H 2 S/H 2 ). CSC samples are compared with conventional dried and calcined ones. W-loading ranging from 1.6 to 1.8 W/nm². Ni/W (at/at) ranging from 0.20 to 0.24. Sulphidations ex-situ were carried out at 350°C, for 2 h, in a 15 % mol. H 2 S/H 2 mixture prior to HYD tests

Figure 112 .Chemical

 112 Figure 112.

Figure 112 :

 112 Figure 112: Morphology diagram of NiWS crystallites as a function of the chemical potential and p(H 2 S)p(H 2 ) at T=650 K (377°C) [Girleanu et al., in preparation]. The proportion (percentage) of Wedge is given by the blue broken line. The S-edge compositions are above the blue line, and the W-edge compositions are below this line. Ni repartition on either W-edge or S-edge in also reported. The green arrow emphasizes our experimental conditions: ∆ ∆ ∆ ∆µ S = -1.03 eV

50%

  These 3 NiWS crystallites exhibit n M = 8 and n S = 4, concomitantly with: 1) Ni substituting 50 % of the W atoms on S-edge, along with 25 % of the W atoms on W-edge, as shown Figure 113-I. This structure is the one expected with our experimental conditions. 2) Ni substituting 50 % of the W atoms on S-edge, along with 100 % of the W atoms on W-edge, as shown in Figure 113-II. 3) Ni substituting 100 % of the W atoms on S-edge and W-edge, as shown in Figure 113-III. Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 265

Figure 113 :

 113 Figure 113: NiWS crystallites with n M =8, n S =4. Mixed sites (if present) are indicated by arrows; I. Partially decorated on S-edge and W-edge; II. Partially decorated on S-edge and fully decorated on W-edge and III. Fully decorated on S-edge and W-edge; IV. W-edge of structure I. Green balls: tungsten. Red balls: nickel, Yellow balls: sulphur [Girleanu et al., in preparation]

  /W) slab. , is obtained by XPS and experimentally corresponding to the amount of Ni in a NiWS phase divided by the amount of W in a WS 2 phase; and where (number of M atoms) stands for either the total number of metal atoms in a crystallite, or the number of metal atoms on edges and corners only. Calculations are based on 2D geometrical models simulated with slabs lengths obtained by TEM analyses of the following NiWS/ASA catalysts prepared: 1) by deposition of Ni(acac) 2 onto [W(OEt) 5 ] 2 /ASA, referred as ex. acac-(Ni/W)/[W(OEt) 5 ] 2 , for Ni/W atomic ratio of 0.21, 0.44 and 1.00 (at/at) 2) by deposition of Ni(acac) 2 onto a sulphide phase, prepared at 350°C, referred as ex. acac/WS 2-350°C

Figure 114 :

 114 Figure 114: Theoretical and experimental atomic Ni-to-W substitution ratio on edges and corners (X subst. ) as a function of (Ni/W) slab (e.g. Ni-to-W atomic ratio in NiWS crystallites). Theoretical values are calculated from 2D geometrical models along with TEM data. Experimental ones (red symbol and arrows) are calculated from 2D geometrical models along with TEM and XPS data (spent catalysts). Only data that match conditions of Eq. 7 are depicted.

Figure 115 :

 115 Figure 115: Theoretical Ni-to-W substitution ratio as a function of the theoretical Ni-to-W atomic ratio in NiWS crystallites (Ni/W) slab_theo . Calculated with DFT data and slabs length, between 3.2 nm and 4.1 nm, with the help of geometrical models

Figure 119 :

 119 Figure 119: Illustration of the strength of NiWS active sites: mixed sites (red arrows) found on NiWS crystallites with 25 %Ni on W-edge and 50 %Ni on S-edge vs. fully decorated NiWS crystallites. Green balls: tungsten. Red balls: nickel, Yellow balls: sulphur. Mol(Ni)* stands for the amount (mole) on Ni incorporated in a NiWS phase.

Figure 120 :

 120 Figure 120: Example of tungsten surface species probable found on non-sulphided [W(OEt) 5 ] 2 -based material

WS 2 )Figure 122 :

 2122 Figure 122: Schematic representation of surface W-species observed for increasing W-loadings on CSC and conventional dried and calcined catalysts

Figure 123 :

 123 Figure 123: STEM-HAADF micrograph of isolated WS 2 slabs found on sulphide catalysts prepared by: a) a conventional calcined method; b) a molecular approach. Experimental conditions: 600°C, 2 h, 15 % mol. H 2 S/H 2 . c) Crystallite structure stabilised in the corresponding experimental conditions, as obtained by DFT calculations

Table des matières (bibliographie)

Table

  NH 4 ) 6 Mo 7 O 24 , xH 2 O ou le métatungstate d'ammonium hydraté (NH 4 ) 6 H 2 W 12 O 40 , xH 2 O, où les métaux (Mo ou W) sont rassemblés sous forme de clusters. En fonction des conditions de préparation (taux de

	chargement en métal, pH de la solution d'imprégnation), différentes espèces peuvent être
	formées à la surface des catalyseurs. Pour des matériaux séchés, préparés par dépôt de
	métatungstate d'ammonium sur alumine, l'espèce tungstate WO 4 2-est la seule mise en
	évidence tandis qu'après calcination, des phases oxyde WO 3 et polytungstate ont été révélées
	par spectroscopies XPS, Raman et IR

I.4.a. Préparation des phases oxydes supportées non promues

Les matériaux conventionnels à base de Mo et W sont obtenus par imprégnation à sec de précurseurs, comme l'heptamolybdate d'ammonium hydraté (

]

  Partie I I.4.b. Préparation des phases oxydes supportées promues La préparation des catalyseurs promus peut être réalisée par imprégnations successives de la phase métallique ou du promoteur, par co-imprégnation des précurseurs, ou bien par imprégnation du promoteur sur une phase déjà sulfurée. Les précurseurs conventionnels les plus utilisés sont les dérivées nitrates, Ni(NO 3 ) 2 , xH 2 O ou Co(NO 3 ) 2 , xH 2 O. Il est aussi possible de déposer un hétéro-polycomposé réunissant le tungstène ou le molybdène, et le promoteur, au sein d'une même structure comme Ni 4 SiW 11 O 39 . [Ben Tayeb, PhD thesis, Lille, 2009] L'étude du système promu NiW/Al 2 O 3 par Reinhoudt et al. [Reinhoudt et al., 2000] a permis de montrer, après calcination, la présence de nickel sous forme d'oxyde mixte plus ou moins fortement lié au support, ou de nickel sous forme de nickel-aluminate NiAl 2 O 4 . Le tungstène est quant à lui présent sous forme d'oxyde WO 3 et d'oxyde mixte avec le nickel Ni(WO). Une autre étude montre par ailleurs la présence d'oxyde de nickel NiO en faible quantité.

Récapitulatifs des résultats d'analyses XPS et MET obtenus pour des catalyseurs NiWS/ASA préparés sur silice, silice-alumine (30 % pds. SiO 2 ) et alumine.

	Partie I
	Tableau 1 : 0	0.7 Fraction aluminique	1
			Silice	Silice-alumine	Alumine
	Dispersion de la phase sulfure (évaluée par calcul du rapport
	atomique W/Al -XPS) a
	Sulfurabilité du tungstène (ou % rel. WS 2 , par rapport à la quantité totale de tungstène détectée) a	76 % rel.	60 % rel.	50 % rel.
	Formation d'une phase mixte NiWS (ou % rel. NiWS, par Longueur moyenne des feuillets sulfures (nm) b rapport à la quantité totale de nickel détectée) a	[4,0 -6,5 nm] 64 % rel.	[2,0 -3,5 nm] 46 % rel. 58 % rel.
	Empilement moyen des feuillets sulfures	b	3,2	2,5
	a obtenu par analyse XPS
	b obtenu par microscopie électronique à transmission

les phases sulfures obtenues sont similaires à celles obtenues sur alumine, en termes de longueur de feuillet, et d'activité catalytique en HDS. Les travaux réalisés à IFPEn

[Raybaud and Toulhoat, 2013, Ed. Technip, Paris]

sur des catalyseurs promus NiW supportés sur silice, silicealumine (30 % pds. SiO 2 ) et alumine et présentant 4,3 W/nm² et Ni/W = 0.4 at/at, ont permis de caractériser l'influence du support sur : la dispersion de la phase WS 2 à la surface du support (vue par XPS), la sulfurabilité du W, la formation de phase mixte «NiWS», la longueur moyenne et l'empilement moyen des feuillets. Ces résultats sont illustrés dans le Tableau 1. Comme observé auparavant par

Kim et al., [1996]

plus un support est silicique, moins bonne est la répartition de la phase sulfure (vue par XPS), pour laquelle les feuillets sont plus longs et plus empilés. Cependant, la diminution de la quantité d'aluminium dans le support offre le bénéfice d'améliorer le taux de sulfuration du W (quantité de phase WS 2 observée par XPS supérieure) et d'accroitre la quantité de nickel engagée dans une phase mixte «NiWS».

  Leroux et al. [LeRoux et al., 2005b] ont appliqué la méthode CSC pour le dépôt de [W(≡CtBu)(CH 2 tBu) 3 ] sur alumine partiellement deshydroxylée à 500°C (ou Al 2 O 3-500 ) afin de générer des catalyseurs de métathèse des alcanes à base de W. Une étude expérimentale[LeRoux et al., 2005a] couplée à des calculs DFT[Joubert et al., 2006] a montré qu'une espèce de surface monopodale du type [(Al s O)W(≡CtBu)(CH 2 tBu) 2 ] est obtenue, et qui traitée sous hydrogène donne un hydrure de W (i.e. WH/Al 2 O 3-450 ), Ces espèces, en particulier l'hydrure de tungstène se sont révélés de très bons catalyseurs de métathèse des alcanes avec des performances supérieures à l'espèce de surface de référence l'hydrure de tantale supporté sur silice, [(≡SiO) 2 TaH].[Vidal et al., 1997] On notera la préparation de catalyseurs similaires, déposés sur silice-alumine (Si/Al = 3 at/at) deshydroxylée à 500°C. Dans ce cas,[LeRoux et al., 2007] le dépôt de W(≡CHtBu)(CH 2 tBu) 3 donne une espèce de surface monopodale du type

	Partie I
	48

[(≡SiO)W(≡CHtBu)(CH 2 tBu) 2 ] par réaction du complexe métallique avec les silanols du support, qui traité sous hydrogène, évolue vers un hydrure de tungstène supporté sur ASA. Ces catalyseurs se sont révélés aussi actif que sont homologue déposé sur Al 2 O 3-500 . Pour plus d'informations sur les précurseurs ou les supports utilisés, ainsi que sur les résultats catalytiques et les mécanismes associés à la métathèse des alcanes, le lecteur est invité à consulter le papier

de Basset et al.

  rapporte le dépôt de W sur γ-Al 2 O 3-450 par photo-irradiation d'une solution de pentane contenant le support, W(CO) 6 et PPh 3 . Par spectroscopie FT-IR, les auteurs ont montré la présence de différentes espèces de tungstène adsorbées à la surface de l'alumine, mais n'ont pas étudié les interactions entre ces espèces et les hydroxyles du support. Compte tenu de la volatilité des complexes carbonylés,

plusieurs travaux se sont intéressés au dépôt de ces complexes par voie CVD. La préparation par dépôt en phase vapeur permet typiquement de mieux contrôler la quantité de métal déposée et de potentiellement améliorer la dispersion

  Par ailleurs, l'imprégnation de précurseurs homoleptiques alkyles comme le tungstène tétra(η 3 -1-butènyle) (W(C 4 H 7 ) 4 ) paraît prometteuse.Yermakov et al. [1984] ont montré que le degré d'oxydation du métal greffé sur le support aurait une influence importante sur la sulfuration, la dispersion de la phase active, ainsi que sur l'activité catalytique. En particulier, pour un catalyseur WS 2 /SiO 2 , le processus de sulfuration est plus favorable en partant d'un métal à degré d'oxydation bas : une espèce de surface formée de W au degré d'oxydation +II étant plus facilement sulfurable qu'une espèce formée de W (IV) ou de W(VI) . Une étude précédemment menée à IFPEn a montré qu'un catalyseur préparé à partir de tungstène (V) pentaéthoxyde [W(OEt) 5 ] 2 déposé sur silice-alumine amorphe (ASA, 30 % pds. SiO 2 ) se sulfurait mieux qu'un catalyseur conventionnel calciné du type WO 3 /ASA d'après des analyses XPS.

	Etude bibliographique
	WCl 6 avec de l'H 2 S pur [Chung et al., 1998], ou issu de la décomposition d'éthanedithiol
	HS(CH 2 ) 2 SH. [Carmalt et al., 2003]
	51

réalisées sur les catalyseurs M(CO) 6 /support préparés par CVD mettent toutes en évidence l'existence d'espèces M(CO) 6 physisorbées, mais présentent des divergences quant à la présence d'espèces sub-carbonyles M(CO) 6-x greffées en surface. Il semblerait que la structure des espèces de surface soit dépendante des étapes de préparation (notamment le post traitement du catalyseur après dépôt du précurseur) et surtout de l'état de surface du support, notamment son taux d'hydroxylation et la présence de sites acides de Lewis Al 3+ plus ou moins forts. De plus, les résultats catalytiques obtenus en HDS du thiophène ne révèlent pas systématiquement une amélioration de l'activité des catalyseurs. En particulier,

Suvanto et al. [1999]

ont montré que pour des catalyseurs W(CO) 6 /γ-Al 2 O 3 , l'augmentation du taux de recouvrement en tungstène (W/nm²) engendre une diminution de l'activité intrinsèque en HDS du thiophène (mol (thiophène) /mol (W) ), probablement provoquée par moins bonne dispersion de la phase active sur le support à fort W/nm². Il convient aussi de mentionner la possibilité de préparer du WS 2 massique par dépôt en couche mince, par réaction en phase gaz de W(CO) 6 ou de l'hexachlorure de tungstène (VI) En HDS du thiophène

Yermakov et al. [1984]

ont mis en évidence que plus le degré d'oxydation du métal greffé est bas, plus l'activité intrinsèque de catalyseurs WS 2 /SiO 2 est importante. Sur la Figure

16

, le catalyseur sulfuré n°2, préparé initialement par réduction de

58 Tableau 3 : Récapitulatif non exhaustif des précurseurs COMS utilisés dans la littérature, et leur intérêt.

	Etude bibliographique Partie I Etude bibliographique
	Le large choix de composés métallo-organiques disponibles permettra de sélectionner des l'utilisation d'un précurseur moléculaire où le tungstène est au degré d'oxydation +VI permettra
	précurseurs avec des ligands variés, pouvant réagir facilement avec les hydroxyles de surface notamment de comparer l'effet de la nucléarité du précurseur de W, en s'affranchissant d'un
	du support (ASA), et développant des interactions « précurseur -support » probablement éventuel effet du degré d'oxydation. Une liste des précurseurs étudiés est présentée Figure 18.
	différentes de celles rencontrées jusqu'ici entre les précurseurs conventionnels et les supports Précurseur Méthode de dépôt Support Application Commentaires Références
	couramment utilisés. De plus, l'emploi de molécules pour lesquelles les liaisons «métal -W(CO) 6 CVD Al 2 O 3 HDS Augmentation du taux de recouvrement en W = diminution de la dispersion du W Suvanto et al. , 1999
	ligand» sont relativement labiles pourrait permettre d'augmenter le taux de sulfuration du tungstène, et éventuellement étudier la genèse de la phase sulfure. Co(CO) 3 NO CVD SiO 2 HDS Sulfuration plus aisée, activité intrinsèque des phases Tungstène (V) pentaéthoxyde Okamoto et al ., 2009 CoWS supérieure à celle des phasesCoMoS Co(CO) 3 NO CVD Al 2 O 3 HDS Promoteur organométallique = activité intrinsèque des phases CoMoS X 2 en HDS -pas d'amélioration de l'activité HYD Maugé et al. , 1989 + V W O Et OEt OEt OEt OEt W O OEt OEt Et OEt OEt
	W(OEt) 5	n-hexane	ASA	HDS	Augmentation du taux de sulfuration du W et de la dispersion de WS2 en surface	Roukoss, 2009
	3 liste certains des précurseurs répertoriés dans cette étude bibliographique, leur utilisation, et W(CO) 6 n-hexadécane + ultrasons Al 2 O 3 HDS Pas de différence d'activité (HDS) vs. catalyseurs conventionnels Vishwakarma et al. , 2007 W(C4H7)4 pentane SiO2 HDS Tungstène (0) hexacarbonyle W Tungstène (VI) hexaéthoxyde Meilleure sulfuration du W et augmentation "dispersion" de WS 2 en surface + activité HDS Yermakov et al. , 1984 OEt EtO 0 OEt
	les résultats d'intérêts. Lors de la thèse, le support sélectionné pour préparer les premiers catalyseurs sera une Ni(MeCp) 2 n-hexane ASA HYD Augmente la quantité de phase promue Roukoss, 2009 Ni(C 3 H 5 ) 2 pentane SiO 2 HDS W EtO OEt + VI OEt Phase NiWS (CSC) : vitesse intrinsèque HDS X 3 Yermakov et al. , 1984 vs. NiWS conventionnels Co 2 (CO) 8 n-hexadécane + ultrasons Al 2 O 3 HDS (phase CoWS) Vishwakarma et al. , 2007 Pas d'augmentation significative de l'activité HDS Tungstène (VI) oxo-tetraéthoxyde
	silice-alumine amorphe (ASA, 30 % pds. SiO 2 ). Ce choix est guidé par la bi-fonctionnalité Meilleure activité HDS pour des catalyseurs
	intéressante des catalyseurs supportés sur ASA (acidité modérée due au support, et fonction Co 2 (CO) 8 hexane Al 2 O 3 HDS/HDN Co (CSC) /MoS 2 Rapport Co/Mo (at/at) = 0,2-0,3 optimal pour les réactions d'HDS. Moins bonnes Halbert et al. , 1991
	hydro-déshydrogénante modérée de la phase sulfure), ainsi qu'aux résultats prometteurs performances HDN que les ref. classiques.
	obtenus lors de précédents travaux réalisés à IFPEn, en hydrogénation du toluène. Co 2 (CO) 8 CVD Al 2 O 3 HDS Augmentation de l'activité intrinsèque en HDS Suvanto et al. , 1999
	Suvanto et al. , 1999; Reddy D'après les travaux présentés dans cette étude bibliographique, il apparait que le dépôt de W(CO) 6 CVD Al 2 O 3 -Présence de W(CO) 6 physisorbé en surface and Brown, 1995; Zecchina
	et al. , 1990 précurseur de W en phase vapeur ne permet pas d'élaborer des catalyseurs WS 2 très actifs et aisément caractérisables. C'est pourquoi une méthode d'imprégnation sera privilégiée, avec un W(CO) 6 + PPh 3 Pentane + ultraviolets Al 2 O 3 -Baibich et al ., 1997 Dépôt facilité par photo-irradiation du complexe en
	solvant organique adapté à chaque précurseur métallo-organique. W(CO) 6 + PPh 3 Pentane + ultraviolets Al 2 O 3 Conversion de NO en N2 présence de PPh 3	Sica et al. , 1999
	Comme les espèces de surface de type polyoxométallates (ou clusters de W, présent sur les catalyseurs conventionnels séchés) ou de type WO 3 (oxyde de grande taille, présent sur les W(OEt) 5 n-hexane Charbon actif Perez-Cadenas et al. , 2003 W(CO) 6 CVD Charbon actif Perez-Cadenas et al. , 2003 Isomérisation du 1-butène Dispersion du W améliorée
	catalyseurs calcinés) ne permettent pas d'obtenir d'importantes quantités de phase sulfure :
	60% rel. WS 2 sur ASA, pour un catalyseur NiW/ASA calciné, 4.3 W/nm², Ni/W = 0.4, il semble Afin d'étudier la réactivité de complexes métallo-organiques pour lesquels le tungstène intéressant d'envisager le dépôt d'espèces de petite taille, pour bénéficier d'une meilleure présente deux états d'oxydation extrêmes, nous avons sélectionné des précurseurs dans répartition du tungstène sur la surface, et pour accéder à des taux de sulfuration plus élevés. lesquels le métal possède un degré d'oxydation 0, +V et +VI, mais nous étudierons plus Pour cela, on privilégiera l'emploi de précurseurs mono ou dinucléaires. particulièrement ceux au sein desquels le métal est au degré d'oxydation +V ou +VI. On
	emploiera donc au moins un précurseur où le tungstène est partiellement réduit (degré
	d'oxydation +V), afin de vérifier si son utilisation permet de mieux sulfurer le W. Enfin,
						57 59

3/2 (S-II)

	Part II
	In the case of Ni atoms detected as Ni(II), NiWS and Ni x S y , the "promotion level"
	expressed as the relative amount of Ni incorporated in NiWS phase is given by Eq. 3:
		Ni	promotion	level	[%]	=	total NiWS Ni A A	x	100	Eq. 3
	with A Ni total = A NiWS + A Ni(II) + A NixSy the experimental XPS area of, respectively, NiWS, Ni(II)
	and Ni x S y species. We can then deduce the effective amount of NiWS phase noted C NiWS by
	multiplying the relative value with the total Ni content (4).
		C	NiWS =	C	Ni	total	x	Ni	100 promotion	l leve	Eq. 4
	Average results found for peculiar binding energies (BE) of W 4f and Ni 2p photopeaks are
	summarized as follows:
	BE (eV)			BE (eV)			BE (eV)	∆BE (eV)	∆BE (eV)
	Ni 2p 3/2 NiWS			Ni 2p 3/2 Ni x S y				Ni 2p 3/2 Ni(II)	W 4f 7/2 W(IV) (NiWS) vs. Ni 2p 3/2	Ni 2p 3/2 NiWS vs. Ni 2p 3/2
	Mean value	32.2					35.9		1.2	129.6
	±	0.1						0.1		0.1	0.1
											76

Ni x S y FWHM (NiWS) / FWHM (Ni x S y )

	Part II
	II.2.d. Carbon monoxide adsorption at 77K, monitored by FT-IR (IR(CO)) outgassed at 25°C to avoid any degradation. BET and BJH methods were used [Lynch, 2001] to
	Carbon monoxide adsorption analyses at 77 K, monitored by FT-IR, were performed with a calculate pore distribution and specific surface area.
	ThermoFisher Scientific Nicolet Nexus 2 apparatus, using an IR cell equipped with CaF 2
	windows, in transmission mode. Prior to analysis, self-supporting pellets (ca. 2.03 cm -2 ) were Elemental analyses (E.A) were used to quantify W, Ni, C and/or H. They were performed at prepared under controlled atmosphere in a glovebox. Sulphide samples were often dark and either the CNRS Central Analysis Service of Solaize (France), at Pasher laboratories (Germany) proved to absorb a lot the IR signal, dramatically degrading its quality. Therefore, they were or at IFPEn (by X-ray fluorescence XRF with a Thermo ARL Advant'x apparatus). In the case of most of the time diluted with α-Al 2 O 3 (S BET < 10m²/g) to improve the sample transparency. conventional or CSC materials analysed at IFPEn, thus not analysed under inert conditions, Before measurements using CO as probe molecule, the samples were outgassed under samples were calcined so as to know to precise ignition weight loss of the materials prior to vacuum (1,3.10 -4 Pa) and cooled down to 77 K. The spectrum of the empty cell was recorded as background reference. Adsorption experiments of CO probe molecule were carried out at low analysis. Corresponding results were corrected with the ignition weight loss.
	temperature, by pulse of increasing amount of CO from 0.12 to 300 µmol. The spectrum of
	sample without CO adsorption was assigned as the reference spectrum. Gas-phase chromatography analyses (GC) were performed on a Hewlett-Packard 5890
	series II gas chromatograph equipped with a flame ionisation detector and a capillary column
	CP-Wax 52 CB (10 m X 0.1 mm). Typically, gas phases were analysed by injecting ca. 500 µl of II.2.e. Transmission electron microscopy (TEM) and Scanning transmission electron gas. Liquid phases were analysed by injecting ca. 0.1 µl of liquid. Gas-phase chromatography microscopy (STEM) coupled with mass spectra analyses (GC/MS) were collected with gas chromatograph Agilent
	TEM micrographs were obtained with a 200 kV JEOL-2010 transmission electron 6890 N equipped with autosamplers and fitted with a PONA column (50 m, 0.20 mm diameter,
	microscope equipped with a digital camera. For sample preparation, extrudates were crushed 0.50 µm thick) or with a HP-5MS column (30 m, 0.25 mm diameter, 0.25 µm thick), coupled with
	into a fine powder, a small amount of which being ultra sonically diluted in ethanol. Two drops of an Agilent 5975B inert XL EI/CI MSD mass spectrometer.
	this solution were deposited on a carbon-coated Cu grid, rinsed with ethanol, and the solvent
	Mean value was evaporated under infrared light. 853.7 852.6 Temperature-programmed reductions (TPR) were performed with a Micromeritics 856.4 821.5 1.1 1.5 Scanning transmission electron microscopy (STEM) in high angle annular dark field AutoChem 2910 analyser equipped with a TCD detector. The samples (ca. 0.5 g) were packed
	Sdt. err. (HAADF) experiments were performed at the Institut de Physique et Chimie des Matériaux de 0.1 0.1 0.2 0.1 0.1 0.2 in a U-shaped quartz tube in a glove box, and the sealed tube was attached to the analyser
	Strasbourg (IPCM Strasbourg) with a Cs aberration corrected scanning transmission electron under inert gas flushing. Gas mixture of 5%H 2 /Ar with a flow rate of 20mL/min and temperature
	II.2.c. Fourier transform infrared spectroscopy (FT-IR) microscope operating at 200 kV. ranging from 36°C to 1000°C (5°C/min) were used for reductions.
	FT-IR spectra of self-supporting pellets (ca. 2.03 cm 2 ) were recorded at IFPEn on a ThermoFisher Scientific Nicolet Nexus 2 spectrometer, equipped with a mercury-cadmium-telluride (MCT) detector cooled with liquid nitrogen. The IR cell was equipped with CaF 2 windows, allowing in-situ studies, in a transmission mode. FT-IR spectra were also recorded at X-ray powder diffraction (XRD) analyses were performed at room temperature, on a II.2.f. Other analyses PANanalytical X'PertPro X-ray diffractometer, equipped with a CuKα raditation (λ = 1.5418 Å) in Fourier transform (FT) Raman spectroscopy was performed at ETH Zurich on a Raman a Bragg Brentano geometry. The incident beam was focused to the sample through a spectrometer equipped with a Diodo Pumped ND: YAG Laser PSU. programmable divergence slit to ensure a constant irradiation length of about 10 mm on the ETH Zurich on a Bruker Alpha FT-IR spectrometer in either transmission, or diffuse reflectance Textural properties were used to calculate the pore distribution and the specific surface sample. The diffracted beam was directed through an anti-scattering programmable slit, a infrared Fourier transform spectroscopy (DRIFT) modes. FT-IR spectra of chemical products area of the materials. They were obtained using a Micromeritics ASAP 2420 apparatus. Prior to 0.2 mm reception slit and a (002) graphite monochromator before reaching the punctual were performed on a Spectrum one FT-IR spectrometer, in attenuated total reflectance mode nitrogen adsorption, samples were outgassed for six hours to remove the adsorbed water and detector. The samples (about 0.5 g of powder) were prepared in a rotating sample holder, and (ATR, ZnSe diamond). Typically, 32 scans were accumulated for each spectrum (resolution, 4 sensitive. Conventional samples were outgassed at 500°C (5°C/min), while CSC samples were cm -1 ). All IR analyses were performed in transmission mode, unless otherwise stated. gases. Note that before outgassing, samples were loaded under inert atmosphere (glovebox) if analysed in a range from 2θ = 2 to 2θ = 70°, with a step of 0.05° and a counting time of
	78

II.3. Preparation of supported W alkoxide materials

	II.3.a. Preparation of ASA-supported materials
	Preparation and characterisation of amorphous silica-alumina, partially dehydroxylated at
	300°C, referred as ASA -300
	Silica-alumina with a specific area of 229 m²/g was calcined for 6h under air (static
	conditions), using a ramp of 5°C/min up to 300°C. Then, the solid was partially dehydroxylated
	at 300°C under high vacuum (5.10 -5 mbar) for ca. 16 h. The system was cooled down to 140°C
	using a ramp of ca. 10°C/min, and the extrudates were stored in glovebox. After this treatment,
	the specific area was 228 m²/g. OH densities were measured by titration of OH by quantification
	of CH 4 evolved after contacting ASA suspended in diethylether with CH 3 MgBr (1.3 M).[Cartes,
	2012] Results: 1.22 mmol OH/g e.g. 3.2 OH/nm². IR (DRIFT): 3743 (isolated SiOH), 3554 (vbr),
	1987, 1852, and 1621 (Si-O-Si) cm -1 .
	Preparation and characterisation of amorphous silica-alumina, partially dehydroxylated at
	500°C, referred as ASA -500

  ASA -CH 2 CH 3 + W-O-CH 2 CH 3 ), 3.7 (O ASA -CH 2 CH 3 ), 4.9 (W-O-CH 2 CH 3 ). 13 C MAS solid state NMR: 14 (O ASA -CH 2 CH 3 ), 16 (W-O-CH 2 CH 3 ), 58 (O ASA -CH 2 CH 3 ), 68, 70 & 75 (W-O-CH 2 CH 3 ). E.A: 5.91 % wt. W, e.g. 0.9 (±0.1) W/nm².

	Synthesis of 13 C labelled [W(OEt * ) 5 ] 2 -IWI-2.0+/ASA -300

, 1607 (w), 1484 (sh), 1469 (w), 1446 (m), 1396 (sh), 1380 (s), Part II 84 1355 (m) cm -1 . 1 H MAS solid state NMR: 1.2 (O

Table 1 : 1 H and 13 C{

 1

{ { { 1 H} } } } NMR data obtained on [W(OEt)

5 ] 2

		1 H	13 C { 1 H}	1 H	13 C { 1 H}
	[W(OEt) 5 ] 2	1.22, triplet	18.8	4.77, quadruplet	70.1

Table 2 :

 2

		1 H	13 C { 1 H}	1 H	13 C { 1 H}
	W(OEt) 6	1.22, triplet	18.8	4.76, quadruplet	70.1
	[W(O)(OEt) 4 ] 2 a	1.32, triplet	18.2	4.77, broad peak	72.4

1 H and 13 C{ { { { 1 H} } } } NMR data obtained on W(OEt) 6 a Impurity

Table 3 :

 3

		1 H	13 C { 1 H}	1 H	13 C { 1 H}
	[W(O)(OEt) 4 ] 2	1.32, triplet	18.2	4.78, broad peak	72.4
	W(OEt) 6 a	1.22, triplet	18.8	4.76, quadruplet	70.1

1 H and 13 C{ { { { 1 H} } } } NMR data obtained on [W(O)(OEt) 4 ] 2 a Impurity

Table 4 : Possible structures for surface species, at low tungsten loading.

 4

Table 5 : Compatibility between our mechanisms and experimental data.

 5

Figure 56: Close-packed "monolayer" for WO 3

  OEt) 5 ] 2 /ASA -300 were prepared by incipient wetness impregnation of a cyclohexane solution of [W(OEt) 5 ] 2 onto ASA -300 , as reported in the experimental section. Afterwards, CSC and conventional materials underwent sulphidation at 350°C for ca. 2 h, with a mixture of H 2 /H 2 S (15 % mol. H 2 S) at atmospheric pressure, unless Insights into the spreading of oxide species on ASA: the case of conventional materials In part IV, we detailed the case of CSC oxide materials where for W-loadings below 0.8 W/nm², formation of a layer of grafted species occurred. For higher loadings, we observed the formation of a multilayer, composed of more loosely bonded species, chemisorbed or physisorbed onto the layer of grafted tungsten species. With this in mind, we investigate in this first paragraph the possible formation of such layered structures on conventional catalysts, especially in the case of calcined ones for which data are already reported in the literature (see below). According to a simple model where WO 3 species form a close-packed layer of species on the surface (see Figure56), Xie et al[Xie and Tang, 1990] estimate the full coverage of a surface (referred as a "monolayer") to be ca. 0.21 g WO3 /100 m² support . The comparison of this theoretical value with an experimental one collected from XRD data[Liu et al., 1985] of WO 3 supported γ-Al 2 O 3 samples revealed that a layer of surface species which correspond to the full coverage of the support was achieved.

	Part V
	V.1.a. O 2-
	W 6+
	otherwise stated.
	158

conventional WS 2 /ASA catalysts, where the tungsten loading (W/nm²) is calculated on the basis of elemental analyses and the support surface area (228 m²/g). Moreover, note that conventional materials were prepared by incipient wetness impregnation of an aqueous solution of ammonium metatungstate (polyoxometallate species) on ASA. Drying the material at 120°C gave materials referred as "dried". Subsequent calcination under air at 450°C gave materials referred as "calcined". CSC materials [W(

Al 2 O 3 SiO 2 -Al 2 O 3 SiO 2 -Al 2 O 3

  Finally, the different oxide species found on conventional calcined materials are depicted on Figure60. At low loadings, small amorphous WO 3 particles are supposed to be spread onto

	the ASA surface. Then, increasing the W-loading causes a growth of amorphous WO 3 directed
	horizontally over the surface, and vertically on top of preformed WO 3 particles. Between
	1.8 W/nm² and 3.7 W/nm² in particular, crystalline WO 3 appears, as represented in white and
	black stripes. It indicates that no more WO 3 can spread onto the ASA surface, e.g. that the
	"(sub)monolayer" is achieved, and that stacking of WO 3 species becomes the main
	phenomenon. WO 3 is strongly linked to the surface.
		Conventional calcined materials
	W/nm² ↑	Side view	Top view
	0.5		10 nm
	1.8
	3.7
	Amorphous WO 3	Crystalline WO 3	Strong interaction

SiO 2 -

SiO 2 -Al 2 O 3 SiO 2 -Al 2 O 3 SiO 2 -Al 2 O 3

		Conventional calcined materials
	W/nm² ↑	Side view	Top view
	0.5		10 nm
	1.8
	3.7
	Amorphous WO 3	Crystalline WO 3	Strong interaction

Table 6 : W/Al atomic ratio (x100) representing the coverage of tungsten on the ASA. Obtained from XPS analyses

 6

	W/nm²	CSC	Dried W/Al (at/at) x 100 Calcined
	0.5	1.1	0.8	0.9
	1.7	4.8	2.7	2.9
	3.7	11.2	5.9	6.1

Table 7 : H 2 consumption obtained from TPR experiments. STP stands for standard condition of temperature and pressure (273.15 K, 100 kPa)

 7

				H 2 consumption (ml/g(W) (STP))
				0.5 W/nm²			1.7-1.8 W/nm²
			CSC	Conv. dried	Conv. calc.	CSC	Conv. dried Conv. calc.
	Total	a	255	118	121	234	270	245
	Std dev.	19	9	9	18	20	18
	Theo. value	309	-	371	309	-	371
	Ratio exp. / theo. (%)	83	-	33	76	-	66
	a H 2 consumption from the start to the end of the experiment

,

  only spectra collected until saturation of the sulphide phase with carbon monoxide are shown.

	350°C 15 % mol H 2 S/H 2				600°C 15 % mol H 2 S/H 2	2124 -2125 cm -1
				2160 cm -1	2121 cm -1
	0.2 a.u						0.2 a.u	2160 cm -1	2076 -2069 cm -1
								CSC
	Absorbance (absorbance units)	Conv. dried 1.8 W/nm² Conv. calc. 1.8 W/nm² CSC 1.7 W/nm²			2068 cm -1	Absorbance (absorbance units)	1.7 W/nm² CSC 0.8 W/nm² CSC 0.5 W/nm² Conv. calc 0.5 W/nm²
		2250	2200	2150	2100	2050	2000	2250 2200 2150 2100 2050 2000
				Wavenumber (cm -1 )		Wavenumber (cm -1 )

Table 8 : Data collected from IR(CO) analyses of CSC, conventional dried or calcined catalysts, sulphided at 350°C (2 h, 15 % mol. H 2 S/H 2 ) at 1.7 W/nm 2 . a.u stands for absorbance units, and mol(W)* stands for "mole of W engaged in a WS 2 phase in the sample", calculated using % rel WS 2 (XPS)

 8

	350°C
	15 % mol. H 2 S/H 2	CSC	Dried	Calcined
	a.u / cm / g(cat.) a	54	1	0
	% rel WS 2 (XPS)	85	75	50
	a.u / cm / g(W)	500	9	0
	a.u / cm / mol(W)*	3.2	0.1	0.0
	a Calculated with the amount of CO adsorbed at saturation of the sulphide phase, and the mass of the pellet

Table 9 : Data collected from IR(CO) analyses of CSC and conventional catalysts sulphided at 600°C, 2 h, H 2 S/H 2 (15 % mol. H 2 S). a.u stands for absorbance units, and mol(W)* stands for "mole of W engaged in a WS 2 phase in the sample", calculated using % rel WS 2 (XPS)

 9

	600°C
	15 % mol. H 2 S/H 2

Table 10 : Experimental data and Geometrical parameters used for WS 2 slab models of catalysts prepared at 350°C, for 2h with 15 %mol. H 2 S/H 2 . Bold numbers represent the best comprises found for the catalysts, and used to normalise the intrinsic activity

 10

			W/nm²	Length L from TEM (Å)	Length L' from the model (Å)	n M n S	Number of W in one slab	% W edge a	% edge sites b	TOF mol(tol)/mol(site)/h
			3.7	38	38	6	6	127	50	28.3	0.79
	CSC	1.7 0.8	38 34	38 38	6 6	6 6	127 127	50 50	28.3 28.3	1.12 0.96
			0.5	40	38	6	6	127	50	28.3	0.79
	Conv.	dried	3.7 1.8 0.5	39 37 38	38 38 38	7 7 7	5 5 5	127 127 127	60 60 60	28.5 28.5 28.5	0.82 0.77 0.87
			3.7	36	35	7	4	107	67	31.0	0.34
	Conv. calcined	3.7 1.8 0.5 0.5	36 40 29 29	38 38 28 28	7 7 5 6	5 5 4 3	127 127 73 71	60 60 56 71	28.5 28.5 36.4 37.4	0.35 0.54 0.54 0.52
			0.5	29	32	6	4	92	63	33.0	0.59

a Calculated from the number of W atoms on W-edge, relative to the total number of W atoms on edges (W-edge + S-edge) b Calculated from the number of W atoms on W-edge, S-edge and corners, relative to the total number of W atoms in one slab.

Looking at Table

10

for CSC materials with 1.7 W/nm², for a mean length L ≈ 3.8 nm, the corresponding 2D hexagonal model exhibit n M = n S = 6, with 50 %W-edge and ca. 127 (±1) W per WS 2 slabs. The so-called active sites (or edge sites), e.g. W located on corners, W-edge and S-edge, represent ca. 28.3 % of the total number of W atom in one CSC slab . For the calcined catalyst with 1.8 W/nm² and a mean length L ≈ 4.0 nm, equations Eq

. 3 and Eq. 4 gave

  {n M = 7, n S = 5}, which leads to about 28.5 % of tungsten atoms on edges and corners of the aforementioned calcined catalyst. As a consequence, CSC and conventional calcined catalysts exhibit WS 2 slabs with close amounts of tungsten sites on corners and edges.

Table 11 : Experimental data and Geometrical parameters used for WS 2 slab models of catalysts prepared at 600°C, for 2 h with 15 % mol. H 2 S/H 2.

 11

	W/nm²	Length L from TEM (Å)	Length L' from the model (Å)	n M n S	Number of W in one slab	% W edge a	% edge sites b	TOF mol(tol)/mol(site)/h
	0.5	34	32	6	6	93	50	32.6	0.99
	0.8	34	32	6	6	93	50	32.6	0.97
	0.8	34	38	6	6	127	50	28.3	1.24
	1.7	51	51	6	6	221	50	22.0	1.00
	0.5	40	38	7	5	127	60	28.5	0.74
	1.8	39	38	7	5	127	60	28.5	0.53

a Calculated from the number of W atoms on W-edge, relative to the total number of W atoms on edges (W-edge + S-edge) b Calculated from the number of W atoms on W-edge, S-edge and corners, relative to the total number of W atoms in one slab.

  . In particular, Rochet, in her study on the sulphidation of calcined Mo/Al 2 O 3 materials, revealed that from K-edge Mo-EXAFS spectrum, the intermediate phase formed through sulphidation is better represented by a {MoOS 2 } model compared to a {MoS 3 } one. However, this {MoOS 2 } model, previously proposed byGenuit et al. from EXAFS data [Genuit et al., 2005], contains Mo in a +VI oxidation state, while from her K-edge Mo-XANES spectrum, Rochet finds that Mo is closer to a +IV oxidation state. Moreover, as an unambiguous characterisation of (oxy)sulphide species MoO x S y , especially by XPS, has not been achieved so far, every interpretation of experimental data as to be taken with great caution. Back to our study, Figure75-b has allowed to pinpoint that for conventional catalysts, there is a maximal amount of this intermediate phase between 250°C and 300°C, which matches the inflexion point of S-shaped % rel WS 2 curves. This result is also in line with XPS data of CoMo/Al 2 O 3 catalysts reported byGandubert [2006]. Gandubert showed that for sulphide catalysts (H 2 S/H 2 , 15 % mol. H 2 S) based on dried materials, the inflexion point of the sulphidation level of Mo was around 50°C, a temperature for which the amount of oxysulphide phase was maximal with ca. 18 (±5) % rel. MoO x S y . Similarly, she found an inflexion point close to 200°C for calcined samples, concomitant with ca. 19 (±5) % rel. MoO x S y . Besides, QEXAFS data reported by A.Rochet [2011] for MoS 2 /Al 2 O 3 (calcined) catalysts shows that the maximal amount of intermediate phase is reached around 275°C, a temperature which is found to be starting point of MoS 2 apparition, revealing that Mo oxide species needs to be (quasi) fully transformed in {MoOS 2 } before being changed into MoS 2 .

With this in mind, our results are consistent with the literature

[Rochet, PhD thesis, Paris, 2011; Gandubert, PhD thesis, Lille, 2006; van Der Vlies, PhD thesis, Zürich, 2002]

describing a sulphidation mechanism which proceeds via different steps, which are:

Table 12 ,

 12 and illustrated by Figure 78. Bar graphs are available in appendices.

	Part V

Table 12 : TEM data. Mean length distribution and mean stacking layer distribution of WS 2 crystallites on WS 2 /ASA catalysts when increasing the sulphidation temperature. Tungsten loading: ca. 1.7 -1.8 W/nm².

 12

		Sulphidation temperature (°C)	Mean Length L (nm)	Sdt. dev.	Mean stacking number N	Sdt. dev.
		-25	No visible slabs	-	No visible slabs	-
		23	3.2	1.1	2.6	1.2
	CSC	150 350	3.2 3.8	1.3 1.3	2.4 3.1	1.1 1.2
		450	4.2	1.6	3.1	1.4
		600	5.1	2.3	3.5	1.8
		23	No visible slabs	-	No visible slabs	-
	Conv.	350.0	3.7	1.2	3.0	1.4
	dried	450.0	4.3	1.4	3.3	1.6
		600.0	4.4	1.6	3.6	1.8
		23	No visible slabs	-	No visible slabs	-
	Conv.	350	4.0	1.4	2.7	1.3
	calcined	450	3.9	1.2	2.9	1.3
		600	4.0	1.2	2.7	1.8

Table 13 : Data collected from IR(CO) analyses of CSC catalysts sulphided at 23°C, 350°C or 600°C (2 h, 15 % mol. H 2 S/H 2 ). a.u stands for absorbance units, and mol(W)* stands for "mole of W engaged in a WS 2 phase in the sample", calculated using % rel WS 2 (XPS)

 13

		23°C	350°C	600°C
	a.u / cm / g(cat.) a	43	54	81
	%rel WS2 (XPS)	53	85	87
	a.u / cm / g(W)	398	500	750
	a.u / cm / mol(W)*	4.1	3.2	4.7

Table 14 : Experimental data and Geometrical parameters used for WS 2 slab models of catalysts sulphided at 350°C, 450°C or 600°C, for 2h with 15 % mol. H 2 S/H 2 . Bold numbers represent the best comprises found for the catalysts, and used to normalise the intrinsic activity

 14

			W/nm²	Length L from TEM (Å)	Length L' from the model (Å)	n M	n S	Number of W in one slab	% W edge a	% edge sites b	TOF mol(tol)/mol(site)/h
			350	38	38	6	6	127	50	28.3	1.16
	CSC	450	42	42	6	6	167	50	25.0	1.15
			600	51	51	6	6	221	50	22.0	1.05
			350	37	38	7	5	127	60	28.5	0.73
	Conv. dried	450 450 600	43 43 44	44 44 44	10 9 10	4 5 4	159 163 159	75 66 75	26.4 25.6 26.4	0.80 0.79 0.70
			600	44	44	9	5	163	66	25.6	0.72
	Conv.	calcined	350 450 600	40 39 40	38 38 38	7 7 7	5 5 5	127 127 127	60 60 60	28.5 28.5 28.5	0.50 0.43 0.49

Table 15 : XPS data, obtained by decomposition of W 4f and Ni 2p photopeaks of NiWS/ASA catalysts. CSC ones were prepared by deposition of Ni(acac) 2 or Ni(1-MeCp) 2 or Ni(NO 3 ) 2 onto [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 . Conventional ones were prepared by co-impregnation of Ni(NO 3 ) 2 and ammonium metatungstate. Additional sample prepared by impregnation of Ni(acac) 2 on a conventional dried W-oxide phase. Sulphidations ex-situ were carried out at 350°C, for 2 h, under a 15 % mol. H 2 S/H 2 mixture.

 15 (Ni/W) slab is calculated using NiWS and WS 2 quantification results from XPS experiments.

		% rel. WS 2	% rel. W(VI)	% rel. W(intermed.)	W/Al at. ratio (x100)
	ex. Ni(acac) 2	71	11	18		2.5
	ex. Ni(1-MeCp) 2	73	12	15		2.6
	ex. Ni(NO 3 ) 2	73	16	12		3.3
		73	12	15		2.7
		56	24	20		3.0
		69	15	16		2.7
		% rel. NiWS	NiWS site / nm²	(Ni/W) a	slab
	ex. Ni(acac) 2	80	0.27 ± 0.04	0.33 ± 0.04
	ex. Ni(1-MeCp) 2	53	0.17 ± 0.03	0.25 ± 0.03
	ex. Ni(NO 3 ) 2	63	0.29 ± 0.04	0.23 ± 0.03
	Conventional dried	66	0.26 ± 0.04	0.30 ± 0.03
	Conventional calcined	57	0.23 ± 0.04	0.30 ± 0.03
	ex. acac/W(POM)	7	0.03 ± 0.01	0.05 ± 0.01

a

Table 15

 15

	reveals that CSC catalysts exhibit similar levels of sulphidation ranging from
	71 (±5) to 73 (±5) % rel. WS 2 , which is about 10 % lower than for the non-promoted WS 2 /ASA
	catalysts prepared in part V. The relative amounts of W(VI) and intermediate phase W(V) are
	not significantly different from each other. The surface coverages of tungsten, as detected by
	XPS (W/Al), are also similar, except for the sample prepared with Ni(NO 3 ) 2 which exhibit a
	higher surface coverage of tungsten. Then, compared to the sample prepared with Ni(1-MeCp) 2 ,
	the amount of active phases, also called mixed phases "NiWS", are higher for catalysts
	prepared with Ni(acac) 2 and Ni(NO 3 ) 2 , and lead to ca. 0.27 (±0.04) NiWS site/nm² and
	0.29 (±0.04) NiWS site/nm² respectively. Note also that "NiWS site/nm²" stands for the amount
	of mixed site per nm², calculated in a first approximation by multiplying the nickel coverage
	Ni/nm² (elemental analyses) by the % rel. NiWS (XPS). Only ca. 0.17 (± 0.03) NiWS sites/nm² are
	found for the Ni(1-MeCp) 2 -based catalyst. Besides, catalysts were also compared with respect
	to their nickel-to-tungsten atomic ratio in NiWS nanocrystallites, denoted (Ni/W) slab . These
	data represent the amount of Ni incorporated in a mixed phase "NiWS", at a crystallite scale,
	and correspond experimentally to the amount of Ni engaged in a mixed phase "NiWS", divided
	by the amount of W in a WS 2 phase. In the table, sulphide slabs of the Ni(acac) 2 -based catalyst
	are characterised by a higher (Ni/W) slab ratio, which is ca. 0.33 (± 0.04), while values ranging
	from 0.23 to 0.25 (± 0.03) are found when Ni(NO 3 ) 2 or Ni(1-MeCp) 2 are used as Ni precursors.

Table 16 : Mean slabs length and mean slabs stacking number of NiWS/ASA catalysts with ca. {1.7 -1.8} W/nm², Ni/W ≈ 0.2 (at/at)

 16 ) identify the 2D morphology of the promoted WS 2 slabs, and (2) investigate the location of Ni atoms on the edges of the slabs, in the spirit of the previous work ofDeepak et al. [Deepak et al., 2011] on Co doped MS 2 (M = W, Mo) nanowire catalysts supported on Al 2 O 3 .

			Mean slabs length L (nm)	Std dev.	Mean slabs stacking number N (nm)	Std dev.
	CSC	ex. Ni(acac) 2	3.7	1.1	3.1	1.4
	Conventional dried	3.6	1.1	3.1	1.4
	Conventional calcined	3.5	1.2	3.1	1.6
	VI.1.d. Characterisation of NiWS sulphide phases by STEM-HAADF
	We performed STEM-HAADF analyses on conventional calcined catalysts in order to:
	(1First, we investigate the 2D morphology of WS 2 crystallites on a calcined catalyst with low
	tungsten loading, e.g. 0.5 (±0.1) W/nm², exhibiting a Ni/W atomic ratio of 0.19, after sulphidation
	at 600°C for 2 h with a H 2 S/H 2 mixture (15 % mol.

Infrared spectra of CO adsorbed at low temperature, IR(CO), on sulphided CSC (pink), conventional dried (blue) and calcined (light blue) NiWS/ASA catalysts. W-loading is ca. 1.7 W/nm². Sulphidations ex-situ were carried out at 350°C, 2 h, under a H 2 S/H 2 mixture (15 % mol. H 2 S), before CO adsorption.

  As in part V, only spectra collected at saturation of the sulphide phase with carbon monoxide are presented. Band attribution and data obtained from spectra analysis are summarized in Table17. Attributions were based on the work of Zuo the clear assignment of CO interacting with NiWS. The broad tail situated at lower wavenumbers can be attributed to peaks of CO interacting with NiS and WS 2 . Then, considering the broad peak obtained for the dried NiWS/ASA catalyst, interpretation must be taken cautiously. However, we can still highlight that CO interacting with a NiWS phase is observed at ca. 2136 cm -1 , in line with the results obtained for the other catalysts.Further quantification of the amount of CO adsorbed, normalised by the number of W atom engaged in a WS 2 phase, reveals that the sulphide phase of the calcined catalyst adsorb about 3.4 times more CO than the dried one, and 1.6 times more CO than its CSC counterparts.These results are surprising as the previous IR(CO) analyses performed on unpromoted catalysts (see parts V.1.f.) show that the sulphide phase of the calcined one was barely interacting with CO. As a conclusion, the sulphide phase of CSC, conventional dried and conventional calcined NiWS/ASA catalysts are different in view of these IR(CO) analyses.

	Part VI
	VI.1.e. Characterisation of NiWS sulphide phases by CO adsorption at low temperature (77K) monitored by IR spectroscopy -IR(CO) CO adsorption at low temperatures, monitored by IR spectroscopy (transmission mode), was performed on the CSC NiWS/ASA catalyst prepared with Ni(acac) 2 , and on conventional support * CSC Conventional dried Conventional calcined 0.01 a.u NiWS WS 2 NiS NiWS WS 2 2134 2121 2100 2080 catalyst only allows Absorbance 2065
	NiWS/ASA catalysts, dried or calcined, sulphided at 350°C (2 h, H 2 S/H 2 mixture with 15 % mol.
	H 2 S). Note that as from the beginning of our study, a post treatment of 2 h at 250°C under argon
	is performed right after sulphidation in order to remove any traces of physisorbed H 2 S. Wavenumber (cm -1 ) 2250 2200 2150 2100 2050 2000 IR(CO) spectra are shown in Figure 96. et al. [Zuo et al., 2004] on alumina supported NiWS sulphide phases (400°C, 10% H 2 S/H 2 ), Figure 96:
	conventionally prepared by calcination at 450°C of alumina supported NiW species, obtained by
	co-impregnation of nickel nitrate and ammonium metatungstate. CO stretching vibrations were
	assigned as follows: ν(CO) NiWS at 2134 cm -1 and 2080 cm -1 , ν(CO) NiS at 2100 cm -1 and ν(CO) WS2
	at 2121 cm -1 and 2065 cm -1 . The CSC catalysts exhibit a spectrum where signals of CO
	interacting with NiWS and NiS are clearly visible, alongside with an additional shoulder
	attributed to CO interaction with WS 2 . Besides, the broad peak observed for the calcined
	234

* * * * stand

for interaction of CO with Lewis and/or Brønsted acid sites

  Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 235

Table 17 : Data collected from IR(CO) spectra analyses. mol(W)* stands for "mole of W engaged in a WS 2 phase, calculated using % rel WS 2 (XPS)

 17

				ν(CO) interacting with		Integration a
		NiWS	NiS	WS 2	NiWS	WS 2	(a.u / cm / mol(W) *
	CSC	2134	2100	2121	2080	2065	3.1
	Conv. dried	2131	2100	2120	2080	-	1.5
	Conv. calcined	2136	2100	2124	-	-	5.1

Table 18 : XPS data, obtained by decomposition of W 4f and Ni 2p photopeaks of CSC NiWS/ASA catalysts prepared by deposition of Ni(acac) 2 onto [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 with W-loadings between 1.5 W/nm² and 1.6 W/nm², and Ni/W atomic ratio between 0.21 and 1.00. Sulphidations ex- situ were carried out at 350°C for 2 h, under a mixture of H 2 S/H 2 (15 % mol. H 2 S).

 18

	W/nm²	Ni/W (at/at) %rel. WS 2	%rel. W(VI)	%rel. W(intermed.)	W/Al at. ratio (x100)
	1.6	0.21	71	11	18	2.5
	1.5	0.44	67	13	20	2.2
	1.5	1.00	69	13	18	2.4
	W/nm²	Ni/W (at/at) %rel. NiWS NiWS site / nm²	(Ni/W) a slab
	1.6	0.21	80	0.27 ± 0.04	0.33 ± 0.04
	1.5	0.44	52	0.35 ± 0.05	0.57 ± 0.06
	1.5	1.00	27	0.41 ± 0.06	0.50 ± 0.06
	a (Ni/W) slab is calculated using NiWS and WS 2 quantification results from XPS experiments.

Table 18 )

 18 reveals that the sample with Ni/W = 1.00 (at/at) contains more Ni inserted in a mixed NiWS phase, thus more Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 237 potentially active sites. Note however that due to the high amount of nickel in the sample, a slight variation of % rel. NiWS causes a rather important variation of NiWS/nm², possibly increasing the experimental error in our calculation. Nonetheless, it is still clear that the more Ni precursor is added, the more NiWS sites are formed, as previously reported for NiMoS/Al 2 O 3 catalysts byMarchand et al. [2009]. Concomitant with the NiWS site/nm² increase, the nickel-to-Ni/W) slab values of about 0.44. The experimental value, lying between 0.57 and 0.50, is thus compatible with the theoretical one, obtained with geometrical model combining DFT and TEM data. These models will be detailed in part VI.6. Note also that experimental values are compatible with the ones reported by Marchand et al. through DFT calculations and experimental results obtained on (Co)NiMoS supported phases ((Co)Ni/Mo) slab ranging from 0.42 to 0.52 for crystallites of about 3.2 nm).[Marchand et al., 2009]

	tungsten ratio in sulphide crystallites (referred as (Ni/W) slab ) increases and reaches a maximum
	located between 0.57 (±0.06) and 0.50 (±0.06) for Ni/W ≥ 0.44 (at/at). Within the experimental
	error, it indicates that a maximal amount of Ni decorating the crystallites edges can be reached,
	due to a complete substitution of tungsten edge atoms by nickel ones, for a given
	2D morphology and slabs length. Combining the 2D morphology of NiWS crystallites modelled
	by DFT calculations (part VI.1.d) and an average slab length of 35 Å (TEM analyses of these
	samples, sulphided at 350°C with 15% mol. H 2 S/H 2 , are discussed in the next part: VI.1.f.2)
	(% crystallites are fully decorated for (Effective Ni content 0.40 1.80 0.60 0.80 1.00 wt. of each phase) 1.20 1.60 1.40	%NiWS %NiS %NiOx
	0.20
	0.00
	0.00 0.20 0.40 0.60 0.80 1.00 1.20
		Experimental Ni/W atomic ratio

Table 19 .

 19 While there are no large differences between the mean slabs length values, the slabs length slightly decreases from 3.7 nm to 3.3 nm when increasing the Ni/W atomic ratio. The stacking number is quasi steady with an average of about 2.9 crystallites stacked together, for all catalysts. These results are in line with the work of Zuo et al on NiWS/Al 2 O 3 catalysts (ca. 3.2 W/nm², calcined at 450°C, before sulphidation at 400°C, 10 % H 2 S/H 2 ), who reported a decrease of the slabs length, from 4.1 to 3.8 nm, respectively for Ni/W = 0.20 and Ni/W = 0.69 (at/at).[Zuo et al., 2004] Moreover, considering a similar 2D morphology for NiWS crystallites of the 3 aforementioned samples, the decrease of the slabs length, observed when increasing the experimental Ni/W atomic ratio, infers an increase of the (Ni/W) slab , ratio from ca. 0.40 to 0.48. This is in line with XPS results reported in part VI.1.f.1 which revealed a maximum lying between 0.50 and 0.57 (±0.06).

Table 19 : Mean slabs length and mean slabs stacking number of NiWS/ASA catalysts prepared by deposition of Ni(acac) 2 onto [W(OEt) 5 ] 2 -IWI-1.7/ASA -300 with ca. {1.5 -1.6} W/nm² and Ni/W atomic ratio varying from 0.21 to 1.00 (at/at). Sulphidations ex-situ were carried out at 350°C for 2 h, under a mixture of H 2 S/H 2 .

 19

	W/nm²	Ni/W (at/at)	Mean slabs length L (nm)	Std dev.	Mean slabs stacking number N (nm)	Std dev.
	1.6	0.21	3.7	1.1	3.1	1.4
	1.5	0.44	3.5	1.2	2.7	1.1
	1.5	1.00	3.3	1.1	2.9	1.3

  M-O-W linkages (M=Si, Al) between sulphide slabs and the surface, not 100 % of isolated silanols SiOH i are involved. Besides, no more IR bands attributed to acetylacetonato ligands of Ni(acac) 2 are visible, which means that the nickel precursor has been transformed, and that Ni belongs to either in NiWS, NiS or NiO x phases.

	3.2
	3.0
	2.8
	2.6
	2.4
	2.2
	2.0
	1.8
	1.6
	1.4
	1.2
	4000	3500	3000	2500	2000	1500

Table 21 : XPS data, obtained by decomposition of W 4f and Ni 2p photopeaks of CSC NiWS/ASA catalysts prepared by deposition of Ni(acac) 2 onto WS 2_23°C -1.7/ASA -300 , pre-sulphided at 23°C. With W-loadings between 1.5 W/nm² and 1.6 W/nm², and Ni/W atomic ratio between 0.24 and 0.85. Sulphidations ex-situ were carried out at 350°C for 2 h, under a mixture of H 2 S/H 2 .

 21

	W/nm²	Ni/W (at/at)	%rel. WS 2	%rel. W(VI)	%rel. W(intermed.)	W/Al at. ratio (x100)
	1.6	0.24	78	11	11	2.8
	1.6 a	0.44 a	74	11	15	2.9
	1.5	0.85	75	13	12	3.1
	W/nm²	Ni/W (at/at)	%rel. NiWS	NiWS site / nm²	(Ni/W) b slab
	1.6	0.24	53	0.21 ± 0.03	0.27 ± 0.03
	1.6 a	0.44 a	41	0.30 ± 0.05	0.41 ± 0.05
	1.5	0.85	10	0.13 ± 0.02	0.16 ± 0.02

b (Ni/W) slab is calculated using NiWS and WS 2 quantification results from XPS experiments.

Table 22 .

 22 The mean slabs length of the catalyst prepared with Ni/W = 0.24 (at/at) is ca. 3.5 nm. This value hardly changes upon increasing the Ni/W atomic ratio. The same trend is observed for the stacking number of WS 2 crystallites, which is close to 2.8, whatever the Ni/W ratio. The mean length and mean stacking layer distributions, obtained with the bar graphs of each catalyst (see appendices), subsequently fitted with a log-normal law, are shown in Figure101. As they are quasi identical, we can assume that the length and stacking number distribution are similar for all catalysts.

  3.2 nm. Then, with all the previous TEM analyses on CSC NiWS/ASA catalysts, the average value of WS 2 slabs length is ca. 3.6 nm, which is similar to the values found here. It means that the length of NiWS crystallites is not significantly Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 247 different when samples, sulphided at 350°C, are initially prepared by successive impregnation of Ni(acac) 2 on either supported alkoxide species or on sulphide ones, prepared at 23°C. However, note that this preparation method enables the preparation of smaller slabs than when a sulphide material prepared at 350°C is used as a support (3.5 nm vs. 4.0 nm).

Table 22 : Mean slabs length and mean slabs stacking number of NiWS/ASA catalysts prepared by deposition of Ni(acac) 2 onto WS 2_23°C -1.7/ASA -300 pre-sulphided at 23°C.with W-loadings between 1.5 W/nm² and 1.6 W/nm², and Ni/W atomic ratio between 0.24 and 0.85. Sulphidations ex-situ were carried out at 350°C for 2 h, under a mixture of H 2 S/H 2 .

 22

		W/nm²	Ni/W (at/at) Mean slabs length L (nm) Std dev.	Mean slabs stacking number N (nm)	Std dev.
		1.6	0.24		3.5		1.2	2.8		1.3
		1.6 a	0.44 a		3.6		1.1	3.0		1.5
		1.5	0.85		3.7		1.2	2.8		1.3
	a Elemental analyses are underway
		0.25						0.50
		0.20				0.24		0.40				0.24
	Frequency	0.10 0.15		0		0.44 0.85	Frequency	0.20 0.30				0.44 0.85
		0.05						0.10
		0.00						0.00
		0	2	4	6	8	10	0	2	4	6	8	10
			Mean slabs length (nm)				Mean slabs stacking number

Table 23 .

 23 After catalytic tests, all CSC catalysts prepared by deposition of nickel onto supported alkoxide species exhibit nearly the same level of sulphidation, comprised between 72 % rel. WS 2 and 81 % rel. WS 2 . Conventional catalysts show a similar amount of sulphide phase, with 77 % rel. and 74 % rel. WS 2 for the dried and the calcined ones, respectively. These values are not significantly different from fresh catalysts for the conventional dried sample, as for CSC catalysts prepared with experimental Ni/W atomic ratios of 0.2. However, for Ni/W = 0.44 (at/at) or Ni/W = 1.00, levels of sulphidation are significantly improved during the catalytic test, by conversion of both W(VI) and the intermediate phase W(V) into WS 2 . The sample prepared by deposition of Ni onto a sulphide material, e.g. WS 2_350°C , exhibits the same % rel. WS 2 before and after test, at ca. 85 % rel. WS 2 .Regarding the tungsten coverage on the ASA surface (W/Al at/at), it is, in average, slightly decreased but the differences with fresh samples are not really significant.More interesting, NiWS, NiS and NiO x phases can be strongly impacted by the catalyst and its experimental Ni/W atomic ratio. Indeed, the promotion level, e.g. the amount on nickel incorporated in a mixed phase "NiWS" (% rel. NiWS) decreases from 80 % rel. to 65 % rel. for the CSC catalysts prepared by impregnation of Ni(acac) 2 onto [W(OEt) 5 ] 2 /ASA with Ni/W = 0.2 (at/at), before and after test. This decrease takes place in favour of the formation of a NiS phase which relative amount increases from 5 % rel. to 26 % rel. A similar but weaker phenomenon is observed for the conventional dried material, which loses 14 % rel. of NiWS. For these samples, it seems like the sulphidation occurring during the catalytic test lower the amount of Ni incorporated into a "NiWS" phase. On the contrary, two catalysts show significantly improved level of promotion, with an increase of 13 % rel. and 18 % rel. respectively for the CSC catalyst prepared with Ni(1-MeCp) 2 , and for the catalyst prepared by impregnation of Ni(acac) 2 onto a W (POM) /ASA support (e.g. a conventional dried oxide phase). This nickel migration between the different phases occurs at the expense of the NiS one. It means that in these last two cases, the sulphidation taking place during the test favours the transfer of nickel Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 249 atoms from NiS particles to WS 2 slabs. The other catalysts that were tested exhibit no significant changes.Moreover, the comparison of the amount of NiWS site/nm² (see Figure102) on fresh and spent catalysts shows that NiWS catalysts mainly exhibit lower amounts of NiWS site per nm² after the catalytic test, except for the samples prepared by deposition of Ni(1-CpMe) 2 on the CSC material (supported alkoxide species) and the catalyst prepared by impregnation of Ni(acac) 2 onto W (POM) /ASA. For these two catalysts, the number of NiWS site/nm² after test is respectively 0.32 and 0.10 site/nm². For the other ones, we find between 0.17 and 0.33 NiWS sites per nm².Similar results are obtained when plotting the Ni-to-W atomic ratio in NiWS crystallites (see Figure103): all NiWS/ASA catalysts display lower (Ni/W) slab values except for the two specific ones detailed just above. Finally, we see that after the HYD test, all the Ni-to-W atomic ratio in NiWS crystallites are lying between 0.12 and ca. 0.40, values respectively found for Ni(acac) 2 -0.2/W (POM) /ASA and Ni(acac) 2 /[W(OEt) 5 ] 2 /ASA with Ni/W between 0.44 and 1.00 at/at.

	Finally, note that analyses of spent catalysts initially prepared by deposition of Ni(acac) 2 on
	a sulphide material prepared at 23°C are underway.

Table 23 : XPS data, obtained by decomposition of W 4f and Ni 2p photopeaks of CSC and conventional NiWS/ASA catalysts before (fresh) and after toluene hydrogenation (spent). W-loadings: 1.5 W/nm² to 1.8 W/nm². Ni/W atomic ratio: 0.20 and 1.00. Sulphidations ex-situ were carried out at 350°C for 2 h, under a mixture of H 2 S/H 2 with 15 % mol. H 2 S.

 23 ASA catalysts were tested in toluene hydrogenation in presence of aniline, in order to evaluate their HYD activity and determine if the CSC method improves the preparation of more active NiWS phases by comparison with conventional catalysts. As mentioned in part V through the discussion about catalytic activities of non-promoted catalysts, interpreting catalytic results with XPS data collected from analyses of spent samples is more accurate than using XPS data obtained on fresh catalysts. Some of the results presented in this part come thus from calculations with data collected from XPS analyses of spent materials, when necessary (see Table

		ex. Ni(1-MeCp) 2 /[W(OEt) 5 ] 2	ex. Ni(acac) 2 /[W(OEt) 5 ] 2	ex. Ni(acac) 2 /[W(OEt) 5 ] 2	ex. Ni(acac) 2 /[W(OEt) 5 ] 2
	W/nm²	1.6		1.6		1.5		1.5
	Ni/W	0.20		0.21		0.44		1.00
	Fresh vs. Spent	Fresh	Spent	Fresh	Spent	Fresh	Spent	Fresh	Spent
	% rel. WS 2 (± 5%)	73	72	71	74	67	81	69	78
	% rel. W(VI)	12	11	11	9	13	10	13	8
	% rel. W(V)	15	17	18	17	20	9	18	14
	W/Al (x100)	2.6	2.6	2.5	2.3	2.2	2.0	2.4	2.2
	% rel. NiWS (± 10%)	53	66	80	65	52	48	27	22
	% rel. NiS	29	20	5	26	29	35	55	54
	% rel. NiO x	18	14	15	9	19	17	18	24
	NiWS site / nm²	0.25 0.17	0.32 0.22	0.27	0.22	0.35	0.33	0.41	0.33
	(Ni/W) a slab	0.17 0.25	0.22 0.32	0.33	0.30	0.57	0.40	0.50	0.39
		Conventional dried	Conventional calcined	ex. Ni(NO 3 ) 2 /[W(OEt) 5 ] 2	ex. Ni(acac) 2 /W (POM)	ex. Ni(acac) 2 /WS 2_350°C
	W/nm²	1.8		1.8		1.5		1.8		1.7
	Ni/W	0.22		0.22		0.30		0.22		0.20
	Fresh vs. Spent	Fresh	Spent	Fresh	Spent	Fresh	Spent	Fresh	Spent	Fresh	Spent
	% rel. WS 2 (± 5%)	73	77	56	74	73	76	69	74	84	85
	% rel. W(VI)	12	12	24	13	16	8	15	16	7	8
	% rel. W(V)	15	11	20	13	11	16	16	10	9	7
	W/Al (x100)	2.7	2.7	3.0	3.1	3.3	2.9	2.7	2.9	2.8	2.7
	% rel. NiWS (± 10%)	66	52	57	62	62	59	7	25	45	42
	% rel. NiS	29	32	33	22	24	25	71	51	41	42
	% rel. NiO x	5	16	10	16	14	16	22	24	14	16
	NiWS site / nm²	0.26	0.21	0.23	0.25	0.28	0.27	0.03	0.10	0.17	0.17
	(Ni/W) a slab	0.30	0.23	0.30	0.27	0.23	0.26	0.05	0.12	0.15	0.14
	a Calculated using NiWS and WS2 quantification results from XPS experiments.

Weight flow rate of toluene converted by different Ni promoted catalysts, with different WO 3 and NiO loadings. Expressed in g(tol)/g(cat)/h. No ex-situ sulphidation for industrial catalysts. Ex-situ sulphidations of CSC and conventional catalysts were carried out at 350°C, for 2 h, in a 15 % mol. H 2 S/H 2 mixture, prior to HYD tests.

  To get further insight into the intrinsic activity of these catalysts, the rate of hydrogenation, expressed in mole of toluene converted per mole of tungsten per hour (mol(tol)/mol(W)/h) is reported in Figure105. Given the tungsten loading of each sample, the CSC catalyst displays the more active sites, expressed by W atoms. Its intrinsic rate of HYD is ca. 4.0 times higher that the industrial counterpart (IndusNiW), and the comparison between the intrinsic HYD rate of the CSC and conventional dried or calcined materials (prepared with similar amount of W and Ni) reveals the CSC NiWS phase is more efficient in hydrogenation.

	Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel catalysts more active than the industrial reference, while lower W loaded (by 40 % wt. ) can be used. Comparison of conventionally prepared NiWS/ASA catalysts, dried or calcined, reveals that both samples are not significantly different, and 30% less active than the CSC sample. 0.00 0.05 0.10 0.15 0.20 0.25 ex. acac/[W(OEt) 5 ] 2 12.9 % wt. WO 3 0.9 % wt. NiO Conv. calc. 14.4 % wt. WO 3 1.0 % wt. NiO Conv. dried 14.4 % wt. WO 3 1.0 % wt. NiO IndusNiW 27.0 % wt. WO 3 3.5 % wt. NiO Weight flow rate of toluene converted in g(tol) / g(cat) / h 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 ex. acac/[W(OEt) 5 ] 2 12.9 % wt. WO 3 0.9 % wt. NiO Conv. calc. 14.4 % wt. WO 3 1.0 % wt. NiO Conv. dried 14.4 % wt. WO 3 1.0 % wt. NiO IndusNiW 27.0 % wt. WO 3 3.5 % wt. NiO Intrinsic rate of HYD in mol (tol) / mol(W) / h Figure 104: Part VI Figure 105:
	8 W/nm², e.g. 14.4 % wt. WO 3 and Ni/W = 0.22,
	e.g. 1.0 % wt. NiO
	(3) a similar conventional calcined catalyst
	(4) an industrial NiWS/ASA sample, with ca. 27.0 % wt. WO 3 (e.g. 4.4 W/nm²) and
	ca. 3.5 % wt. NiO (e.g. Ni/W = 0.4)
	Note that CSC and conventional samples underwent pre-sulphidation ex-situ (350°C, 2 h,
	15 % mol. H 2 S/H 2 ) prior to the test, while industrial catalysts were not.
	The weight flow rate of toluene converted, expressed by gram of toluene converted per
	gram of catalyst per hour (g(tol)/g(cat)/h) is shown in Figure 104. The CSC sample is ca. 1.5
	times more active than the industrial NiW one, while it contains at least 2.0 times less WO 3
	equiv. This results shows that the CSC method is really promising as it provides NiWS/ASA
	253 254

Intrinsic HYD rate of different Ni promoted catalysts, with different WO 3 and NiO loadings. Expressed in mol(tol)/mol(W)/h. No ex-situ sulphidation for industrial catalysts. Ex-situ sulphidations of CSC and conventional catalysts were carried out at 350°C, for 2 h, in a 15 % mol. H 2 S/H 2 mixture prior to HYD tests.

	Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of
	nickel
				0.25
	Weight flow rate of	toluene converted	in g(tol) / g(cat) / h	0.05 0.10 0.15 0.20
				0.00
			non-promoted W(OEt) 5 ] 2 /ASA 1.7 W/nm²	1.6 W/nm², Ni/W = 0.21 ex. MeCp/[W(OEt) 5 ] 2	1.8 W/nm², Ni/W = 0.22 ex. acac/W(POM)	Conv. calc. 1.8 W/nm², Ni/W = 0.22
				ex. acac/[W(OEt) 5 ] 2 1.6 W/nm², Ni/W = 0.21	ex. NO 3 /[W(OEt) 5 ] 2 1.5 W/nm², Ni/W = 0.30	Conv. dried 1.8 W/nm², Ni/W = 0.22
	Figure 106:
	Therefore, even if not normalised by the amount of sulphide phase on each catalyst, these
	results reveal an improvement of activity (g(tol)/g(cat)/h) and intrinsic HYD rate
	(mol(tol)/mol(W)/h) brought by the use of a molecular approach in the preparation of NiWS/ASA
	catalysts.
	VI.5.b. Influence of the nickel precursor
	Then, we evaluated the performances of CSC and conventional NiWS/ASA catalysts,
	prepared with different Ni-precursors, which characterisation is described in part VI.1. All these
	catalysts exhibit similar W-loading (1.5 to 1.8 W/nm²) and Ni content (Ni/W = 0.21 to 0.30), and
	underwent sulphidation under the same conditions as described before: 15 % mol. H 2 S/H 2 mixture
	at 350°C for 2 h. Figure 106 shows the weight flow rate of toluene converted by these catalysts,
	expressed in g(tol)/g(cat)/h.
					255

Weight flow rate of toluene converted [g(tol)/g(cat)/h] by different (Ni)WS 2 /ASA catalysts, prepared with either Ni(acac) 2 , Ni(1-MeCp) 2 or Ni(NO 3 ) 2 . CSC samples are compared with conventional dried and calcined ones. W-loading ranging from 1.5 to 1.8 W/nm². Ni/W (at/at) ranging from 0.21 to 0.30. Sulphidations ex-situ were carried out at 350°C, for 2 h, in a 15 % mol. H 2 S/H 2 mixture prior to HYD tests.

Weight flow rate of toluene converted [g(tol)/g(cat)/h] by different Ni promoted catalysts, prepared with either Ni(acac) 2 deposited onto supported tungsten alkoxide species, or deposited onto sulphide phases prepared at either 350°C or 23°C (2 h , 15 % mol. H 2 S/H 2 ). CSC samples are compared with conventional dried and calcined ones. W-loading ranging from 1.6 to 1.8 W/nm². Ni/W (at/at) ranging from 0.20 to 0.24. Sulphidations ex-situ were carried out at 350°C, for 2 h, in a 15 % mol. H 2 S/H 2 mixture prior to HYD tests

				0.25
	Weight flow rate of	toluene converted	in g(tol) / g(cat) / h	0.05 0.10 0.15 0.20
				0.00
			ex. acac/[W(OEt) 5 ] 2 1.6 W/nm², Ni/W = 0.21	Conv. calc. 1.8 W/nm², Ni/W = 0.22
				ex. acac/WS 2-350°C 1.7 W/nm², Ni/W = 0.20	Conv. dried 1.8 W/nm², Ni/W = 0.22
				ex. acac/WS 2-23°C 1.6 W/nm², Ni/W = 0.24
	Figure 108:

  6.

	Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of
	nickel
			4.50
	Intrinsic rate of HYD	in mol (tol) / mol(W) / h	1.00 1.50 2.00 2.50 3.00 3.50 4.00
			0.50
			0.00
		ex. acac/[W(OEt) 5 ] 2 1.6 W/nm², Ni/W = 0.21	Conv. calc. 1.8 W/nm², Ni/W = 0.22
			ex. acac/WS 2-350°C 1.7 W/nm², Ni/W = 0.20	Conv. dried 1.8 W/nm², Ni/W = 0.22
			ex. acac/WS 2-23°C 1.6 W/nm², Ni/W = 0.24
				259

Figure 110: Intrinsic HYD rate of CSC NiWS/ASA catalysts depending on their Ni/W experimental atomic ratio. Catalysts (diamonds) were prepared by deposition of Ni(acac) 2 onto supported W species (non sulphided) or sulphided ones (23°C, 2 h, 15 % mol. H 2 S/H 2 ), with W-loading between 1.5 and 1.6 W/nm². HYD rates of conventional catalysts (4.3 W/nm², circles) were obtained from ref. [Raybaud and Toulhoat, 2013, Ed. Technip, Paris, p255]. Ex-situ sulphidations were carried out at 350°C for 2 h, under a mixture of 15 % mol H 2 S/H 2 , prior to HYD tests

  Then, we investigated the effect of the amount of Ni engaged in a mixed phase "NiWS" (active phase) on the weight flow rate of toluene converted by our catalysts. Figure111shows the weight flow rate of toluene converted, in g(tol)/g(cat)/h, as a function of the effective Ni content in a NiWS phase (% wt. ). Note that the effective Ni content is calculated by multiplying the Ni content (elemental analyses) by the relative amount of NiWS phase (% rel. NiWS) detected by XPS on spent catalysts. The activity increases rather linearly when the amount of Ni incorporated in a mixed phase "NiWS" increases. Note in particular, the striking decrease of Synthesis of supported NiWS phases by the use of [W(OEt) 5 ] 2 and molecular precursors of nickel 261 activity observed for the CSC sample with Ni/W = 1.00 (at/at), which is probably due to the presence of numerous NiS particles, which is supported by the high amount of NiS phase detected by XPS (ca. 54% rel. , see Table23). The NiS phase could cover the active NiWS phase, thus lowering the amount of NiWS phase detected by XPS, or preventing toluene to react with active sites (low accessibility), thus decrease the HYD activity.

	Intrinsic rate of HYD in g(tol) / g(cat) / h in mol (tol) / mol(W) / h Weight flow rate of toluene converted	1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 0.00 0.05 0.10 0.15 0.20 0.25	0	0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Ni/W = 1.00 Ni/W = 0.21 Ni/W = 0.44	ex. acac/[W(OEt) 5 ] 2 1.5 -1.6 W/nm² ex. acac/WS 2_23°C 1.5 -1.6 W/nm² conventional calcined 4.3 W/nm² Conventional calcined-0.22 ex. acac/[W(OEt) 5 ] 2 ex. acac-0.20/WS 2_350°C ex. MeCp-0.21/[W(OEt) 5 ] 2 Conventional dried-0.22 ex. NO 3 -0.30/[W(OEt) 5 ] 2 Non-promoted WS 2 /ASA ex. acac-0.22/W (POM)
		0.50	Effective Ni content in a NiWS phase (% wt. )
	0.00 0.00 Figure 111:	0.20	0.40	0.60	0.80	1.00	1.20
					Experimental Ni/W atomic ratio

Weight flow rate of toluene converted [g(tol)/g(cat)/h] for NiWS/ASA catalyst prepared by CSC or conventional method, as a function of the effective Ni content in a NiWS phase (% wt. ). Catalysts exhibit between 1.5 to 1.8 W/nm², with experimental Ni/W atomic ratio between 0.20 and 1.00. Ex-situ sulphidations were carried out at 350°C for 2 h, under a mixture of 15 % mol. H 2 SH 2 S/H 2 prior to HYD tests

  In this part, we define the 2D morphology of NiWS crystallites in the same spirit as in part V, e.g. with a geometrical model taking into account TEM data (mean slabs length) and DFT calculations. DFT modelling, reported earlier in this study, revealed that the 2D morphology of WS 2 crystallites was changed upon addition of the Ni promoter: the M-edge length, L W-edge , is diminished, in favour of the S-edge length, L S-edge , as summarized in Table24

	Part VI
	VI.6. Discussion
	VI.6.a. Morphology and edge decoration of NiWS crystallites
	In the next part, we will discuss these results and tentatively explain them by the
	combination of 2D geometrical models, XPS and TEM data, together with the help of DFT
	calculations.
	262

Table 24 : Morphology parameter of W-edge and S-edge for our experimental conditions: -1.03 eV

 24

	s ∆ (eV) µ	S W	edge edge	non	promoted

Table 25 : NiWS crystallites data obtained from calculations based on geometrical models and theoretical values of %Ni on S-edge and %Ni on W-edge, obtained by DFT modelling

 25

	Length L from TEM (Å)	Length L' from the model (Å)	nM	nS	%Ni on S-edge	%Ni on W-edge	(Ni/W) slab_theo	X subst_theo (%)
					100	100	0.37	100
					50	100	0.30
	40				50 100	25 100	0.14 0.36	100
					50	100	0.27
					50	25	0.14
					100	100	0.41	100
					50	100	0.34
	37				50 100	25 100	0.15 0.40	100
					50	100	0.31
					50	25	0.15
					100	100	0.44	100
					50	100	0.33
	35 -36				50 100	25 100	0.17 0.45	100
					50	100	0.37
					50	25	0.16
					100	100	0.49	100
					50	100	0.39
					50	25	0.16
					100	100	0.48	100
					50	100	0.35
					50	25	0.19

Figure 121: Example of a multilayer formed by alkoxide W-species. Arrows stand for electrostatic interactions

  Upon sulphidation under standard conditions (350°C, 2 h, 15 % mol. H 2 S/H 2 ), the CSC catalysts display greater or similar amount of WS 2 phase (level of sulphidation up to 85 (±5) % rel.

	EtO O EtO	W Et EtO EtO	W Et O O Et OEt O O OEt EtO W	O O OEt W OEt	Et OEt OEt	O EtO EtO	W	O OEt EtO O Et EtO EtO	W OEt OEt O OEt W O Et OEt O Et OEt	O EtO EtO OEt W OEt	W OEt OEt	O EtO OEt O Et	W	O OEt OEt

  3 CH 2 -O-ASA)CH 2 = 4.4, as calculated from CH 2 integration of CH 3 CH 2 -O-ASA

								70	29.2	98
	0.20	37	38	7	5	0.30	127	60	28.5	81
	0.20	37	38	7	5	0.40	127	60	28.5	100
	0.44	35	35	7	4	0.30	107	67	31.0	74
	0.44	35	35	7	4	0.40	107	67	31.0	92
	0.44	35	35	7	4	0.45	107	67	31.0	100
	0.44	35	35	6	5	0.30	109	56	30.4	76
	0.44	35	35	6	5	0.40	109	56	30.4	94
	0.44	35	35	6	5	0.44	109	56	30.4	100
	1.00	33	32	6	4	0.30	92	63	33.0	70
	1.00	33	32	6	4	0.40	92	63	33.0	87
	1.00	33	32	6	4	0.49	92	63	33.0	100
	1.00	33	32	5	5	0.30	93	51	32.6	71
	1.00	33	32	5	5	0.40	93	51	32.6	88
	1.00	33	32	5	5	0.48	93	51	32.6	100
	species (δ = 3.7 ppm)

Table F .b: NiWS crystallites data obtained from calculations based on geometrical models and experimental values of (Ni/W)slab, obtained from XPS analyses of spent catalysts.

 F

		Experimental Ni/W (at/at)	Length L from TEM (Å)	Length L' from the model (Å)	nM nS	(Ni/W) slab (exp.)	( number W atom) total for one slab	% W-edge a	% edge sites b	X subst (%)
		0.20	40	41	8	5	0.17	145	64	26.9	54
		0.20	40	41	7	6	0.17	147	54	26.6	55
		0.20	37	38	8	4	0.30	123	70	29.2	79
		0.20	37	38	7	5	0.30	127	60	28.5	81
	ex.	0.44	35	35	7	4	0.40	107	67	31.0	92
	acac/[W(OEt) 5 ] 2	0.44	35	35	6	5	0.40	109	56	30.4	94
		1.00	33	32	6	4	0.39	92	63	33.0	85
		1.00	33	32	5	5	0.39	93	51	32.6	86
		0.22	36	35	7	4	0.23	107	67	31.0	60
		0.22	36	35	6	5	0.23	109	56	30.4	62
	Conv. calcined	0.22 0.22	36 36	35 35	7 6	4 5	0.27 0.27	107 109	67 56	31.0 30.4	69 70

Remerciements

Outline (Part III) Outline (Part III) .......................................................................................................................97 Introduction .............................................................................................................................99 III.1. Characterisation of molecular complexes of W(V) and W(VI) ......................................99 III.1.a. Tungsten pentaethoxide -W(OEt) 5 ....................................................................... III.1.b. Tungsten hexaethoxide -W(OEt) 6 ........................................................................ III.1.c. Tungsten oxotetraethoxide -[W(=O)(OEt) 4 ] 2 ......................................................... III.2. Preparation and characterisation of W-supported materials, from W(V) or W(VI) molecular precursors. .......................................................................................................... III.2.a. Characterisation of CSC materials by Infrared spectroscopy (IR) ......................... III.2.b. Characterisation of CSC materials by X-ray photoelectron spectroscopy (XPS) ... III.3. Characterisation of sulphide catalysts prepared from W(V) or W(VI) precursors .... III.4. Benchmarking catalytic activities with conventionally prepared catalysts .............. III.5. Conclusion .................................................................................................................... III.6. References ..................................................................................................................... Preparation of non-promoted ASA-supported W catalysts: impregnation of W(V) and W(VI) alkoxides

We can see that the signal area, is much higher for the CSC catalyst compared to the conventional ones. This result means that on the CSC catalyst, interactions between CO and W atoms on the edges of the WS 2 slabs can be stronger, or that there can be more sites readily available for CO interaction.

On Figure 67-b, all samples including the conventional one, exhibit a rather narrow band at ca. 2124 cm -1 , tentatively assigned to CO adsorbed on W-edge sites following the same hypothesis as aforementioned. A rather broad one distinguishable between 2076 cm -1 and 2069 cm -1 , is tentatively attributed to CO adsorbed on the S-edge sites. However, considering the weak signal/noise ratio, it was difficult to refine the location of this latter vibration band. Besides, the broad band centred at ν(CO) between 2165 cm -1 and 2170 cm -1 is assigned to CO interacting with Brønsted acid sites.

Finally, for CSC catalysts, independently of the tungsten loading, the signal exhibit the same features, proving that when sulphidation is carried out at 600°C, CO interacts with the same types of sites, whatever the tungsten loading. In particular, the similar shape of the band resulting from CO interaction with W-edge site (≈ 2124 cm -1 ) of WS 2 slabs could indicate that the sulphide phase of conventional and CSC catalysts are rather identical when sulphided at 600°C, from the point of view of a carbon monoxide molecule, while they are different when sulphided at 350°C. On top of that, as the IR(CO) spectrum of CSC (0.8 W/nm²) strongly resembles to the one of conventional calcined (0.5 W/nm²) sample, it means that whatever the 2D morphology (respectively hexagonal, and truncated triangular-like), the frequency of the vibration band of CO adsorbed on W-edge sites is barely changed.

Then, data collected from integration of the IR(CO) spectra between ca. 2140 cm -1 and 2050 cm -1 , and normalised by the amount of sulphide phase WS 2 , are reported in Table 9, where a.u stands for absorbance units and where mol(W)* stands for mole of tungsten engaged in the sulphide phase, in the sample CSC catalysts, one hypothesis is that it could be linked to the hexagonal morphology of the CSC sample, which present a more favourable edge structure providing a synergy effect between W-edge and S-edge. This synergy effect enhances the H 2 activation into MSH and MH species as well as toluene activation when adsorbed.

At this point, we have described the preparation of catalysts with a molecular approach, from surface species (chapter IV) to the sulphide phase (chapter V). Surface species were characterised depending on the tungsten loading. Then the reactivity of these catalysts was compared with conventional ones', dried or calcined, when sulphided at different tungsten loadings and different sulphidation temperatures.

We showed that CSC catalysts exhibit higher (hydrogenation) TOF than conventional ones, which is promising for the further preparation of promoted samples. Indeed, adding a promoter (Ni, Co) is known to drastically increase the activity of supported MS 2 catalysts (M= W, Mo).

With this in mind, we will describe in the next part (chapter VI) the preparation, the characterisation and the catalytic activity of Ni-promoted WS 2 phases. crystallites than conventional NiWS samples would thus be expected. To do so, we studied the deposition of a nickel precursor (Ni(acac) 2 ) onto WS 2 samples sulphided at 23°C, followed by an additional sulphidation at 350°C to anchor the NiWS phase. In the same spirit as the studies of Yermakov [Yermakov et al., 1984], Marchand [Marchand et al., 2009] and Gandubert [Gandubert et al., 2008] (in hot toluene) on a sulphide phase originating from sulphidation of W(OEt) 5 ] 2 -IWI-1.7/ASA -300 at 23°C (2 h, 15 % mol. H 2 S/H 2 ). Catalysts are referred as follows:

Outline (

-NiWS ex. acac-IWI-0.2/WS 2_23°C -1.6/ASA -300 with 1.6 W/nm² and Ni/W = 0.24 -NiWS ex. acac-IWI-0.5/WS 2_23°C -1.6/ASA -300 with 1.6 W/nm² and Ni/W = 0.44 (a) -NiWS ex. acac-IWI-0.9/WS 2_23°C -1.5/ASA -300 with 1.5 W/nm² and Ni/W = 0.85 where (a) refers to a sample for which the Ni content is based on the amount of Ni added in the impregnation solution, and needs to be confirmed by elemental analyses.

XPS data are summarized in Table 21. These catalysts exhibit levels of sulphidation ranging from 74 (±5) to 78 (±5) % rel. WS 2 , which is slightly higher than the sample prepared by deposition of Ni(acac) 2 on supported alkoxides, with 71 (±5) % rel. WS 2 (see part VI.1.b). In addition, they are slightly lower than the level of sulphidation of the sample prepared by addition of Ni(acac) 2 on WS 2-350°C /ASA, e.g. 84 (±5) % rel WS 2 (see part. VI.2.b.). Besides their relative amount of W(VI) and partially sulphided phase (Wintermed.) do not show large differences. The tungsten surface coverage (W/Al) is similar, with values slightly greater than that found for NiWS/ASA catalysts prepared by deposition of the nickel precursor directly onto the supported Synthesis of supported NiWS phases by the use of [W(OEt) First, we evaluated the hydrogenating potential of our samples by investigating the weight flow rate of toluene converted. Samples prepared by a molecular approach appear to be promising hydrogenating catalysts. Indeed, they proved to be as active as or more active than industrial references containing higher amounts of Ni and W (NiWS phases supported on ASA).

To deepen one's understanding of this better HYD behaviour, the study of corresponding intrinsic HYD rates has been undertaken, revealing that deposition of a nickel precursor [Gandubert et al., 2008;Krebs et al., 2009;Marchand et al., 2009], the simultaneous presence of Ni close to W atoms at the edge should be optimal for activity, whereas the sole presence of Ni atoms at the edges would be less favourable. The reason for that was given by the presence of Ni Lewis site and W-SH groups mandatory to promote the hydrogenation of toluene. A second effect must also be underlined: for high Ni content, high amounts of NiS phase are observed, and thus can somehow hinder of the accessibility to HYD active sites located on crystallites' edges.

Hence, reaching high intrinsic HYD rates is expected for optimal edge decoration of NiWS crystallites. We previously showed that the parameter (Ni/W) slab could be modified by the

Part VII. General conclusion and perspectives

VII.1. General conclusion

The aim of this thesis was to improve and understand at a molecular level the sulphidation of tungsten-based hydrotreating catalysts, whether promoted or not by Ni. It required the control and the understanding of each step of the catalyst preparation; and we have decided to approach the problem through "controlled surface chemistry" (CSC). In particular, we chose to control the density and the distribution of metal sites (W or Ni/W) through the grafting of welldefined molecular precursors (W and Ni/W) onto partially dehydroxylated amorphous silica-alumina with a given density of reactive sites (3.2 OH/nm 2 ), and to thereafter carry out the sulphidation step in a controlled way (controlled growth of WS 2 from well-defined isolated W sites under a 15 % mol. H 2 S/H 2 mixture, at 350°C). Each step was evaluated by means of multiple characterisation techniques such as infrared (IR), nuclear magnetic resonance (NMR) and X-ray photoelectron (XPS) spectroscopies as well as transmission electron microscopy (TEM).

The "controlled surface chemistry" (CSC) concept had been widely used for the preparation of highly active single-site catalysts, in particular for reactions such as alkene metathesis, hydrogenation or polymerization ; it usually referred to as Surface Organometallic Chemistry since organometallics are used. This concept has also been applied to control the growth of supported metallic nanoparticles, and few examples have discussed its use to the preparation of hydrotreating catalysts. In fact, the literature survey has revealed that preparation of supported surface species with metallo-organic precursors (small mono or bimetallic metal centre(s) linked to a wide variety of ligands, typically allyl) could be used to improve the sulphidation of W-based catalysts, to increase the amount of active phase of promoted NiWS/ASA catalysts, e.g. the so-called mixed phase "NiWS" and to increase the catalytic activities of such catalysts in HDS or HYD reactions.

In this work, tungsten molecular complexes with reactive anionic ligands towards surface hydroxyl functionalities of the ASA support had to be selected. In the view of promising preliminary results obtained at IFPEn, tungsten alkoxides were selected, more specifically, Part VII 284 tungsten (V) and tungsten (VI) alkoxide precursors, either monomeric of dimeric, such as

First, a series of ASA-supported alkoxide W-species were prepared by impregnation of the aforementioned W alkoxide precursors on partially dehydroxylated ASA (typically at 300 °C) and characterised by IR and NMR spectroscopies. The corresponding sulphide materials were then obtained by sulphidation (2 h, 15 % mol. H 2 S/H 2 , 350°C) and subsequently characterised by XPS (materials referred to as "CSC" samples). Independently of the structure of the molecular precursor and its oxidation state, similar final materials are obtained with high levels of sulphidation (71% rel. to 72 % rel. WS 2 ) and good catalytic performances in toluene hydrogenation in the presence of aniline. In fact, their catalytic performances are either similar or greater than the benchmark catalysts prepared by the conventional approach (e.g. impregnation of an aqueous solution of ammonium metatungstate on ASA, followed by a drying step, and a calcination one if needed).

In view of this promising results and the commercial availability of [W(OEt) 5 ] 2 in a pure form, the effect of metal loading (W/nm²) and of preparation methods, on the structure of the surface species at each step, and the activity of the resulting sulphide phases in the hydrogenation of toluene in the presence of aniline, was evaluated.

Combined mass balance analysis, extensive IR, and solid-state NMR analyses on materials prepared by impregnation of [W(OEt) 5 ] 2 on ASA partially dehydroxylated at 300°C as well as computational studies show that:

(1) at low loading (below 0.8 (±0.1) W/nm²), grafting of [W(OEt) 5 ] 2 leads to the formation of dinuclear species, having an average of 7 remaining ethoxy ligands, and being attached by The CSC materials undergo sulphidation at much lower temperatures, well below 200 °C, than the conventional catalysts. The sulphide phases formed on CSC and dried materials suffer from significant sintering according to TEM, compared to the calcined sample (vide supra), probably because of the weaker interactions between the support and the more mobile surface species. Note that STEM-HAADF could not clearly distinguish 2D morphology of WS 2 crystallites when sulphidation is performed at 350°C. Higher temperatures such as 600°C would thus be a requirement for the observation of clear 2D morphologies, indicating that WS 2 slabs are not well crystallised at lower temperature.

Catalytic performances in toluene hydrogenation are also influenced by the length of WS 2 crystallites. The CSC catalysts are intrinsically more active catalysts, based on TOF calculated from the geometrical models, DFT modelling, TEM and XPS data, with ca. 2.0 mole of toluene converted per mole of edge sites and corner per hour. Such improved intrinsic activity could be linked to the hexagonal morphology of their WS 2 crystallites with an edge structure providing a synergy effect between W-and S-edge. This synergy effect possibly enhances the H 2 activation into MSH and MH species as well as toluene activation when adsorbed on edges.

Overall, the preparation of non-promoted catalysts via a molecular approach has allowed a better understanding of the genesis of the sulphide phase through the detailed characterisation of surface species at each step (prior and post-sulphidation). It has also provided WS 2 /ASA catalysts with improved sulphidation level and with WS 2 crystallites exhibiting enhanced intrinsic HYD rates in toluene hydrogenation in the presence of aniline (see Figure 125).

Part Ni-promoted catalysts, known to be more active, were also prepared via the CSC approach.

Ni-promoted samples were targeted with a W-loading of ca. 1.7 (±0.1) W/nm², a W content found to be optimal for CSC samples. Different Ni-precursors, for instance bis-acetylacetonato nickel, Ni(acac) 2 , bis-1-methylcyclopentadienyl nickel, Ni(1-MeCp) 2 , and nickel nitrate, Ni(NO 3 ) 2 , were impregnated on ASA supported tungsten alkoxide species, with a nickel content corresponding to Ni/W ≈ 0.2 (at/at), considered to be optimal for HYD reactions. For Ni(acac) 2 in particular, such a preparation method have probably promoted the formation of rather welldispersed nickel and tungsten species where Ni and W are in close vicinity, since alkoxide/acac ligand can readily bridge two metal centres. Upon sulphidation, these surface species, while not fully characterised, generate NiWS crystallites with high amount (up to 80 (±10) % rel. NiWS) of Ni incorporated in a NiWS mixed phase, which is considered to be very important for the catalytic reaction. Given tungsten and nickel contents of all samples, XPS analyses of spent catalysts show that the amount of active sites is strongly influenced by the nature of tungsten surface species on which the nickel precursor was deposited: the amount of NiWS sites per nm² is improved from 0.10 (±0.02) NiWS site/nm² (Ni deposited on a conventional dried oxide phase) to 0.33 (±0.04) NiWS site/nm², if Ni is impregnated on supported surface alkoxide W-species (CSC material).

Characterisation by TEM has revealed that no significant difference of slab length and stacking number is observed as a function of the preparation method (CSC vs. conventional).

Noteworthy, STEM-HAADF analyses performed on conventional calcined samples (0.5 W/nm², Ni/W ≈ 0.2) reveal that the 2D morphology of promoted sulphide crystallites is more hexagonal General conclusion and perspectives 291 than the non-promoted ones', as proposed/rationalised by DFT calculations. [Girleanu et al., in preparation] These calculations highlighted the presence of Ni lowers the edge energy of S-edge in a greater extent than of that of W-edge: the ratio The nickel precursor was found to have no influence on the catalytic properties of CSC NiWS/ASA samples, which are found to be more active that conventionally prepared samples.

Results can be rationalized in the same spirit as for non-promoted samples, by combining DFT modelling, TEM data and geometrical models, together with XPS data.

VII.2. Perspectives

Concerning surface chemistry, the structure of surface alkoxide species, revealed by NMR and IR analyses, has to be refined by complementary spectroscopic techniques such as EXAFS or High Resolution Ultrafast MAS NMR [Roussey et al., 2011] combined with MultiQuantum MAS NMR experiments (MQ-MAS) and computational approaches. [Chizallet and Raybaud, 2009;Chizallet and Raybaud, 2010] Such methods would allow having a more detailed structure analysis of the first coordination sphere and the environment of W surfaces species.

In addition, it should be possible to evaluate the location of ASA-supported W-surface species, whether on silica, alumina, or both, through Dynamic Nuclear Polarisation Surface Enhanced NMR spectroscopy (DNP SENS) [Lesage et al., 2010], which could interrogate the special proximity of protons of the surface species with 27 Al or 29 Si.

Concerning tungsten sulphide phases, we have shown that improving the levels of sulphidation of tungsten was possible. For non-promoted samples, 87 (±5) % rel. WS 2 was reached according to XPS, for catalysts prepared via CSC using [W(OEt) 5 ] 2 as a molecular

precursor. An interesting question is thus: is it possible to improve further sulphidation (deeper and at lower temperature), for instance by using tungsten molecular precursors having sulphurcontaining ligand, for instance by using W(=S) x (SR) 6-2x derivatives or/and sulphided surfaces ?

Besides, interactions between the surface of the support and tungsten surface species, as well as between the W species themselves have been proposed to partly explain the different behaviour upon sulphidation of materials (the weaker the interaction (supported dinuclear species vs. polyoxometallates vs. oxide) the more favoured the sulphidation). Therefore, probing and characterising these interactions between the ASA support and the (1) surface alkoxide species as well as the (2) WS 2 crystallites would probably help understanding phenomena taking place at the interface between ASA and tungsten species upon sulphidation and provide clues on how to improve this step with the objective to reach a pure sulphide phase.

One approach would be to monitor the formation of the surface species at each step using 17 O-NMR on 17 O-doped ASA since oxygen-17 is highly sensitive to its environment (quadrupolar nuclei).

Another important observation of this PhD is that the sulphide phases are different between conventional and CSC sulphided catalysts according to IR(CO) spectroscopy at low temperature. Yet such differences are not understood, and complementary analyses and computational studies are clearly needed.

Concerning Ni-promoted samples, the use of a molecular approach in the preparation of NiWS/ASA materials proved to give highly active hydrogenation catalysts. Improved catalytic activities have been interpreted as a result from the balance between the strength and the amount of active sites observed on sulphide phases, which is probably influenced by the surface species formed upon impregnation of Ni and W molecular precursors. As previously performed on non-promoted samples, extensive spectroscopic studies are necessary to obtain insights in the characterisation of surface species along the catalyst preparation steps. NiW materials prepared by grafting of molecular complexes should be studied by NMR. Note however that considering the (probable) paramagnetic behaviour of Ni entities, NMR signals originating from tungsten and nickel surface species would probably be strongly broadened and difficult to interpret. However, IR, XANES and EXAFS combined with computational studies could help refining the structure of surface species. In addition, model mixed metal complexes could also be used to obtain spectroscopic signatures for interactions between Ni and W.

From a more industrial point of view, NiWS/ASA CSC catalysts have shown promising activity for the hydrogenation of toluene in the presence of aniline, typically greater than these observed for the conventional ones. Considering that catalytic tests on model molecules are far from realistic test conditions, catalytic tests on a more realistic feed, such as Vacuum Gas Oil, should be and will be performed to ascertain the high catalytic activity of CSC NiWS/ASA catalysts, in more practical hydrogenation reactions.

Finally, trimetallic phases are expected to be more active than bimetallic ones. Yet Nipromoted CSC samples (prepared with Ni and W) display comparable hydrogenating activity as the trimetallic industrial reference samples (prepared with Ni, Mo and W). It is thus clear that the preparation of ASA supported NiMoW catalysts via a controlled surface chemistry approach should be the next step. One possibility, in the view of the results presented in this PhD, is to investigate the co-or successive impregnation of molybdenum alkoxides such as Mo(OEt) 5 with [W(OEt) 5 ] 2 and Ni(acac) 2 molecular complexes followed by the sulphidation step. Achieving the formation of well dispersed species for each metal should help the formation of high amount of active sulphide phases.

To conclude, the preparation of supported NiWS catalysts by "CSC" appears to provide more active catalysts for HYD reactions. While scarcely applied for the synthesis of HDS catalysts, such a molecular approach, using well-defined molecular precursors with tunable ligands and thereby tunable reactivities, could enable the preparation and improvement of Part VII 296 sulphide catalysts specifically designed for other hydrotreating processes such as HDN, or HDO. Préalablement à l'imprégnation, des tests de solubilité de W(CO) 6 dans le toluène, le pentane et le cyclohexane ont montré que le cyclohexane était le plus approprié pour solubiliser le précurseur, avec une solubilité évaluée à 0,30 mol/L à chaud (90°C, reflux). Une doubleimprégnation à chaud a été effectuée afin de maximiser la faible quantité de W déposée. Cette imprégnation a été réalisée suivant la procédure générale, décrite dans la partie expérimentale.

Appendices Outline of appendices

Pour la voie de préparation CVD, 3 méthodes ont été testées :

-la 1 ère a été réalisée en mettant en contact des extrudés d'ASA -300 et le complexe moléculaire dans un réacteur sous vide statique (10 -2 mbar), chauffé à 110°C durant 4 à 6h.

Durant la manipulation, le précurseur cristallise dans la partie supérieure du réacteur, froide car située en dehors du four. En fin de manipulation, la couleur initiale des extrudés (blanc) n'a pas changé.

-la 2 nd a été effectuée en mélangeant des extrudés (ASA -300 ) et le précurseur dans une Les travaux de modélisation moléculaire réalisés par Leydier [Thèse, Paris, 2012] ont permis de simuler en parallèle des configurations de W(CO) 6 physisorbé et chimisorbé sur un modèle théorique de surface d'ASA [Chizallet et Raybaud, 2009 ;Chizallet et Raybaud, 2010]. Appendix B: Decomposition of 1 H MAS solid state NMR spectra with Dmfit software.

The 1 H spectrum of ASA -300 was decomposed with a good fit (sdev = 4.93) with a minimal number of sites: three peaks placed at ca. 0.5 ppm, 1.7 ppm and 3.0 ppm (see main text for details).

-6 -4 -2 10 8 6 4 2 0

Chemical shift δ (ppm)

ASA-300

Data obtained with dmfit software: #1 -SiOHn1" "pos(ppm)" 1.7 "wid(ppm)" 0.4 #2 -SiOHn2 "pos(ppm)" 0.5 "wid(ppm)" 1.7 #3 -AlOH" "pos(ppm)" 3.0 "wid(ppm)" 4.4

Model Integration: # Name % 1 "SiOH n°1" 30.2 2 "SiOH n°2" 9.9 3 "AlOH" 59.9

For NMR spectra of the various [W(OEt) 5 ] 2 -IWI-/ASA -300 materials, besides using the peak of silanols and aluminols described above for ASA -300 , additional peaks are introduced to include the signals associated with ethoxides bound to the ASA surface and these bound to tungsten. software.

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