M Nikulshina

P Blanchard

Christine Lancelot
email: christine.lancelot@univ-lille.fr

Anne Griboval-Constant

M Marinova

V Briois

P Nikulshin

C Lamonier

Genesis of active phase in MoW/Al 2 O 3 hydrotreating catalysts monitored by HAADF and in situ QEXAFS combined to MCR-ALS analysis

Keywords: MoW catalyst, Time-resolved XAS, Chemometric methods, Sulfidation intermediates, HAADF

Alumina supported MoW hydrotreating catalyst was synthesized by using bimetallic H 4 [SiMo 3 W 9 O 40 ] Keggin heteropolyacid (HPA). Catalysts based on monometallic H 4 [SiMo 12 O 40 ] and H 4 [SiW 12 O 40 ] and their mixture were also studied. Genesis of the active phase was studied during atmospheric gas sulfidation by H 2 S/H 2 of the catalysts by in-situ Quick X-ray absorption spectroscopy (XAS) and High-Angle Annular Dark-Field (HAADF) imaging. The combination of different chemometric tools such as Principal Component Analysis (PCA) and Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) allowed to determine the number of intermediate species, their chemical nature and concentration profiles during sulfidation. It was found that tungsten sulfidation using bimetallic HPA precursor started at lower temperature, compared to W sulfidation in the monometallic and in the mixture of monometallic HPA catalysts. Simultaneous sulfidation of Mo and W atoms in case of the bimetallic molecular precursor can govern the formation of mixed MoWS 2 phase, which formation during activation was evidenced by HAADF.

Introduction

Development of more active hydrodesulfurization (HDS) catalysts remains a challenge for the deep refining of lower quality feedstocks. Traditionally, bimetallic catalysts based on Mo or W sulfides, promoted by Ni or/and Co and supported on γ-Al2O3 are used in HDS processes. These catalysts exhibit high activity in removing sulfur from thiophene and benzothiophene compounds, and some non-refractory dibenzothiophenes (DBT). However, their activity is significantly lower in the HDS of refractory compounds such as 4,6dibenzothiophene due to steric hindrance of substituent alkyl groups. To avoid costly developments of more efficient processes, the use of mixed MoWS catalysts has been considered as a solution. A leap to a new level of activity of hydrotreating catalysts was achieved in the early 2000 with the advent of the "Nebula" catalyst, a commercial bulk NiMoW catalyst with improved catalytic performances, at least three times higher than conventional alumina supported catalysts [1]. Beneficial effect was attributed to the trimetallic character and formation of a mixed NiMoWS active phase, which appeared more efficient than their bimetallic NiWS, NiMoS and CoMoS counterparts [2]. The use of unsupported trimetallic catalysts indeed allowed to obtain high content of metals, however, this advantage is at the same time the cause of the main drawback of "Nebula", its cost. Keggin structures have been successfully used to replace conventional precursors in the preparation of oxidic precursors of metal sulfide catalysts [3,4]. The observed better promotion in the sulfided active phase has been attributed to proximity of metals in the oxidic precursors. From a catalytic point of view, the use of mixed metals Keggin-type HPAs may enhance activity due to the introduction of a second metal in the HPA cluster. We recently reported the synthesis of β-H 4 [SiMo 3 W 9 O 40 ] HPA and its use as precursor for hydrotreating alumina supported catalyst [5]. This HPA presents the advantage to introduce simultaneously both metals in the same compound allowing to maintain a Mo-W nanoscale proximity. We have shown that better catalytic properties for DBT HDS and naphthalene hydrogenation have been obtained when using this HPA compared to the use of a mixture of monometallic SiMo 12 and SiW 12 HPA precursors, in relation with the formation of a mixed Mo x W 1- x S 2 phase [5]. In this paper, genesis of the active phase will be monitored by High-angle annular dark-field imaging (HAADF) and Quick-XAS. Using in situ time-resolved characterizations of the sulfidation by H 2 S/H 2 of the catalysts by Quick-XAS associated with Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) chemometric method, we will unravel differences in sulfidation pathways and sulfidation intermediates between supported catalysts prepared from monometallic Keggin HPAs and bimetallic ones.

Experimental

Catalyst preparation

The bimetallic SiMo 3 W 9 HPA was synthesized according to the published method [6].

The obtained HPA has been extensively characterized at the solid state by FTIR and Raman spectroscopies, single crystal X-ray diffraction and Mo K and W L III edges XAS in a previous work [5]. Two monometallic SiMo 12 and SiW 12 HPAs were also prepared. Catalysts with the same surface density of metals d(Mo+W) = 3.9 at/nm 2 were synthesized by incipient wetness method via impregnation of -Al 2 O 3 extrudates (S BET = 275 m 2 /g, V p = 0.85 cm 3 /g) with aqueous solutions containing the required amounts of HPAs. One bimetallic SiMo 3 W 9 /Al catalyst was prepared by using the corresponding bimetallic HPA. MoW reference supported catalyst (RefMo 3 W 9 ) was synthesized using as impregnating solution a mixture of monometallic HPAs with the same Mo/W ratio as in the bimetallic SiMo 3 W 9 /Al one. Finally, SiMo 12 /Al and SiW 12 /Al samples based on the corresponding monometallic HPAs were also synthesized for comparison purposes. After impregnation and maturation, the catalysts were dried at 100 ºC for 10 h in air atmosphere without further calcination. Chemical compositions of the catalysts, together with the nomenclature at which they are referred to in the paper, are shown in Table 1.

In situ time-resolved measurements

The sulfidation process as well as oxide and sulfide states of the prepared catalysts were studied in situ by XAS at the ROCK beamline at SOLEIL synchrotron [7]. The sulfidation was performed in a flow of 10 % H 2 S in H 2 at atmospheric pressure. Powdered oxide catalysts were loaded in the cell [8] and were then heated from room temperature (RT) to 400 °C with a heating rate of 3 °C/min followed by a plateau of 2 h. The remotely-controlled edge jumping capability of the beamline was used in order to record XAS spectra simultaneously at different edges: Mo K edge and W L I , L II and L III edges on the same sample during one sulfidation treatment [7]. In that case a monochromator equipped with Si (111) channel-cut was used alternatively with Bragg angle centered around 10.36° (cam amplitude 2.4°) at the W edges and around 5.50° (cam amplitude 0.5°) at the Mo K edge whereas harmonic rejections were ensured changing stripes, from B 4 C for W edges to Pd for Mo edge, of both mirrors surrounding the monochromator aligned with a grazing incidence of 2.5 mrad. For the whole measurements, XAS spectra were measured in transmission mode with ionization chambers as X-Ray detectors. Ionization chambers were filled with a mixture of argon and nitrogen (50:50) for Mo K edge and (73:27) for W L edges.

Mo and W-edges EXAFS regions of the spectra were extracted and analyzed using Athena and Artemis software packages [9]. For Mo K edge, k 3 χ(k) EXAFS signals were Fourier transformed in R-space pseudo-radial distribution functions using a Kaiser-Bessel window between k min = 4.8 Å -1 and k max = 10.5 Å -1 (E 0 =20004.3 eV) and dk window sill parameter equal to 2. For W L III edge, Fourier transforms (FT) of the k 3 χ(k) EXAFS data were carried out from 3.5 to 16.8 Å -1 (E 0 =10218.8 eV) with a dk parameter equal to 2.

Identification of the phases present during the in situ sulfidation treatment can be obtained using the MCR-ALS chemometric method as reported in recent time-resolved XAS studies [10][11][12][13][14][15][16][17][18]. The basic assumption for applying MCR-ALS method is the inner linear structure of the data set, which is fully verified for spectroscopic techniques following the Lambert-Beer law as X-ray Absorption Spectroscopy does. In that case, experimental data are first represented in a matrix form, D, where spectra are arranged as rows. Taking into account the linear structure of the data set, a bilinear decomposition of the matrix D can be done into the matrix containing pure concentration profiles C arranged as columns and the matrix containing pure spectra S T of the n species of the unknown mixtures according to relation: D = CS T + E, where the matrix E contains the residual variation of the data (typically the experimental noise). The superscript T means the transpose of matrix S, where pure spectra are rows. Matrices C and S T are responsible for the observed data variance. MCR techniques do not require a priori information concerning the data for resolving C and S T , except an estimation of the number of pure components. The description of the MCR-ALS methodology applied to XAS has been detailed [10,13,15]. The MCR-ALS minimization algorithm developed under Matlab by the group of R. Tauler was used [17]. The methodology recently used is detailed in [18,19]. MCR-ALS analysis was carried out on normalized XAS data obtained using the normal_gui graphical user interface available at the SOLEIL's ROCK beamline and described in [19]. The normalization was carried out over the full collected energy range i.e.~1100 eV above the Mo K edge, ~ 1300 eV above the W L III edge and ~ 220 eV above the W L I edge. The spectra of pure species isolated by MCR-ALS at the Mo K and W L III edges can be analyzed as a conventional experimental spectrum: EXAFS can be extracted and corresponding FT can be calculated. Simulations of the so-obtained EXAFS spectra of pure species using Artemis [9] allowed us to subsequently determine the nature of the neighbours in the first and second coordination shells and the distances between the metallic centers and those neighbours. This information leads to propose possible structural models for the species involved during sulfidation.

High resolution transmission electron microscopy (HRTEM)

HRTEM was carried out using a Tecnai G2 20 electron microscope with a 0.14 nm lattice-fringe resolution and an accelerating voltage of 200 kV. Freshly sulfided samples were ground under an inert atmosphere and dispersed in ethanol. The suspension was collected on carbon films supported on copper grids and 20 representative micrographs were obtained for each catalyst in high-resolution mode.

High resolution high-angle annular dark-field (HRHAADF) imaging has been performed at 200 kV on a TITAN Themis FEI scanning transmission electron microscope (STEM). The microscope is equipped with a monochromator and a Cs probe corrector. For HAADF acquisition, the spot size was 9 with a screen current of ∼50 pA, semi-convergence angle of 21 mrad and camera length of 115 mm, corresponding to collection angles for the HAADF detector between ∼50 and ∼200 mrad. More than 50 images were observed on each studied catalyst.

Results

In situ measurements

Sulfidation of the dried oxidic precursors was followed by continuous and alternate recording of XAS data at both Mo and W edges, with an incremental change in temperature of 6 °C along the full heating ramp from RT to 400 °C. Evolution of the XANES spectra at the Mo K and W L I edges and Fourier transforms at the Mo K and W L III edges Quick-EXAFS functions are reported in Figure S1 and S2 respectively, for SiX 12 /Al (X=Mo or W), SiMo 3 W 9 /Al and RefMo 3 W 9 catalysts. In order to emphasize the main transformations and differences characterizing the sulfidation of those samples, Fourier transforms of EXAFS signals recorded at several intermediate temperatures were extracted and gathered in Fig. 1 at the Mo K edge and in Fig. 2 at the W L III edge.

SiMo 12 /Al

Before H 2 S introduction, the position of the edge in the XANES spectra of SiMo 12 /Al catalyst is characteristic of hexavalent molybdenum species [20]. The observed pre-edge feature is related to transition from 1s toward molecular orbitals in which 4d Mo orbitals are hybridized with p Mo orbitals due to the presence of a non-centrosymmetric environment for Mo [18] (Figure S1a). In the FT of the spectra before addition of H 2 S at RT (Fig. 1a), the signal between 0.5 and 2 Å (not phase corrected) can be assigned to the octahedral coordination of the Mo absorber atom with oxygen atoms [18]. The signal at around 3Å (not phase corrected) can be associated to Mo-Mo and Mo-Al contributions [21][22][23]. These features have been previously assigned to the formation of the 6-molybdoaluminate Anderson-type heteropolyanion (AlMo 6 O 24 H 6 3-) in the case of a dried Mo/Al 2 O 3 catalyst [18] and of a dried promoted NiMo/Al 2 O 3 catalyst [23]. This is in agreement with Raman analysis of SiMo 12 /Al catalyst that has shown that SiMo 12 HPA was not preserved on alumina and decomposed in AlMo 6 O 24 H 6 3-Anderson heteropolyanion species [5].

Just after H 2 S introduction at RT, Mo atoms remain mainly in oxygen surrounding, the FT of the spectrum being unchanged compared to that obtained for the oxidic precursor at RT (Fig. 1a and Figure S2a). When increasing the temperature, the pre-edge of the Mo XANES spectra disappears with simultaneous shift to lower energy of the edge position, which is characteristic of an exchange of oxygen ligands by sulfur ones accompanied by a reduction of the Mo oxidation state [18]. As expected, evolution of the position and intensity of the peaks in the FT of the spectra indicates gradual modification of the local order around Mo throughout the sulfidation process (Fig. 1a and Figure S2a). On the FT of the spectrum recorded at 100 °C, the contribution of the first oxygen coordination shell corresponding to the Mo-O contribution is shifted from 1.2 to 1.4 Å. In addition, a strong contribution centered at 1.9 Å has appeared. This observation has been previously reported in the literature and was related to Mo-S contribution in oxysulfide species [18,19]. Moreover, a new peak centered at

SiW 12 /Al

Before addition of H 2 S an intense pre-edge peak on the W L I edge XANES data (Figure S1b) is observed at RT for SiW 12 /Al catalyst. According to dipolar selection rules, L I edge probes the same p empty states than K edges, except that the photoelectron is ejected from the 2s level for the former and from the 1s ones for the later. Accordingly, the intensity of the pre-edge structure at the W L I edge is associated to hybridization between 5d states and 6p levels gaining intensity for non-centrosymetric environments around W [24]. The FT of the RT EXAFS spectrum recorded at W L III edge (Fig. 2a and Figure S2b) is characteristic of W oxide species. Indeed the first peaks in the spectra recorded at RT between 1 Å and 2 Å

(not phase corrected) are attributed to W-O bonds [25][26][27], the second peak at ~ 3.4 Å (not phase corrected) being mainly associated to W-W bonds [27]. In contrast to SiMo Just after addition of H 2 S the features of XANES and EXAFS spectra remain unchanged over an extended temperature range. In particular, the pre-edge resonance which vanishing is ascribed for Mo K edge to the exchange of oxygen ligands by sulfur ones is observed at the W L I edge up to ≈ 350 °C (Figure S1b) against 100 °C for SiMo 12 /Al. The most significant changes in the first coordination shell start after 200 °C (Fig. 2a) but it is clearly seen from Fig. 2a and Figure S2b that, despite the sulfidation treatment, the oxidic phase is still present at 300 °C, in contrast with the results obtained at Mo K edge for SiMo 12 /Al.

The peak centered at 2 Å corresponding to the W-S coordination in WS 2 [28] appears only after 300 °C, with a second metal-metal contribution at 2.8-3.3 Å (not phase-corrected) attributed to the formation of WS 2 particles [28]. The intensity of the W-S signal keeps on increasing during the plateau under H 2 /H 2 S at 400 °C (Figure S2b), indicating an incomplete sulfidation of tungsten at the end of the temperature ramp. These results are in agreement with the more difficult sulfidation of tungsten oxide compared to molybdenum oxide, due to stronger W-O bonds and a stronger tungsten-support interaction. and W L III edges indicating bimetallic heteropolyanion preservation at the alumina surface [5]. From the strong structural differences between SiMo 3 W 9 /Al and the monometallic supported catalysts, we assume that different intermediates species for the bimetallic catalyst and the monometallic ones should be involved during activation leading to different sulfidation pathways.

During in situ sulfidation, Mo K edge XANES spectra (Figure S1a) and FT moduli of EXAFS spectra (Fig. 1 and Figure S2a) exhibit with time different evolution for the SiMo S2b). The peak located between 1.9 and 2.3 Å, which is attributed to the W-S coordination in WS 2 , is present at 300 °C in the SiMo 3 W 9 /Al catalyst and only at 400 °C in the monometallic one.

As observed on the monometallic catalyst, the intensity of the W-S signal increases faster during plateau for SiW 12 /Al (Figure S2b) than for the bimetallic catalyst. In SiMo 3 W 9 /Al, the second coordination shell observed in the monometallic solid at the end of the plateau is not present. This feature is still ascribed to the presence of Mo and W backscatterers in the Mo(W)S 2 slabs also confirmed at W L III edges by the analysis of RT fully sulfided phases [5].

The pathways for the RefMo 3 W 9 catalyst will share common intermediates species with the monometallic catalysts. As a matter of fact, as it will be described in the next section, quasi equivalent evolutions are observed in temperature upon sulfidation for the monometallic catalysts and for RefMo 3 W 9, specially at the W L III edges (Figure S2b). We verified that the XANES of the 1 st component (MoK-comp.1) obtained by MCR-ALS for all catalysts are superimposable to the XANES of the corresponding oxidic catalysts (Fig. 6a). Similarly, for all catalysts, the XANES of extracted MoK-comp.4 is very similar to the XANES of the sulfided catalyst at the end of the ramp and to that of the pure MoS 2 reference (Fig. 6b). As expected from the use of the mixed solution of monometallic HPAs, the RefMo 3 W 9 catalyst shares the same MoK-comp. 2.

Scheme 1 displays possible models for MoK-comp.2 for which good agreements were achieved for the fitting of the EXAFS spectra presented in Fig. S3. For SiMo 12 /Al and RefMo 3 W 9 , MoK-comp.2 is described as an oxysulfide species with two molybdenum centers at a distance of 2.80 Å. This distance is currently found in Mo(V) based oxysulfide compounds [18]. For SiMo 3 W 9 /Al, MoK-comp.2 is still described as an oxysulfide species with oxygen bridging ligands at 1.97 Å, terminal sulfide (at 2.10 Å) and disulfide (at 2.41 Å) ligands.

However, the striking result coming out from the simulation is the strong similarity with the pristine HPA bimetallic structure, since marked contribution of W at 3.32 Å is still present.

We surmise that the sulfidation of the bimetallic HPA starts first from the side of Mo leading potentially to fragmentation of Mo trimeric unit without breaking the link between Mo and W.

The partial depolymerization of the HPA at the Mo side could decrease the steric hindrance and release constraints in the distance between Mo and W explaining that a slightly shorter distance is found compared to the pristine HPA for this contribution. Si and Al being backscatters with close atomic numbers, they cannot be distinguished by XAS simulation.

Herein the Mo-Si(Al) contribution is located at 3.18 Å which is a rather short distance to be ascribed to the Mo-Si distance in the Keggin structure (at 3.58 Å) [5] except if we consider a strong relaxation of distances due to partial depolymerization. Otherwise, this distance could be ascribed to a Mo-Al distance characteristic of an anchorage of the HPA to the alumina surface [29].

The second intermediate extracted for SiMo 3 W 9 /Al, MoK-comp.3, is a fully sulfided species with two contributions at 2.39 Å and 2.51 Å, which is the fingerprint of a MoS x like species [18]. The attempt to improve the fit by introducing a Mo-O contribution was unsuccessful.

W L I and L III edges

As mentioned before, W L I edge XANES displays more resolved features than W L III XANES for discriminating between sulfide and oxide environment around W, the spectra of W-based pure components and corresponding concentration profiles were determined for the catalysts on the basis of the evolution recorded at the W L I edge. Considering the slower sulfidation kinetics observed for W-based species and that completion proceeds during the plateau, the MCR-ALS analysis at the W-L I edge was performed considering the experimental data recorded during heating and isothermal treatment under sulfiding atmosphere (Fig. 7).

Due to the fact that the three W L edges were recorded simultaneously, the information extracted at the W L I edge can be transposed at the other W edges. Consequently, the concentration profiles determined at the W L I edge were then constrained at the W L III edge to isolate the spectra of intermediates and allowed us to analyze their EXAFS contributions. The obtained spectra corresponding to these pure components are presented in Fig. 8 and9.

Irrespective of the catalysts, three main components were found for explaining the variance of the data during heating ramp and isothermal treatment under sulfiding atmosphere. W L I XANES of the 1 st component isolated by MCR-ALS (Fig. 10a 3.

The FT of the W L III EXAFS spectrum of the second intermediate species (Fig. 8b green curve) determined for SiW 12 /Al displays short and medium range order contributions which can be simulated using W-O, W-W and W-Si contributions. This is a strong indication that this second intermediate is a partially decomposed HPA. No sulfur contribution has been evidenced from the simulation (Table 3).

The FT of the W L III EXAFS spectrum of the second intermediate species (Fig. 8b green curve) determined for SiMo 3 W 9 /Al displays only two resolved contributions of almost equal intensity centered at 1.4 Å and 1.9 Å. Those contributions are satisfactorily simulated considering only oxygen contributions at 1.83, 2.06 and 2.43 Å (Table 3). The lack of medium range order contribution, in contrast to what can be observed for SiW 12 /Al, suggests that the process of depolymerization occurring upon sulfidation is more efficient for the bimetallic supported catalysts. At the Mo K edge, it was evidenced for the second intermediate a Mo-W contribution with a distance close to the one encountered in the bulk HPA. Herein the lack of W-Mo contribution at the W L III edge could result from the existence of this intermediate on a more extended temperature range (from 30 to 400 °C) than the second intermediate at the Mo K edge: the expected high Debye Waller factor resulting from the temperature increase could lead to a vanishing of this contribution at the W L III edge.

Genesis of the sulfided phase followed by HRTEM

The genesis of the active phase has been followed by TEM and HAADF. The samples were analyzed after sulfidation at different temperatures, without any plateau, in order to monitor the active phase formation during the heating ramp. Indeed, TEM will only provide an overall view of the morphology of the sulfide phase, as Mo and W cannot be discriminated by this technique. Moreover, only sulfide slabs parallel to the electron beam can be visualized.

Typical TEM images of the SiMo 3 W 9 /Al sample sulfided at 150, 250, 300 and 350 °C are presented in Figure S4. After sulfidation at 150 and 250 °C, only some black spots are visible on the micrographs, in agreement with the low sulfidation degree (M atoms in the MS 2 phase)

of both metals at these temperatures as determined by XAS (Figure S4a andb). At 300 °C, the typical layered structures of sulfide slabs appear, with an average length of 2.7 nm and an average stacking of 1.2 (Figure S4c). When increasing the sulfidation temperature to 350 °C, the number of slabs increases, from 288 slabs on 20 images at 300 °C to 493 at 350 °C (Figure S4d). The average stacking is not modified, while the average length reaches 3.1 nm, with a decrease of the number of slabs with a length below 2 nm.

HAADF provided more detailed information allowing the visualization of the supported phase with atomic resolution, even if not in sulfide phase and even if the sulfide slabs are perpendicular to the electron beam, in contrast to classical TEM. Moreover, since annular dark field images are formed by collecting electrons scattered at high angles, intensities of the atomic columns in the HAADF images increase with the atomic number Z of the atom as approximately Z 1.7 , thus allowing the discrimination between Mo and W atoms due to the Z difference. After sulfidation at 150 and 250 °C, small aggregates of atoms below 2 nm are observed, with no visible organization (Fig. 11a andb). At 350 °C, sulfided slabs with their characteristic atomic arrangement are visible. Moreover, mixed structures with Mo and W can be identified, W appearing brighter than Mo due to the Z difference, showing that mixed Mo-W slabs are formed at this temperature (Fig. 11c). This finding is fully in agreement with the previous EXAFS analysis performed on the RT fully sulfided phases at the Mo and W L III edges, which evidenced in the second coordination shell of the MS 2 phase the presence of Mo and W atoms.

Discussion

We studied the genesis of the active phase during in situ sulfidation by H 2 S/H 2 of the catalysts prepared from heteropolyanions by Quick-XAS combined to multivariate analysis and by electron microscopy.

EXAFS results, together with published Raman characterization [5], evidenced that the SiMo 12 HPA deposited on alumina support is decomposed into AlMo 6 species after drying due to the "buffer effect" of alumina and Al 3+ extraction from the support as already reported in the literature [31,32]. Indeed, during impregnation the important parameter is the pH of the solution in alumina pores, which evolves towards the point of zero charge (PZC) of alumina (around 7 These results can be correlated with a previous work, where we have observed by HAADF analysis of the SiMo 3 W 9 /Al sample after sulfidation at 400 °C the formation of a mixed sulfided phase with a core of Mo atoms surrounded by W shell [38]. In contrast HAADF images of the RefMo 3 W 9 catalyst prepared from two separate HPAs showed a large majority of monometallic MoS 2 and WS 2 slabs with only few bimetallic particles, in agreement with our EXAFS results [5]. The study of catalytic activities has shown that the SiMo 3 W 9 /Al sample with a mixed MoWS 2 phase displays enhanced activity in HDS of DBT as well as in naphthalene hydrogenation, compared to the RefMo 3 W 9 catalyst [5,39]. The comparison of activation procedures (gas phase versus liquid phase) confirmed that sulfidation in gas phase led to more efficient catalysts, even in the case of the formation of mixed slabs [38]. The beneficial effect of the mixed MoWS 2 phase was even more pronounced in the case of HDS of a more refractory molecule, 4,6-dimethyldibenzothiophene, which was attributed to the improved hydrogenating properties of mixed sulfides.

Conclusion

The MCR-ALS applied to time-resolved Quick-XAS spectra allowed to study the

2. 4 Å 9 Å to 1 . 8 Å

 4918 can be seen which could be attributed to a Mo-Mo contribution. At 200 °C, the intensity of the Mo-O contribution is almost vanished and the Mo-S contribution centered at 1.9 Å and the Mo-Mo one centered at 2.4 Å become dominant. At 300 °C a new contribution emerges at 2.8 Å corresponding to the Mo-Mo signal in MoS 2 and the Mo-S contribution shifts from 1.which corresponds in non phase-shift corrected FT to the R-space position of the first coordination shell in MoS 2 crystallites. The amplitude of the Mo-S (1.8 Å) and Mo-Mo (2.8 Å) signals increases with increasing the temperature up to 400 °C. At 400 °C the Mo-O peak at 1.2 Å has completely disappeared indicating total reduction of Mo in MoS 2 .

3. 1 . 3 .

 13 SiMo 3 W 9 /Al and RefMo 3 W 9comparison with monometallic catalysts At the oxidic state, differences are observed in the Mo K edge and W L III edges FT of the SiMo 3 W 9 /Al and SiX 12 /Al catalysts (X=Mo or W) (Fig 1a and b). In a previous work Raman analysis of the dried precursors has shown that SiMo 3 W 9 HPA was preserved on alumina in contrast to the aforementioned decomposition in AlMo 6 of SiMo 12 . This result was confirmed by EXAFS characterization after drying performed simultaneously at the Mo K

3. 2 .

 2 Chemometrics analysis3.2.1. Mo K edgeAs molybdenum is almost completely sulfided before the onset of isothermal treatment at 400 °C for all catalysts, data analysis at the Mo K edge was performed on spectra collected during the heating ramp. As already evidenced in other studies on Mo, CoMo and NiMo based catalysts[18,23,29] several intermediate species are involved in the complex activation process starting from the oxidic precursor and resulting in the sulfided solid. PCA applied to the set of Mo K edge time-resolved XAS data revealed that 4 components are necessary to describe the variance contained in the data irrespective of the analyzed catalysts. This result is in agreement with Rochet et al who also observed 4 components when monitoring the sulfidation of a dried Mo based catalyst supported on δ-alumina and prepared from MoO 3 dissolved in H 2 O 2[18]. According to the matrix rank previously determined by PCA, the MCR-ALS minimization of the Mo K edge data of all SiMo(W)/Al catalysts was thus performed with four components, named hereafter MoK-comp.1, MoK-comp.2, MoK-comp.3 and MoKcomp.4, which concentration profiles are presented in Fig.3. Fig.4and 5 display the Mo K edge XANES and EXAFS spectra and corresponding FT moduli of the four components determined by MCR-ALS.

  2 and MoK-comp.3 intermediates than SiMo 12 /Al and consequently the evolution of concentrations of the four species are rather similar for both catalysts. In contrast, due to the vicinity of Mo and W in the SiMo 3 W 9 HPA based catalyst, the intermediate MoK-comp.2 and MoK-comp.3 species isolated upon sulfidation of the bimetallic HPA, together with their evolution of concentrations profiles are different to the ones measured for SiMo 12 /Al. First simulation of intermediates was carried out without constraints on the coordination numbers in order to orientate second simulations with constrained coordination numbers, which support possible structural models. Those models take into account the pristine structure of the molybdenum or tungsten based compounds supported on alumina identified through comparison with Raman and EXAFS spectra of pure HPA. Results of those simulations are reported in Table

  Each Mo center is bound to one terminal oxygen (d(Mo-O t ) = 1.63 Å) whereas the distribution of disulfudic ligands (d(Mo-S) = 2.45 Å) is described with one terminal and one bridging {S 2 } 2-ligands leading to a mean coordination number for the sulfur shell around Mo of 3. A reminiscence of the pristine AlMo 6 structure is found with the presence of the Mo-Al contribution at 3.53 Å (3.46 Å in bulk AlMo 6 ). Two oxygen bridging ligands complete the coordination of Mo: one associated to the Mo-O-Al contribution of AlMo 6 and one which could be potentially ascribed to the anchorage of the species at the surface of alumina although the fit does not reveal additional Mo-Al contribution. The fitting of the second intermediate species of SiMo 12 /Al, MoK-comp3, reveals a higher coordination by sulfide ligands (N=4.0) at 2.40 Å which could be described as a fragment of the chain-like MoS 3 species [30].

  blue curve) is superimposable with the spectrum of their respective catalyst before sulfidation. It displays a general shape with a pre-edge structure characteristic of tungsten surrounded by oxygen atoms observed on the catalysts before sulfidation (Fig.10ared curve). It is noteworthy that the second component displays also a pre-edge structure in the rising edge suggesting the transformation of the pristine supported HPA into another oxidic phase. XANES spectra of the 3 rd components (Fig.10bblue curve) are well in phase with corresponding spectra of the sulfided catalysts after 2 h duration in H 2 S/H 2 (Fig.10bgreen curve) and in agreement with the XANES spectrum of the bulk WS 2 reference (Fig.10b red curve). The rising edge of the 2 nd component is shifted at high energy compared to the one of the 3 rd component characteristic of tetravalent W species and is located nearly at the same position than the pristine hexavalent W compound. This feature strongly indicates that in the 2 nd component, W is still at the hexavalent oxidation state. Results of the fit of W L III EXAFS spectra of the 2 nd component are gathered in Table

  speciation of Mo-W based catalysts supported on alumina. It has been shown that the introduction of molybdenum in the HPA tungsten structure (SiMo 3 W 9 /Al compared with W 12 /Al) favors the sulfidation of tungsten. The onset of formation of the fully tungsten sulfided phase appears at a lower temperature than in the monometallic tungsten catalyst (160°C instead of 330 °C) and at 400 °C the sulfidation of tungsten is higher (90% instead of 65%). A 3-stepped route has been evidenced for the tungsten sulfidation involving the transformation of the oxidic catalyst into an oxysulfide species and finally to a mixed MoWS 2 phase. By opposition, molybdenum in the SiMo 3 W 9 HPA based catalyst begins sulfidation at the same temperature as in SiMo 12 /Al and is completely sulfided at ~ 380 °C. The main difference for Mo consists in the formation of the second intermediate at a higher temperature for SiMo 3 W 9 /Al (200 °C) than for SiMo 12 /Al (110 °C). For molybdenum sulfidation a 4stepped route has been evidenced with the transformation of molybdenum oxide first into oxysulfide, then into intermediate fully sulfided species and finally to the MoWS 2 phase. All the results are in agreement with the simultaneous sulfidation of both Mo and W metals in the SiMo 3 W 9 /Al catalyst, with the formation of mixed Mo-W sulfide slabs, which formation was also evidenced by HAADF. On the contrary, the use of RefMo 3 W 9 prepared from a mixture of two monometallic HPAs with the same Mo/W ratio as in the bimetallic SiMo 3 W 9 /Al sample did not allow to observe similar synergetic effects between W and Mo sulfidation. Although a slight decrease in temperature of formation of MoS 2 is observed for RefMo 3 W 9 compared to the parent monometallic catalyst, it appears that the formation of a MoWS 2 is limited for this sample, as evidenced by HAADF. This catalyst looks more like a juxtaposition of monometallic sulfide phases.AknowledgementsChevreul Institute (FR 2638), Ministère de l'Enseignement Supérieur et de la Recherche, Région Nord -Pas de Calais and FEDER are acknowledged for supporting and funding partially this work. This work was supported by a public grant overseen by the French National Research Agency (ANR) as part of the "Investissements d'Avenir" program (reference: ANR-10-EQPX-45) as well as the Kolmogorov PHC (project number 38175WC). Authors thank Russian Science Foundation for financial support of instrumental and theoretical part of the investigation by Grant No. 17-73-20386.The work was also supported by the Ministry of Science and Higher Education of the Russian Federation within the framework of the baseline of the State Assignment (project 10.7458.2017/6.7). The TEM facility at the University of Lille (France) is supported by the Conseil Régional du Nord-Pas de Calais, and the European Regional Development Fund (ERDF).

  12 /Al catalyst, the Raman spectrum of the oxidic SiW 12 /Al was similar to that of the corresponding bulk HPA, indicating its preservation on alumina at the dried state[5], in agreement with the more stable structure of H 4 SiW 12 O 40 compared to that of H 4 SiMo 12 O 40 .

  12 /Al and SiMo 3 W 9 /Al catalysts, in particular for T < 300 °C. At 200 °C, almost all Mo atoms in the SiMo 12 /Al catalyst are in sulfidic form, while an oxidic contribution is still present at this temperature for SiMo 3 W 9 /Al. At 400 °C a higher contribution of the Mo-O signal (1.2 Å) is present for SiMo 3 W 9 /Al compared to the SiMo 12 /Al catalyst. The second coordination shell located at ~ 3.0 Å at 400 °C which indicates the formation of well-developed Mo(W)S 2 At the W L III edge, despite the sulfidation treatment, the oxidic phase is still present up to 300 °C on the bimetallic MoW samples as observed on the monometallic SiW 12 /Al one, in contrast to what is observed at the Mo edge, with a sulfidation occurring at lower temperature. However, significant changes in the FT start only after 200 °C in SiW 12 /Al whereas transformation of the oxidic phase in the bimetallic HPA based catalyst SiMo 3 W 9 /Al begins between 100 and 200 °C (Figure

particles is less pronounced for the bimetallic samples. Such decrease in second shell of the bimetallic MoW catalysts could be caused by the presence of W neighboring atoms with opposite backscattering phases in this shell. Actually in our previous work, we clearly evidenced from the EXAFS simulations of signals recorded for both sulfided catalysts after cooling down at RT that the bimetallic catalyst consists in mixed Mo(W)S 2 particles

[5]

.

During the 2h isothermal treatment at 400 °C this Mo-M contribution kept on evolving for both catalysts, ending with a higher Mo-M contribution in SiMo 12 /Al than that in SiMo 3 W 9 /Al.

  comparison of RT EXAFS spectra of the RefMo 3 W 9 catalyst prepared from the mixture in solution of SiMo 12 , and SiW 12 in the proportion 1:3 displays quasi superimposable spectrum at the W L edges to the one reported for SiW 12 /Al and slight differences in position and amplitude with the Mo K edge EXAFS spectrum of SiMo 12 /Al. The difference is ascribed to a mixture of 85% AlMo 6 HPA and 15% of MoO 4 species. Indeed, we have previously shown that SiMo 12 anions were not preserved on alumina and decomposed in AlMo 6 O 24 H 6 3-Anderson heteropolyanion species. The proportion of MoO 4 species observed in the case of the RefMo 3 W 9 catalyst is due to the different pH value in solution. Due to the full preservation of the monometallic SiW 12 HPA upon preparation of RefMo 3 W 9 and formation of more than 85% of AlMo 6 , which composes SiMo 12 /Al, we surmise that sulfidation

  ). In contrast to the SiMo 12 /Al catalyst, the SiW 12 HPA structure is preserved on alumina at the dried state, in agreement with the more stable structure of H 4 SiW 12 O 40 compared to that of H 4 SiMo 12 O 40 upon pH increases[START_REF] Souchay | Ions minéraux condensés[END_REF][START_REF] Jürgensen | [END_REF]. The EXAFS characterization of the SiMo 3 W 9 /Al catalyst after drying performed simultaneously at the Mo K and W L III edges indicated mixed heteropolyanion preservation at the alumina surface. For the RefMo 3 W 9 catalyst, prepared from the mixture in solution of SiMo 12 and SiW 12 HPAs in the proportion 1:3, we have observed that the RT EXAFS spectra at the W L edges are quasi identical to the one reported for SiW 12 /Al and that the RT EXAFS spectrum at the Mo K edge presents slight differences in position and amplitude with the EXAFS spectrum of SiMo 12 /Al corresponding to transformation of ~15 % of the pristine AlMo 6 HPA into MoO 4 species. , while MoS 2 in the monometallic sample appeared when the first oxide (MoKcomp.1) and the second component (MoK-comp.2) have completely disappeared (Fig.3). The evolution of concentration profiles obtained for RefMo 3 W 9 (Fig.7) is quasi equivalent to the ones observed for SiMo 12 /Al with a slight delay in the appearance of MoK-comp.3 (+ 29 °C) and MoK-comp.4 (+37 °C).For all catalysts, WL III -comp.1 progressively decreases in a similar way, and has completely disappeared at 400 °C. WL III -comp.2 evolves quasi similarly in SiW 12 /Al and RefMo 3 W 9 , with a maximum at ~ 350-357 °C (Fig.7). On SiMo 3 W 9 /Al, this intermediate compound displays a maximum in concentration at a lower temperature than SiW 12 /Al and RefMo 3 W 9 (~ 280 °C). For all catalysts, tungsten requires the 2 h sulfidation plateau to be fully sulfided. However, at 400 °C, the tungsten sulfide contribution reaches 90% and 78% for SiMo 3 W 9 /Al and RefMo 3 W 9, respectively, and 65% for the monometallic SiW 12 /Al catalyst. The low sulfidation state of tungsten in tungsten containing catalysts is in agreement with the literature[35][36][37]. By XPS analysis, a sulfidation degree for W of 50% has been reported after sulfidation at 400 °C and atmospheric pressure for 4 h on WO 3 /Al 2 O 3[35].Mangnus et al. also showed that WO 3 /Al 2 O 3 catalysts were only partially sulfided at commonly applied sulfiding temperature, the degree of sulfidation increasing from 24 to 95% upon an increase of temperature from 300 to 600 °C[36,37]. At 400 °C the degree of sulfidation is equal to 67%. As can be seen from the concentration profiles, the formation of final tungsten sulfide in the monometallic SiW 12 /Al catalyst begins at 330 °C. The substitution of three W atoms into the structure of the SiW 12 HPA by three Mo atoms led to a significant decrease of the onset of WS 2 formation from 330 °C to 160 °C, while the onset of WS 2 formation in the catalyst prepared from the mixture of the monometallic HPAs appears at an intermediate temperature compared to SiW 12 /Al and SiMo 3 W 9 /Al with a startup temperature ~ 215 °C. It is interesting to note that in the SiMo 3 W 9 /Al sample the final WS 2 contribution appearing at 160 ºC intensively increases only at 230-250 ºC, temperature at which MoS 2 also appears, with further similar evolution of the sulfidation for both metals (FigureS5). It is not the case for the other two samples: indeed, at 300 ºC, around 50-60 % of Mo is transformed into MoS 2 while 45-50 % of W is in WS 2 in the SiMo 3 W 9 /Al catalyst, whereas at the same temperature, WS 2 is not present on SiW 12 /Al and only at 10% in Ref Mo 3 W 9 at this temperature. All these results are strong evidences that the presence of Mo leads to a synergetic effect on W, which is more efficient when a close vicinity between W and Mo exists. The EXAFS fitting result at the Mo K edge reported for MoK-comp.2 of SiMo 3 W 9 /Al has evidenced the presence of a mixed Mo-W phase with the presence of a Mo-W contribution[5]. Simultaneous sulfidation of Mo and W in SiMo 3 W 9 /Al seems to be related to the formation of this mixed MoWS 2 phase. These results are comforted by HAADF, where the morphology of the supported phase was monitored during sulfidation. After sulfidation at 150 and 250 °C, clusters of atoms below 2 nm are observed, with no visible organization, while mixed sulfide slabs with Mo and W were identified after sulfidation at 350 °C, with Mo atoms surrounded by tungsten ones.

	Our study shows that the sulfidation of the MoW alumina supported dried catalysts
	involves a four-step pathway for Mo and a three-step pathway for W irrespective of the
	catalysts. The use of the MCR-ALS method applied to the study of Quick-XAS spectra
	allowed us to isolate the intermediates formed during sulfidation. The sulfidation pathway for
	the RefMo 3 W 9 catalyst presents common intermediates species with the monometallic
	catalysts. Quasi-equivalent evolutions are observed in temperature upon sulfidation for the
	monometallic catalysts and for RefMo 3 W 9 . At the opposite a different behavior is observed
	for SiMo 3 W 9 /Al.
	Indeed, on the bimetallic SiMo 3 W 9 /Al mixed HPA based catalyst MoK-comp.2
	appears at the same low temperature as on SiMo 12 /Al (around 30°C). However, third and
	fourth components begin to be formed at higher temperature, around 200 °C and 250 °C
	respectively instead of 110 °C and 235 °C for the SiMo 12 /Al catalyst. It should be noticed that
	the final sulfide phase is present in parallel with the first three components (in the range of
	250 -300 °C)


John R Dolan
email: john.dolan@imev-mer.fr

On Saville-Kent's "A Manual of the Infusoria"

Introduction

William Saville- Kent (1845Kent ( -1908) ) had a most remarkable and productive life. He was, successively, an amateur naturalist, an assistant at the British Museum, a curator in a number of public aquariums, the would-be founder of two marine stations, Superintendent of Fisheries in Tasmania in Australia, and finally Commissioner of Fisheries in Queensland in Australia (Harrison 1998). Given his diverse roles, it is perhaps not surprising that his works, published over a nearly 40-year period, covered a wide variety of topics. His first article was on a hydra (i.e., [START_REF] Kent | Polyzoon from Victoria Docks[END_REF] and his last publication was on color photography (Saville- [START_REF] Saville-Kent | The photography of colour as applied to obtaining correct colour records of natural history subjects[END_REF]. A true polymath, holding no diplomas, he authored four major scientific works on very distinct topics. His first book was "A Manual of the Infusoria: Including a Description of All Known Flagellate, Ciliate, and Tentaculiferous Protozoa, British and Foreign, and an Account of the Organization and the Affinities of the Sponges", from here on Manual of Infusoria, (Saville [START_REF] Kent | Infusoria as parasites[END_REF]Kent -1881)). His second book was "Handbook of the Marine and Freshwater Fishes of the British Islands (including an enumeration of every species)" (Saville [START_REF] Kent | Handbook of the Marine and Freshwater Fishes of the British Islands:(including an Enumeration of Every Species)[END_REF]. The third was "The Great Barrier Reef of Australia; Its Products and Potentialities" (Saville-Kent 1893), and the last was "The Naturalist in Australia" (Saville- [START_REF] Saville-Kent | The Naturalist in Australia[END_REF]. The work on the Great Barrier Reef is no doubt the one for which he is best known. A relatively complete account of the life and work of William Saville-Kent, including summaries of both his troubled adolescence, and his protistological work, can be found in Esteban et at. (2002).

Here the focus will be on the story of his major work of interest to protistologists, his Manual of Infusoria. Commonly cited as 1880-1881 as the title page indicates (Fig. 1), we will see that it was actually published over a three year period. It has been relatively neglected in histories of protistology. It is cited but not mentioned in the text of Cole's history of protozoology [START_REF] Cole | The History of Protozoology[END_REF]. [START_REF] Corliss | A salute to fifty-four great microscopists of the past : a pictorial footnote to the history of protozoology. Part I[END_REF] remarked that it was more or less eclipsed by Bütschli's monographs (Bütschli 1880(Bütschli -1882(Bütschli , 1883(Bütschli -1887)). In Leadbeater and McCready's account of the beginnings of protozoology in Britain [START_REF] Leadbeater | How it all began[END_REF], Saville-Kent is credited with contributing to the debates around the relationship of sponges and protists, but the value of the Manual of Infusoria at the time of its publication, or today, received little attention. As the complete title reflected, Saville-Kent attempted to describe all known species of 'infusoria'. Infusoria originally were the microscopic forms which appeared in 'infusions' of vegetable matter described by early microscopists such as Leeeuwenhoek and Joblot (Dolan 2022a). For Saville-Kent, the infusoria consisted of the largely heterotrophic taxa: flagellates, rhizopods, ciliates and 'tentaculiferous' (suctoriarelated). As we will shall see, he specifically excluded autotrophic taxa such as diatoms and desmids. When he embarked on the very ambitious project, he had little apparent experience, or expertise, with regard to microscopic organisms. It was a landmark work, the first book on protists in English with original content. In reality, there were few authoritative manuals in English at the time.

Before Saville-Kent's Manual of Infusoria appeared, the most widely used guide was Pritchard's venerable "A History of Infusoria" a constant companion of many early naturalists such as the American Jacob Bailey (Dolan 2022b). It was a replacement for Pritchard's earlier "The Natural History of Animalcules" (Pritchard 1834) that was based on O. F. Müller's "Animalcules Infusoria Fluviatilia et Marina" [START_REF] Müller | The Natural History of Animalcules: Containing Descriptions of All the Known Species of Infusoria; with Instructions for Procuring and Viewing Them, etc[END_REF]). Pritchard's 'Infusoria' book, in its first edition [START_REF] Pritchard | A History of Infusoria, Living and Fossil: Arranged According to "Die Infusionsthierchen[END_REF], was largely a translation of Ehrenberg's "Die Infusionsthierchen" [START_REF] Ehrenberg | Die infusionsthierchen als vollkommene organismen. Ein blick in das tiefere organische leben der natur[END_REF] with his illustrations copied and re-arranged. In the fourth and last edition [START_REF] Pritchard | A History of Infusoria, including the Desmidiace and Diatomace, British and foreign, 4th ed. Enlarged and Revised[END_REF], the text had been updated to include consideration of the work of Dujardin, Claparède and Lachmannn, etc., but the illustrations of flagellates and ciliates were still largely the same as those in the first 1841 edition, taken from Ehrenberg 1838. Thus, Pritchard's Infusoria it was quite outdated in Saville-Kent's time and there was a need for a "new" English language manual. The essay that follows consists of three major parts. The first section will cover the mysterious genesis of Saville-Kent's "Manual of Infusoria", the gradual appearance of the work, its reception at the time, and the contents will be briefly described. The second section will provide a consideration of the value of Saville-Kent's manual throughout the years since its publication to the present era in terms of citation data, and discuss the difficulties encountered as variants of Saville-Kent's name have been used. Finally, some misconceptions concerning Saville-Kent's name will be addressed, and suggestions as to how his works should be cited will be given.

The Mysterious Genesis and Gradual Appearance of "A Manual of the Infusoria"

In the first sentence of the preface to "Manual of Infusoria" (dated May 1882), Saville-Kent states that ten years had passed since he decided to concentrate his microscopical efforts on studies of the infusoria, but he gave no hints as to why he decided to focus on the 'infusoria'. It appears to be a curious action considering that at that point in time, based on his publication history, he had shown relatively little apparent interest in microscopic organisms. By late 1872, Saville-Kent had published quite extensively on various invertebrate taxa, but particularly on corals and sponges, and he could be credited with a certain expertise on both of the groups. He had published nine papers on sponges, seven papers on corals, and one paper on the relationship between sponges and corals (see the supplementary file for bibliographic details). In contrast, Saville-Kent's work on infusoria consisted of only two papers [START_REF] Wm | On some new infusoria from the Victoria Docks[END_REF][START_REF] Kent | Notes on Prof. James Clark's flagellate infusoria, with description of new species[END_REF]. Indeed, the first sentence of the second paragraph of the preface gives the impression that the project of a new manual on infusoria may have been suggested to him and it provided justification for restricting the manual to flagellate, ciliate, and suctoria-related taxa:

"It was in the first instance suggested that this Manual should be based upon the same lines as the, at the time, only other English treatise devoted to the subject, ' A History of the Infusoria/ by Andrew Pritchard, the fourth and last edition of which was published so long since as the year 1861; that it should include in a similar manner an account of the several distinct groups of microscopical organisms known as the Rotifera, Desmidiaceae, Diatomaceae, and other Protophytes which form, as being a reproduction of Ehrenberg's ' Infusionsthiere/ so conspicuous a feature of Mr. Pritchard's book. It soon became apparent, however, that to compass so comprehensive a task with any degree of efficiency would extend the size of this treatise far beyond convenient limits, and that indeed more than sufficient material for a work on the same scale as the one above-named had accumulated in connection with the Infusoria in the most limited and restricted sense as represented by the Flagellate, Ciliate, and Tentaculiferous Protozoa."

In 1872, Saville-Kent held a low salary position in the British Museum as an "assistant', and he had just married (Harrison 1998). If Saville-Kent sought to increase either his reputation or his income or both, authoring a book may well have been his idea. However, given that he had little evident expertise with regard to 'infusoria', the idea of producing a new 'infusoria manual', may have originated not with Saville-Kent, but rather a publisher. In 1872, the first public announcement that a new "Manual of Infusoria", was in preparation appeared in the October 31st issue of Nature; it was not by Saville-Kent but by the publisher John Van Voorst (Anon. 1872), and it showed that the taxa to be covered in the work had already been defined (Fig. 2). John Van Voorst was a very well regarded publisher of books and journals and long time Fellow of the Linnean Society [START_REF] Anon | John Van Voorst[END_REF]. Van Voorst did not publish the Manual of Infusoria. Exactly why is unknown. One might speculate that he dropped the project early on as it does not appear in any of the listings of 'works in progress' in catalogues included in the end papers of books published by Van Voorst from 1872-1874 that are available in the Biodiversity Heritage Library. The year following Van Voorst's announcement, 1873, was quite eventful for Saville-Kent. His changes in employment were chronicled in the pages of Nature. In January of 1873, he left his position at the British Museum to become curator at the Brighton Aquarium (anon. 1873a) but his tenure was short-lived as he resigned in July due to a dispute with directors of the aquarium (Anon 1873b) and he returned to London. By February of 1874, Saville-Kent was said to be moving to New York City to become Superintendent of a new aquarium to be built in Central Park (Anon. 1874a). One can speculate that, with the changes in jobs and locations, Saville-Kent made little progress on the Manual of the Infusoria in 1873, and Van Voorst may have consequently dropped the project.

Regardless of who was to be the publisher, in June of 1874 there appeared evidence that Saville-Kent was actively working on the manual project. A notice was published in the "Microscopy" section of Hardwicke's Science Gossip, shown in Fig. 3A (Anon. 1874b). It was a call for information concerning new forms and stated that his treatise was 'to be shortly published', which turned out be overly optimistic. The eventual publisher, David Bogue, first announced "A Manual of the Infusoria" by 'Mr. W. Saville Kent' in a notice of 'soon to appear' books in 1879 in the October 16th issue of Nature (a full seven years after Van Voorst's announcement!). In the notice, it stated that the work would likely be ready by March 1880, and no mention was made that it would actually be published in separate parts, or installments (Anon. 1879). In reality, the first part of the manual did not appear until late 1880. Advance copies of some of the plates destined to be part of the first installment were provided to Hardwicke's Science Gossip, and a short but glowing review, presumably by the editor John Taylor, appeared in the September 1880 issue (Anon. 1880a), and is shown in Fig. 3B. With regard to the enthusiasm of the review, and the fact that it was based on receiving advance copies of the plates, it should be noted that by 1880, Hardwicke's Science Gossip was published by David Bogue. The review included the first mention that work would be published in installments. Once again, the publication schedule given, parts to appear at monthly intervals, was overly optimistic. However, the price per part was accurate, ten shillings and six pennies. In today's currency each part, which included plates, would sell for about €75. Thus the price of the complete work, sold unbound in 6 parts, and would actually require 3 years to acquire, would run to about €450 in today's currency. From 1874, when Saville-Kent asked for information on new infusoria, to 1880 when the first parts of the manual appeared, he was not occupied exclusively with protists. He continued to publish extensively on a variety of topics. For example, he published three papers, and a letter, on observations of giant squids and two papers on sponges (see supplementary file). He published only two papers in which he described new species of protists (Saville [START_REF] Kent | A new field for the microscopist[END_REF][START_REF] Kent | Infusoria as parasites[END_REF].

The first installment of the Manual of Infusoria appeared in 1880. It consisted of the substantial general introductory material of 143 pages with first eight plates. In Britain, it was reviewed quite positively in Hardwicke's Science Gossip (Anon. 1880b) and in the Popular Science Review (Anon. 1881a), perhaps not surprisingly, as both serials were published by David Bogue. However, very positive reviews also appeared in the foreign press. The first installment was reviewed in The American Naturalist (Anon. 1880c), and in the Annales de la Sociéte Belge de Microscopie [START_REF] Deby | A Manual of the Infusoria[END_REF]. While the quality of the plates was praised, oddly, the reviews did not mention the fact that none of the plates were referred to in the text. The first eight plates included illustrations of many new species of choanoflagellates (Fig. 4). No mention was made of plate legends but presumably they were included with the plates. As the work was being sold by subscription, it seems likely that including plates with each 'installment', even if the plates had no relation to the portion of text published, was a means to keep interest in the work among subscribers. The second and third installments also included eight plates each. They were supposedly published in 1880 but may have actually been available only in early 1881 (Fig. 5). The fourth installment was not described, but was listed in the 'Books Received" in the July 1881 issue of Hardwicke's Science Gossip. It presumably consisted of about 150 pages of text, and plates 25 to 32, covering the last group of flagellates, the dinoflagellates, and the beginning of the sections on ciliates. It appears not to have been reviewed in the journals that carried reviews of the previously published parts.

Part five was reviewed in the November 1881 issue of Hardwicke's Science Gossip and described as 'just been published', and stating "The interesting genus Vorticella is treated at great length" (Anon. 1881e). The sixth and final part was reviewed in the August 1882 issue of the same journal. The review concluded with the rather odd sentence, given the considerable cost of the complete work, "It will be but a short time before this book has increased in money value; for, all things considered, it is by far the cheapest and most comprehensive work connected with Microscopy we have ever seen." [START_REF] Anon | Manual of the Infusoria-Part VI[END_REF]. One could speculate that the review was written by the publisher!

The complete work was reviewed by Edwin Ray Lankester, in a three page article published in Nature that appeared on April 26th 1983 [START_REF] Lankester | A Manual of the Infusoria[END_REF]. From the review, it appears that in 1882, Bogue published a complete edition, with the preface dated May 1882, consisting of two volumes of text and a volume of plates with Saville-Kent's famous frontispiece (Fig. 6). Lankester's review likely carried a great deal of weight as he was a very important figure in his time among biologists. He was the editor of the Quarterly Journal of Microscopical Science, and had a recognized expertise with regard to protists (e.g., Goodrich 1929). Lankester's review was overall quite positive. It pointed out, at some length, that the work was much more than an accurate review of work up to the time of publication; it incorporated new observations and descriptions of many new species, especially among the flagellates. Lankester however begged to differ with Saville-Kent with regard to the opinions expressed by the latter concerning the phylogenetic relationships of flagellates with sponges and ciliates with worms. However, Lankester also stated that opinions as to possible relationships with metazoan taxa did not detract from the obvious value of Saville-Kent's Manual of the Infusoria. (1917,1941,1942,1945,1958,1958,1962). The overall average number of citations per year is 5.7 ±4.65. To date (November 2023), it has been cited over 800 times. Many of the works citing Saville-Kent's manual are taxonomic works and reference is made to his species descriptions, both of species he described as new, as well as those previously described but whose presence he documented. For many species, occurrence details were noted such as in his text on Monosiga fusiformis (page 331): "... found congregated upon the carapace and ovisacs of a species of Cyclops obtained from one of the water-fowl ponds in the Zoological Gardens, Regent's Park, in May 1879." Many such details proved valuable.

The citation data are undeniable evidence of the enduring value of the manual.

Citing Saville-Kent's Publications

As stated above, Saville-Kent's works have been cited in a variety of manners. One could say it is largely his own fault as he used different forms of his name. In the years before 1870 and until mid 1870, he signed his articles "S.W. Kent" or "Wm. S. Kent". He starting using "W. Saville Kent" in August of 1870 (Saville Kent 1870). In 1885 he began using "W. Saville-Kent " (Saville-Kent 1885), but not consistently. It was only from 1887 onward, that he usually, but not always, signed his works W. Saville-Kent.

Further confusing exactly how his works should be cited is an odd contention that his 'real name' was W. S. Kent (he was born William Saville Kent) and that he started using Saville Kent, and later Saville-Kent, to disassociate himself from the enormous family scandal of the murder of his young half-brother in 1860 [START_REF] Ehrenberg | Die infusionsthierchen als vollkommene organismen. Ein blick in das tiefere organische leben der natur[END_REF][START_REF] Harrison | Oxford Dictionary of National Biography[END_REF]. Saville-Kent's sister, Constance, eventually confessed to the killing, years after the event. The spectacular murder, and Saville-Kent's possible involvement in the crime, has been explored in several books in the year since (i.e., [START_REF] Stapelton | The Great Crime of 1860[END_REF][START_REF] Rhode | The Case of Constance Kent[END_REF][START_REF] Bridges | The Tragedy at Road Hill House[END_REF][START_REF] Taylor | Cruelly Murdered, Constance Kent and the Killing at Road Hill House[END_REF][START_REF] Summerscale | The Suspicions of Mr[END_REF][START_REF] Kyle | A Greater Guilt: Constance Emilie Kent and the Road Murder[END_REF], and is still today a mystery. However, the murdered child, born Francis Savill Kent, was commonly called 'Francis Savill Kent' in press accounts at the time. So, using Saville Kent or Saville-Kent, as a family name could only call more attention to a possible connection with the family scandal than simply using "Kent". As to why he began using Saville Kent in mid 1870, one can only speculate that when he reached 25 years of age he sought to establish a new professional identity. He remains today an enigmatic character. His only known portrait (Fig. 8) was published in 1897 as the frontispiece in his book "The Naturalist in Australia" in which, curiously, infusoria or protozoa are completely absent. Today, it is commonly recognized that one has the right, but not the obligation, to use one's birth name. William Saville-Kent was clearly his ultimate choice as he was buried under the name (Fig. 9). However, when citing a published work, one needs to provide accurate information, including the authorship shown on the publication, to allow the cited work to be located by a reader. While one must respect the right of an author to be called as they desire, actual reference listings should use the authorship as listed on the work cited. The contention put forward here is that William Saville-Kent's works should be cited as they were signed. The early works should be cited as in texts as "Kent xxxx" and listed in the reference listed under "Kent, W.S. xxxx" or Kent, "Wm.S. xxxx" as appropriate. Works published after mid-1870 should cited in text as "Saville Kent xxxx" and the reference listed under "Saville Kent, W. xxxx". The works from 1885 onward should be cited in the text cited as "Saville-Kent xxxx", as appropriate, and in the references under "Saville-Kent, W. xxxx". A compromise of sorts has been attempted here as the man is always given as Saville-Kent but in citations in the text to a particular publication the last name as he used in the publication is used and in the references listings as well. and provides a temporal coverage of his works greater than those of Harrison (1998) or [START_REF] Ehrenberg | Die infusionsthierchen als vollkommene organismen. Ein blick in das tiefere organische leben der natur[END_REF]. Furthermore, the file is spreadsheet allowing sorting by: authorship form used, year, journal/publication type, and major subject.

Fig. 1 .

 1 Fig. 1. The title page of Saville-Kent's Manual of Infusoria. The publication years given, '1880-1881' are inaccurate. The last part was actually published in 1882, and the preface is dated 'May 1882'. Hence, full references to the work should probably include the note 'published 1880-1882' (as is done here). Original image from the Biodiversity from the Biodiversity Heritage Library : https://www.biodiversitylibrary.org/item/40541#page/9/

Fig. 2 .

 2 Fig. 2. The announcement of books in progress by the publisher Van Voorst in October of 1872 (Anon. 1872) included a description of the contents of a new "Manual of the Infusoria" by Mr. W. Saville Kent.

Fig. 3 .

 3 Fig. 3. A public notice that Saville-Kent was soliciting material for his Manual of the Infusoria appeared in Hardwicke's Science Gossip in the June issue of 1874, (Anon. 1874). He sought information and specimens of new and interesting forms (3A). The first 'review' of Saville-Kent's manual (Anon. 1880a) appeared in Hardwicke's Science Gossip in the September issue of 1880, and was based on advance copies of some of the plates (3B).

Fig. 4 .Fig. 5 .

 45 Fig. 4. Plate 3 showing choanoflagellates was part of the first installment published. The actual size of the box enclosing the figures is 22 x 15.4 cm. According to the plate legend, most of species were shown were new: Codosigma cymosa (3-7), Codosigma candelabrrum (8-9), Salpingoeca minuta (10-12), Salpingoeca pyxidium (16), Salpingoeca ampulla (17-21), Lagenoeca cuspidata (25), Salpingcoea petiolata (26), Polyoeca dichotoma (27-28). Original image from the Biodiversity Heritage Library: https://www.biodiversitylibrary.org/item/40503#page/23

Fig. 6 .

 6 Fig. 6. The famous frontispiece of the volume of plates of Saville-Kent's Manual of Infusoria, the only color illustration. It shows a choanoflagellate fed carmine particles. The arrows indicate the direction of the feeding current resulting from the movement of the flagella. The actual size of the box enclosing the figures is 22 x 15.4 cm. The illustration is an enlarged, detailed version of fig. 19 in plate 3 of "A new field for the microscopist" (Saville Kent 1878). The image is a scan of the author's personal copy.

Fig. 7 .

 7 Fig. 7. The cumulative number of publications published, by year, containing the phrase "A Manual of the Infusoria" demonstrating usage of the manual since 1883 to November 2023.

Fig. 8 .

 8 Fig. 8. The only known portrait of William Saville-Kent appeared, with his signature, as the frontispiece of his book "A Naturalist in Australia" (Saville-Kent 1897).

Fig. 9 .

 9 Fig. 9. The gravestone of William Saville-Kent in the All Saints Churchyard at Milford-on-Sea. Image courtesy of Barry Leadbeater; the added inset is an enlargement showing more clearly that the family name is Saville-Kent.

Acknowledgments

David J. S. Montagnes parted with his copy of Saville-Kent's Manual of Infusoria for an improbably small sum, and my possession of his copy inspired this essay. Barry Leadbeater kindly provided the image of the gravestone of Saville-Kent as well as valuable encouragement and aid.

Supplementary Material

To aid in the referencing of works by Saville-Kent, a supplementary file is included with this essay. It lists all the publications by Saville-Kent that I was able to inspect and verify the authorship form he used. The supplementary file is not a complete listing of Saville-Kent's works as some works listed in the bibliographies provided in Harrison (1998) and [START_REF] Ehrenberg | Die infusionsthierchen als vollkommene organismen. Ein blick in das tiefere organische leben der natur[END_REF] could not be located. However the file contains 88 references