Caroline Gérard
email: caroline.gerard@mnhn.fr

Ameline Bardo

Jean Pascal Guéry

Emmanuelle Pouydebat

Bruno Simmen

Victor Narat

V Simmen

Manipulative repertoire of bonobos (Pan paniscus

Keywords: <i>Pan paniscus</i>, Food manipulation, Grasping postures, Tool use Pan paniscus, food manipulation, grasping posture, tool-use 47 48

come

Introduction

51

Grasping ability is defined as "movements in which an object is seized and held securely More generally, tool use is not the only interest of non-human primate manual abilities 122 as the hand serves to explore and interact with the environment as a whole. Manual, but also 123 pedal, skills in primates can be observed during more diverse grasping and manipulative 124 behaviors, such as locomotion, feeding behavior and social interactions. Even if it is now 125 known as insufficient and non-exclusive, one of the historical hypotheses on the origins of 126 grasping abilities in primates has focused on the selective pressures linked with food 127 properties and the arboreal environment . Bonobos express arboreal and terrestrial feeding 128 behaviors and although this environmental context has been well-studied in chimpanzees 129 since 1960s (e.g., [START_REF] Jones-Engel | Precision Grips in Young Chimpanzees[END_REF][START_REF] Marzke | Grips and hand movements of 693 chimpanzees during feeding in Mahale Mountains National Park, Tanzania: Chimpanzee 694 Feeding Grips and Hand use in Mahale[END_REF][START_REF] Marzke | Chimpanzee and human grips: A new classification with a 697 focus on evolutionary morphology[END_REF]; [START_REF] Altmann | Observational study of behavior: Sampling methods[END_REF]. Videos were divided 197 according to our definition of a "manipulative sequence", including contact, grasping and 198 manipulation of the food items. It began with the first contact between an individual and an 199 item (direct or through the use of a tool) and ended when the food was consumed in its 200 entirety (whole fruit/vegetable, bunch, branch previously sectioned, bark, buds, etc.) or 201 abandoned before total consumption (partially or not consumed). A total of 3h30 of recorded 202 sequences (N=792) were analyzed. The parameters recorded during the sequence were the 203 individual, the food item (details of food items are available in Appendix 1), the manual/pedal 204 grip adopted, the hand(s)/foot used and the duration of each behavior. We recorded data 205 with the frequencies technique, in which every sequence was considered and not only the first 206 of a series of similar actions (i.e., bout technique) (e.g., [START_REF] Bardo | Behavioral and functional 557 strategies during tool use tasks in bonobos[END_REF][START_REF] Hopkins | Hand preferences for a coordinated bimanual task in 110 chimpanzees (Pan 649 troglodytes): Cross-sectional analysis[END_REF]. 207 208

Grasping postures

209

Every encountered grasping posture involving the hands or the feet was described and 210 linked to the existing literature on humans and apes [START_REF] Bardo | Behavioral and functional 557 strategies during tool use tasks in bonobos[END_REF][START_REF] Bardo | Manual function and performance in 560 humans, gorillas, and orangutans during the same tool use task[END_REF]Jones-Engel & 211 Bard, 1996;[START_REF] Marzke | Grips and hand movements of 693 chimpanzees during feeding in Mahale Mountains National Park, Tanzania: Chimpanzee 694 Feeding Grips and Hand use in Mahale[END_REF][START_REF] Marzke | Chimpanzee and human grips: A new classification with a 697 focus on evolutionary morphology[END_REF][START_REF] Napier | The prehensile movements of the human hand[END_REF][START_REF] Parry | Rehabilitation of the Hand[END_REF] 212 [START_REF] Pouydebat | Diversity of grip in adults and young humans 745 and chimpanzees (Pan troglodytes)[END_REF]. To name the grasping postures, we used Marzke's grasping typology All statistics were computed using the R 3.6.3 statistical environment (R Core Team The two accumulation curves plateaued (Figure 2), which meant that there was little 283 benefit in carrying out additional sampling to extend our evaluation of the manipulative 284 repertoire [START_REF] Colwell | Interpolating, extrapolating, and comparing incidence-599 based species accumulation curves[END_REF]. Manual manipulations appeared in 83.5% of all sequences recorded (N=661/792; Table 288 1), and the remaining 16.5% are for the use of the mouth only (N=131/792; Table 1). Every 289 individual (N=17) was represented in the sequences (mean ± SEM=47 ± 5 sequences per 290 individual, including mean ± SEM=39 ± 6 sequences with manual manipulation per individual).

291

We found 22 distinct grasping postures (Table 2): the most frequent was the "lateral thumb-292 index grip" (N=325/792 or 41% of the sequences) and the second most frequent were the 293 power grips (with thumb (N=158/792 or 20% of the sequences) and without thumb (N=49/792 294 or 6% of the sequences). This repertoire also included one new variant, never described for 295 bonobos in the literature. The dorsal scissor hold (in the "without thumb" category) is a variant 296 of the palmar scissor hold, with the hand in supination and the fingers flexed.

297

Every age category was represented in the sample with N=416/792 (or 53%) sequences 298 involving adults, N=135/792 (or 17%) with subadults and N=241/792 (or 30%) sequences with 299 juveniles (Table 3). Manual manipulation occurred in 80.0% (N=333/416) of the sequences in 300 adults, 78.5% (N=106/135) in subadults and 92.1% (N=222/241) in juveniles, and the 301 remaining 20.0% for adults, 21.5% for subadults and 7.9% for juveniles were are for the use 302 of the mouth only (respectively N=83/416, N=29/135 and N=19/241; Table 3). Both males and 303 females were also represented in the sample with N=530/792 (or 67%) sequences involving 304 females and N=262/792 (or 33%) sequences with males.

305

We detected a very limited use of the feet, always with an alternating use of the hands, 306 in 1.1% of the sequences (N=9/792), involving only one foot at a time and with only two 307 different postures (Table 4). These foot grips were used for storage only, not to grasp the item 308 or carry it to the mouth and occurred in both adults and juveniles (Tables 3 and4). There was 309 no significant difference between the two age categories in the sequence distribution The whole repertoire of the group included 28 distinct grip associations (bimanual 315 manipulation or compound grips) and 21 graspingle postures used in isolation (Table 5). One 316 of the grasping postures was never used in isolation (i.e, the "fifth finger probe" is always used 317 in association with "power grips") and only 28 grip associations out of the 484 possible ones GERARD-p15 334 different between the three age categories (mean adults ± SEM=13 ± 1; mean subadults ± SEM=14 335 ± 6; mean juveniles ± SEM=9 ± 2;) (Kruskal-Wallis test: khi2= 2.8006, df=2, p > 0.05). The most 336 frequent grip associations or grasping postures used in isolation were the same in the three 337 age categories: "lateral thumb-index grip" (N=145/416 or 35% of the sequences in adults, 338 N=58/135 or 43% of the sequences in subadults and N=122/241 or 51% of the sequences in 339 juveniles; Table 5) and "power grip with thumb" (N=62/416 or 16% of the sequences in adults, 340 N=25/135 or 19% of the sequences in subadults and N=48/241 or 20% of the sequences in 341 juveniles; Table 5). The major differences between adults and juveniles was the use of the fifth 342 finger for probing in adults and the middle finger in juveniles. Unlike the adults, the juveniles 343 did not use the "cup hold" grip and the "lateral thumb index" in grip associations. 344 Furthermore, juvenile individuals only used the "palmar scissor hold" grip and never used the 345 other variant (i.e., "dorsal scissor hold" grip). They also did not use the "finger tips support" 346 to maintain the food item.

347

The number of distinct grip associations and graspingle postures used in isolation per We observed tool use in the three age categories (4/9 individuals in adults, 1/2 in 361 subadults and 1/6 in juveniles) and there was no significant difference in frequencies between 362 these categories (Fisher's exact test, p>0.05) (Table 3). [START_REF] Almécija | The evolution of human and ape hand 553 proportions[END_REF][START_REF] Harrison | The hands of fossil non-hominoid anthropoids[END_REF][START_REF] Kivell | Evidence in hand: Recent discoveries and the early evolution of human manual 672 manipulation[END_REF][START_REF] Pouydebat | Evolution of grasping among anthropoids[END_REF], little is 370 known about the manipulative repertoire of bonobos, either in natural conditions or in zoos.

371

Our study provides the first description of the manipulative repertoire spontaneously used by 372 zoo-housed bonobos in a feeding context and is the first to include diverse foods and physical 373 environments. Our analyses show a large manipulative repertoire, including precision and 374 power grips, as well as one new grasping posture, labeled "dorsal scissor hold".. This study 375 also shows the enrichment of this manipulative repertoire from juveniles to adult individuals.

376

The following discussion details the implications of our findings with regard to the evolution 377 of manual abilities in hominids. tool-use context because of a greater variety of consumed food and environments than in 384 experimental settings. We also expected to describeobserve a similar variety of manual 385 postures to that documented in chimpanzees given their closely similar hand anatomy. Our 386 results confirm these predictions with a wide variety of grip categories, from precision to 387 power grips. This species has proportionally longer fingers and shorter thumb than humans, 388 and lacks a true flexor pollicis longus muscle (FPL) [START_REF] Marzke | Chimpanzee and human grips: A new classification with a 697 focus on evolutionary morphology[END_REF][START_REF] Susman | Hand function and tool behavior in early hominids[END_REF] 389 van Leeuwen et al., 2018), all of which constrain the use of powerful opposition of the thumb 390 to the other digits in comparison to human hands. The use of precision grips, close to those 391 used by humans, confirms the results of previous studies in bonobos for both tool use (Bardo 392 et al., 2016) and for grasping small items [START_REF] Christel | Grasping techniques and hand preferences in Hominoidea[END_REF][START_REF] Christel | How precisely do bonobos (Pan paniscus) grasp small 597 objects? 30[END_REF]. Our study 393 supports the general capacities of great apes to manipulate items with a great variety of 394 grasping postures since we have identified 22 distinct grasping postures used in 49 grip 395 associations and graspingle postures. Twenty-one used in isolation. All the grasping postures 396 of the repertoire were already described in the literature on apes and humans (Bardo et al., 397 2016(Bardo et al., 397 , 2017;;[START_REF] Jones-Engel | Precision Grips in Young Chimpanzees[END_REF][START_REF] Marzke | Grips and hand movements of 693 chimpanzees during feeding in Mahale Mountains National Park, Tanzania: Chimpanzee 694 Feeding Grips and Hand use in Mahale[END_REF][START_REF] Marzke | Chimpanzee and human grips: A new classification with a 697 focus on evolutionary morphology[END_REF]Napier, 398 1956;[START_REF] Parry | Rehabilitation of the Hand[END_REF][START_REF] Pouydebat | Diversity of grip in adults and young humans 745 and chimpanzees (Pan troglodytes)[END_REF], and we described one new variant (i.e, the "dorsal 399 scissor hold") never observed in other species, including chimpanzees. These but these new 400 data enrich our knowledge on grasping postures and grip associations variety in bonobos.

401

In our study a focus has been made on the compound grips as there is a lack of their 402 description in bonobos and more broadly, few studies have taken them into account in non-403 human primates (e.g., "digit role differentiation" and "compound grips" in gorillas (Gorilla 404 gorilla beringei) in respectively [START_REF] Byrne | Manual dexterity in the gorilla: Bimanual and digit role 591 differentiation in a natural task[END_REF][START_REF] Neufuss | Manual skills for food 721 processing by mountain gorillas (Gorilla beringei beringei) in Bwindi Impenetrable National 722 Park, Uganda[END_REF]"unimanual 405 multitasking" in chimpanzees in [START_REF] Corp | The ontogeny of manual skill in wild chimpanzees: Evidence from 602 feeding on the fruit of Saba florida[END_REF]; "compound grips" in macaques (Macaca 2016)). Only two cases were recorded in our study because 408 of our consideration of one item in a time according to our definition of a manipulative 409 sequence. These two cases correspond to one item broken into two pieces but we suspect 410 that the study of storage behavior, especially in a competitive environment like in zoo, 411 including the manipulation of several items in aat the same time, would have led to many 412 more observations of compound grips. As described in the literature (and named "the one-413 handed storage grip" in [START_REF] Macfarlane | Diversity of grip in Macaca mulatta[END_REF], the two compound grips were an 414 association between a power grip ("power grip with thumb") used to store the first piece 415 against the palm and a more precise grip (respectively "lateral thumb index grip" and "palmar 416 scissor hold") involving two digits. These compound grips involve a high level of coordination 417 with independent digit movements. So, despite the low frequency of these behaviors in our 418 study, our results confirm this ability in bonobos, as previously shown in chimpanzees. 419 Furthermore, although present, the in-hand movements have not been considered in this 420 study. But, the passage from one grip to another, without a change of hand, are "transfer 421 movements" [START_REF] Fragaszy | Functions of the hand in primates[END_REF]. These would be interesting to describe in the 422 manipulative behavior as a dynamic process in further studies [START_REF] Bardo | Behavioral and functional 557 strategies during tool use tasks in bonobos[END_REF].

423

The existence of preferred grasping postures in bonobos is consistent with previous 424 results in human and other great apes (e.g., [START_REF] Christel | Grasping techniques and hand preferences in Hominoidea[END_REF][START_REF] Pouydebat | Diversity of grip in adults and young humans 745 and chimpanzees (Pan troglodytes)[END_REF]Bardo et 425 al., 2016). In our study, the most frequent grasping posture is the "lateral thumb index grip", 426 as also reported in the literature, whether it involves tools [START_REF] Bardo | Behavioral and functional 557 strategies during tool use tasks in bonobos[END_REF] or to grasp 427 small objects [START_REF] Christel | How precisely do bonobos (Pan paniscus) grasp small 597 objects? 30[END_REF]. The second preferred grasping postures used by the 428 bonobos were the power grips involving the thumb and without the thumb. This strong 429 preference for powerful postures has been described in stone hammer tasks in sanctuary [START_REF] Neufuss | Nut-cracking behaviour in wild-born, 717 rehabilitated bonobos ( Pan paniscus ): A comprehensive study of hand-preference, hand 718 grips and efficiency[END_REF]) but these postures were not as frequent in previous studies focusing on 431 tool use [START_REF] Bardo | Behavioral and functional 557 strategies during tool use tasks in bonobos[END_REF] or small object manipulation [START_REF] Christel | How precisely do bonobos (Pan paniscus) grasp small 597 objects? 30[END_REF]. Thus, this is 432 the first report showing a high prevalence of the powerful postures used by bonobos coping 433 with a wide range of food items (in size, shape and hardness) not exclusively in a tool use 434 context. This result is also consistent with the manipulation of large objects in chimpanzees, 435 in which the preferred grasping postures are the "power grips" [START_REF] Pouydebat | Diversity of grip in adults and young humans 745 and chimpanzees (Pan troglodytes)[END_REF]. Our 436 results highlight the importance of considering the size and shape of manipulated objects in 437 studies addressing manipulation of food/objects/tools, in non-human primates as well as 438 humans, to better understand the evolution of these behaviors (e.g., [START_REF] Key | Hand grip diversity and frequency during the use of Lower 666 Palaeolithic stone cutting-tools[END_REF] 439 [START_REF] Pouydebat | Biomechanical study of grasping according to 739 the volume of the object: Human versus non-human primates[END_REF]. 440 Despite their marked differences in whether or not to use tools in natural conditions 441 (but see [START_REF] Hohmann | Culture in Bonobos? Between-Species and Within-Species Variation 647 in Behavior[END_REF], chimpanzees and bonobos are very similar not only in their 442 hand morphology [START_REF] Diogo | Bonobo anatomy reveals stasis and mosaicism in 607 chimpanzee evolution, and supports bonobos as the most appropriate extant mode l for the 608 common ancestor of chimpanzees and humans[END_REF][START_REF] Druelle | 611 Segmental morphometrics of bonobos ( Pan paniscus ): Are they really different from 612 chimpanzees ( Pan troglodytes )?[END_REF]van Leeuwen et al., 2018), but also 443 in their manipulative abilities. However, some differences appear when comparing our 444 findings to the literature on apes, specifically the preference for the "palmar thumb index" 445 grip in human and chimpanzees with small object manipulation (including both "tip-to-tip" 446 and "pad-to-pad" grips) [START_REF] Christel | Grasping techniques and hand preferences in Hominoidea[END_REF][START_REF] Pouydebat | Diversity of grip in adults and young humans 745 and chimpanzees (Pan troglodytes)[END_REF]. Nevertheless, our findings Based on the literature in chimpanzees, our predictions were a more limited 455 manipulative repertoire in juveniles and no significant differences between sexes. These are 456 confirmed by our results showing that juveniles used less diverse grip associations and 457 grasping postures used in isolation than adults, and that males and females used the same 458 diversity of grip associations and grasping postures used in isolation.

459

Nevertheless, whileWhile sharing the same preference for the "lateral thumb index 460 grip" in adults and juveniles, juvenile individuals also used the precision grips as the "palmar 461 thumb-index grip" and the "dynamic tripod grip", showing the same ability as the adults to 462 use precision in their manipulative behavior. These results are consistent with the previous 463 studies in young chimpanzees where they used the two categories (i.e., precise and unprecise 464 grips) but more often "the unprecise grip category" [START_REF] Pouydebat | Diversity of grip in adults and young humans 745 and chimpanzees (Pan troglodytes)[END_REF] including the use 465 of the lateral side of the index finger. But the third precision grip of our study, the "middle-466 thumb grip", has not been observed in juveniles. This result suggests that this grip could be an 467 additional manipulative strategy developed by individuals later in ontogeny. A study focusing 468 on mother-juvenile pairs would be useful to evaluate the resemblance between mother and 469 juvenile manipulative repertoire and to better understand the developmental processes of 470 the manipulative behaviors in bonobos, especially the influence of individual and social 471 learning [START_REF] Hayashi | Cognitive development in apes and humans 644 assessed by object manipulation[END_REF]. Indeed, young chimpanzees are particularly observant of their 472 mother's behavior while they use tools [START_REF] Biro | Cultural 574 innovation and transmission of tool use in wild chimpanzees: Evidence from field 575 experiments[END_REF][START_REF] Lonsdorf | Sex differences in the development of termite-fishing skills in the wild 678 chimpanzees, Pan troglodytes schweinfurthii, of Gombe National Park, Tanzania[END_REF].

473

Besides sex and age, additional individual parameters also could be important in the 474 range of the manipulative repertoire and the preference for grasping postures, as suggested 475 by the inter-individual differences found in previous manipulative studies in zoo and sanctuary 476 bonobos [START_REF] Bardo | Behavioral and functional 557 strategies during tool use tasks in bonobos[END_REF][START_REF] Neufuss | Nut-cracking behaviour in wild-born, 717 rehabilitated bonobos ( Pan paniscus ): A comprehensive study of hand-preference, hand 718 grips and efficiency[END_REF] and chimpanzees [START_REF] Pouydebat | Diversity of grip in adults and young humans 745 and chimpanzees (Pan troglodytes)[END_REF]. 477 Social status could be particularly important [START_REF] Garber | Primate cognition: 627 Integrating social and ecological information in decision-making[END_REF]

  observed during the day in an indoor building where two large 170 cages, connected to each other (98m 2 and 8 m height each), were visible. They also had access analyzed frame by frame with VLC Media Player (VideoLan, 196 2020), using the individual focal sampling method

  movement" in[START_REF] Marzke | Grips and hand movements of 693 chimpanzees during feeding in Mahale Mountains National Park, Tanzania: Chimpanzee 694 Feeding Grips and Hand use in Mahale[END_REF] and these contacts are 241 called "non-prehensile movements" in[START_REF] Jones | Human hand function[END_REF].242During the same sequence, the passage from one grip to another, without a change of 243 hand, involved in-hand movements but this part of the sequence was not described included the cases of bimanual manipulation where the grasping 248 posture of each hand was recorded and compiled. In the case of asymmetric coordinated 249 bimanual movements, individuals held or maintained the food or the enrichment with one 250 hand and extracted or picked up the food with the other hand.251We also included the compound grips (e.g.,[START_REF] Jones | Compound grips in tufted capuchin monkeys ( Sapajus spp and 658 Sapajus libidinosus )[END_REF] Neufuss et al., 252 2018) in which several pieces of the same item were held in one hand. Compound grips could 253 be used when the item broke during the course of manipulation. extent to which our observations maximized the number of possible 258 grasping posturesincluded the whole manipulative repertoire, we plotted two accumulation 259 curves[START_REF] Colwell | Interpolating, extrapolating, and comparing incidence-599 based species accumulation curves[END_REF] of the number of grip associations and graspingle postures used 260 in isolation (i.e., only one grasping posture used during unimanual manipulation) as a function 261 of the number of sequences and as a function of the number of food items.

  (Fisher's exact test, p>0.05) nor between males and females (Fisher'

  318(N=22 ^2) were actually observed. The number of distinct grip associations and graspingle 319 postures used in isolation per sequence ranged from 1 to 8 (mean ± SEM=1.46 ± 0.04) and 320 each individual used between 3 and 19 distinct grip associations and graspingle postures used 321 in isolation (mean ± SEM=11 ± 1 or 23.3 ± 2.4% of the recorded grip associations and graspingle 322 postures used in isolation).323The bimanual manipulations represented the large majority of the grip associations 324 while only two cases of compound grips were observed. The first one was the "Palmar scissor 325 hold + Power grip with thumb" that occurred in one sequence involving an adult female during 326 the prehension of an item that broke into two pieces. The second one was the "Power grip 327 with thumb + Lateral thumb-index grip" in one sequence involving a subadult female in the 328 same context (i.e., prehension of one item broken into two pieces).329The manipulative repertoire was significantly larger in adults with 43 grips associations 330 and graspingle postures used in isolation used againstcompared with 24 in juveniles (Pearson's 331 Chi-squared test, p<0.05). We also detected 21 grips associations and graspingle postures 332 used in isolation in the two subadult individuals. But the number of distinct grip associations 333 and graspingle postures used in isolation used observed per individual was not significantly

363

  The use of tools occurred significantly more frequently in female (N=77/530 or 15% of 364 the sequences in 11 individuals) than in males (N=4/262 or 2% of the sequences in 6 365 individuals) (Pearson's chi-squared test, p<0.05). -recognized importance of hand functionality in hominid evolution 369

  manipulative repertoire and preferred grasping postures 380The aim of our study was to provide a first description of the spontaneous repertoire 381 used by bonobos in a feeding context, under zoo conditions. Our hypothesis was that bonobos much wider range of manipulative behaviors than those described previously in a 383

  [START_REF] Macfarlane | Diversity of grip in Macaca mulatta[END_REF] and in capuchins in Jones and Fragaszy, 2020) (and 407 see the review ofFragaszy & Crast (

  447confirm the ability of bonobos to execute this grip. Our observations suggest that bonobos are 448 not markedly different from chimpanzees in terms of morphological constraints associated 449 with food manipulation. This supports the hypothesis that the functional mechanisms 450 underlying flexible manipulation are shared by both species and would have already

Figures:Figure 1 .Figure 2 .

 12 Figures:

  All the means were calculated with the standard error of the mean (SEM). The 265 distribution of sequences and the number of distinct grip associations and graspingle postures 266 used in isolation in the manipulative repertoire were compared between the three age

			GERARD-p12
	264
	267	categories and between males and females using a Pearson's Chi-squared test or a Fisher's
	268	exact test (if the expected test values were less than 5). The different number of individuals in
	269	categories (fewer juveniles and subadults than adults and fewer males than females) could
	270	have induced an important bias. So, in every contingency table, we weighted the distribution
	271	by the proportion of individuals in the sample: males (N=6/17), females (N=11/17), adults
	272 273	F (N=9/17), subadults (N=2/17) or juveniles (N=6/17) according to the test. o r Multiple comparisons of the mean number of grips associations and graspingle
	274 275	P postures used in isolation used observed per individual between age categories were e r e performed using the Kruskal-Wallis test and we used the Wilcoxon rank sum test for the
	276 277	comparisons between males and females.	R v e
			i e w
	262
	263	3.2. Age and sex effects

Table 1 )

 1 . Sequences with tool use included 27 grip associations and graspingle postures used i.e., 55.1% of the whole repertoire) of which 8 (i.e., 16.5% of the repertoire) are 359 not found in sequences without tools (Table5).

	348	individual was not significantly different between males (N=6/17 individuals; mean ± SEM=12
	349	± 1) and females (N=11/17 individuals; mean ± SEM=11 ± 2) (Wilcoxon test, W=31, p > 0.05).
	350	The manipulative repertoire was slightly larger in females with 42 grips associations and
	351	graspingle postures used in isolation used againstcompared with 35 in males but this
	352	difference was not significant when weighted by the number of individuals (Fisher's Exact Test,
	353	p>0.05).
	354
	355	4. Tool use
	356	Branches were used as tools to reach food in about 10% of the sequences (N=81/792;
	357

  in bonobos since dominant Vanhoof, M. J. M., Kerkhof, F. D., Stevens, J. M. G., & Vereecke, E. E. (2018). Insights 775 into the musculature of the bonobo hand. Journal of Anatomy, 233(3), 328-340.

		GERARD-p21 GERARD-p23 GERARD-p27 GERARD-p33 GERARD-p34
	478 479 480 481 482 483 526 527 528 529 530 531 532 533 623 624 774 534	F o r females are less impacted by intra-group feeding competition and can spend more time manipulating food compared to males. So, it is needed, especially in complex social structures such as bonobo communities, to incorporate not only the ecological context but also the individual and social parameters in a further study. 3. Tool-use F o r manipulative abilities in bonobos similar to that previously described in chimpanzees, from precision to power grips. The comparison of our results with data on free-ranging bonobos in further studies is now essential to have an insight into the flexibility of manipulative behaviors in bonobo. More broadly, the investigation of manipulative behavior as a more complete dynamic process and including a consideration of the socio-ecological context is needed to go further into our understanding of the mechanisms underlying bonobos manipulative strategies. F F F F Furuichi, T., Sanz, C., Koops, K., Sakamaki, T., Ryu, H., Tokuyama, N., & Morgan, D. (2015). Why do wild bonobos not use tools like chimpanzees do? Behaviour, 152(3-4), 425-460. F F F F F F van Leeuwen, T., F o r o r o r o r o r o r o r o r o r o r o r
		P P P P P P P P P P P P P
		e e r e e r e e r e e r e e r e e r e e r e e r e e r e e r e e r e e r e e r
		R e v R e v R e v R e v R e v R e v R e v R e v R e v R e v R e v R e v R e v
		i e w i e w i e w i e w i e w i e w i e w i e w i e w i e w i e w i e w i e w

Table 1 .

 1 Distribution and characteristics of the sample of manipulative sequences.

	Page 35 of 49
	Tables:
		N sequences	Proportion of the	ID
			sample (%)
	Total	792	100	17
	With manual manipulation	661	83.46	17
	With unimanual manipulation	615	77.65	17
	With bimanual manipulation	115	14.52	12
	With pedal manipulation	9	1.14	4
	With the mouth only	131	16.54	10
	Without tool	711	89.77	17
	With tool	81	10.23	6
	Complete	769	97.10	17
	Incomplete	23	2.90	NA

F o r P e e r R e v i e w

Table 2 .

 2 Variability of grasping postures involving the hands: occurrence in isolation or in grip associations (number of sequences) and individuals using them in isolation or in grip associations.

Table 3 .

 3 Distribution and characteristics of the sample of manipulative sequences in every age category (adults, subadults and juveniles).

	Age category	Adults	Subadults Juveniles
	N total sequences (/792)	416	135	241
	N sequences with manual manipulation	333	106	222
	N sequences with the mouth only	83	29	19
	N sequences with pedal manipulation	3	0	6
	N sequences with tool use	55	3	23

[START_REF] Marzke | Grips and hand movements of 693 chimpanzees during feeding in Mahale Mountains National Park, Tanzania: Chimpanzee 694 Feeding Grips and Hand use in Mahale[END_REF][START_REF] Marzke | Chimpanzee and human grips: A new classification with a 697 focus on evolutionary morphology[END_REF] and we divided manual postures into six grip

categories (Table2):

 Precision grips (PCG): contact between distal phalanges of the thumb and the index

Acknowledgements


Patricia García-Muñoz
email: patricia.gmunoz@upm.es

Javier Ivanez

Víctor A De La Peña O'shea

Nicolas Keller
email: nkeller@unistra.fr

Solar hydrogen production from ethanol-water vapours over metal/TiO2 photocatalysts supported on β-SiC alveolar foams

In this work, we have explored the feasibility of alveolar open-cell β-SiC foams as catalyst support for solar hydrogen production. For that purpose, Pt and Ru nanoparticles have been obtained, by means of photoassisted synthesis, on TiO2-coated foams and tested in gas-phase hydrogen production from water-ethanol mixtures in a tubular reactor coupled to a compound parabolic solar collector (CPC). Subnanometre-sized metal or metal/oxide nanoparticles are obtained for Pt/TiO2/SiC and Ru/TiO2/SiC foams, respectively, where co-catalyst nanoparticles decorate the TiO2 coating which in turn is attached to the SiC foam through an amorphous SiO2 washcoat formed by SiC pre-calcination. In solar photocatalytic reactions, all of the assayed foam-supported photocatalysts are active for the production of hydrogen, with Pt/TiO2 ones being the most active and foam pore size exerting little influence on hydrogen outcome. In the best conditions, 14% UV-tohydrogen (equivalent to 0.49% solar-to-hydrogen) conversion efficiency, with photonic efficiency higher than 30%, is attained.

Introduction

In view of a full integration of hydrogen as a cost-effective vector in a future renewable energy system, direct methods for the conversion of solar energy into hydrogen energy are particularly interesting, and the decomposition of water by means of photocatalysis appears as an appealing alternative [START_REF] Dufour | Life cycle assessment of alternatives for hydrogen production from renewable and fossil sources[END_REF]. However, the oxygen evolution half-reaction, with the kinetically hindered four-electron transfer per produced oxygen molecule, dramatically limits the efficiency of photocatalytic water splitting [START_REF] Melchionna | Updates on the Roadmap for Photocatalysis[END_REF]. Therefore, a sacrificial agent is usually added to water in research works to scavenge the photoproduced holes and thus alleviate the inherent inefficiency of pure water splitting and focus on the hydrogen evolution (water reduction) half-reaction [START_REF] Schneider | Undesired role of sacrificial reagents in photocatalysis[END_REF][START_REF] Costantino | Do Sacrificial Donors Donate H2 in Photocatalysis?[END_REF]. However, in practice, this addition results in the consumption of reagents other than water and in the unavoidable generation of waste, and therefore only makes sense, in terms of energy efficiency and environmental friendliness, if aqueous waste or renewable feedstock are used. Regarding the former, the medium-low concentrations of pollutants in water at which photocatalytic oxidation is efficient [START_REF] Malato | Decontamination and disinfection of water by solar photocatalysis: The pilot plants of the Plataforma Solar de Almeria[END_REF] may limit the actual applicability of wastewater as a matrix for hydrogen production. Consequently, the study of biomass derivatives for this purpose has grown significantly in the last decade to become one of the most rapidly evolving applications of photocatalysis [START_REF] Skillen | Photocatalytic Reforming of Biomass: What Role Will the Technology Play in Future Energy Systems[END_REF], and the term photobiorefinery has been recently coined to account for all photocatalytic processes for biomass valorization, including not only hydrogen production coupled to the oxidation of biomass-derived organics, but also lignocellulose depolymerization, partial oxidations, hydrogenolysis and (de)hydrogenation [START_REF] Butburee | Beyond Artificial Photosynthesis: Prospects on Photobiorefinery[END_REF]. Ethanol appears there as an interesting platform, since it can be obtained from waste biomass and, in addition to its direct use as biofuel, alternatively used to obtain fully renewable hydrogen.

Concerning photocatalytic materials, the concourse of co-catalysts in heterogeneous photocatalysis can significantly enhance critical aspects of the process, like light absorption, charge transfer to adsorbed species, reaction selectivity and stability of the catalyst [START_REF] Yang | Roles of cocatalysts in photocatalysis and photoelectrocatalysis[END_REF]. Amongst the different existing methods for the decoration of photocatalysts with co-catalyst nanoparticles, photoassisted synthesis stands out as an elegant and green alternative to obtain well-defined, highly dispersed and size-controlled nanoparticles of metals and metal oxides on the surface of semiconductor photocatalysts in the absence of strongly reducing reagents and without the need for high temperature or applied potential, with light (ideally solar) as the only energy source driving the reaction. For instance, platinum, gold or silver nanoparticles obtained by photoassisted synthesis on TiO2 or CdS have been shown as very attractive catalytic systems for photocatalytic reactions [START_REF] Wenderich | Methods, Mechanism, and Applications of Photodeposition in Photocatalysis: A Review[END_REF].

Regarding oxides, although scarcer, examples like those of lead or ruthenium can be highlighted [START_REF] Kobayashi | Effective surfaces of semiconductor catalysts for light-induced heterogeneous reactions evaluated by simultaneous photodeposition of both oxidation and reduction products[END_REF][START_REF] García-Muñoz | Irradiance-Controlled Photoassisted Synthesis of Sub-Nanometre Sized Ruthenium Nanoparticles as Co-Catalyst for TiO2 in Photocatalytic Reactions[END_REF].

Open-cell alveolar foams have attracted significant interest as supports for immobilizing photocatalysts because of their ability of acting as an active static mixer while working at an ultralow pressure drop and maintaining a better light transmission than packed-bed supports [START_REF] Kouamé | β-SiC foams as a promising structured photocatalytic support for water and air detoxification[END_REF][START_REF] García-Muñoz | Ti-Modified LaFeO3/β-SiC Alveolar Foams as Immobilized Dual Catalysts with Combined Photo-Fenton and Photocatalytic Activity[END_REF]. Self-bonded β-SiC foams stand out compared to polymer, metallic, and other ceramic foams [START_REF] Martín-Sómer | Novel macroporous 3D photocatalytic foams for simultaneous wastewater disinfection and removal of contaminants of emerging concern[END_REF][START_REF] Švagelj | Titania-Coated Alumina Foam Photocatalyst for Memantine Degradation Derived by Replica Method and Sol-Gel Reaction[END_REF] in terms of thermal/chemical stability, allowing them to withstand harsh conditions for catalyst immobilization or for the reaction of application, and of density of oxygenated surface groups for catalyst anchorage, since their surface consists of an amorphous SiO2 overlayer, formed upon thermal treatment and characterized by a high density of hydrophilic hydroxyl groups [START_REF] Rico-Santacruz | Coating-free TiO2@β-SiC alveolar foams as a ready-to-use composite photocatalyst with tunable adsorption properties for water treatment[END_REF].

In this work, we have explored the feasibility of alveolar open-cell β-SiC foams as catalyst support for gas-phase solar hydrogen production from water-ethanol mixtures. In this particular application, these foams appear as an excellent possibility due to the mentioned static mixer effect that enhances the turbulence in the reactor, giving rise to higher reaction rates than a coated wall [START_REF] Kouamé | β-SiC foams as a promising structured photocatalytic support for water and air detoxification[END_REF], especially at the usual low space velocities in gasphase photocatalytic hydrogen evolution reactions [START_REF] Molins | Reaction Condition Effects on the Photocatalytic Production of H 2 from Ethanol in the Gas Phase over Pt/TiO 2[END_REF]. For this purpose, Pt and Ru nanoparticles have been photo-synthesized on TiO2-coated foams. Platinum is known to be the most active metal for hydrogen evolution reactions [START_REF] Meng | Dual Cocatalysts in TiO2 Photocatalysis[END_REF] and therefore appears as the ideal candidate for the purpose of this work, while ruthenium, photo-deposited most frequently in the form of an oxide or metal/oxide mixture [START_REF] García-Muñoz | Irradiance-Controlled Photoassisted Synthesis of Sub-Nanometre Sized Ruthenium Nanoparticles as Co-Catalyst for TiO2 in Photocatalytic Reactions[END_REF], is regarded as a good oxidation (hole transfer) co-catalyst [START_REF] Meng | Dual Cocatalysts in TiO2 Photocatalysis[END_REF] that can boost the oxidation sacrificial reaction of the biomass-derivative-assisted hydrogen evolution process. The so-obtained foamsupported photocatalytic systems have been tested in a tubular reactor coupled to a compound parabolic solar collector (CPC), and using natural sunlight as the irradiation source, which has been scarcely reported for H2 production from water and biomass derivatives [START_REF] Skillen | Photocatalytic Reforming of Biomass: What Role Will the Technology Play in Future Energy Systems[END_REF][START_REF] Maldonado | Hydrogen generation by irradiation of commercial CuO + TiO2 mixtures at solar pilot plant scale and in presence of organic electron donors[END_REF]. To the best of our knowledge, this is the first report on the use of this kind of foams as photocatalyst support for this application.

Materials and methods

Preparation of photocatalysts

Self-bonded β-SiC alveolar foams were synthesized by the SICAT SARL company (Strasbourg, France) using the SMS replica method, in which a pre-shaped polyurethane foam is transformed into the corresponding β-SiC carbide [START_REF] Nguyen | Innovative porous SiC-based materials: From nanoscopic understandings to tunable carriers serving catalytic needs[END_REF]. The shape of the β-SiC foams can thus be adjusted to the reactor geometry. In this work, cylindrical foams with 45 mm diameter and 40 mm length, with two different PPI (pores per inch) values of 8 and 13, were used [START_REF] Masson | β-SiC alveolar foams as a structured photocatalytic support for the gas phase photocatalytic degradation of methylethylketone[END_REF]. The as-obtained foams were calcined in air at 1000 ºC to remove any residual carbon species and to form an amorphous silica washcoat that favours the anchorage of the TiO2 catalyst [START_REF] Allé | Efficient photocatalytic mineralization of polymethylmethacrylate and polystyrene nanoplastics by TiO2/β-SiC alveolar foams[END_REF]. The so-obtained pre-calcined foams were dip-coated with an automatized system, using a suspension of 15 g L -1 Aeroxide P25 TiO2 from Evonik in ethanol containing titanium isopropoxide (8 mL L -1 ), which acts as a binder for the suspended commercial powder [START_REF] M'bra | Heterogeneous photodegradation of Pyrimethanil and its commercial formulation with TiO2 immobilized on SiC foams[END_REF]. After 35 dip-wash-dry cycles, the foam was dried at 100 ºC and calcined in air at 450 ºC. Metal nanoparticles (Pt, Ru) were synthesized on the TiO2-coated ceramic foams by means of photoassisted synthesis. For that purpose, the appropriate amount of RuCl3•xH2O or H2PtCl6 for nominal 0.5 wt.% metal with respect to TiO2 was dissolved in an aqueous 10 vol.% methanol solution, in which the foam was immersed and maintained with vigorous magnetic stirring in the dark for 1 h at 20 ºC.

Irradiation was then provided by a box equipped with five UV lamps (Philips, λmax= 365 nm, 70 mWm -2 UVA total irradiance). The metal concentration drop in solution was followed with a VWR UV-1600 PC UV-vis spectrophotometer.

Characterization techniques

The metal contents were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) carried out on a Perkin Elmer Optima 7000 DV spectrometer after digestion of the solid samples with a HNO3:HCl:HF 3:2:3 mixture in a microwave oven. Transmission electron microscopy (TEM) was performed in a JEOL 2100F microscope with a point resolution of 0.2 nm working at 200 kV. X-ray photoelectron spectroscopy (XPS) was performed on a SPECS GmbH system equipped with Al Kα anode (hν= 1486.6 eV) and a PHOIBOS 150 9MCD energy analyzer. Data were analyzed with the CasaXPS software. The C 1s peak of adventitious carbon was used for energy calibration. Surface atomic ratios were determined using the peak areas of high-resolution spectra and the CasaXPS sensitivity factors. X-ray diffraction (XRD) patterns were recorded with a PANalytical X'Pert Pro equipment using Ni-filtered Cu Kα radiation and a 0.04 º step.

Solar photocatalytic reactions

Solar hydrogen production tests were carried out between June and August 2021 in a tubular reactor (50 mm ø, 400 mm long) made of borosilicate glass and coupled to a compound parabolic collector (CPC) with anodized aluminium mirrors and concentration factor 1. The reactor is placed on the rooftop of the IMDEA Energy Institute, Móstoles (Madrid), Spain (40.34º N, 3.88º W), and the inclination angle with respect to the horizontal plane equals the local latitude for maximum solar collection efficiency. Two pieces of catalyst-loaded foam were placed in the centre of the reactor, which was fed in continuous mode with an argon flow (40 mL min -1 ) bubbled through a 10 vol.% aqueous ethanol solution kept at 60 ºC. In these conditions, the gas-phase concentrations of ethanol and water are 1.5 and 16 vol.%, respectively, according to Raoult's law and Antoine's equation [START_REF] Sapsanis | Insights on Capacitive Interdigitated Electrodes Coated with MOF Thin Films: Humidity and VOCs Sensing as a Case Study[END_REF]. The reactor was kept in the dark until air was completely removed, then it was uncovered and kept under sunlight for at least 5 h. Solar UVA irradiance (300 -400 nm wavelength) was measured with an ACADUS 85-PLS radiometer, while the outlet gas was analyzed with an Agilent 490 micro-GC equipped with an MS5A column and a TCD detector. A scheme of the whole reaction system is shown in Supplementary Material, Fig. S1.

Results and discussion

Catalyst characterization

SiC alveolar foams show in X-ray diffraction patterns (Supplementary Material, Fig. S2) the cubic structure of the β-SiC phase. After the pre-calcination step described in Materials and Methods, a wide feature corresponding to an amorphous SiO2 washcoat, with the incipient formation of a cubic cristobalite phase, appears. This washcoat favours the anchorage of the TiO2 catalyst during the dip-coating process [START_REF] Allé | Efficient photocatalytic mineralization of polymethylmethacrylate and polystyrene nanoplastics by TiO2/β-SiC alveolar foams[END_REF]. After dip-coating and calcination, white foams with average 3.2 wt.% TiO2 are obtained. These TiO2-coated foams contain, in addition to the phases of the support, the expected mixture of anatase and rutile in a similar weight ratio as that present in the used TiO2 Aeroxide P25, as observed in XRD (Fig. S2 and Table S1). Crystal sizes are also essentially unchanged upon deposition of P25 on the foam (Table S1). Additionally, comparison of the positions of the reflection peaks of the XRD patterns with the reference patterns suggests that the lattices corresponding to the different crystalline phases have not been modified upon TiO2 coating and calcination, indicating that the interaction between titania and the support is limited to the surface, in line with the XPS discussion below. As reported in previous works [START_REF] M'bra | Heterogeneous photodegradation of Pyrimethanil and its commercial formulation with TiO2 immobilized on SiC foams[END_REF], the TiO2 coating is obtained with a homogeneous morphology thanks to the addition of titanium tetraisopropoxide acting as binder. Regarding surface areas (Table S2), the BET value of the titania-coated foam increases with respect to the naked one in a proportion equivalent to the mass percentage of Aeroxide P25 (SBET = 44 m 2 g -1 [START_REF] Fresno | Influence of the structural characteristics of Ti1-xSnxO2 nanoparticles on their photocatalytic activity for the elimination of methylcyclohexane vapors[END_REF]) it holds. X-ray photoelectron spectra of the TiO2/SiC foams (Fig. 1 a-d) confirm the formation of the SiO2 washcoat on the foam surface and its interaction with TiO2. Thus, the Ti 2p region shows, in addition to the doublet corresponding to Ti 4+ in TiO2, another component at higher binding energies that has been ascribed to Ti-O-Si linkages [START_REF] Rico-Santacruz | Coating-free TiO2@β-SiC alveolar foams as a ready-to-use composite photocatalyst with tunable adsorption properties for water treatment[END_REF], indicating a chemical interaction between the TiO2 layer and the SiO2 washcoat at their interface. In line with this, three contributions are observed in the Si 2p region, which include, in addition to those corresponding to SiC and SiO2, a signal with intermediate binding energy that has been interpreted both as SiOxCy silicon oxycarbide from the oxygen-rich natural washcoat of the SiC foam [START_REF] Kouamé | β-SiC foams as a promising structured photocatalytic support for water and air detoxification[END_REF], and as Si-O-Ti linkages in SiO2/TiO2 composites [START_REF] Dulski | Innovative Bioactive Ag-SiO2/TiO2 Coating on a NiTi Shape Memory Alloy: Structure and Mechanism of Its Formation[END_REF]. This last feature can be seen more clearly in the high-resolution O 1s spectrum, in which a component ascribed to interfacial Si-O-Ti cross-linking bonds appears with a binding energy intermediate to those of the SiO2 and TiO2 photopeaks [START_REF] Sahu | Synthesis, analysis and characterization of ordered mesoporous TiO2/SBA-15 matrix: Effect of calcination temperature[END_REF]. Photoassisted syntheses of Ru and Pt co-catalysts on the TiO2/SiC foams starting from metal salt solutions leads to a progressive decrease of the metal precursor in the reaction medium that is considerably slower in the case of ruthenium than in the case of platinum (Fig. S3). Thus, after nearly 7 h of reaction the concentration of the Ru precursor has dropped to ca. 50% the initial one, while in the case of Pt a thirty-minute reaction is long enough for the precursor concentration to drop to virtually zero. 1) gives a bulk Ru/Ti atomic ratio corresponding to ca. 33% photosynthesis yield. The difference between the absorbance drop and reaction yield suggests that some Ru species remain undetected in the solution.

In contrast, the bulk Pt/Ti ratio obtained from ICP/OES is considerably closer to the practically stoichiometric photosynthesis yield indicated by UV-vis spectroscopy, in line with the higher reactivity of platinum for this process [START_REF] Wenderich | Methods, Mechanism, and Applications of Photodeposition in Photocatalysis: A Review[END_REF]. As expected from the low metal nominal contents, neither Ru/TiO2/SiC nor Pt/TiO2/SiC foams give rise to additional reflections in their XRD patterns compared to those of the TiO2/SiC foams (Fig. S2). In turn, the features of the XRD patterns corresponding to the TiO2 phases show no displacement in the reflection angles with respect to the TiO2/SiC sample, as well as no significant difference in crystal size, suggesting that doping of titania with Ru or Pt does not occur. TEM images, on the other hand, do show the obtained Ru or Pt nanoparticles, as observed in Fig. 2, located selectively on TiO2 as expected from the photocatalytic synthesis process, with subnanometre size and a narrow size distribution according to the histograms included in Fig. 2 obtained over several images. This demonstrates that not only photoassisted synthesis gives rise to very small nanoparticles, with the interest this involves for catalytic reactions, but also it produces co-catalyst/catalyst systems with homogeneous coverage and good dispersion of the co-catalyst nanoparticles. Analysis of the high-resolution Ru 3d (plus C 1s) and Pt 4f XPS spectra (Fig. 1 e andf) resulted in the parameters collected in Table 1. Ruthenium nanoparticles show to be mostly in the metallic oxidation state, even though contributions of oxidized species appear in a significant amount, as is common for this metal when obtained by photoassisted synthesis [START_REF] García-Muñoz | Irradiance-Controlled Photoassisted Synthesis of Sub-Nanometre Sized Ruthenium Nanoparticles as Co-Catalyst for TiO2 in Photocatalytic Reactions[END_REF][START_REF] Wojciechowska | Light-driven synthesis of sub-nanometric metallic Ru catalysts on TiO2[END_REF]. The high-resolution spectrum of Pt/TiO2/SiC in the Pt 4f region is highly distorted by the presence of a Ti 3s energy loss peak that is usually negligible but becomes significant due to the low platinum amount [START_REF] Torres-Garcia | Effect of the TiO2 Nanocrystal Dispersion Over SBA-15 in the Photocatalytic H2 Production Using Ethanol as Electron Donor[END_REF]. Once this is considered, the spectrum fits well with the only contribution of metallic platinum, without any contribution of oxidized species. Metal/titanium surface atomic ratios are in both cases one order of magnitude higher than the bulk ones obtained from ICP-OES analyses, in good agreement with the low particle sizes determined from TEM, by virtue of which essentially all metal atoms should be detected by XPS against only the first surface layers of titanium atoms.

In line with this, the smaller ruthenium nanoparticles show a higher surface exposure of Ru as revealed by the higher relative surface/bulk metal content. Regarding surface areas (Table S2), no modification is observed upon deposition of Ru with respect to the TiO2/SiC foam, while only a slight decrease occurs after platinum decoration.

Solar photocatalytic hydrogen production

The SiC-foam-supported photocatalysts described above were tested for gas-phase hydrogen production from ethanol-water mixtures in a tubular reactor coupled to a compound parabolic collector (CPC) under sunlight irradiation, in the conditions described in section 2.3. In blank photocatalyst-free experiments, naked pre-calcined SiC foams gave rise to a negligible amount of hydrogen (0.6 µmol W -1 h -1 ), indicating that the SiC foam acts only as a macroscopic support, without a role in the reactivity of the catalysts. Fig. 3 shows the results of hydrogen evolution reactions over the three different TiO2, Ru/TiO2 and Pt/TiO2 foam-supported catalysts in clear, sunny days during the summer of 2021 in Madrid. The hydrogen produced has been quantified per unit of received energy (insets of Fig. 3) in order to make results on different days, with slightly different solar irradiance, comparable.

Once photocatalysts are loaded onto the foam supports, hydrogen evolution is detected as soon as the reactor is uncovered after the dark stabilization period (sudden increase in irradiance in Fig. 3), and then follows a curve that is essentially parallel to that of solar UV irradiance, which is more clearly observed in the graphs corresponding to metaldecorated TiO2-loaded foams (Fig. 3 b andc). As a result of this, cumulative hydrogen productions follow in all cases good linear correlations against received energy, revealing a truly photocatalytic regime and the absence of catalyst deactivation, the latter further proved by maintained activity after three consecutive reactions (Fig. S4). These results show, in the first place, that the employed SiC alveolar foams are suitable supports for gas-phase solar photocatalytic hydrogen production. Regarding the photocatalyst materials themselves, photoassisted synthesis is demonstrated to be an appropriate method to include a co-catalyst in these foam-supported photocatalytic system. Quantitatively, it is observed that photoassisted decoration with ruthenium increases the hydrogen production activity of TiO2 by an order of magnitude, extending what had been already observed in the laboratory [START_REF] Gu | Constructing Ru/TiO2 Heteronanostructures Toward Enhanced Photocatalytic Water Splitting via a RuO <sub>2</sub/TiO2 Heterojunction and Ru/TiO2 Schottky Junction[END_REF] to truly solar reactions. However, the best results in this study are obtained with photoassisted decoration with Pt, which improves the activity of TiO2 by a factor of ca. 165 and reaches a hydrogen production over 1.2 mmol per gram of catalyst and received Wh, as represented by the slope of the linear fit in the inset of Fig. 3 c. Again, this result insists in the well-known high activity of Pt/TiO2 photocatalysts for hydrogen evolution [START_REF] Skillen | Photocatalytic Reforming of Biomass: What Role Will the Technology Play in Future Energy Systems[END_REF][START_REF] Younas | An Overview of Hydrogen Production: Current Status, Potential, and Challenges[END_REF], demonstrating it in this solar approach. In this respect, this high activity of Pt/TiO2 is essentially due to its large work function and low overpotential for the reduction of protons [START_REF] Meng | Dual Cocatalysts in TiO2 Photocatalysis[END_REF]. For its part, Ru (RuOx)

is more likely to act as a hole transfer component and, therefore, as an oxidation cocatalyst [START_REF] Meng | Dual Cocatalysts in TiO2 Photocatalysis[END_REF]. The present results highlight the higher influence of a reduction co-catalyst on the rate of the reaction studied here.

Fig. 4a shows the hydrogen yields per unit energy obtained with Pt/TiO2/SiC foams with different PPI as a function of the gas flow rate in the reactor. Comparing both curves, it is observed that the influence of gas flow is lower in the case of the foam with larger pore size (lower PPI), revealing a lower limitation with respect to mass transfer. In both cases, an optimum activity is obtained at 75 mL min -1 , which can be interpreted as a compromise situation between residence time and reactants transfer. As observed in Fig. 4b, overall hydrogen yields are higher in the 8 PPI foam for all three studied catalysts, although differences are relatively smaller in TiO2 and Ru/TiO2 coated foams. This can be related both to the improved mass transfer in large-pore foams and to the better light transmission through the length of these foams compared to the smaller-pore ones [START_REF] Masson | β-SiC alveolar foams as a structured photocatalytic support for the gas phase photocatalytic degradation of methylethylketone[END_REF]. Hydrogen yields per unit energy obtained with the different catalysts supported on 8 and 13 PPI foams, at 75 mL/min gas flow.

Regarding photonic efficiency, this is defined as [START_REF] Braslavsky | Glossary of terms used in photocatalysis and radiation catalysis (IUPAC recommendations 2011)[END_REF]:

x !""#$"" &' = )*+,-*. */*,-)012 31,3.*1-4ℎ0-012 !""#$"" &'
An estimation of the number of incident photons by applying the AM1.5 spectrum to the average irradiance obtained from the radiometer during the reaction gives a x300-400 nm value of 32 %, which is the line of previously reported laboratory-based reports [START_REF] Guayaquil-Sosa | Photocatalytic hydrogen production using mesoporous TiO2 doped with Pt[END_REF][START_REF] Fontelles-Carceller | Measuring and interpreting quantum efficiency for hydrogen photo-production using Pt-titania catalysts[END_REF].

In terms of energy efficiency, a first approximation to the efficiency of the conversion of light energy into hydrogen energy, considering only the photocatalytic reaction, can be estimated as: h 6789 = : ;<= × ? 9 @ × AAB 9 @ where:

h 6789 : UV-to-hydrogen efficiency : ;<= : mass of catalyst used (g) ? 9 @ : hydrogen yield (mol [Wh] -1 g -1 ) AAB 9 @ : higher heating value of hydrogen (= 78.89 Wh mol -1 )

In the case of the best result obtained in this study, this calculation results in a hUVTH of 14% which, considering that the UV region represents approximately 3.5% of the solar spectrum in terms of energy, corresponds to a solar-to-hydrogen conversion efficiency (hSTH) of 0.49%. This can be clearly considered as a low efficiency value in order for photocatalytic hydrogen production to be competitive with more mature hydrogen production technologies [START_REF] Younas | An Overview of Hydrogen Production: Current Status, Potential, and Challenges[END_REF], highlighting the idea that this is still a developing field and there is much room for improvement in order for this technology to be deployed [START_REF] Skillen | Photocatalytic Reforming of Biomass: What Role Will the Technology Play in Future Energy Systems[END_REF]. In this respect, for instance, some approaches have recently been reported to exceed the activity of Pt/TiO2 for this reaction [START_REF] Torres-Garcia | Effect of the TiO2 Nanocrystal Dispersion Over SBA-15 in the Photocatalytic H2 Production Using Ethanol as Electron Donor[END_REF][START_REF] López-Calixto | Hybrids Based on BOPHY-Conjugated Porous Polymers as Photocatalysts for Hydrogen Production: Insight into the Charge Transfer Pathway[END_REF].

Conclusions

We have shown that b-SiC open-cell alveolar foams are suitable catalyst supports for solar photocatalytic hydrogen production, and that dip-coating followed by photoassisted synthesis is an appropriate method to obtain metal/TiO2/SiC foams for that purpose. Thus, subnanometre-sized metal or metal/oxide nanoparticles are obtained for Pt/TiO2/SiC and Ru/TiO2/SiC foams, respectively, where co-catalyst nanoparticles decorate the TiO2 coating which in turn is attached to the SiC foam through an amorphous SiO2 washcoat formed by SiC pre-calcination. The so-obtained TiO2/SiC, Ru/TiO2/SiC and PtTiO2/SiC foams are all active for the production of hydrogen from ethanol and water in a gas-phase reactor coupled to a compound parabolic collector and irradiated with natural sunlight.

The pore size of the foams exerts little influence on the resulting hydrogen yield, while, among the three compositions, Pt/TiO2/SiC is the most active one, reaching in the best conditions 14% UV-to-hydrogen (equivalent to 0.49% solar-to-hydrogen) conversion efficiency, with photonic efficiency higher than 30%.

Fig. 1 .

 1 Fig. 1. X-ray photoelectron spectra of TiO2/SiC (a-d), Ru/TiO2/SiC (e) and Pt/TiO2/SiC (f) foams.

Fig. 2 .

 2 Fig. 2. TEM images of Ru/TiO2/SiC (a) and Pt/TiO2/SiC (b) foams together with Ru and Pt size distributions, respectively.

Fig. 3 .

 3 Fig. 3. Hydrogen evolution reactions over 8 PPI SiC-foam-supported photocatalysts: (a) TiO2, (b) Ru/TiO2 and (c) Pt/TiO2. Large panels represent the hydrogen evolution rates and solar irradiance (300-400 nm) along the day. The vertical rise of irradiance corresponds to the time when the reactor is uncovered. Insets represent for each reaction the cumulative amount of hydrogen produced vs. the cumulative energy received by the foams, the slope of the linear fit representing the amount of hydrogen produced per gram of catalyst and received Wh of solar energy.

Fig. 4 .

 4 Fig. 4. (a) Hydrogen yield per unit energy obtained with Pt/TiO2/SiC foams with different pore dimension (PPI: pores per inch) as a function of the gas flow through the reactor. (b)

Table 1 .

 1 Characteristics of the metal-decorated TiO2/SiC foams.

	Metal M	M/Ti at. nominal	M/Ti at. bulk a	M/Ti at. surface b	M 0 /(M 0 +M d+ ) b
	Ru	0.0042	0.0013	0.020	0.69
	Pt	0.0022	0.0018	0.015	1

a From ICP-OES b From XPS ICP-OES analyses of the finally obtained foams (Table

Acknowledgements

This work has received financial support from Spanish MCIN/AEI/ 10.13039/501100011033 and "ERDF A way of making Europe", through projects PID2020-118593RB-C22 and ENE2017-89170-R, and from Comunidad de Madrid European Structural Funds through FotoArt-CM project (S2018/NMT-4367). The University of Strasbourg IdEx Program is thanked for funding the PhD fellowship of Javier Ivanez.

Supplementary Material

Solar hydrogen production from ethanol-water vapours over metal/TiO2 photocatalysts supported on β-SiC alveolar foams Patricia García-Muñoz, a Javier Ivanez, b Víctor A. de la Peña O'Shea, c Nicolas Keller, b, * Fernando Fresno.