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[EN] The possible pathways of sugars transformation into 1,2-propanediol (PDO)have been studied, using new bifunctional catalysts for this catalytic multistep reaction. The catalysts are based on an acidic active phase (polyoxometalates, POMs)and a metallic function (Ru nanoparticles)supported over activated carbon (AC, S = 1190 m/g). This support was loaded with 15 wt% of polyoxometalate, either phosphotungstic acid (TPA)or tungstosilicic acid (STA), while the amount of loaded ruthenium was close to 2 wt%. The catalytic materials were characterized by X-ray diffraction and electron microscopy techniques (SEM and TEM), while the surface active sites were evaluated using model reaction tests: cyclohexane dehydrogenation for metallic surface sites and isomerization of 3,3-dimethyl-1-butene for acid sites. For different sugars (sucrose, pentoses or hexoses)hydrogenation/hydrogenolysis using these catalysts in batch reactor was studied. The higher PDO selectivity was obtained in ethanol:water media and this study aims to establish the possible ways that sugars follow to achieve this transformation. The best catalytic material, 2%Ru-15%STA supported on AC, yields up to 50% of PDO selectivity when fructose is used as reactant, under moderate reaction conditions (413 K and 30 bar H)., The financial support from the Spanish Ministerio de Economía y Competitividad under projects (CTQ2017-89443-C3-1-R and -3-R) is recognized.

International audience; The influence of Ir content on sulphur tolerance for the selective ring opening of decalin was investigated. Ir/SiO2-Al2O3 catalysts (70 and 80 wt% SiO2) were used. In the absence of sulphur, slight differences were observed on the yields according to the metallic content regardless of the support used. Although the results of cyclopentane hydrogenolysis showed that the metallic function acquires importance as the metal content increases, for these metal percentages the acid function limits the rate of decalin opening reaction. Products distribution are strongly modified using decalin with S content compared to pure decalin. The formation of dehydrogenated products is virtually null due to S adsorbed on the metal sites. The support has low influence on the thiotolerance. The results related to the amount of S per Ir surface atom, showed that for a moderate S content (S/Irsurf  0.30) 1.5 Ir/Sy appears to be less poisoned than 1Ir/Sy and 2Ir/Sy.

Fil: Sanchez, Maria Amparo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto de Investigaciones en Catalisis y Petroquimica "Ing. Jose Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catalisis y Petroquimica "Ing. Jose Miguel Parera"; Argentina

International audience; Re–Pd catalysts supported on TiO2 (P25 or DT51) prepared by successive impregnation (SI) or by Re deposition on Pd/TiO2 by catalytic reduction (CR) were characterized by XANES and EXAFS at the Pd and Re edges. These samples were shown to be efficient for the selective hydrogenation in aqueous solution of succinic acid (SUC) to 1,4-butanediol (BDO) (T = 160 °C, P(H2) = 150 bar). This study clearly highlights the need for in situ re-activation of Re-based systems before their characterization or use, since Re species are fully re-oxidized (Re7+) by contact with air. The XANES quantitative analysis at the Re LIII-edge reveals that after in situ reduction, the Re average reduction state is in most cases inferior or equal to +3, indicating the presence of a mixture of Re3+ and Re0 species in all reduced catalysts. EXAFS study indicates that the Re species are mainly located at the Pd-support interface for the CR sample, whereas a part of Re entities is also deposited as isolated forms on the support in the case of the SI catalyst. The Re–Pd/DT51-SI system leading to the best BDO yield displays a specific arrangement of the Pd and Re species (Re deposit on Pd sites of high coordination). In this sample, the Re0 species, present in none negligible proportion, would contribute similarly as Pd metal to the efficient transformation of SUC towards GBL, which is further converted to BDO on sites involving Pd0 and oxidized Re3+ species nearby

International audience; Bimetallic Co–Re/TiO2 catalysts were developed for efficient citral hydrogenation. Bimetallic catalysts were prepared by co‐impregnation (CI), successive‐impregnation (SI), and surface redox method (SR). The arrangement between the Co and Re species on these systems was fully characterized using several techniques (TEM–energy‐dispersive X‐ray spectroscopy, H2 temperature‐programmed reduction, temperature‐programmed desorption, XRD, CO FTIR spectroscopy, model reaction of cyclohexane dehydrogenation), and their catalytic performances were evaluated for the selective hydrogenation of citral towards unsaturated alcohols. The Re and Co species are completely isolated in the CI sample, presenting a very limited Co–Re interaction. In SI samples, the metals coexist in a Janus‐type structure with a concentration of Re around Co. Decoration/core–shell structures are observed for SR samples resulting from the redox exchange between the metallic surface of the parent Co/TiO2 catalyst and the Re7+ species of the modifier precursor salt. The contact degree between the two metals gradually increases as follows: Isolated structure (CI)

The catalytic performances of Ru&ndash, Pt/SiO2&ndash, Al2O3 catalysts synthetized by three methods (co-impregnation (CI), successive impregnations (SI) and redox deposition (CR)) were compared for their sorbitol transformation to hexane under hydrothermal conditions. The existence of Pt&ndash, Ru interaction was demonstrated by TEM-EDX only on SI and CR samples, with a PtRu alloy suspected by XRD and XPS. The chemical nature of the Ru species differed according to the synthesis method with the presence of Ru4+ species on SI&ndash, (Ru&ndash, Pt) and CR catalysts. The SI&ndash, Pt)/SiO2&ndash, Al2O3 system displayed the best metal&ndash, acid function balance leading to the highest selectivity to hexane. The study of the reactivity of isosorbide and 2,5-dimethylfuran intermediates highlighted that the first one was poorly reactive compared to the second one, and the latter was selectively convertible to hexane. The synergy effect on SI&ndash, Al2O3 catalyst was attributed to the presence of small-sized bimetallic particles favoring an electronic exchange from Ru to Pt, and increasing the formation of 2,5-dimethylfuran.

International audience; TiO2-supported Re-Pd catalysts were evaluated for the selective hydrogenation of succinic acid (SUC) to 1,4-butanediol (BDO) in aqueous solution at 160 °C under 150 bar of H2. Rhenium immobilized on Pd/TiO2 catalysts by ex situ preparation methods, namely successive impregnation (SI) or deposition by catalytic reduction (CR), was partially leached after handling in air and introduction into the SUC aqueous solution in the batch reactor; it was then re-deposited under H2 pressure. It was demonstrated in this study that Re can be deposited by CR on a monometallic Pd catalyst directly in situ in the autoclave under hydrogen pressure before the catalytic test. The Re loading and the activation time under reducing atmosphere in the autoclave were optimized. Finally, the best bimetallic catalysts synthesized in situ demonstrated an intermediate selectivity to BDO compared to the systems prepared ex situ from the same parent monometallic catalyst, in the following order: ex situ CR < in situ CR < ex situ SI.

International audience; A bifunctional Ni2Si/SiO2‐Al2O3 catalyst was prepared by one‐step chemical vapor deposition (CVD), and used for hydrode‐oxygenation (HDO) of diphenyl ether (DPE). During the one‐step CVD process, metallic Ni species as the HDO active sites were isolated by intermetallic modification of Si atoms and partial electron transferred from Ni to Si, as inferred by XRD, XPS, and theoretical calculation. Furthermore, the characterization results revealed that the acidity and structure of Al2O3 were tuned due to the formation of Al‐O−Si bonds. Consequently, compared with Ni/Al2O3 catalyst, the Ni2Si/SiO2‐Al2O3 catalyst showed a higher benzene selectivity (60% vs 47%), O‐free products selectivity at the similar conversion of DPE, and high stability for the HDO of DPE. This work provides insight for design of bifunctional catalysts with specific catalytic properties by one‐step CVD method.

International audience; Hydrogenolysis of methylcyclopentane was studied in the presence of supported platinum catalysts, with particle sizes between 0.9 and 2.4 nm. The distribution of ring-opening products (n-hexane, 2-methylpentane, 3-methylpentane), which are virtually the only products at 573 K, mainly depended on the platinum particle size, with no effect of the methylcyclopentane conversion. This distribution was well described by the selective or non-selective mechanisms previously proposed in the literature except for the smallest particles (d

Sorbitol hydrogenolysis in aqueous medium was carried out over Pt based catalysts supported on SiO 2 -Al 2 O 3 and modified by a second metal (Re, Ir, Rh and Pd). The catalysts were synthetized by two preparation methods, co-impregnation and successive impregnations. The metallic properties of these catalysts were characterized by transmission electron microscopy and X-ray diffraction, H 2 chemisorption, temperature programmed reduction and by the model reaction in gas phase of cyclohexane dehydrogenation. The acidic properties were characterized by ammonia thermodesorption and by the model reaction in gas phase of 3,3-dimethyl-1-butene. The catalytic performances were compared to those of corresponding monometallic catalysts under hydrothermal conditions, in a batch reactor at 240 °C under 60 bar H 2 pressure. The main products were poly- and mono‑oxygenated compounds in liquid phase and hydrocarbons in gaseous phase. Among the studied modifiers, Re allowed to promote the catalytic performances of Pt leading to a synergistic effect for the transformation of sorbitol into liquid fuels (hexane). The highest efficiency of the Re-Pt/SiO 2 -Al 2 O 3 catalyst prepared by co-impregnation was explained by an optimal balance between the acidic and metallic functions constituted of bimetallic particles of small size dispersed on the acidic support.

Bimetallic Rh-Pd catalysts prepared by various impregnation methods were evaluated in the selective ring-opening of decalin and methylcyclohexane (MCH) used as model molecules of hydrogenated aromatics of the Light Cycle Oil fraction. Rh and Pt were deposited on Al2O3 and SiO2-Al2O3 (S40) by coimpregnation (CI) or successive impregnations (SI) with different orders of metal addition. Catalysts were characterized by H2 chemisorption, temperature programmed reduction, temperature-programmed desorption of pyridine, and test reactions of cyclopentane hydrogenolysis and isomerization of 3,3-dimethyl-1-butene. Their catalytic behaviors for the ring-opening reaction were deeply influenced by the acidity of the support, and in a lesser extent by the metal deposition method. On both supports, the CI catalysts, displaying the highest dispersion values, exhibited the best ring opening performances. In the case of the SI catalysts, the addition order of both metals modified in a moderate way the properties of the catalyst. The yield to ring opening products obtained in MCH ring opening with CI catalysts supported on Al2O3 was 39-69% higher than those prepared by SI (conversion = 55-60%) while for the catalysts supported on S40, the yield to ring opening products was 8-48% higher for the CI catalysts compared to SI catalysts (conversion = 72-77%). The conversion of decalin for the bimetallic catalysts supported on Al2O3 was lower than 20% being dehydrogenated compounds the main reaction products regardless the preparation method. The catalyst supported on S40 showed decalin conversion values between 46-53% and yield to ring opening near to 30%. Moreover, the CI catalysts have yield to ring opening 10 to 20% higher than the catalysts prepared by SI. The catalyst prepared by coimpregnation supported on S40 was the most appropriate for opening the MCH and decalin due to an optimal balance between the metal and acid functions. Fil: D'ippolito, Silvana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentina Fil: Especel, Catherine. Université de Poitiers; Francia Fil: Epron, Florence. Université de Poitiers; Francia Fil: Pieck, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentina

Tungstated oxides were prepared from several supports and characterized. The tungsten surface repartition and availability depends on the initial support. The acidity in water was evaluated through a model compound reaction, cyclohexanol dehydration. The results show that acidity in water is completely different from gas phase acidity (from NH 3 -TPD), evidencing the crucial role of water in the acid catalytic activity. The tungstated oxides were then mixed with Pt/ZrO 2 to obtain a bifunctional catalytic system, which was used for transforming sorbitol in water. The activity and selectivity is highly dependent on the acid phase. TiO 2 –WO x led to increased activity and higher selectivity for long chain hydrocarbons (C5-C6 alkanes) which can be valorized as biofuels, when compared to traditional sorbitol transformation catalyst. Al 2 O 3 –WO x is not acid in water but produces short alcohols by C C cleavage. These results provide an incentive for further catalysts preparation.

International audience; The influence of the Bronsted acidity, SiO2/Al2O3 ratio and Rh-Pd content on the ring opening of decalin was studied. Rh- and Pd-based monometallic and bimetallic catalysts were prepared by impregnation on three commercial SiO2/Al2O3 supports (SIRAL 5, 20 and 40). The catalysts were characterized by TPD of pyridine, X-ray diffraction, H-2 chemisorption, isomerization of 3,3-dimethyl-1-butene (33DM1B) and selective ring opening (SRO) of decalin. It was found that the support acidity is strongly influenced by the SiO2/Al2O3 ratio, the SIRAL 40 being more acid. The metal accessibility has the following order: supported catalysts on SIRAL 40 > SIRAL 20 > SIRAL 5. The incorporation of Rh and/or Pd modifies the conversion and the product distribution on decalin reaction. The support acidity has a strong influence on the conversion and product distribution on the decalin reaction at 350 degrees C, SIRAL 5 series have low selectivity to RO and high selectivity to dehydrogenated compounds. On the other hand, SIRAL 40 series lead to the highest yield to cracking products of the three studied series. Catalysts with Rh/Pd atomic ratios equal to 2 and monometallic Rh1 supported on SIRAL 40 are the most active and selective catalysts to ring opening products

International audience; Carbon-supported Re–M (M = Pt and Rh) bimetallic catalysts with controlled size and composition were synthesized by using a microwave-assisted thermolytic method and evaluated in the aqueous phase hydrogenation of succinic acid. The Re–M interaction contributes to the inhibition of aggregation of particles and to the improvement in the catalytic activity for succinic acid hydrogenation through decreasing the activation energy. The Re–M interaction favors the ring opening of γ-butyrolactone, an intermediate product, to 1,4-butanediol instead of the hydrogenation and dehydration to tetrahydrofuran observed over a Re/C catalyst. The kinetic study proves that the Re–M interaction can increase the relative formation rate of 1,4-butanediol more than that of tetrahydrofuran, while the strength of the Re–M interaction has a limited influence on the product selectivity. It was shown that the Re–Rh interaction can reduce the direct hydrogenolysis of succinic acid, but it cannot avoid the hydrogenolysis of 1,4-butanediol, thus limiting the selectivity to this product. According to the kinetic mechanism, ring opening of γ-butyrolactone is favored at low temperature while direct hydrogenation to tetrahydrofuran is favored at high temperature.

Sorbitol hydrogenolysis in aqueous medium was carried out over Ru-Pt based catalysts supported on SiO2-Al2O3 and synthetized by three preparation methods (co-impregnation, successive impregnations or a surface redox deposition). These catalysts were characterized by N2 isothermal adsorption desorption, transmission electron microscopy, H2 chemisorption, temperature programmed reduction and by the model reaction in gas phase of cyclohexane dehydrogenation. The catalytic performances were compared to those of monometallic catalysts (Pt/SiO2-Al2O3 and Ru/SiO2-Al2O3) under hydrothermal conditions, in a batch reactor at 240 °C under 60 bar H2 pressure. The main products were poly- and mono-oxygenated compounds in liquid phase and hydrocarbons in gaseous phase. The best yield of hydrocarbons was obtained in the presence of Ru-Pt bimetallic catalyst prepared by successive impregnations, for which a synergetic effect was observed. This effect can be explained by the existence of bimetallic particles of small size favoring an electronic exchange from Ru to Pt. Under the experimental conditions used in this study, it appeared that the reaction pathway of sorbitol transformation was not the same on Pt- or Ru-based catalysts.

n -Butanol oxidation was studied using noble metals (Pt, Pd, Rh and Au) supported on a highly structured mesoporous material: CMI-1. The catalysts were characterized by several physico-chemical techniques, i.e. N 2 sorption, ICP, H 2 chemisorption, XRD and TEM. The Pt based catalyst was the most active material, followed by Pd/CMI-1, Rh/CMI-1 and Au/CMI-1. Difference in size of the particles was proposed as origin of these results, this parameter being well-known to strongly influence the catalytic activity. The comparison of two Pt/CMI-1 catalysts prepared from various precursor salts (with and without chlorine) showed that n -butanol oxidation was sensitive to the nature of the metallic salt. Finally the modifications induced by the nature of the support were studied by comparing Pt/Al 2 O 3 and Pt/TiO 2 systems. Pt dispersion and specific surface area of the support seemed to be important parameters influencing the activity of the materials. In the studied conditions, Pt/CMI-1 was still the most active catalyst.

International audience; A series of supported Pt-Rh bimetallic systems was prepared either (i) by the refilling method (a surface redox reaction), or (ii) by the classical coimpregnation or (ii) by mechanical mixture of supported monometallic Pt and Rh catalysts and acidic support (chlorinated alumina). Two oxide supports were used for these preparations, i.e. alumina and silica. All these systems, largely characterized in a previous work dedicated to methylcyclopentane (MCP) hydrogenolysis, were studied for the methylcyclohexane (MCH) ring opening (RO) performed under high pressure (39.5 bar). During MCH transformation, synergetic performances were observed with some supported Pt-Rh bimetallic catalysts, since better performances in terms of activity and RO selectivity were obtained compared to those of monometallic Pt and Rh systems. The metallic particle size acts as a determining parameter modulating the catalytic properties, since the best RO performances were obtained on bimetallic catalysts presenting the largest particle sizes, for which a Pt surface enrichment and the presence of a Pt-Rh alloy were previously detected. On these bimetallic catalysts, the ring opening occurs mainly according to a bifunctional mechanism, the chlorinated alumina support bringing the required acidic function for the first isomerization step of C6 ring to alkylcyclopentanes further opened on the metallic function. The acidic function and the metal sites should not be necessarily in close vicinity since the mechanical mixture of non-acidic Pt-Rh/SiO2 catalyst with chlorinated alumina leads also to high RO selectivities. Finally, as for MCP ring opening, the refilling method allows synthesizing supported bimetallic Pt-Rh catalysts particularly efficient in terms of activity and RO selectivity. (C) 2011 Elsevier B.V. All rights reserved.

International audience; Pt/x% Ti-SBA15 catalysts (x corresponding to the wt.% TiO2 loading in the Ti-SiO2 composite, in the range 25-60%) were synthesized by titanium precursor grafting in preformed mesoporous silica. Materials were characterized by several techniques, including elemental analysis, XRD, TEM and N-2-sorption isotherms to achieve structural and textural properties description. Different pore sizes were obtained for the SBA15 materials, by using or not hexane as swelling agent. The catalytic performances of these original materials were evaluated for the selective hydrogenation of citral (alpha, beta-unsaturated aldehyde), and compared with those of Pt/SBA and Pt/TiO2 P25 reference catalysts. Pt/x% Ti-SBA15 catalysts present high specific surface, with TiO2 nanoparticles and Pt-0 clusters located inside the hexagonal mesopore structure of silica. During citral hydrogenation, the selectivity towards unsaturated alcohols (nerol and geraniol) varies as a function of the support nature as follows: Pt/x% Ti-SBA15 > Pt/TiO2 P25 >> Pt/SBA. The results are discussed in term of variable metal-support interaction (SMSI) generated by the partial reduction of TiO2 species, this SMSI effect being reported more important over anatase TiO2 nanoparticles dispersed inside the mesostructure than over large crystals encountered in the classical P25 support.

International audience; During citral hydrogenation, the products distribution obtained on Rh/TiO2 and Pt/TiO2 catalysts depends on their preparation and activation protocols: (i) the unsaturated alcohols (the intended products) are formed in higher quantity on samples reduced at 500 degrees C and more notably with Pt/TiO2 catalyst; (ii) samples prepared by impregnation of the metallic precursor salt in HCl medium and activated at 300 degrees C are the only ones to lead to the formation of isopulegol as by-product. On the catalysts activated at 500 degrees C, these results can be explained by the presence of the SMSI effect beneficial to hydrogenate selectively the C=O bond of citral towards unsaturated alcohols.

International audience; Silica-supported Co catalysts with different metal loadings were prepared by water-in-oil (w/o) microemulsion (ME) and tested for the selective hydrogenation of citral. The performances of the ME samples were compared to those of previously studied Co impregnated catalysts. Compared to impregnated Co catalysts, ME samples show more homogeneously dispersed Co particles, the crystallite mean size increasing with the Co content. For the ME samples, the selectivity to unsaturated alcohols (i.e. nerol and geraniol) increases with the metal content then reaches a plateau from approximately 15 wt% Co, suggesting that particles of large enough size are required to optimize the C=O group activation. Above 15 wt% Co content, the selectivity is markedly higher on the ME catalysts compared to the impregnated ones (90% versus 45-65% depending on the nature of the support). This result can be directly related to the higher proportion of beta H-Co species detected by temperature-programmed desorption of hydrogen (H(2)-TPD) on these ME samples.

Pt-Re-Ge/γAl2O3 catalysts were prepared by the catalytic reduction method using different impregnation media (H2O, HCl and NH3) and different Ge contents (0.0, 0.1, 0.3, 1.0 and 2.0%). The influence of these preparation parameters on the activity for n-heptane conversion and the selectivity to toluene at atmospheric pressure was assessed. The catalysts were also characterized by ICP-AES, temperature programmed reduction, pyridine temperature programmed desorption and CO pulse chemisorption. The results show that as the pH is increased the Ge content increases and the catalysts present a lower hydrogenolytic activity and a lower toluene selectivity. Ge addition modifies both metal and acid functions. The catalyst with minimum Ge content prepared using water as impregnation medium has the best performance.

Pt-Rh bimetallic catalysts on alumina support were prepared according to three different techniques, one leading to random deposition of the two metals at the support’s surface, the two others, namely the organometallic grafting and the colloidal route, favoring the formation of bimetallic particles with strong Pt-Rh interactions. Catalysts were characterized by ICP, H2 chemisorption, TPR, FTIR of chemisorbed CO and NO-CO. Then they were evaluated in cyclohexane dehydrogenation and methylcyclopentane hydrogenolysis reactions. Strong interaction between Pt and Rh was demonstrated for catalysts prepared by controlled preparation method, which leads to a strong synergetic effect for methylcyclopentane ring-opening, in terms of activity and selectivity, whereas these interactions do not play a role in cyclohexane dehydrogenation. Fil: Hérault, Nelly. Université de Poitiers; Francia Fil: Olivet, Lilian. Université de Poitiers; Francia Fil: Pirault Roy, Laurence. Université de Poitiers; Francia Fil: Especel, Catherine. Université de Poitiers; Francia Fil: Vicerich, Maria Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentina Fil: Pieck, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentina Fil: Epron, Florence. Université de Poitiers; Francia

MICROSCOPIE+CDFA+BKL:MAO:PDE:CPI:MBE; International audience; ReOx-Pd/TiO2 catalysts prepared from different 2wt%Pd/TiO2 catalysts using two protocols for the deposition of the Re promoter (successive impregnation and catalytic reduction) were characterized by different techniques to better understand the nature of the active and selective sites implied in the aqueous-phase hydrogenation of succinic acid to 1,4-butanediol. Regardless of the support and Re introduction method, it was established that varying amounts of Pd and Re were in very close proximity without electronic interaction in the reduced catalysts. A high fraction of Re always remained partially oxidized to generate a bimetallic catalyst that can provide the necessary bifunctional sites to enable the selective hydrogenolysis of the intermediate -butyrolactone to 1,4-butanediol. Depending on the method of promotion, the ReOx species that interact with Pd were deposited as clusters with different spatial Re-Re interactions

International audience; Pt/SBA-15 catalysts, modified by zinc addition (at different Zn/Pt atomic ratios) via the co-impregnation method, were tested for the liquid phase hydrogenation of citral. The influence of the Zn insertion on the Pt monometallic catalyst properties was evaluated by different physico-chemical techniques, including X-ray diffraction, N-2-physisorption, transmission electron microscopy, hydrogen chemisorption, and cyclohexane dehydrogenation as model reaction for platinum accessibility and zinc covering evaluation. On the catalysts, the hexagonal periodic structure of SBA-15 framework was maintained indicating that neither Pt and Zn impregnations, nor thermal treatments affect the organized structure of the support. A decrease of the platinum metallic accessibility was observed with the increase in the Zn concentration in the materials, which was explained, on the basis of the TEM analysis, by a poisoning of the platinum accessible sites by zinc species. For the citral hydrogenation, Pt/SBA-15 monometallic catalyst is very active, with 100% conversion obtained after 30 min reaction time, but very poorly selective in unsaturated alcohols. Zinc addition led to an inhibition of the hydrogenating activity, in agreement with the decrease of the active surface, but contributed to an increase in the selectivity to unsaturated alcohols. Selectivity in unsaturated alcohol was observed to reach a maximum of 75%, for a Zn content equal to 0.3 wt.%, that is a very interesting value if compared to performances obtained with other more classical dopant including titania and germanium.

Bimetallic TiO 2 -supported Rh-Ge and Pt-Ge catalysts were prepared by surface redox reaction between hydrogen activated on a parent monometallic rhodium or platinum catalyst and a germanium salt dissolved in water (catalytic reduction method). They were characterized by elemental analysis, transmission electronic microscopy (TEM), temperature-programmed reduction (TPR) and by their activity for the gas phase dehydrogenation of cyclohexane. Elemental analysis of the bimetallic catalysts showed that germanium can effectively be deposited by the catalytic reduction method on titania-supported Rh and Pt catalysts. Moreover, the different characterization methods (TEM, TPR and cyclohexane dehydrogenation) proved that germanium is in great interaction with rhodium and platinum. Nevertheless, some germanium deposition occurred also separately on the titania support. TEM and cyclohexane dehydrogenation results revealed that both rhodium and platinum particles were stable on titania support under the conditions of bimetallic catalyst preparation contrary to previous results obtained with silica or alumina supports. Effectively, no sintering has been observed when they were immersed in an aqueous solution under hydrogen bubbling (catalytic reduction protocol). Their catalytic performances for the cyclohexane dehydrogenation reaction indicate that all the catalysts reduced at high temperature (500 °C versus 300 °C) developed the strong metal–support interaction (SMSI) effect, which implied the formation of TiO (2− x ) species. Whatever the nature of the parent metal (Rh and Pt), this effect was totally destroyed by air exposure of the samples at ambient temperature whereas one part of the TiO (2− x ) moieties remained after immersion of the catalysts in an aqueous medium.

International audience; A series of bimetallic Al2O3-supported Rh-Ge catalysts was prepared by surface redox reactions under controlled hydrogen atmosphere. The surface properties of these catalysts were probed via in-situ FTIR spectroscopic studies of adsorbed CO and were compared to those of monometallic Rh catalysts that had undergone similar treatments. The results indicate that Ge addition results in the formation and stabilization of smaller rhodium ensembles at the expense of larger Rh-0 surfaces. A charge-transfer mechanism from Ge to Rh is also inferred by the IR results for the high Ge loading samples. Air exposure of the catalysts leads to an irreversible segregation of the two metals and formation of large Rh crystallites.

International audience; To selectively transform sorbitol into hydrocarbons in aqueous phase, new bifunctional catalytic systems are designed by associating a hydrogenating metallic catalyst (M/ZrO2, M = Pt, Ir or Pd) and a dehydratingacidic catalyst (TiO2–WOx) in a mechanical mixture. Zirconium oxide was chosen as support because ithas virtually no dehydration activity and gives a good stability to the metal in water. This stability isevaluated through several characterizations before and after contact with the aqueous reaction medium.It is proposed that stability in water is driven by two parameters. The support stability is a key parameterfor the overall catalyst stability, and the metal–support interaction determines the sintering extent. Thenature of the metal has also an important influence on the activity and selectivity of the bifunctionalM/ZrO2+ TiO2–WOxsystem for sorbitol transformation. Pd and Ir are slightly active and mainly trans-form sorbitol into isosorbide, whereas Pt is selective for long-chain alkane production. The mass ratiobetween metallic and acidic catalysts in the mechanical mixture also modifies the yield structure, witha Pt/ZrO2:TiO2–WOx20:80 ratio for optimal liquid hydrocarbons production.

Rh–Pd catalysts supported on Al2O3, SiO2 and SiO2–Al2O3 (SIRAL 40) were studied for methylcyclohexane (MCH) and decalin ring opening reactions. It was found that the Rh/Pd atomic ratios were similar to the theoretically expected one and the metal dispersion values varied between 30 and 50%. On bimetallic catalysts supported on Al2O3 and SiO2, Pd and Rh were present mainly in the form of monometallic particles, whereas a heterogeneous distribution constituted of large Pd particles and small bimetallic ones were observed on SIRAL 40. Total and Bronsted acidities followed the order: SIRAL 40 >> Al2O3 > SiO2. Al2O3 supported catalysts were the most suitable for MCH ring opening, while the opening of decalin was favored by using SiO2–Al2O3 (SIRAL 40). The catalysts supported on SiO2 produced mainly dehydrogenated compounds. The higher total and Bronsted acidities of SIRAL 40 series had a great impact on the opening of bicyclic naphthenes, whereas the metal function of the catalyst and the hydrogenolytic activity of Rh had a major role during MCH reaction. Using bimetallic catalysts in the MCH reaction decreased the formation of cracking and dehydrogenated products, and the selective formation of RO products could be optimized by tuning the working temperature. Fil: D'ippolito, Silvana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentina Fil: Especel, Catherine. Centre National de la Recherche Scientifique; Francia. Université de Poitiers; Francia Fil: Vivier, Laurence. Centre National de la Recherche Scientifique; Francia. Université de Poitiers; Francia Fil: Pronier, Stéphane. Centre National de la Recherche Scientifique; Francia. Université de Poitiers; Francia Fil: Epron, Florence. Centre National de la Recherche Scientifique; Francia. Université de Poitiers; Francia Fil: Pieck, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentina

Activity and selectivity of bimetallic catalysts for two model reactions, citral hydrogenation in isopropanol and nitrate reduction in water, are reviewed on the basis of results obtained over bimetallic systems prepared in our laboratory, notably by redox techniques. The parent metal is generally a noble metal (Rh, Pd, Pt), while the additive is most often a non-noble metal (Ge, Sn, Cu…) whose oxidation state plays an important role in hydrogenation. Dramatic improvements of the selectivity to unsaturated alcohols are observed in citral hydrogenation with adequate deposition of the additive and pretreatment of the final catalyst. In nitrate reduction, the second metal essentially affects the first step of the process (conversion of nitrate to nitrite) but the global selectivity (limitation of NH3 formation) may be significantly improved by tuning the couple parent metal–additive. Other aspects such as the choice of the support and the optimization of reaction conditions (temperature, pressure, pH effects in water) are also discussed.

Activity and selectivity of bimetallic catalysts for two model reactions, citral hydrogenation in isopropanol and nitrate reduction in water, are reviewed on the basis of results obtained over bimetallic systems prepared in our laboratory, notably by redox techniques. The parent metal is generally a noble metal (Rh, Pd, Pt), while the additive is most often a non-noble metal (Ge, Sn, Cu…) whose oxidation state plays an important role in hydrogenation. Dramatic improvements of the selectivity to unsaturated alcohols are observed in citral hydrogenation with adequate deposition of the additive and pretreatment of the final catalyst. In nitrate reduction, the second metal essentially affects the first step of the process (conversion of nitrate to nitrite) but the global selectivity (limitation of NH3 formation) may be significantly improved by tuning the couple parent metal–additive. Other aspects such as the choice of the support and the optimization of reaction conditions (temperature, pressure, pH effects in water) are also discussed.

Monometallic and bimetallic Pd-Rh catalysts with various Rh/Pd atomic ratios (=0.5, 1 and 2) and a total metal charge of 1 wt% supported on SiO2-Al2O3(SIRAL 40, 20, 5) were studied for the ring opening of methylcyclohexane (MCH). The results were compared with those obtained previously for ring opening of decalin. It was found that the total acidity and the Brønsted acidity of the support have a higher influence on the activity for ring opening of naphthenic bicycles than on the activity for opening single rings. The influence of the metal charge is more important on the reaction of MCH. All the catalysts display a high MCH conversion, which increases with the reaction temperature. The bimetallic catalyst with the Rh/Pdratio equal to 2 and supported on SIRAL 40 has the highest yield to ring opening products. Fil: D'ippolito, Silvana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina Fil: Especel, Catherine. Universite de Poitiers. Laboratoire de Catalyse En Chimie Oranique; Francia Fil: Vivier, Laurence. Universite de Poitiers. Laboratoire de Catalyse En Chimie Oranique; Francia Fil: Epron, Florence. Universite de Poitiers. Laboratoire de Catalyse En Chimie Oranique; Francia Fil: Pieck, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

International audience; Pt-based catalysts supported on TiO2 and SIRAL 20 (Al2O3-20 wt.%SiO2) were prepared and characterized by H-2 chemisorption, FTIR of adsorbed pyridine and 3,3-dimethyl-1-butene isomerization. The catalysts were evaluated for the transformation under aqueous phase of glycerol and 1,2-propanediol at 210 degrees C, under 60 bar as total pressure (H-2 atmosphere). Under similar conditions, 1,2-propanediol is easier converted than glycerol, indicating that in the glycerol transformation process in aqueous phase, the 1,2-propanediol reactivity is inhibited by the presence of glycerol. This behavior is explained by a strong adsorption of glycerol compared to 1,2-propanediol on the catalyst surface

International audience; Sorbitol can be selectively transformed into liquid alkanes over a bifunctional catalytic system Pt/ZrO2 + TiO2–WOx. In this paper, we investigated the reaction mechanism by carefully analyzing the numerous products issued from sorbitol and by studying the reactivity of some identified intermediates (1-hexanol 2-hexanol, 2-hexanone, 2,5-dimethyltetrahydrofuran, 1,2-hexanediol and 1,2,6-hexanetriol). This led us to propose that C C cleavage reactions occur on terminal C C bonds and mainly consist of dehydrogenation-–decarbonylation reactions. The limiting steps of the sorbitol transformation are the isosorbide and mono-oxygenated intermediate transformations, especially the hydrogenation of ketones. It is also assessed that diols or triols with n carbon atoms are mainly converted in compounds with n − 1 carbon atoms. Short compounds (1 to 3 carbon atoms) are obtained via a dehydrogenation-retroaldol reaction pathway and not from isosorbide conversion.

BIOVERT+BKL:CPI; International audience; Bimetallic Re-Pd catalysts were prepared by addition of Re onto a Pd/TiO2 monometallic catalyst, either by a catalytic reduction method or by successive impregnation. The physical and chemical properties of the bimetallic catalysts were evaluated by several characterization techniques, including analysis by transmission electronic microscopy, hydrogen chemisorption, temperature programmed reduction and X-ray photoelectron spectroscopy to explain their different catalytic performances in the selective hydrogenation of succinic acid to 1,4-butanediol in aqueous solution. The localization of the Re deposit on the parent Pd catalyst surface varied according to the Re introduction mode. The catalytic reduction method induced a selective Re deposit at the Pd-TiO2 interface compared to a random distribution obtained by successive impregnation. The oxidation state of the Re species (Re3+, Re-0) on the reduced bimetallic samples was also linked to their preparation mode. (C) 2014 Elsevier B.V. All rights reserved.

International audience

BIOVERT+LCD:BKL:CPI; Supported noble-metal catalysts (Ru, Pd or Pt) and the corresponding Re-promoted catalysts exhibit a high activity for the hydrogenation of biobased carboxylic acids. Levulinic acid and succinic acid are converted into the lactones or the diols depending on the nature of the catalyst and the reaction conditions. The highest selectivity to 1,4-pentanediol of 82% is achieved at 140 degrees C in the presence of the 1.9%Ru-3.6%Re/C catalyst.

The influence of Ir content on the properties of Pt-Ir/Al2O3 and Pt-Ir/TiO2 catalysts for selective ring opening of naphthenes was studied. It was found that these catalysts display a strong Pt–Ir interaction but only a weak metal–support interaction. Catalyst acidities depend on the metal loading, but opposite effects were observed on alumina (decrease) or titania (increase) as the metal loading increased. The results obtained from test reactions (cyclohexane dehydrogenation and cyclopentane hydrogenolysis) showed that titania supported catalysts were less active than their alumina supported counterparts. This behavior could be due to the partial blockage of metallic sites by migrated TiOx species and the sinterization of metallic phase during the reduction step. The methylcyclopentane ring opening reaction was found to occur through a partially selective mechanism, and an increase in activity as the Ir loading increased was observed. The selective mechanism was favored by higher total metal loadings, possibly due to an increase in the size of metallic aggregates. Alumina supported catalysts present higher ring opening selectivities. The activity for decalin ring opening increased both with metal loading and reaction temperature level. Fil: Vicerich, Maria Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones En Catalisis y Petroquímica "ing. Jose Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones En Catalisis y Petroquímica "ing. Jose Miguel Parera"; Argentina Fil: Benitez, Bibiana M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones En Catalisis y Petroquímica "ing. Jose Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones En Catalisis y Petroquímica "ing. Jose Miguel Parera"; Argentina Fil: Especel, Catherine. Université de Poitiers. Institut de Chimie des Milieux et Matériaux de Poitier; Francia Fil: Epron, Florence. Université de Poitiers. Institut de Chimie des Milieux et Matériaux de Poitier; Francia Fil: Pieck, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones En Catalisis y Petroquímica "ing. Jose Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones En Catalisis y Petroquímica "ing. Jose Miguel Parera"; Argentina

Pt, Ir and Rh were deposited on SiO 2 or Al 2 O 3 using chlorinated precursors and various amounts of HCl in the impregnation medium. The Bronsted and Lewis acidities increased with the chlorine content of the alumina supported catalysts. The silica-supported catalysts only presented Lewis acid sites. The catalysts were evaluated in methylcyclopentane (MCP) and methylcyclohexane (MCH) ring-opening (RO) under pressure (2.85 and 3.95 MPa, respectively), from 200 to 425 C. For MCP conversion, the acidity of the alumina support had no sensitive effect on the activity and selectivity to RO products, and few effects on the distribution of RO products. No isomerization or hydrocracking products were observed, confirming that these reactions occurred mainly on the metal function, which was not modified by the presence of chlorine. The nature of the support, SiO 2 or Al 2 O 3 , had a strong effect on both the activity (1.9 against 0.5 mol h −1 g −1 metal for Ir/Al 2 O 3 and Ir/SiO 2 , respectively at 225 C) and selectivity to RO products (99.6% against 97.5% for Ir/Al 2 O 3 and Ir/SiO 2 , respectively, at 80% of MCP conversion) for Ir catalysts only. Interestingly, the Rh/SiO 2 exhibited a high selectivity for converting MCP to RO products, similar to Ir/Al 2 O 3 , i.e. 99.6% at 80% of conversion. Depending on the metal and the supports, three types of behavior were observed for MCH ring-opening: (i) a direct ring-opening on the metal function whatever the support for Ir, (ii) a first step of isomerization, and then a need of a sufficiently acidic support, for Pt and (iii) an intermediate behavior for Rh, which was able to either directly convert MCH in absence of acidic support or favor a bifunctional mechanism on chlorinated alumina.

International audience; Decreasing oil supplies and increasing energy demand provide incentives to find alternative fuels. First, the valorisation of edible crops for ethanol and biodiesel production led to first generation biofuels. Nowadays, research is focused on lignocellulosic biomass as a source of renewable carbon (second generation biofuels). Whereas the cellulosic ethanol production is in progress, a new way consisting of the transformation of ex-lignocellulose sugars and polyols towards light hydrocarbons by heterogeneous catalysis in aqueous phase has been recently described.This process is performed under mild conditions (T < 300 °C and P < 50 bar). It requires on one hand hydrogen formation by catalytic reforming of carbohydrates in aqueous phase and on the other hand, the dehydration/hydrogenation of polyols leading to alkanes by selective C-O bond cleavages. The challenge here is to conceive multifunctional catalytic systems that are stable, active and selective under the reaction conditions.The aim of this article is to present the involved reactions, the catalytic systems described in literature for that kind of transformation and examples of industrial applications.

BIOVERT+BKL:CPI; A series of 2 wt % Pd/TiO2 monometallic catalysts were prepared by varying some parameters, such as the nature of the precursor salt, the titania support, and the preparation method. The structural and textural properties of the catalytic systems were fully characterized by several physical and chemical techniques (inductively coupled plasma optical emission spectrometry, N-2 physisorption, H-2 chemisorption, transmission.electron microscopy coupled with energy dispersive X-ray spectroscopy, powder X-ray diffraction, temperature programmed reduction, X-ray photoelectron spectroscopy, and gas phase reaction of cyclohexane dehydrogenation). The catalytic performances were further estimated for the hydrogenation of an aqueous solution of succinic acid (SUC) performed in a batch reactor at 160 degrees C and under 150 bar total pressure. The results showed that all the Pd catalysts are very Selective to produce gamma-butyrolactone, the first hydrogenated product. However, the rate of succinic acid conversion is a function of both the Pd dispersion and the preparation method. The deposition-precipitation method allows one to obtain the highest performing 2 wt % Pd/TiO2 samples during SUC hydrogenation in terms of activity and stability.

Platinum-based catalysts supported on TiO 2 -modified mesostructured silica were prepared using the direct co-condensation of silica and titania precursors to synthesize the mixed-oxide support. The physico-chemical properties of the Pt/ x Ti-SBA15 samples with various x Ti contents (in mol%) were further evaluated using several techniques, including elemental analysis, X-ray diffraction, N 2 -physisorption, H 2 -chemisorption, transmission electronic microscopy and the probe reaction of cyclohexane dehydrogenation to evaluate the metal–support interaction (SMSI effect). All the Pt/ x Ti-SBA15 samples display high specific surface areas (650–820 m 2 g −1 ) and high mesopore volumes (0.44–0.68 cm 3 g −1 ), with the formation of TiO 2 anatase nanoparticles since the low titanium content, i.e. 2 mol%. The hexagonal organized pore structure of SBA silica is also strongly altered by the titanium adding, but mixed oxides so obtained present very particular morphology with maintaining of high surface areas. The catalytic performances of the Pt/ x Ti-SBA15 catalysts were estimated for the citral hydrogenation performed at 70 °C under hydrogen pressure (7 MPa), and discussed in terms of activity and unsaturated alcohols (UA: nerol and geraniol) selectivity. A synergetic effect on the UA selectivity was obtained on the Pt/ x Ti-SBA15 catalysts, compared to both Pt/SBA15 and Pt/TiO 2 P25 reference samples (reduction temperature = 300 °C), and was explained by the specific role of the reducible TiO 2 species, which under the nano-anatase form generate a strong metal–support interaction (SMSI effect) with platinum after reduction at 300 °C. The formation of partially reduced support species was finally modulated by varying the reduction temperature of the catalysts. It is then possible to achieve high selectivity after reduction at 350 °C, while maintaining high conversions.

The effect of the metal/acid balance of Pt/SiO 2 –Al 2 O 3 catalysts on the catalytic transformation of sorbitol in aqueous medium was investigated, using four mechanical mixtures of Pt/SiO 2 –Al 2 O 3 and SiO 2 –Al 2 O 3 (100:0; 50:50; 25:75; 0:100). The results show that the metal/acid balance has a strong impact on catalytic performances, tuning the yields in alkanes, alcohols, ketones and heterocycles. An optimum in the metal/acid balance is obtained with the 50:50 mechanical mixture: when the metallic function is introduced in higher quantity, the C–C cleavage pathway is favoured and leads to an important CO 2 yield; on the contrary, a too low proportion of platinum atoms induces a lack of metallic sites for the hydrogenation reaction. Nevertheless many hydrocarbons containing 1–4 carbon atoms are still obtained with the best balanced catalyst, evidencing some C–C cleavage activity. Hydrocarbon selectivity could be improved by new more hydrogenating metallic phases and new supports with a stronger acidity in water.

International audience; Hydrogenation of succinic acid aqueous solutions was performed using TiO2-supported 2 wt% Pd and 2 wt%Pd–x wt%Re catalysts, using either impregnation method or surface redox reduction of the monometallic catalyst. The former catalysts were superior in terms of activity and selectivity to 1,4-butanediol than the latter ones. However, higher Re loadings (3.4–3.6 wt% compared to 0.6–0.8 wt%) were necessary to initiate this synergy.

International audience; Pt/y%Ti-Al2O3 (y corresponding to the atomic percent of Ti in alumina, in the range 10-33%), and derived bimetallic Pt-Ge/10%Ti-Al2O3 nanocomposite catalysts were synthesized, characterized, and reduced either at 300 degrees C and 500 degrees C (this latter temperature being performed in order to generate strong metal-support interactions, i.e. a SMSI effect). The materials were characterized in detail with techniques including elemental analysis, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and nitrogen physisorption to evaluate their structural and textural properties. Due to the templating approach used, well-defined mesopore structures with high surface areas and mesopore volumes are obtained for all materials. The SMSI effect, evaluated using a structure insensitive model reaction, i.e. the cyclohexane dehydrogenation, is observed to be more pronounced on the Pt/y%Ti-Al2O3 catalysts with y = 20 and 33% than on a Pt/TiO2 P25 (Degussa P25 titania) sample, showing the beneficial effect of Ti fine dispersion through incorporation in alumina matrix on the generated metal-support interaction. During citral hydrogenation reaction, the selectivity toward unsaturated alcohols (UA: nerol and geraniol) is related to Ti and/or Ge loadings on the nanocomposite, as well as reduction temperature. Both SMSI effect and Ge addition promote the UA selectivity leading to similar values than on Pt/TiO2 P25 sample. (C) 2011 Elsevier B.V. All rights reserved.

International audience; Sorbitol transformation in aqueous medium can be used to produce alkanes from lignocellulosic sugars over a bifunctional catalyst, usually Pt/SiO2-Al2O3. However, the catalyst is modified by the hydrothermal medium. In this study, the separated effects of water and medium generated during sorbitol transformation reaction on a Pt/SiO2-Al2O3 catalyst have been investigated. Reaction products, in particular acidic ones, also alter catalyst properties. Catalyst pre-treatment by steaming appears to be an interesting way to obtain a catalyst which is less sensitive to liquid water in terms of platinum dispersion and textural properties. Steaming pre-treatment has no impact on selectivity. These investigations provide an incentive for the development of new sorbitol transformation catalysts more suitable under hydrothermal conditions.

The influence of gallium on the properties of Pt–Re/Al 2 O 3 catalysts used in naphtha reforming was studied. The catalysts were prepared by the coimpregnation method. It was found that the addition of gallium to the Pt–Re/Al 2 O 3 catalyst diminishes its acidity (Bronsted and Lewis). It also produces an inhibition of the metal function, i.e. dehydrogenation and hydrogenolysis activity. Activity tests for n -C 5 isomerization showed that gallium addition decreases the total activity of the Pt–Re catalyst but increases its selectivity to i -C 5 isomers. The selectivity to low value light gases (C 1 –C 3 ) is particularly decreased. Catalytic tests for n -C 7 reforming showed that addition of gallium increases both catalyst stability and selectivity to aromatics, and decreases the production of light gases.