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G Djegamariadassou - One of the best experts on this subject based on the ideXlab platform.
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deep hds on doped Molybdenum Carbides from probe molecules to real feedstocks
Catalysis Today, 2005Co-Authors: Patrick Da Costa, C Potvin, J M Manoli, G DjegamariadassouAbstract:Abstract Deep HDS on phosphorus and nickel–alumina-supported Molybdenum oxyCarbides was studied, first, with probe molecules then with real feedstocks. Catalysts were characterized by elemental analysis, X-ray diffraction, CO chemisorption, transmission electron microscopy, X-ray photoelectron spectroscopy and infrared spectroscopy. Propene and tetralin hydrogenation were used to probe the activity of the doped materials. Hydrodesulfurization of 4,6-dimethyldibenzothiophene was investigated as a probe for the deep HDS of diesel fuel. For contact times ranging from 0 to 0.4 s, the HDS of 4,6-DMDBT is zeroth-order with respect to the reactant and proceeds via two parallel routes, direct desulfurization and hydrogenation pathways, the former being preponderant. Phosphorus and nickel modify the catalytic behaviour and induce the highest HDS activity. Deep hydrodesulphurization (HDS) of diesel fuels was carried out on promoted or non-promoted Mo2C-supported γ-Al2O3 and on bulk Mo2C under standard industrial conditions. The effect of the promoter was investigated for different feedstocks on HDS and hydrogenation (HDA) with very low levels of sulfur. The HDS conversion indicated that P-doped alumina supported carbide catalysts were as active as a commercial Co–Mo/Al2O3 catalyst for low level of sulfur in the feed. Furthermore, the refractory compounds, such as 4,6-DMDBT were only transformed on Molybdenum carbide catalyst under industrial conditions for hydrotreated gas oils. For feeds containing less than 50 wt. ppm in sulfur, P-doped Carbides were more active than commercial catalysts for HDA, as well as deep HDS or HDN.
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synthesis and characterization of highly dispersed Molybdenum Carbides in mesoporous silica
Catalysis Letters, 2004Co-Authors: Jeanyves Piquemal, C Potvin, J M Manoli, G DjegamariadassouAbstract:Highly dispersed Molybdenum Carbides in MCM-41 mesoporous silica are synthesized by temperature-programmed carburization and are characterized. Two methods of preparation are examined: (i) insertion of Molybdenum during the synthesis of the MCM-41 silica and (ii) postsynthesis incorporation into a MCM-41 silica matrix by the incipient wetness method. Propene transformation (hydrogenation and metathesis) was used as a probe reaction; the observed catalytic behavior can be explained as a result of the preparation method, i.e., of the relative strength of interaction between the Molybdenum oxide precursor and the support.
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phosphorus doped Molybdenum oxynitrides and oxygen modified Molybdenum Carbides synthesis characterization and determination of turnover rates for propene hydrogenation
Journal of Catalysis, 2002Co-Authors: P Perezromo, C Potvin, J M Manoli, M M Chehimi, G DjegamariadassouAbstract:The effect of phosphorus on Molybdenum oxynitrides and oxygen-modified Carbides has been studied. Phosphorus was introduced via heteropolyanions. Catalysts were characterized by elemental analysis, X-ray diffraction, N2 BET surface area, CO chemisorption, and X-ray photoelectron spectroscopy (XPS). XPS measurements show higher concentrations of lower Mo oxidation states on P addition to Molybdenum oxynitrides. Two types of phosphorus were revealed by XPS spectra: phosphatelike at about 134 eV, and phosphide at 130 eV. Propene hydrogenation was used to probe the activity of the doped materials. Reactivity experiments over P-containing oxynitrides and oxygen-modified Carbides show enhanced hydrogenating properties, in particular for the oxynitride materials. Turnover rate was studied as a function of P content.
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novel phosphorus doped alumina supported Molybdenum and tungsten Carbides synthesis characterization and hydrogenation properties
Catalysis Letters, 2001Co-Authors: P Da Costa, C Potvin, J M Manoli, M Breysse, G DjegamariadassouAbstract:The effect of atomically dispersed phosphorus on Mo2C- and WC-supported γ-Al2O3 has been studied. Phosphorus was introduced via Molybdenum or tungsten heteropolyanions. Mo- and W-based heteropolyanions were used to synthesize supported materials. Propene and tetralin hydrogenation were used as molecular probe reactions to test the activity and selectivity of the alumina-supported Molybdenum or tungsten Carbides. The effect of phosphorus on the hydrogenation activity of materials was also considered. Catalysts were characterized by X-ray diffraction, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and CO chemisorption. Phosphorus was found to increase significantly the activity of Molybdenum and tungsten Carbides. Supported Molybdenum Carbides are highly dispersed. Tungsten carbide particles are well dispersed with sizes ranging from 2 to 4 nm. To check the stability of Carbides they were characterized after catalytic runs.
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influence of the degree of carburization on the density of sites and hydrogenating activity of Molybdenum Carbides
Journal of Catalysis, 2000Co-Authors: Jaesoon Choi, Guy Bugli, G DjegamariadassouAbstract:Abstract Temperature-programmed carburization of molybdic acid with CH 4 /H 2 mixtures led to hexagonal Mo 2 C with specific surface areas ranging from 40 to 91 m 2 g −1 . The carburization was found to go through Mo 4 O 11 , MoO 2 , and Mo metal. Whatever was the parameter of carburization, no significant change of the lattice parameters of Mo 2 C was detected by XRD. The primary particles of the resulting Carbides were found to be single crystals. Elemental analysis evidenced different bulk carbon contents of Carbides depending on the conditions of synthesis. Nevertheless, this kind of analysis only gives global data to monitor the completion of carburization. Without free carbon contamination, all accessible Mo atoms were able to chemisorb oxygen. So oxygen chemisorption was proposed as a molecular probe to control the free carbon deposition. Counting of noble metal-like sites was possible by selective CO chemisorption, which was found to selectively deactivate active sites in benzene hydrogenation. CO titrated from 3 to 58% of a monolayer of surface Mo atoms. This evolution of the density of sites titrated by CO was interpreted in terms of the “degree of carburization” of materials linked to both surface carbidic carbon and residual oxygen contents as evidenced by TPR measurements of Mo 2 C prepared in situ . The evaluation of the quality of each Mo site titrated by CO was done by benzene hydrogenation at room temperature. The Carbides were found to be as active as Ru/Al 2 O 3 . A significant increase of the activity per site was observed on Mo 2 C, when the density of sites titrated by CO was increased. It means that the degree of carburization affects not only the number of active sites, but also the quality of these sites. These results are in good agreement with the general concept speculated on the noble metal-like behavior of Mo 2 C: the higher the carbidic carbon content and the lower the residual oxygen content in Mo lattice, the higher will be the noble metal-like behavior.
Masatoshi Nagai - One of the best experts on this subject based on the ideXlab platform.
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Reverse water gas shift reaction over Molybdenum carbide
Journal of Chemical Engineering of Japan, 2020Co-Authors: Masatoshi Nagai, Tatsuhiko KurakamiAbstract:The reverse water gas shift reaction on Molybdenum Carbides was studied at 573 K and atmospheric pressure. Molybdenum Carbides with various C/Mo atomic ratios were synthesized on γ-Al 2 O 3 using a vertical tube hot-wall chemical vapor deposition (CVD) reactor in a stream of MoCl 5 , benzene, and hydrogen at 1000 K and total pressure of 0.13 kPa. The activities of the Molybdenum carbide catalysts prepared by the CVD method were compared with those by the temperature-programmed reaction (TPR). The ratio of the C Is peak of carbidic carbon to the Mo 3d peak of the alumina-supported Molybdenum carbide, prepared by changing the benzene/MoCl 5 ratio, was determined by XPS spectroscopy. The activities of the CVD and TPR catalysts with the C/Mo ratio of Molybdenum Carbides for CO 2 hydrogenation were discussed. The turnover frequencies of the CVD catalysts were 0.347-0.498 s -1 and higher than those of the TPR catalysts.
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hydrogenation of co on Molybdenum and cobalt Molybdenum Carbides
Applied Catalysis A-general, 2012Co-Authors: Hiroyuki Tominaga, Yusuke Aoki, Masatoshi NagaiAbstract:Abstract The DFT calculation of CO hydrogenation was studied based on the reaction of co-adsorbed CO and 2H 2 on β-Mo 2 C(1 0 0) and Co Mo carbide slabs. The hydrogenation of CO occurred on the two carbide slabs; undissociative adsorbed CO reacted with three dissociative H's to successively yield CHO, CH 2 O and CH 2 OH adsorbed on the β-Mo 2 C(1 0 0) slab, while the fourth hydrogen attack produced the adsorbed CH 2 and H 2 O. On the other hand, the Co Mo carbide slab produced the adsorbed CH 3 , O and H through CHO and CH 2 O but not through CH 2 OH. CH 3 OH was not produced on both the β-Mo 2 C(1 0 0) and Co Mo carbide slabs, which corresponded to the mass spectroscopic measurement results of no CH 3 OH formation. Furthermore, electronic structure calculations revealed the CO hydrogenation mechanism. A strong peak of the density of states on the Mo contributes to the CO activation, and the addition of Co increases the number of electrons around this peak position, which improves the CO activation.
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electronic structures of tungsten and Molybdenum Carbides as a fuel cell anode catalyst
Bulletin of the Chemical Society of Japan, 2010Co-Authors: Hiroyuki Tominaga, Masatoshi NagaiAbstract:The band structures of W2C(001), WC(001), β-Mo2C(001), and Pt(111) slabs as an anode catalyst with two adsorbed hydrogen molecules using periodic DFT calculations revealed the anode performance of ...
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steam reforming of ethanol over nickel Molybdenum Carbides for hydrogen production
Catalysis Today, 2009Co-Authors: Yukihiro Miyamoto, Masato Akiyama, Masatoshi NagaiAbstract:Abstract The steam reforming of ethanol over carburized NiMo catalysts was studied to determine the effects of the Ni content, carburization temperature in 20% CH4/H2, GHSV, potassium addition and a comparison of the reduced catalyst. The catalysts were characterized by CO adsorption, XRD, X-ray electron spectroscopy (XPS) and temperature-programmed surface reaction after ethanol adsorption. The 798 K-carburized NiMo catalyst gradually increased below 500 min and it exhibited a higher activity than the reduced NiMo catalyst. The addition of potassium promoted more hydrogen selectivity than the non-potassium-added catalysts. The 798 K-carburized catalyst exhibited the high intensity peaks of MoO2 and small peaks of β-Mo2C and Ni metal (or NiMo) were present, while the 823 K-carburized catalyst showed broad and small peaks. The 873 and 848 K-carburized catalysts contained a strong intensity of β-Mo2C and clear Ni metal (or NiMo). The XPS measurements revealed that the hydrogen production was proportional to Ni0 of the carburized NiMo catalyst. The addition of potassium significantly increases the Ni0 ratio, which was stabilized instead of increasing the Mo oxidation during the reaction.
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cobalt Molybdenum Carbides as anode electrocatalyst for proton exchange membrane fuel cell
Journal of Power Sources, 2008Co-Authors: Shamsul Izhar, Masatoshi NagaiAbstract:Abstract Cobalt Molybdenum (Co-Mo) Carbides were prepared by the carburization of Co-Mo oxides at temperatures of 723–973 K in a stream of CH4/H2 gas. The carburized catalysts were evaluated using a single-stack fuel cell and three-electrode cell. The results showed high activities for the anodic electrooxidation of hydrogen over the Co-Mo catalysts carburized at 873 and 923 K. The 873 K carburized Co-Mo catalyst had the highest activity and achieved 10.9% of the performance of a commercial Pt/C catalyst in a single-stack fuel cell. The XRD, TPC, TPR and XPS results showed that the Co-Mo oxycarbide in the bulk and on the surface are the active species for the hydrogen oxidation reaction.
Gerald Djegamariadassou - One of the best experts on this subject based on the ideXlab platform.
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kinetic study of the hydrodesulfurization of dibenzothiophene over Molybdenum Carbides supported on functionalized carbon black composite influence of indole
Applied Catalysis B-environmental, 2007Co-Authors: A Hynaux, C Sayag, S Suppan, J Trawczynski, Marek Lewandowski, A Szymanskakolasa, Gerald DjegamariadassouAbstract:Different carbon black composite (CBC) supported Molybdenum Carbides were synthesized. The support was functionalized with nitric acid at different pH of the impregnation solution (pH 5.2; 0), in order to improve the active phase dispersion. After characterization of these supported catalysts, the kinetic study of the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was for the first time performed over functionalized CBC supported Molybdenum Carbides. It was found that the HDS of DBT proceeds via the two classical parallel routes: the hydrogenation route (HYD) leading to cyclohexylbenzene and bicyclohexyl and the direct desulfurization route (DDS) leading to biphenyl. In all cases the DDS route was more favored than the HYD route, as well as more inhibited by indole. A global kinetic model suitable for all catalysts is proposed. It could describe all experimental data, and global rate constants were calculated for the HDS of DBT. The corresponding detailed kinetics of the HDS of DBT was also put forward, considering two types of active sites and expressions for the global rate constant could be determined. Furthermore, when the CBC support was preoxidized with HNO3, the dispersion of the Molybdenum carbide active phase was improved and a higher HDS activity was observed both in the absence or in the presence of indole.
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comparative kinetic study of the hydrodenitrogenation of indole over activated carbon black composites cbc supported Molybdenum Carbides
Applied Catalysis A-general, 2004Co-Authors: C Sayag, S Suppan, J Trawczynski, Mersaka Benkhaled, Gerald DjegamariadassouAbstract:Abstract A carbon black composite (CBC) support was synthesized and activated with HNO 3 for three time periods 0.5, 2, 3 h. These samples were impregnated by ammonium heptamolybdate and carburized to prepare the Molybdenum carbide active phase. Characterization of the samples by X-ray diffraction, temperature programmed reaction, CO chemisorption and surface area measurements showed that the HNO 3 treatment of the carbon increased the dispersion of the active phase. This was clearly evidenced by transmission electron microscopy which showed a corresponding decrease in Mo 2 C particle size. The kinetic study of the hydrodenitrogenation of indole demonstrated that the catalyst activity was dependent on the active phase dispersion and the global kinetic order were found to vary between zero and one, depending on the dispersion of the active phase on carbon support.
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deep desulfurization reactions catalysts and technological challenges
Catalysis Today, 2003Co-Authors: M Breysse, Gerald Djegamariadassou, Stephanie Pessayre, Christophe Geantet, Michel Vrinat, G Perot, Marc LemaireAbstract:Very stringent regulation in the maximal S content of gas oil have led to an intense activity of research dealing with all the aspects of desulfurization. The design of future processes is based on the identification of the refractory sulfur compounds and the knowledge of their individual reactivity and in the presence of inhibitors, as illustrated in this paper. This knowledge have oriented the research towards new catalysts such as Molybdenum sulfide supported on zeolites, combination of sulfide and noble metal catalysts, and Molybdenum Carbides. Non-catalytic approaches like charge transfer complex were also examined. This paper summarises these various aspects of desulfurization.
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supported Molybdenum Carbides lie between metallic and sulfided catalysts for deep hds
Catalysis Letters, 2003Co-Authors: P Da Costa, M Breysse, Claude Potvin, Jeanmarie Manoli, Gerald DjegamariadassouAbstract:Hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene on alumina-supported Mo2C has been studied. These catalysts are stable and active under deep HDS conditions (0-250 wt ppm S). However, although they are well known to have hydrogenation properties, they lead preferentially to a non-hydrogenated product of the HDS reaction: dimethylbiphenyl. For the same reaction, supported platinum and sulfided Molybdenum oxide lead to the hydrogenated products dimethyldicyclohexyl and methylcyclohexyltoluene, respectively. The ranking of HDS activity is as follows: MoS2/Al2O3 < Mo2C/Al2O3 < Pt/SiO2.
C Sayag - One of the best experts on this subject based on the ideXlab platform.
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kinetic study of the hydrodesulfurization of dibenzothiophene over Molybdenum Carbides supported on functionalized carbon black composite influence of indole
Applied Catalysis B-environmental, 2007Co-Authors: A Hynaux, C Sayag, S Suppan, J Trawczynski, Marek Lewandowski, A Szymanskakolasa, Gerald DjegamariadassouAbstract:Different carbon black composite (CBC) supported Molybdenum Carbides were synthesized. The support was functionalized with nitric acid at different pH of the impregnation solution (pH 5.2; 0), in order to improve the active phase dispersion. After characterization of these supported catalysts, the kinetic study of the hydrodesulfurization (HDS) of dibenzothiophene (DBT) was for the first time performed over functionalized CBC supported Molybdenum Carbides. It was found that the HDS of DBT proceeds via the two classical parallel routes: the hydrogenation route (HYD) leading to cyclohexylbenzene and bicyclohexyl and the direct desulfurization route (DDS) leading to biphenyl. In all cases the DDS route was more favored than the HYD route, as well as more inhibited by indole. A global kinetic model suitable for all catalysts is proposed. It could describe all experimental data, and global rate constants were calculated for the HDS of DBT. The corresponding detailed kinetics of the HDS of DBT was also put forward, considering two types of active sites and expressions for the global rate constant could be determined. Furthermore, when the CBC support was preoxidized with HNO3, the dispersion of the Molybdenum carbide active phase was improved and a higher HDS activity was observed both in the absence or in the presence of indole.
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comparative kinetic study of the hydrodenitrogenation of indole over activated carbon black composites cbc supported Molybdenum Carbides
Applied Catalysis A-general, 2004Co-Authors: C Sayag, S Suppan, J Trawczynski, Mersaka Benkhaled, Gerald DjegamariadassouAbstract:Abstract A carbon black composite (CBC) support was synthesized and activated with HNO 3 for three time periods 0.5, 2, 3 h. These samples were impregnated by ammonium heptamolybdate and carburized to prepare the Molybdenum carbide active phase. Characterization of the samples by X-ray diffraction, temperature programmed reaction, CO chemisorption and surface area measurements showed that the HNO 3 treatment of the carbon increased the dispersion of the active phase. This was clearly evidenced by transmission electron microscopy which showed a corresponding decrease in Mo 2 C particle size. The kinetic study of the hydrodenitrogenation of indole demonstrated that the catalyst activity was dependent on the active phase dispersion and the global kinetic order were found to vary between zero and one, depending on the dispersion of the active phase on carbon support.
Hiroyuki Tominaga - One of the best experts on this subject based on the ideXlab platform.
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hydrogenation of co on Molybdenum and cobalt Molybdenum Carbides
Applied Catalysis A-general, 2012Co-Authors: Hiroyuki Tominaga, Yusuke Aoki, Masatoshi NagaiAbstract:Abstract The DFT calculation of CO hydrogenation was studied based on the reaction of co-adsorbed CO and 2H 2 on β-Mo 2 C(1 0 0) and Co Mo carbide slabs. The hydrogenation of CO occurred on the two carbide slabs; undissociative adsorbed CO reacted with three dissociative H's to successively yield CHO, CH 2 O and CH 2 OH adsorbed on the β-Mo 2 C(1 0 0) slab, while the fourth hydrogen attack produced the adsorbed CH 2 and H 2 O. On the other hand, the Co Mo carbide slab produced the adsorbed CH 3 , O and H through CHO and CH 2 O but not through CH 2 OH. CH 3 OH was not produced on both the β-Mo 2 C(1 0 0) and Co Mo carbide slabs, which corresponded to the mass spectroscopic measurement results of no CH 3 OH formation. Furthermore, electronic structure calculations revealed the CO hydrogenation mechanism. A strong peak of the density of states on the Mo contributes to the CO activation, and the addition of Co increases the number of electrons around this peak position, which improves the CO activation.
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electronic structures of tungsten and Molybdenum Carbides as a fuel cell anode catalyst
Bulletin of the Chemical Society of Japan, 2010Co-Authors: Hiroyuki Tominaga, Masatoshi NagaiAbstract:The band structures of W2C(001), WC(001), β-Mo2C(001), and Pt(111) slabs as an anode catalyst with two adsorbed hydrogen molecules using periodic DFT calculations revealed the anode performance of ...
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cobalt Molybdenum Carbides surface properties and reactivity for methane decomposition
Applied Catalysis A-general, 2007Co-Authors: Shamsul Izhar, Hiroyuki Kanesugi, Hiroyuki Tominaga, Masatoshi NagaiAbstract:Abstract The methane decomposition over cobalt Molybdenum catalysts (CoMo100-x; x = 0, 25, 50, and 75) carburized at temperatures of 700–973 K was performed using a microreactor at 973 K. The active species for the production of hydrogen during the methane decomposition was studied on the basis of XRD, TPC, TPR, and XPS. The Co50Mo50C-800 catalyst exhibits a higher conversion and hydrogen production rate compared to the Mo100C-, Co25Mo75C-, and Co75Mo25C-800 catalysts. The XRD measurement showed the presence of β-Mo2C and cobalt Molybdenum oxyCarbides in the catalyst before and after 6-h reaction. Cobalt Molybdenum carburized at 800 K produced a surface oxycarbide based on the formation of H2O during the TPC and production of CH4 and H2O during the TPR. The active species of the cobalt Molybdenum carbide catalyst for the CH4 decomposition was the cobalt Molybdenum oxycarbide (Co1.0Mo5.6C0.3O0.7 by XPS analysis) on the surface that was formed during the carburization. The catalyst also exhibited a longer lifetime during methane decomposition.