The reducibility of sulfate species by CO was studied over ceria and Ce0.63Zr0.37O2 mixed oxide with or without platinum, using infrared spectroscopy and thermogravimetry. The mechanism for sulfate reduction appeared to be based on three main points. Firstly, the exchange between surface and bulk-like sulfate species is required. The sulfate reduction indeed occurs at the oxide surface and bulk-like species need to migrate toward the surface to be further reduced. Secondly, it was observed that surface sulfate species are more easily reduced by CO on the reduced oxide. Therefore, platinum loading which favors the oxide reduction, also favors the sulfate reduction by CO. Finally, the reduction of sulfated Pt-free samples occurs in only one step, which is linked to the own reducibility of the surface sulfate species, probably through a direct interaction with CO. The amount of sulfur stored from sulfate reduction with CO is markedly more important than the one detected from reduction with H2. Furthermore, the oxygen storage capacity (OSC) for sulfated samples is higher than the one for sulfate-free samples. This is tentatively explained by the partial replacement of oxygen by sulfur atoms in the compound lattice.

The catalyst 1 wt% Rh supported on ZrO2(73.8 wt%)-La2O3-Nd2O3-Y2O3(26.2 wt%) was tested for the reforming of exhaust gas recirculation (REGR) on gasoline engines. Isooctane (C8H18) was used as molecule representative of gasoline, and N-2, H2O, CO2 and O-2 were used as model exhaust gas. Despite the moderate C8H18 conversion (58-70%) and a slight initial deactivation, good stability and activity were obtained even after hydrothermal treatment of the catalyst, leading to a gas phase composition close to thermodynamic equilibrium. The volume proportion of H-2 produced in the gas phase achieved 14% which is consistent with the sake of the application.The high hydrogen yield was linked to the very low methane production. C8H18 steam reforming (SR) and C8H18 dry reforming (DR) reactions in REGR conditions were also studied. The presence of CO2 decreased the H-2 yield expected with respect to SR reaction. A suitable model based on experimental isooctane conversion and thermodynamic calculations predicted this result. (C) 2010 Elsevier B.V. All rights reserved.

The nature, concentration and reducibility by H2 of sulfate species formed from SO2 oxidation were studied over a range of Pt/CexZr1−xO2 catalysts using infrared spectroscopy and thermogravimetry. Ionic sulfates were formed over ceria and Ce-containing catalysts, even at high Zr content. The sample-specific surface area, the presence of platinum and the zirconium proportion affected the rate and extent of formation of sulfate in the bulk of the materials. Sulfate reduction by H2 first occurred at the CexZr1−xO2 surface. Bulk-like S-containing species subsequently migrated towards the surface to continuously replace surface sulfates removed by the reduction. The temperature required for sulfate migration as well as that necessary for sulfate reduction increased with the Zr content. The amount of stored sulfur is closely linked to the specific surface area of the sample. Finally, we have clearly shown that thermogravimetry was an appropriate technique for evaluating the oxygen storage capacity (OSC) of sulfated ceria–zirconia mixed oxides, despite the additional complexity due to the presence of sulfate compounds and various reduced S-species that can be formed during sample reduction.

In the field of hydrotreating (HDT) catalysis, density functional theory (DFT) calculations are of great help to explore new active phases on the basis of volcano curve relationships correlating HDT activities and the sulfur–metal (S–M) bond energy chemical descriptor, calculated in transition metal sulfides catalysts. In the present study, we synthesize Mo1−xWxS2 solid solutions supported on γ-alumina. For non-promoted systems, the catalytic tests reveal that a continuous and linear evolution of the catalytic activity is obtained for solid solutions for x varying between 0 and 1. As expected from the calculated S–M bond energy values, no synergy effect is observed in that case. For Ni and Co promoted Mo1−xWxS2 active phases (ternary metal sulfides), the S–M bond energy values determined with an interpolation model of the binary sulfides predict that NiMo1−xWxS2 phases should be more active than NiMoS and NiWS ones. In contrast, CoMo1−xWxS2 phases are expected to develop weak synergetical effect with respect to CoMoS and CoWS ones. Experiments performed on Co and Ni promoted Mo1−xWxS2 active phases confirmed the DFT-volcano curve prediction and an increment of about 30% in HDS catalytic activity is obtained for NiMo0.5W0.5S catalysts in both model molecule conversion and gas oil treatment.

Operando measurements were carried out in a quartz reactor to evaluate the catalytic performance of NOx storage and reduction materials containing Pt and Ba supported on Al2O3. Carbonates present on the surface after activation were removed after the first exposure of the sample to the nitration flow. Nitrite species bound to barium were observed at low temperatures. Barium nitrates are the predominant species in the studied temperature range under wet and dry conditions. These species are not stable at temperatures above 723K. The presence of water inhibits the formation of alumina nitrates favoring the coordination of nitrates with the barium sites.

Synchrotron and Neutron Solutions to Oil Industry ProblemBulk and alumina-supported Mo0.5 W0.5 S2 compounds were prepared. The presence of both molybdenum and tungsten in every [MS2 ] layer (intralayer solid solution) was evidenced using EXAFS spectroscopy, the only local method which can provide such relevant structural information. The catalytic interest of such solid solution is to provide a continuous variation of M-S bond strength which is considered as the key parameter of the catalytic activity transition metal sulfides. The solid solution is maintained after promotion by Ni either on unsupported or supported state.

Heteropolyanions (HPAs) based on molybdenum and cobalt could be used as an alternative to the conventional ammonium heptamolybdate and cobalt nitrate precursors for the preparation of Co-Mo/Al2O3 hydrotreating catalysts. With this objective in mind, a cobalt salt of decamolybdocobaltate anion has been synthesized. This salt allows us to prepare catalyst with a Co/Mo atomic ratio of 0.5 corresponding to the optimum value encountered with classical catalyst preparation. The crystal structure refinement has been performed and reveals the formation of a new heteropolyoxomolybdate related to the well-known Anderson structure. Its structural, spectroscopic, and thermal properties have been investigated by physical techniques such as thermogravimetric analysis mass spectroscopy, X-ray diffraction, X-ray absorption spectroscopy, and vibrational spectroscopy. With the use of this new HPA precursor, initial catalytic results show a significant improvement of hydrodesulfurization catalytic performance.

This study is aimed at using and identifying Al- and Co-containing Anderson-type heteropolyanions in the synthesis of (Co)Mo/alumina and (Co)Mo/zeolite HDS catalysts oxidic precursors. Various techniques such as Raman spectroscopy, NMR and EXAFS are used to show the apparition of the AlMo6O24H63- entity upon impregnation of an alumina or a zeolite with an ammonium heptamolybdate solution. The question of the Mo-Co interaction in the promoted precursors is also tackled through the use of the CoMo6O24H63- entity.

WxMo(1−x)S2 compounds with both molybdenum and tungsten present in every disulfide layer, i.e., as an intralayer solid solution, can be obtained. Several synthesis routes have been used but all of them do not allow this solid solution, which evidences the decisive role of the nature of the precursor, to be obtained. We never observed formation of a WxMo(1−x)S2 solid solution resulting from stacking of homocationic [WS2] and [MoS2] layers (interlayer solid solution).

NiMo/Al2O3 (sulfided and oxide) catalysts were coked in an autoclaves reactor at 400°C with anthracene as a precursor of coke. When the carbon content increased, the specific surface and the pore volume decreased. This corresponds to a partial blockage of the catalyst pores. The presence of dimetnyldisulfide (DMDS) promoted the coke formation on the catalyst surface. The formation of CH3S radicals from the decomposition of DMDS could promote the polycondensation of anthracene.

By means of 27Al triple quantum Magic-Angle Spinning Nuclear Magnetic Resonance (3QMAS NMR) and 27Al{19F} WISE MAS NMR, we were able to detect three different AlF sites on the surface of fluorinated γ-alumina. Three 19F resonances at 9, 20, and 33 ppm (from C6F6) correlated to 27Al resonances in the octahedral range. While the positions of the maxima in the 27Al dimension were ill-defined due to the inherently low efficiency of the 27Al{19F} CPMAS process, the center of gravity of the lines shifted significantly upfield in that dimension with increasing wt.% F. Tentatively, these three resonances were assigned to VIAl(O6−nFn) (n=1, 2, 3) environments on the F/γ-Al2O3 surface. At F contents above levels corresponding to the full fluorination of the γ-Al2O3 surface, neoformation of an AlF3·3H2O phase was also evidenced with an 19F resonance at −8 ppm and with an 27Al resonance at −17 ppm.

Ortho-xylene was hydrogenated at 300 degrees C under 60 bar total pressure over sulphided Ni, Mo and NiMo alumina catalysts. Among the 1,2-dimethylcyclohexanes formed, the ratio of the stereoisomers cis/trans was found to be sensitive to the electronic state of the catalysts' active sites. Applied to a series of NiMo catalysts containing increasing amounts of nickel, the reaction suggests a successive decoration of MoS(2) slabs with the promoter. Hydrogenation of ortho-xylene is a powerful new method for probing electronic effects specifically on active sites of sulphide catalysts under typical hydrotreating conditions.

Sulfided NiMo/Al2O3 catalyst was coked in an autoclave reactor at 440 degrees C with pur anthracene to give catalysts containing 1-20 wt% C. After Toluene extraction, physical properties and catalytic activities using model compounds (phenanthrene, 4,6-dimethyldibenzothiophene and 1,2,3,4-tetrahydroquinoline) for hydrogenation (HYD), hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) were measured on the coked catalysts. All the physical properties (BET, pore volume) decreased when the coke content increased, which corresponds to a partial blockage of the catalyst pores.All the catalytic activities in the various hydrotreating reactions (HYD, HDN and HDS) decreased when the coke content increased. An order of deactivation was able to be established : HDN > HDS approximate to HYD.

Molybdenum and cobalt-molybdenum catalysts have been prepared over Al2O3 and a TiO2-Al2O3 mixed oxide in order to get more insight on the relation between the nature of the support and the promoting effect of cobalt. These catalysts were characterized by UV-visible diffuse reflectance spectroscopy (DRS), analyzed by energy dispersive spectroscopy (EDS) and evaluated in dibenzothiophene hydrodesulfurization. For the unpromoted catalysts, the Mo/TiO2-Al2O3 sample presented a very high activity as compared to the Mo/Al2O3 catalyst. However, over the titania based support a limited activity enhancement by Co promotion was observed. Such a drawback of the TiO2-Al2O3 support was correlated to a large amount of cobalt involved in the formation of CoMoO4; moreover, variations observed in the stability of the sulfide phase support these explanations.