R. Hubaut

Catalytic properties of bismuth vanadates based catalysts in oxidative coupling of methane and oxidative dehydrogenation of propane

The oxidative coupling of methane (OCM) and the oxidative dehydrogenation of propane (ODHP) have been performed on new mixed Bi-V oxides having a -γ-Bi2MoO6-like structure. The results yield a correlation between the methane conversion and the oxygen diffusivity. The introduction of metals (Fe, Cu, Sr with 10 mol%) improves the C2 selectivity. The use of an oxide with a scheelite structure (BiVO4) shows that, under catalytic conditions, this oxide has the same behaviour as the above solids.

Silica and alumina impregnated with dimethylformamide solutions of molybdophosphoric or tungstophosphoric acids for hydrotreatment reactions

Heteropolyacid (HPA) based catalysts were prepared by impregnation of silica and alumina with dimethylformamide solutions of molybdophosphoric and tungstophosphoric acids. This solvent allows the preservation of the Keggin unit during the impregnation independently of the nature of the support. Ni-promoted catalysts were prepared by impregnation with nickel nitrate solutions of the supported HPA. The stronger interaction of the HPA with alumina than with silica allows a better dispersion of the polyoxometallate species on the former one whereas the formation of bulk oxides is observed on silica. The performance of these HPA–Ni/support catalysts for hydrodenitrogenation and hydrodesulfurization reactions is related to the precursor–support interaction.

X-ray photoelectron spectroscopy and infrared spectroscopy studies for the mechanism of the enantioselective hydrogenation of methyl acetoacetate over mixed nickel-cerium oxides

Abstract Mixed nickel cerium oxides have been used for studying the enantioselective hydrogenation of methyl acetoacetate (MAA) in methyl (3)-hydroxybutyrate (MHB). X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR) provide interesting information about the adsorption of both the reagent and the modifying agent (viz: tartaric acid). From the XPS results, we can assume that the presence of Ce3+ species, the amount of which is depending on the Nickel extent, stabilises a complex tartarate salt. The whole information lead to a new model with a stable six-membered cycle, in which the methylenic group of the reagent is involved.

Comparative Study of the Acidity of Sulphated Zirconia Supported on Alumina Prepared by Sol-Gel and Impregnation Methods

Sulphated and unsulphated alumina-zirconia with atomic ratio Zr/Al = 0.5 were prepared by sol-gel and impregnation methods. The solid prepared by the sol-gel method exhibits the higher specific surface area. The Kelvin probe shows that the value of unsulphated sample is around 400 mV. This value grows up to 1100 mV for sample prepared by impregnation of aerogel alumina by sulphated propoxide zirconium and up to 1450 mV for sulphated alumina-zirconia aerogel catalyst. The modification of the work function is probably due to the charge transfer from the zirconium and aluminium to an oxygen species, responsible for the increase of Lewis acidity. XPS results show that the aluminium and zirconium exist in oxide form as Al2O3 and ZrO2. The sulphur is present as sulphate species in the solids bonded to the Al—Zr—O framework. Furthermore, the oxygen species exist in different types created by the introduction of sulphur in the bulk of solids.Compared to the impregnated catalyst the sol-gel sulphated alumina zirconia exhibits higher activity in the isopropanol dehydration reaction in the temperature range 423 K–523 K.

HDS of Dibenzothiophene and Vanadyl Porphyrin HDP on bulk Fe-Mo mixed sulphides

Abstract Bulk Fe-Mo mixed sulphides were prepared by homogeneous precipitation. The obtained solids were characterised by chemical analysis, X-ray diffraction, X-ray photoelectron spectroscopy, 57 Fe Mossbauer spectroscopy, and nitrogen adsorption (BET) for surface area determinations. HDS of dibenzothophene (in a batch reactor) and HDP of vanadyl octaethyl porphyrin, at high pressure, were used as catalytic tests. It was found that Fe strongly promotes Mo for both reactions, with a more marked synergy for the HDP than for the HDS. 57 Fe Mossbauer spectroscopy suggests that Fe exist in only one phase, for the mixed Fe-Mo sulphides. This phase could be the results of some Fe substitution in the MoS 2 structure. For HDP the activity is maximum at a Fe(Fe+Mo) atomic ratio of 0.68, and increases linearly with the weighted average hyperfine field, which is related to changes in the density of states of d electrons at the Fermi level, clearly suggesting that synergy is related to an electronic effect. For HDS of DBT the activity maximum is located at a Fe/(Fe+Mo) atomic ratio of 0.52.

Hydrotreating on mixed vanadium-nickel sulphides : A study of the synergetic effect

Abstract The preparations of pure and mixed vanadium–nickel sulphides were carried out by the homogeneous precipitation method (under inert atmosphere). Thiophene HDS, pyridine HDN, toluene hydrogenation and vanadyl porphyrin HDP, were carried out as catalytic tests. The catalysts were also characterized by XPS, TPR, BET surface area and XRD. These solids, after sulphidation procedure, exhibit a synergetic effect, the importance of which depends on the hydrotreating reaction. The product distributions obtained in the thiophene hydrodesulphurization and the pyridine hydrodenitrogenation and the activity observed for toluene hydrogenation suggest that the synergy is mainly related to the hydrogenation step. The cause of this synergy could tentatively be assigned to an electronic transfer between the two metallic components in the mixed sulphides.

Surface characterization of bulk Fe–Mo mixed sulphide catalysts

Abstract Difference of work function potential measurements and X-ray photoelectron spectroscopy (XPS) were used to characterize bulk Fe–Mo mixed sulphides. Thiophene hydrodesulphurization (HDS) and toluene hydrogenation (HYD), at high pressure, were used as catalytic tests. A clear synergetic effect is observed for both reactions. According to difference of work function potential values, mixed sulphides are not a mixture of Mo and Fe sulphides but rather Fe–Mo bimetallic sulphides. They also suggest electron enrichment around the Fe atom for mixed sulphides.

Catalytic methane combustion over alumina supported palladium catalysts prepared by sol-gel method: investigation of the activity evolution

In this work, The evolution of activity for methane combustion with time on stream is studied on different alumina supported palladium catalysts (SG, SGI and Imp). The textural and the structural properties of the studied catalysts are characterised by nitrogen physisorption, hydrogen chemisorption, transmission electron microscopy (TEM) and XPS measurements in-situ.

Isomerization of n-Hexane over Silica-Supported Heteropolyoxometallates Promoted by Pt-Ce Oxides

Abstract Catalysts based on Keggin-type heteropolyacids and reduced Pt-Ce oxides supported on silica were prepared for their use in isomerization of n-hexane in the presence of hydrogen. These mixed oxides are either used alone or mixed with silica-supported heteropolyacids. The catalyst after oxidation, reduction, and catalytic tests was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Fourier transform Raman, thermogravimetry, and N 2 adsorption. The objective of the present study is to select the catalyst having the best isomer (branched) yield under optimal operating conditions (reaction temperature, reduction temperature, flow duration, etc.). The results show that the presence of the reduced oxides is not only beneficial for eliminating coke position but also effective for maintaining the structure of silica-supported heteropolyacids during reaction. Moreover, the better activity and the higher selectivity for isomers can be found with these samples.

Silica-Supported Heteropoly Acids Promoted by Pt/Al2O3 for the Isomerization of n-Hexane

Silica-supported heteropoly acids promoted by Pt/Al2O3 present efficient catalytic activity for the isomerization of n-hexane, and among them 50 wt% HSiW/SiO2 promoted by Pt/Al2O3 shows the best catalytic performance, which might be closely related to the maintenance of the surface structure of heteropoly acids during reaction.