A new approach of selective Ge deposition for RhGe/Al₂O₃ catalysts: characterisation and testing in 2,2,3-trimethylbutane hydrogenolysis

A series of Rh monometallic and RhGe/Al2O3 catalysts was prepared in a dynamic reactor by anchoring Ge(n-C4H9)(4) on Rh surface, containing preadsorbed hydrogen and by subsequent hydrogenolysis of the surface organometallic complexes. Different amounts of organometallic Ge compound were introduced, corresponding nominally to 1/20, 1/2, 2 Ge monolayers. The samples were characterized by FTIR of CO, transmission electron microscopy (TEM), hydrogen chemisorption and hydrogenolysis of 2,2,3-trimethylbutane (223TMB) as a test reaction. Hydrogen chemisorption and TEM results are consistent with (i) the effect of preparation procedure on the morphology of the monometallic sample, (ii) the surface deposition of Ge on Rh particles. Concerning the effect of preparation, the grafting procedure led for blank experiments (Ge-free catalysts) to a slight sintering which can be avoided by Ge anchoring. On the other hand, we used the relative normalized intensities of linear and bridged CO species of FTIR measurements to identify the location of Ge deposits. The amount of the Ge compound introduced had a pronounced effect on the final landing position of Ge. Excess Ge(n-C4H9)(4) resulted in a statistical deposition on the surface of Rh or a slight diffusion in Rh lattice, while low-Miller-index microfacets were preferentially occupied when the amount of tetra-n-butylgermanium was markedly lower than that for monolayer coverage. The presence of quaternary carbon atom in the reactant molecule (223TMB) induced changes in the chemisorption geometry deduced from the shift of maximum activity towards lower p(H-2). In the wide negative hydrogen order region breaking of C-C bonds can be the slowest step. Low-Miller-index microfacets of Rh particles may be active in multiple C-C bond cleavage during one residence time of the reactant molecule

Study of effect of chromium on titanium dioxide phase transformation

International audienceMTiX samples with different atomic chromium percentages were synthesized by sol gel method and calcined at 400 degrees C under air. The effects of Cr and temperature on titanium dioxide phase transition were studied. In situ measurement showed the presence of anatase phase for all samples at temperature <500 degrees C. Without Cr content, the anatase rutile transition takes place at 600 degrees C and the rutile fraction increases with increase of temperature. In the presence of Cr content, rutile phase appeared at 700 degrees C. Cr2O3 phase was shown only in the case of CrTi20 content at 800 degrees C which indicates that the segregation remains modest. We have also studied the anatase rutile transition kinetics by using in situ X-ray measurements. It was found that the anatase phase stability increases as the chromium content increases. Results confirm that the transformation of anatase rutile is of first order

Preparation and characterization of MTiX for the catalytic oxidation of cyclohexane

International audienceMTiX (M = Cr and V) samples, with 0, 5, 10 and 20 atomic percent, were synthesised by a sol-gel method and calcined at 400 degrees C in air. The XRD analysis results indicated that the materials presented a crystalline structure with the presence of TiO2 anatase forms. BET analysis showed that the surface area varied with the variation of metal content. EDX analysis showed a heterogeneous distribution of samples. The results of pyridine adsorption followed by FT-IR indicated that Bronsted and Lewis acid sites are present on the surface of catalysts. Liquid phase oxidation of cyclohexane was carried out under milder reaction conditions over MTiX catalysts using tert-butyl hydroperoxide (TBHP) as oxidant, acetic acid and acetonitrile as solvents. The results indicated that conversion depends on metal content and solvent polarity. Chromium is selective for cyclohexanol. The best result was obtained with VTi20 with 35% of conversion and 92% of olone selectivity

Synthesis, characterization and activity in cyclohexene epoxidation of V2O5-TiO2 anatase xerogel

International audienceThe system of V2O5-TiO2 catalysts with V2O5 contents from 5 to 20 wt% were prepared by the sol-gel route and calcined at 500 A degrees C. The mixed oxide series presented the crystalline structure of TiO2 anatase phase. BET analysis showed a medium surface area decreasing from 73 to 19 m(2) g(-1) when V2O5 content rose from 5 to 20 wt%. The results of pyridine adsorption followed by FT-IR indicate that the catalysts display identical surface acid densities, independently of the V2O5 content, and both Bronsted and Lewis acid sites are present on their surfaces. The V2O5 system presents an activity and selectivity during the cyclohexene oxidation reaction. The presence of V2O5 increases the catalyst efficiency and leads to a selectivity change from cyclohexenol (blank test) to epoxide, with a maximum for 15 wt% V2O5. The conversion of cyclohexene was 46 % while the selectivity to epoxide was higher (75 %)

Oxygen Storage Capacity of Pt-CeO2 and Pt-Ce0.5Zr0.5O2 Catalysts

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Modification by sulfur of automotive exhaust catalysts: effects of the preparation procedure of the catalysts

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Influence of the redox properties of ceria on the preparation of three-way automotive platinum—rhodium/ alumina—ceria catalysts

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