Blaise Didillon

Pd–Sn/Al2O3 catalysts from colloidal oxide synthesis: II. Surface characterization and catalytic properties for buta-1,3-diene selective hydrogenation

Abstract Surface and catalytic properties of alumina-supported bimetallic Pd–Sn catalysts prepared via a colloidal oxide synthesis have been studied. In-depth characterization of the supported metallic particles has been performed by techniques such as XPS, FTIR(CO), or LEIS, indicating a strong surface enrichment by Sn and suggesting a modification of the electronic properties of Pd ensembles. EXAFS results also demonstrate the core shell structure of the supported particles in agreement with our previous study of the oxidation state of tin species by 119 Sn Mossbauer spectroscopy. This in-depth characterization of the bimetallic catalysts allows us to demonstrate the influence of both Pd x Sn y alloy formation and particle aggregation state on the selectivity of buta-1,3-diene hydrogenation.

Surface organometallic chemistry on metals in water : Chemical modification of platinum catalyst surface by reaction with hydrosoluble organotin complexes : application to the selective dehydrogenation of isobutane to isobutene

Abstract Surface organo-metallic chemistry on metals can be a new route to generate supported bimetallic catalysts. According to previous works on Pt–Sn catalysts, the reaction of tetra n-butyl-tin on the reduced platinum surface leads to well-defined bimetallic catalysts which are very active and selective in the dehydrogenation of isobutane into isobutene. The presence of tin not only isolates the surface platinum atoms from each other (EXAFS) and thus prevents a fast deactivation by decreasing the processes of C–C bond cleavage but also favors the regeneration processes under air. So far the catalyst preparations were carried out either in the gas phase or in organic solution (e.g. heptane). However, in order to meet the industrial criteria of process simplicity, there is a need to carry out such catalyst preparation in water. In this work, Pt–Sn/Al2O3 and Pt–Sn/SiO2 catalysts was prepared by reacting tris n-butyl-tin hydroxide on the platinum surface, in water solution under atmospheric pressure of hydrogen. The kinetics of the reaction was followed by measuring the amount of butane evolved as a function of time. The solids obtained were characterized by CO, O2 or H2 chemisorption and electron microscopy (CTEM and EDAX). Clearly, the (n-Bu)3Sn(OH) reacts selectively on the platinum surface and not with the support, with evolution of butane, leading to a bimetallic catalyst where the platinum atoms are isolated from each other by the tin atoms. Very high selectivities (>95%) and activities were obtained for the reaction of isobutane dehydrogenation into isobutene and it was concluded that surface organo-metallic chemistry on metal in water can be an alternative route to prepare well-defined supported bimetallic Pt–Sn catalysts.

Pd–Sn/Al2O3 catalysts from colloidal oxide synthesis: I. Preparation of the catalysts

Abstract Colloidal oxide synthesis is a new technique for the preparation of bimetallic supported particles which provides the opportunity to control particle size distribution and interaction between both metals. It consists in synthesizing in aqueous medium a sol of colloidal oxide Pd–Sn nanoparticles which is further deposited onto a porous support. In this work, this method has been applied to the preparation of Pd–Sn/Al2O3 dedicated to the selective hydrogenation of unsaturated hydrocarbons. Two synthesis routes, surface precipitation and surface adsorption, are described to demonstrate the potential of colloidal oxide chemistry to generate a bimetallic interaction in aqueous solution which is strengthened during the reduction step after deposition onto alumina. 119Sn Mossbauer spectroscopy (119Sn MS) and transmission electron microscopy (TEM) were used to characterize the sols and the supported catalysts. This allowed us to determine the key parameters of colloidal oxide synthesis as far as formation of bimetallic PdxSny phases is concerned.