Stephan Verdier

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.

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.

Synthesis of Palladium-Based Supported Catalysts by Colloidal Oxide Chemistry

In the field of heterogeneous catalysis, the control of the characteristics of supported particles is one of the main objectives of all researchers who want to establish relationships between structure and reactivity. Catalysts with the same macroscopic composition may exhibit very different catalytic performances because of large variations of the active site properties at the nanometer scale. Because of the structure sensitive nature of most of the phenomena involved in heterogeneous catalysis, future improvements of heterogeneous catalysts, in terms of reaction rate, selectivity, stability in operation or sensitivity to poisons, will necessarily be obtained through the nanoscaled control of the physical and chemical characteristics of active sites. For this purpose, many sophisticated preparation methods have been explored including controlled surface reactions such as redox reactions, electrochemical methods, and surface grafting or physical techniques such as vapor deposition of metallic precursors. Chemical methods to prepare supported heterogeneous catalysts generally use the different possible