57 Characterisation and modelling of metal deposition in catalytic composite membranes © 2009 Advanced Study Center Co. Ltd. Rev.Adv.Mater.Sci. 21(2009) 57-74 Corresponding author: N. Guilhaume, e-mail: Nolven.Guilhaume@ircelyon.univ-lyon1.fr CHARACTERISATION AND MODELLING OF METAL DEPOSITION IN CATALYTIC COMPOSITE MEMBRANES N. Wehbe 1 , A. Bonilla Sanchez 2 , J.-A. Dalmon 1 , N. Guilhaume 1 , N. Homs 2 , Y. Li 3 , S. Miachon 1 and P. Ramirez de la Piscina 2 1 Institut de Recherches sur la Catalyse et lEnvironnement de Lyon (IRCELYON), UMR 5256 CNRS-Université Claude Bernard Lyon 1, 2 Avenue Albert Einstein, F-69626 Villeurbanne Cédex, France 2 Departament de Qui´mica Inorganica, Universitat de Barcelona, Marti i Franques 1-11, 08028 Barcelona, Spain 3 Present address: School of Materials Science and Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China Received: July 12, 2008 Abstract. A wet impregnation technique based on the evaporation-crystallisation method was used to prepare mono- and bi-metallic catalytic membranes, using Al 2 O 3 or TiO 2 multilayer porous tubes with a top-layer pore size of 5, 10, 25, 30 or 100 nm. The metal deposition was characterized by weight uptakes, chemical analyses, SEM-EDS and XPS analyses. In all tubes with a mesoporous top-layer bearing pores of 5, 10 or 25 nm, whatever the nature of the tube and the impregnation solvent (water or acetone), a strong metal enrichment was evidenced in the top-layer. This enrich- ment was less noticeable in tubes with a 30 or 100 nm top-layer pore size. A mathematical model describing the metal salts deposition during the drying step is proposed. This model is discussed in relation with the physical parameters involved in the drying of complex porous systems. 1. INTRODUCTION Bimetallic catalysts are widely used in the fields of hydrogenation, fine chemistry, selective oxidation and many others. The beneficial presence of a co- metal can be interpreted in terms of geometric (di- lution), electronic, and/or mixed sites effects. Pd-Cu bimetallic catalysts are very active in the catalytic hydrogenation of nitrates in aqueous so- lution. Copper has been identified as the active el- ement for primary nitrates (NO 3 - ) reduction into ni- trites (NO 2 - ) by a redox mechanism, whereas Pd achieves the final reduction of nitrites into N 2 [1]. The Pd/Cu ratio has a decisive effect on activity and selectivity, the optimum atomic ratio being close to 2 [2]. However, the catalytic activity is often lim- ited by diffusion, whereas undesirable NH 4 + can be formed as by-product. In order to improve the ac- tivity and to control the reaction selectivity towards N 2 , catalytic membrane contactors represent a promising alternative to conventional reactors [3]. Similarly, Pd-Zn catalysts have been identified as efficient catalysts for the direct dehydrogenative dimerization of ethanol to produce ethyl acetate in a single step [4], avoiding handling corrosive or toxic reactants. The high activity of the Pd-Zn bimetallic catalyst was related to the formation of an alloyed Pd-Zn phase. Catalytic membrane reactors (CMRs) combine, in the same unit, a conversion effect (catalyst) and a separation effect (membrane). These reactors, beside the obvious interest of coupling two classi-