Tailor-made morphologies for Pd/SiO 2 catalysts through sol–gel process with various silylated ligands

Abstract

With the aim of obtaining highly dispersed, immobilized and accessible catalytically active palladium nanoparticles in a silica support with a tailored morphology, a sol–gel cogelation method is developed. Pd/SiO 2 catalysts are synthesized in ethanol by concomitant hydrolysis and condensation, i.e. cogelation, of a Pd 2+[L–X–Si(OR) 3] n complex with Si(OC 2H 5) 4 (TEOS) as network-forming reagent followed by calcinations in air and by reductions of the resulting xerogel catalysts in hydrogen. By varying the nature of L, X and R in the Pd 2+ complex, the purpose of the present work is to determine the influence of the nature of the L–X–Si(OR) 3 ligand on textural properties of silica and on palladium dispersion in Pd/SiO 2 catalysts. By changing the molecular weight of L–X– and thus its bulkiness of L and X, it is observed that with bulkier silylated ligand, the textural properties of resulting gels are strongly modified from micro- and macroporous materials to very highly micro- and mesoporous materials. In the latter ones, the size of silica particles is smaller and their void fraction is very high. In such a case, palladium particles are not trapped inside silica particles and are then able to migrate and to sinter. The Pd/SiO 2 xerogel catalysts were evaluated in the hydrodechlorination of 1,2-dichloroethane.