Nucleation phenomenon in silica xerogels and Pd/SiO2, Ag/SiO2, Cu/SiO2 cogelled catalysts

Pd/SiO2, Ag/SiO2 and Cu/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Pd, Ag and Cu with 3-(2-aminoethylamino) propyltrimethoxysilane (EDAS). It appears that, in cogelled samples, the metal complex acts as a nucleation agent in the formation of silica particles. The resulting catalysts are then composed of completely accessible metallic crystallites with a diameter of about 3 nm located inside silica porous particles with a monodisperse microporous distribution. Xerogels without metal synthesized with EDAS and TEOS (C. Alie, R. Pirard, A. J. Lecloux, and J.-P. Pirard, J. Non-Cryst. Solids 289, 88 (2001)) verify this hypothesis of nucleation by EDAS.