Nucleation Phenomenon in Silica Xerogels and Pd/SiO_2,Ag/SiO_2,Cu/SiO_2 Cogelled Catalysts

摘要

Pd/SiO_2,Ag/SiO_2 and Cu/SiO_2 xerogel catalysts have been synthesized by cogelation of tetraethoxysi-lane (TEOS) and chelates of Pd,Ag and Cu with 3-(2-aminoethylamino)propylrimethoxysilane(EDAS).It appears that,in cogelled samples,the metal comples acts as a nucleation agent in the firmation 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 synthe-sized 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.