RH SIO2 CATALYSTS PREPARED BY THE SOL-GEL METHOD/

A series of Rh/SiO2 catalysts were prepared by the sol-gel method. The precursors used were tetraethoxysilane (TEOS) dissolved in ethanol an d rhodium(III) acetylacetonate dissolved in acetone. Preparative varia bles include the amount of water added to the sol and the gelation tem perature. Typical BET surface areas were 550-700 m(2) g(-1) with very narrow pore size distributions centered at approximately 4 nm. Sample characterization studies were performed using TGA-DTA-MS to determine the effect of O-2 pretreatment and Si-29 solid-state NMR to determine the extent to which silica was condensed. Sintering studies of Rh/SiO2 catalysts for which there was a reasonable match between metal partic le size and pore diameter were performed. Catalysts prepared by ion-ex change having comparable dispersions to those prepared by the sol-gel method also showed considerable resistance to sintering in O-2. Follow ing heat treatment in O-2 at 650 degrees C, the particle size distribu tion of catalysts prepared by ion-exchange appear to broaden to a grea ter extent than catalysts prepared by the sol-gel method. This suggest s that the sol-gel preparation is more effective in retaining the meta l particles within the narrow pores of the support. (C) 1997 Elsevier Science B.V.