THE PREPARATION OF HIGH-SURFACE-AREA PT/SIO2 CATALYSTS WITH WELL-DEFINED PORE-SIZE DISTRIBUTIONS

Thermally stable supported metal catalysts can be prepared by matching the metal particle size to the average pore diameter. Preparative variables aimed at achieving this match are presented. In the 3-8 pH range, blank silica gels prepared using tetraethoxysilane (TEOS) were observed to have BET surface areas of 350-800 m(2)/g and mesoporous structures with an average pore diameter of between 4 and 25 nn at a constant H2O/TEOS ratio of 10. Silica aerogels have comparable BET surface areas, larger pore diameters, and pore volumes than xerogels. In the case of supported Pt catalysts prepared by sol-gel synthesis, the effect of preparative variables, including metal precursor, metal loading, reactant stoichiometries, and solvent removal, have been studied. The use of Pt(AcAc)(2) resulted in average pore diameters which could be varied in the 4-20-nm range by adjusting the H2O/ TEOS ratio during synthesis. BET surface areas in the 500-800 m(2)/g and metal dispersions of 50-85% can be achieved. The H-2/n-hexane reaction was studied on these catalysts. Catalytic activities were found to be comparable or slightly superior to supported metal catalysts prepared by traditional methods. (C) 1995 Academic Press, Inc.