The effect of pH and metal loading on the properties of sol-gel Rh/SiO2

Rh/SiO2, to be used as a potential catalytic material, was prepared using s ol-gel processing. Tetraethoxysilane (TEOS) was used as the support precurs or and Rh(acac)(3) was used as the metal precursor, Nitrogen full-sorption was used to determine surface area, average pore size, and total pore volum e of the support, while hydrogen chemisorption and electron microscopy were used to determine metal particle size, Samples prepared at a pH of about 3 had a high metal dispersion and well-defined pore size distribution. Desig ned metal loading was varied from 0.5 to 1.5wt%. Dried gels were probed usi ng Si-29 Solid state MASNMR, and the relative amount of partially and fully condensed (Q(2), Q(3), Q(4)) silicon centers was quantified, As the metal loading was increased, the gels became more fully condensed. Silica prepare d at a pH of about 8 showed a significant increase in the degree of condens ation regardless of the rhodium content, (C) 2001 Academic Press.