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 sol–gel processing. Tetraethoxysilane (TEOS) was used as the support precursor 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 volume 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. Designed metal loading was varied from 0.5 to 1.5 wt%. Dried gels were probed using 29Si Solid state MAS NMR, and the relative amount of partially and fully condensed (Q2, Q3, Q4) silicon centers was quantified. As the metal loading was increased, the gels became more fully condensed. Silica prepared at a pH of about 8 showed a significant increase in the degree of condensation regardless of the rhodium content.