A sintering study of novel sol-gel-based nanocluster catalysts

We introduce two novel synthesis strategies to make nanoclusters on silica and alumina supports using inverse micelle technology and sol-gel processin g. In the first method, sol-gel chemistry (hydrolysis and condensation of m etal alkoxides) is performed in alcohol-free inverse micelle, metal cluster solutions. In the second method, metal clusters formed in traditional inve rse micelle solutions are allowed to diffuse into preexisting wet monoliths formed using traditional sol-gel techniques. The different materials produ ced are characterized and compared with respect to particle size and the su bstrate properties using N-2 porosimetry methods, chemisorption, atomic abs orption, and transmission electron microscopy. The effect of calcination on particle and support stability is determined and discussed in terms of the metal coverage and the relationship between particle size and pore dimensi ons. We conclude that the relative sizes of particles and pores has no clea r effect on sintering behavior. Sintering appears to be predominately depen dent on metal loading normalized against the support surface area suggestin g Ostwald ripening as the sintering mechanism. (C) 1999 Academic Press.