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 processing. In the first method, sol-gel chemistry (hydrolysis and condensation of metal alkoxides) is performed in alcohol-free inverse micelle, metal cluster solutions. In the second method, metal clusters formed in traditional inverse micelle solutions are allowed to diffuse into preexisting wet monoliths formed using traditional sol-gel techniques. The different materials produced are characterized and compared with respect to particle size and the substrate properties using N-2 porosimetry methods, chemisorption, atomic absorption, 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 dimensions. We conclude that the relative sizes of particles and pores has no clear effect on sintering behavior. Sintering appears to be predominately dependent on metal loading normalized against the support surface area suggesting Ostwald ripening as the sintering mechanism. (C) 1999 Academic Press.