In this paper, we describe the characterization and catalytic properties of mesoporous silica supported Cs-substituted tungstophosphoric acid salt (Cs-TPA/MS) with improved dispersion of the active clusters compared to materials described previously in the literature. In particular, transmission electron micrographs and the activity results for a model alkylation reaction are presented as evidence for the enhanced dispersion and performance. In addition, we demonstrate improvements in the physical and thermal stability of these materials with Cs-substitution using various characterization techniques. (C)2000 Elsevier Science B.V. All rights reserved.