Dependence of the Reactivity of Ag and Ni Clusters Deposited on Solid Substrates on the Cluster Size

Bulk silver and nickel are less reactive than small clusters of these elements, as reactivity studies with O2 as well as with H2S and CO prove. The dissociation of O2 on small Ag clusters is favored, and the proportion of O2 molecules cleaved does not depend upon temperature, as is the case for larger clusters and silver metal. The change in reactivity is greatest at the metal–insulator transition—a finding that has implications for heterogeneous catalysis.