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 O 2 as well as with H 2 S and CO prove. The dissociation of O 2 on small Ag clusters is favored, and the proportion of O 2 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.