Synergy in Catalytic Reactions Involving Hydrogen: Possible Role of Surface-Mobile Species

This chapter provides evidence for the role that surface-mobile hydrogen plays in various heterogeneously catalyzed react ions where synergy occurs. The reactions of spill-over hydrogen with organic molecules or inorganic solids are considered. The chapter shows that spill-over hydrogen can have important effects on activity, selectivity, and deactivation of heterogeneous catalysts, surveys the synergistic effects in catalyzed reactions involving hydrogen and discusses the possible origins of synergy. The possible mechanisms involving surface-mobile species and how these species might change the activity and selectivity of catalysts are discussed. Synergy in hydrogenation and in other reactions involving hydrogen is considered. The chapter describes how synergy may develop in various catalytic systems, including: (1) classical bifunctional catalysis; (2) synergy through the formation of compounds between two phases acting synergistically; (3) contamination of the surface of one phase by elements from another; (4) react ion of spill-over hydrogen, produced on one phase, with a reactant adsorbed on another phase; and (5) the “remote control” concept—that is, creation or regeneration of active centers on one phase by spill-over hydrogen emitted by the other phase.