Specificity in Catalytic Hydrogenolysis by Metals

Hydrogenolysis reactions of hydrocarbons involve the rupture of carbon–carbon bonds and the formation of carbon–hydrogen bonds. The reactions are exothermic and are catalyzed by various transition metals. This chapter discusses the catalytic hydrogenolysis on metals. At temperatures much lower than are required for hydrogenolysis, the chemisorption of hydrocarbons on metals is accompanied by evolution of hydrogen. Exchange reactions between paraffins and deuterium to yield deuteroparaffins occur at similar temperatures. These results indicate that carbon–hydrogen bonds are activated more readily than carbon–carbon bonds and that dehydrogenative chemisorption of the hydrocarbon is the initial step in hydrogenolysis. The hydrogen deficient surface species formed from the hydrocarbon then undergoes carbon–carbon bond scission, followed by hydrogenation and desorption to complete the reaction. The chapter describes the specificity of metal catalysts for hydrogenolysis reactions. This includes an extensive comparison of the catalytic activities of various metals and an attempt to relate the resulting “activity patterns” to properties of the metallic state.