Investigations on hydrogen spillover. Part 2.—Hydrocarbon conversion on bifunctional catalysts
The effect of hydrogen spillover on the cracking of n-hexane on erionite has been investigated. Changes in selectives have been found depending on the nature of the carrier gas and the presence of platinum. It has been demonstrated that platinum activates hydrogen that is able to migrate over large distances (spillover hydrogen). On acidic centres the activated hydrogen has been found to be involved in the hydrocarbon conversion. When hydrogen was substituted by nitrogen, Pt/H–erionite was found to exhibit only a monofunctional acidic property which has been characterized by a C3 : C4 ratio of almost 1 : 1 and the appearance of C5 compounds formed via secondary reactions of intermediate alkenes. Based on these results an extended model of the bifunctional catalysis has been proposed that includes activation, migration and consumption of spillover hydrogen. The product distribution was then satisfactorily explained, assuming that hydrogen dissociates into radicals on platinum and then spills over onto the support surface where a dynamic equilibrium is established between the hydrogen radicals and protons.