Mechanism of deuterium addition and exchange of propene over silica-supported gold and silver catalysts

Abstract

The mechanism of the C₃H₆–D₂ reaction over silica-supported Au and Ag catalysts has been studied by applying microwave spectroscopy as well as kinetic measurements. A large kinetic isotope effect was observed for the rate of propane formation between the C₃H₆–H₂ and C₃H₆–D₂ reactions, indicating that hydrogen dissociation is the rate-determining step. Both deuterium addition and exchange processes proceeded via an associative mechanism involving n-propyl as well as s-propyl species, although the methyl hydrogen of propene was less active for exchange through this process. In addition, intramolecular 1,3- and 2,3-hydrogen-shift processes were observed for the first time; they proceeded only in the presence of gaseous hydrogen and caused the exchange of the methyl hydrogen of propene. The characteristic features of supported Group IB metals in this reaction are compared with those of Group VIII metals, and the possible structures of reaction intermediates are discussed in detail.