Influence of strong metal–support interaction on exchange with deuterium and other reactions of hydrocarbons. Part 2.—Studies with Pt/Nb2O5 and Rh/Nb2O5

Abstract

The changes in the catalytic properties of Pt/Nb₂O₅ and Rh/Nb₂O₅ caused by raising the reduction temperature from 523 to 773 K have been investigated for the hydrogenolysis of 2-methylbutane and n-pentane. The exchange of deuterium with 2-methylbutane was also studied over the Pt catalyst. The so-called strong metal–support interaction (SMSI) brought about by the high-temperature reduction decreased the rates of hydrogenolysis by factors of 10⁴ or 10⁵ with both catalysts, despite the comparatively low metal dispersions which were measured mainly by CO adsorption. The effects of SMSI were reversible and eliminated by oxidation at 673 K followed by reduction at 523 K. The use of a static reactor system enabled small amounts of initial products, e.g. alkene, to be determined during exchange or hydrogenolysis of 2-methylbutane over Pt/Nb₂O₅ reduced at 773 K and in all cases, gave detailed information about changes in the patterns of products as the contact time is increased. The relative rates of exchange, dehydrogenation, isomerisation and hydrogenolysis at 572 K over the Pt/Nb₂O₅ reduced at 773 K were 1000 : 100 : 4 : 1. The alkene formed initially from the reaction of D₂ and 2-methylbutane was highly exchanged. The results are used to discuss possible effects of SMSI on the catalysts.