Reactions of unsaturated hydrocarbons on rutile and anatase

Abstract

The isomerisation of cyclopropane, various methylcyclopropanes and some C₆-alkenes has been followed on rutile catalysts. The relative reactivities of the unsaturated compounds are consistent with a mechanism involving the formation of carbocationic intermediates σ-bonded to Lewis-acid sites. Subsequent reactions include 1,2-hydride and -methyl shifts, and also hydrogen-transfer processes in which surface oxide ions may be involved.

The hydrogenation of various alkenes, the equilibration of H₂/D₂ and the isomerisation of some C₆-alkenes have been studied over a range of temperatures on anatase catalysts. The similarities between the catalytic properties of rutile and anatase are more marked than the differences. The relative rates of the catalytic processes over both oxides are isomerisation > H₂/D₂ equilibration > hydrogenation. Some self-poisoning accompanied by blackening of the catalyst is found in a number of the alkene/H₂ reactions, e.g. with cyclopentene or 2-methylpropene over anatase.