Catalytic reactions with deuterium of several polymethylcycloalkanes on cobalt films

Abstract

The exchange with deuterium of several polymethylcycloalkanes catalysed by cobalt films in the temperature range 373–488 K has been studied. Multiple exchange was pronounced and propagated from the hydrogens on one side of the rings to those on the other side by a combination of the αβ-process plus roll-over of intermediate cycloalkenes, and the αα-process. The exchange reactions were first order, but only commenced with simultaneous evolution of methane, a reaction which was invariably zero order and increased in importance with temperature. The only significant products due to cracking, apart from methane, still contained a gem-dimethyl group. Such a group obviously exerts a greater steric hindrance in methanation than in exchange. The intermediates participating in the different mechanistic pathways for each of these reactions are described. We discuss the significance of the present results, and of previous studies of the reactions of the same cycloalkanes with deuterium on other transition metals, for a broader understanding of the role of carbonaceous residues on metal surfaces in creating selective sites for non-destructive reactions of hydrocarbons, e.g., hydrogenation of alkenes.