The H/D exchange and hydrogenolysis of propane on alumina-supported nickel catalyst

Abstract

The exchange of propane with deuterium on an alumina-supported nickel catalyst has been studied over a range of temperature (80–190°C) and two hydrocarbon/deuterium ratios. The results are interpreted in terms of a model containing three parameters in which two different adsorbed species are assumed: in the “alkyl” species one H-atom is exchanged in a single adsorption step, and the triadsorbed species exchanges at least three H-atoms per sojourn of the hydrocarbon molecule on the surface of the catalyst. The adsorbed species may undergo multiple exchange per adsorption step. The exchange of CH 3 · CD 2 · CH 3 and CD 3 · CH 2 · CD 3 with H 2 and D 2 was also studied. This showed that the monoadsorbed species is mainly adsorbed at the methyl group and the triadsorbed species twice at a methyl group and once at the methylene group. The hydrogenolysis reactions of propane were studied in the same system between 190 and 240°C. A wide range of conversion was covered, and the product distributions were fitted to kinetic equations in order to obtain the initial rate constants, i.e., selectivities. The nickel/alumina catalyst leads to multiple hydrogenolysis. Several CC bonds are broken before the adsorbed species are desorbed. Under the conditions used in these experiments, surface cracking is the rate-limiting step.