Catalysis on evaporated metal films - IV. Exchange between propane and deuterium and iso butane and deuterium

Abstract

The exchange reactions of propane and isobutane have been followed on evaporated films of tungsten, rhodium and nickel by means of a mass-spectrometer. The energies of activation and frequency factors were approximately the same as those for the exchange reaction of ethane on tungsten and rhodium. Nickel films were effective at a slightly lower temperature for the exchange of propane and iso butane than for ethane but showed the same phenomenon of decreasing energy of activation above 0° C as had been observed for the reaction of ethane. The orders of reaction with respect to gas pressures were determined for the exchange of propane on all three catalysts. It appeared from the study of the initial products that the ability of rhodium to bring about multiple exchange is a characteristic property of that metal for hydrocarbon exchange reactions, in contrast to tungsten where the exchange is mainly brought about by successive replacement of the hydrogen atoms. Nickel showed appreciable differences in the rate of exchange of primary, secondary and tertiary hydrogen atoms. The rates of exchange of the secondary hydrogens in propane and the tertiary hydrogen in tsobutane were ten times faster than the rates for the primary hydrogens in the respective compounds.