Catalysis on evaporated metal films II. The efficiency of different metals for the reaction between methane and deuterium

Abstract

The exchange reaction between methane and deuterium is followed on evaporated films of rhodium, platinum, palladium and tungsten. On all four catalysts there is evidence of two different mechanisms for the exchange as had been found on nickel catalysts (Kemball (1951): one produces CH$_{3}$D and the other gives the compounds CH$_{2}$D$_{2}$, CHD$_{3}$ and CD$_{4}$. The energies of activation, frequency factors and orders of reaction with respect to the pressures of the two gases for both mechanisms are determined. The energies of activation on tungsten are much lower than on the other metals, and this fact is attributed to the low activation energy for the adsorption of methane on tungsten which occurs readily at 0 degrees C. A section is devoted to a discussion of the effect of an inhibiting gas on the frequency factor of a catalytic reaction. It is shown that a relationship between the logarithm of the frequency factor and the energy of activation on different catalysts may be caused by a relationship between the entropy and heat of adsorption of the inhibiting gas on the catalysts. Iron films are found to have no catalytic activity for this reaction at temperatures up to 420 degrees C.