Catalysis on evaporated metal films - I. The efficiency of different metals for the reaction between ammonia and deuterium

Abstract

The exchange reaction between ammonia and deuterium has been followed on evaporated films of platinum, rhodium, palladium, nickel, tungsten, iron, copper and silver by means of a mass spectrometer. In all cases the initial product was deutero-ammonia (NH$_{2}$D), and the other deutero-ammonias were formed by successive reactions. Despite a considerable variation in the catalytic activity from metal to metal the relative concentrations of the deutero-ammonias formed throughout each reaction were identical in every case, and differential equations are developed to show that this is a consequence of the fact that only one hydrogen atom is exchanged at a time. The energies of activation varied from 5$\cdot $2 kcal/mole for platinum to 14$\cdot $1 kcal/mole for silver and there is a correlation between the energies of activation and the work functions of the metals. The frequency factors were almost identical on all the metals except tungsten. Possible mechanisms for the reaction are discussed. The catalysis of the exchange reaction by films of oxidized copper, tungsten, nickel and zinc and by zinc oxide was also investigated.