The catalytic decomposition of nitrous oxide on the surface of gold: a comparison with the homogeneous reaction

Abstract

The bimolecular reaction 2N 2 O = 2N 2 + 2N 2 was recently shown to belong to the rather rare class of homogeneous reactions. Decomposition of two molecules of nitrous oxide takes place when a collision of a certain critical degree of violence occurs in the gas. At the moment of collision the two molecules must possess a combined energy of at least 58,000 calories (per 2 gram molecules), and it is probable that most of the collision in which this condition is fulfilled are fruitful. A comparison between the kinetics of this homogeneous decomposition and the corresponding reaction proceeding catalytically at the surface of a solid might be expected to throw light on the mechanism of heterogeneous catalysis. Previous efforts ( loc. cit .) to accelerate the reaction catalytically by the introduction of metals into the bulb in which the homogeneous reaction was going on were fruitless, since the reaction, if any, which took place at the surface of the metal was slow in camparison with the gaseous reaction. This difficulty was overcome by using as a catalyst a fine metal wire heated electrically. This could be raised to a sufficiently high temperature to cause the surface reaction to proceed with measurable velocity while the bulk of the gas was kept cold, thus eliminating the homogeneous reaction. Experiments made with platinum wires in this way were successful. The kinetics of the decomposition of nitrous oxide on the surface of platinum are summarized in the equation – d [N 2 O]/ dt = k [N 2 O]/1 + b [O 2 ]. The reaction is unimolecular, but is complicated by the strong retarding action of the oxygen formed.