A study of the catalysis by silver of the union of hydrogen and oxygen

Abstract

D. R. Hughes and R. C. Bevan discovered a simple and delicate method of testing whether a metallic nickel surface is covered with a layer of oxide. The investigation was conducted with metal drawn into the form of a wire. It was found, that when the wire was heated electrically at a temperature of 164° C., hydrogen molecules (temperature 14° C. and pressure 12910 × 10 -6 mm.) removed nearly twice as much heat from a surface known to be oxidised, as from one completely reduced to the metallic state on reflection from the surfaces under similar conditions. Consequently, in an atmosphere of hydrogen, a given current raised the wire to a higher temperature when all oxide had been previously removed from the surface. The accommodation coefficient ( i. e. , the ratio of the energy actually removed from the wire by an escaping hydrogen molecule to that which would have been removed if the molecule had attained the temperature of the metal) was found to be 0⋅25 for a metallic surface, and 0⋅48 for an oxidised surface. Invisible films of oxide, only a few molecules deep, could thus with certainty be detected. They were thereby enabled to show that a nickel surface was immediately oxidised by exposure to oxygen at the temperature of the laboratory. The invisible oxide thus formed and the black oxide produced by contained heating in an atmosphere of oxygen catalysed the combination of hydrogen and oxygen at the same temperature occurred. Concerning the catalysis by nickel of the reaction between hydrogen and oxygen, they came to the inevitable conclusion that, during the combination of the gases the metal was completely covered by a layer of oxide, and the mechanism of the catalysis was similar to that of other readily oxidisable metals like copper, and was merely alternate oxidation and reduction of the surface.