I. The Reduction of Nickelous and Ferric Oxides by Hydrogen. II. The Catalytic Synthesis of Water Vapor on the Presence of Metallic Nickel

A study has been made by a flow method of the combination of hydrogen and oxygen in contact with reduced nickel, using oxygen concentrations up to 5%. 1. At all temperatures at which any water formation could be detected it was found that superficial oxidation of the nickel readily took place. At the lower temperatures this oxidation eventually covered the whole surface, with the result that the rate of catalysis suddenly decreased to a small value. 2. When hydrogen was passed over a catalyst superficially oxidized in this way, the rate of reduction accelerated auto-catalytically, in conformity with the previous observation that the reduction of ordinary nickel oxide is an interfacial reaction, that is, a reaction whose rate depends on the area of contact between the two solid phases. However, the maximum rates of reduction so obtained were always very small in comparison with the rates of the hydrogen-oxygen catalysis at the same temperature. 3. It was found that under certain conditions the rate of reduction was considerably increased by the presence of oxygen in the hydrogen. 4. Arguments are presented to show that the area of contact between the nickel oxide and the nickel, and therefore also the rate of reduction, are very much greater in the catalytic process than in the reduction of a completely oxidized surface by hydrogen alone. 5. The conclusion is reached that the catalytic water formation can be largely and perhaps entirely accounted for on the theory of successive oxidation and reduction of the catalyst. In conclusion we wish to record our indebtedness to the Carnegie Institution of Washington for financial aid in this investigation from a grant made to Prof. A. A. Noyes.