2746.     PRICHARD, C. R., AND HINSHELWOOD, C. N.  Interaction of Hydrogen and Carbon Dioxide on the Surface of Platinum.  Jour. Chem. Soc., vol. 127, 1925, pp. 806-811; Chem. Abs., vol. 19, 1925, p. 3411.

        At 1,000°, when the pressure of CO₂ is kept constant, the rate of formation of CO increases almost linearly with the pressure of H₂ at least up to 30 mm.  At constant H₂ pressure, the rate of reaction is at first proportional to the pressure of CO₂ and then passes through a maximum when the pressure of CO₂ is approximately double that of H₂.  Large pressures of CO₂ have a greater retarding influence on account of its relatively strong adsorption by the catalyst.  CO has a slight retarding influence.  When the reacting gases are in equimolecular proportions, the pressure of each being 100 mm., the course of the reaction is very nearly unimolecular; but this result is to some extent a coincidence.  A simple mechanism, which accounts for most of the observed facts, is that reaction occurs when H₂ and CO₂ become adsorbed adjacent to each other on an active part of the surface.  It must be assumed also, that the fraction of the active surface covered by CO₂ increases from 0° to 400 mm., while the adsorption of H₂ at these points left free from CO₂ is never very great so that the zone of reaction is in that portion of the H₂ adsorption isotherm where adsorption is more or less directly proportional to pressure.