Tracer investigations of catalysed chemical reactions

Abstract

The catalytic hydrogenations of propylene and cyclopropane have "been studied using evaporated nickel films as the catalysts at 25ºC The effect of the presence of mercury in these two reactions has also been investigated and it was found that the catalyst was poisoned by mercury for the cyclopropane hydrogen- atlon hut not for that of propylene. As it was considered that chemisorption differences would explain this selective poisoning of the catalyst, adsorption studies have "been made for cyclopropane, propylene, and hydrogen on nickel films and the effect of mercury on the chemisorption investigated. The adsorption of mercury on nickel films has been measured using a radiochemical technique. Mercury was found to prevent hydrogen chemisorption and the inhibition of the cyclopropane hydrogenation in the presence of mercury has been interpreted in terms of this. Theoretical considerations of the problem of propylene hydrogenation have been made, and these have thrown some light on phenomena observed in the catalytic hydrogenation of ethylene. A detailed study of the displacement of hydrogen adsorbed on nickel by mercury has been made, and it was found that the displacement was not complete. The amount of hydrogen retained after the action of mercury on films has been measured at different degrees of coverage by a radiochemical method and has been found to be a function of the adsorptive capacity of the surface rather than of the amount of hydrogen adsorbed. This has been interpreted in terms of the isolation of individual hydrogen atoms on the surface, and the adsorption of hydrogen in pores which are subsequently blocked by mercury.