Activity of metallic catalysts: IV. Influence of the nature of the support and effect of sulfur-containing poisons on two examples of “demanding reactions”

Abstract

Platinum catalysts were prepared from two transition aluminas with respective surface areas of 120 and 180 m 2 g and two α-aluminas. Their metallic surface areas were varied by thermal treatment at various temperatures. Their activities with respect to the hydrogenation of benzene (“facile reaction”), the hydrogenolysis of cyclopentane (“demanding reaction” of the first type) and the exchange between benzene and deuterium (“demanding reaction” of the second type) were measured. It is shown that the effect caused by the support does not arise from a difference in crystallinity, but rather from a selective poisoning brought about by the reduction of sulfate, in certain aluminas. Moreover, it is shown that certain poisons such as H 2S and SO 2 are “nonselective,” i.e., they have the same effect on the three reactions in the same way. On the contrary, the mixture H 2S + SO 2, which produces atomic sulfur, is a selective poison which reduces the rate of the hydrogenolysis of cyclopentane more than that of the hydrogenation of benzene, whereas the exchange between benzene and deuterium is far less affected than the hydrogenation. The cause of this selective poisoning is discussed.