Structure-sensitivity of the deactivation of Pd/SiO2 for methylcyclopropane hydrogenolysis by CO

Abstract

Silica-supported palladium catalysts ranging from 5 to 80% metal exposed have been characterized as to their reactivity for methylcyclopropane hydrogenolysis as a function of poisoning by CO. Both the level of surface coverage by CO and the metal crystallite size are seen to be important in the net deactivation behaviour of the catalyst. In addition, pretreatment conditions are important in determining patterns both of reaction and of deactivation structure sensitivity; these effects appear to be related to differences in surface morphology induced by both the atmosphere and the temperature of the final treatment before reaction.

In general, CO poisoning in this system is structure sensitive: as CO coverage increases a monotonic decrease in activity occurs for large Pd particles, while catalysts with percentage metal exposed >40% exhibit a near-step drop in activity between 20 and 30% CO coverage. A maximum in turnover frequency is observed near 65% exposed metal for coverage levels >30%.