CORRELATION BETWEEN THE SINGLE TURNOVER (STO) SITE DENSITIES AND THE RATES OF 4-TERT-BUTYL-1-METHYLCYCLOHEXENE HYDROGENATION OVER SILICA SUPPORTED PALLADIUM CATALYSTS

A systematic study of a set of silica supported palladium catalysts wa s undertaken. The catalysts were prepared by impregnation. Some of the impregnated samples were reduced isothermally, others by thermoprogra med reduction (TPR). The percentage of the exposed metal was determine d both by hydrogen and CO chemisorption with the values ranging from 6 % to 39% over the series. The catalysts prepared by TPR had higher dis persions and their activities were less sensitive to the final reducti on temperature used in their preparation. A set of these catalysts hav ing different reaction site densities as determined by the single turn over (STO) characterization procedure were used to catalyze the hydrog enation of 1-methyl-4-tert-butylcyclohexene (1). The correlation betwe en these rate data and the STO saturation site densities for each cata lyst provided the values for single site reactivities. The hydrogenati on of 1 on palladium was found to proceed with a higher trans/cis rati o than was observed using a platinum catalyst. This was apparently due to the formation of a pi-allyl absorbed intermediate in the palladium catalyzed reaction. Substrate self-inhibition behavior and non-compet itive reversible inhibition by phosphine additives on the surface reac tivity and stereoselectivity were also observed.