THE EFFECT OF HYDROGEN PARTIAL-PRESSURE ON METHYLCYCLOPENTANE RING-OPENING

The ring opening of methylcyclopentane (MCP) over well-characterized Pt/SiO2(EUROPT-1), Pt/gamma-Al2O3, and Pt/K-LTL catalysts was studied as a function of hydrogen partial pressure and reduction temperature. The MCP ring opening selectivity did not change in the range of H-2:MCP ratios studied (8-200). The turnover frequency (TOF) went through a maximum as the H-2:MCP ratio increased. The maximum TOF of the Pt/gamma-Al2O3 after reduction at 450 degrees C is about three times higher than the maximum specific activity of ttle Pt/K-LTL and Pt/SiO2 catalysts. The H-2:MCP partial pressure ratio at which maximum activity is obtained increases in the. series Pt/K-LTL < Pt/gamma-Al2O3 < Pt/SiO2. This sequence is rationalized using reported adsorption energies of H-2 and assuming a decreased adsorption energy of MCP on Pt/K-LTL. The data can be described with a reaction mechanism that includes the cleavage of a C-C bond as the rate-determining step. Kinetic analysis of the changes in specific reaction rate as a function of the H-2:MCP ratio showed that the reaction proceeds through multiple adsorbed MCP species. The surface reaction rate is more than an order of magnitude higher for the Pt/gamma-Al2O3 catalyst than for the Pt/K-LTL catalyst, but decreases with increasing reduction temperature for both catalysts. (C) 1995 Academic Press, Inc.