The Effect of Hydrogen Partial Pressure on Methylcyclopentane Ring Opening.

Abstract

The ring opening of methylcyclopentane (MCP) over well-characterized Pt/SiO{2}(EUROPT-1), Pt/@c-Al{2}O{3}, 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/@c-Al{2}O{3} after reduction at 450}o{C is about three times higher than the maximum specific activity of ttle Pt/K-LTL and Pt/SiO{2} catalysts. The H{2}:MCP partial pressure ratio at which maximum activity is obtained increases in the. series Pt/K-LTL < Pt/@c-Al{2}O{3} < Pt/SiO{2}. 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/@c-Al{2}O{3} catalyst than for the Pt/K-LTL catalyst, but decreases with increasing reduction temperature for both catalysts.