Methane activation on Ni(111) at high pressures

Abstract

High pressure CH 4 decomposition experiments on Ni(111) have been conducted to discriminate between a direct reaction mechanism involving hot CH 4 molecules and a precursor-mediated mechanism. It has been found that the direct process for CH 4 decomposition is kinetically significant in depositing adsorbed carbon. Using absolute carbon coverage measurements the absolute efficiency of carbon deposition on Ni(111) at 600 K was found to be 4×10 −8 C atom per CH 4 collision at 1.0 Torr CH 4 pressure. By the use of He, Ne, and Ar buffer gases, it has been shown that the major process leading to CH 4 dissociation involves heating CH 4 followed by return of excited CH 4 back to the surface where the CH 4 dissociates. These experiments demonstrate that CH 4 translational excitation and vibrational excitation, as studied by molecular beam methods, are the kinetically important CH 4 activation processes leading to dissociation in the high pressure regime.