Pulse flow reactor studies of the oxidation of methane over palladium catalysts

Abstract

A kinetic and mechanistic study of the oxidation of methane over palladium and palladium oxide catalysts has been carried out in a pulse flow micro-reactor. The system used was designed especially for the identification of unstable intermediates, but only trace quantities of formaldehyde, carbon monoxide and hydrogen could be observed among the principal products, carbon dioxide and water. The overall oxidation was found to obey approximately a rate law of the form : –d [CH₄]/dt=k[CH₄]^0.5[O₂]⁰, and the apparent activation energy was 22.6 kcal mol^–1 over palladium and 19.0 kcal mol^–1 over a palladium/palladium oxide catalyst. A mechanism has been proposed for the overall reaction in which the rate-determining step appears to be a surface reaction between oxide ions and dissociatively adsorbed linearly-bound methylene radicals.