Does Platinum Generate Gas Phase Methyl Radicals in the Catalytic Combustion of Methane?

Abstract

Using a matrix isolation technique an attempt was made to detect gas phase methyl radicals which had been formed at 500°C on a polycrystalline Pt catalyst dispersed with SiO₂, and at 900°C on a Pt single-crystal catalyst. Reaction products were condensed onto a sapphire rod which was then lowered into an EPR microwave cavity for analysis. No increase in the amount of radicals over the background was detected. Thus, the role of the Pt catalyst in the catalytic combustion of methane is to provide a catalytic surface for the reaction of CH₄ and O₂, and not to facilitate the gas phase reaction by generating free radicals.