Effect of vanadium pentoxide on gas-phase combustion. II. The methane-oxygen system†

The slow combustion of methane in a static system, using reaction vessels coated with vanadium pentoxide, has been studied. Coating a vessel eliminated autocatalysis and retarded the oxidation, the rate of which was only measurable at above 500°. Both the overall order (5.9) and the overall activation energy (about 78 kcal/mole) were very high and the initial rate was markedly dependent on the pressure and nature of added inert gas. The products were carbon monoxide, carbon dioxide (CO/CO2 ratio about one) and water, with only traces of formaldehyde and formic acid. Packing the coated vessel virtually eliminated the pressure change, the products being almost exclusively CO2, but did not appreciably alter the rate of consumption of methane. It is concluded that the oxidation involves an unbranched chain mechanism, in which both initiation and termination occur on the walls and the propagation reactions are: the formaldehyde being rapidly oxidised at the surface so that it cannot act as a branching agent.