The reaction of methane and oxygen sensitized by nitrogen peroxide. Part I—Thermal ignition

Nitrogen peroxide has been shown to be effective in lowering the ignition temperature of several gases in air. Dixon found that 1% nitrogen peroxide gave a maximum lowering of the ignition temperature of methane in air, whilst only a trace of the peroxide lowered the ignition temperature of hydrogen in oxygen by as much as 200°C. This effect in the hydrogen-oxygen reaction has been studied by Dixon, Hinshelwood, and their co-workers, and by Norrish and Griffiths, and in the carbon monoxide-oxygen reaction by Semenoff. Gibson and Hinshelwood and Thompson and Hinshelwood working with hydrogen-oxygen mixtures found that over a wide range of temperature there are two pressures of nitrogen peroxide between which there is an explosion and above and below which there is a very slow reaction. Thus for small increasing pressures of nitrogen peroxide the reaction is catalysed, but beyond a certain concentration the nitrogen peroxide acts as an anti-catalyst; consequently the graph of ignition temperature against pressure of nitrogen peroxide showed a minimum. The catalytic effect was explained by Thompson and Hinshelwood as due to the initiation of chains by reaction between molecules of hydrogen and nitrogen peroxide to give ultimately activated molecules of hydrogen peroxide and branching chains leading to explosion; the inhibition was explained as being due to the breaking of the chains by the deactivation of the hydrogen peroxide molecules by collision with nitrogen peroxide molecules.