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The reaction of the partial oxidation of methane was investigated over Ni/La 2 O 3 catalysts prepared by impregnation. Two different reactors were used, a perfectly jet-stirred reactor and a fixed-bed reactor. The influences of nickel content, calcination temperature, reaction temperature, residence time, and contact time were investigated. Mechanistic information was derived from the comparison of the results obtained in both reactors. Characterization techniques such as X-ray diffraction, temperature-programmed oxidation, temperatureprogrammed reduction, and transmission electron microscopy were used to assess the state of the catalyst prior to and after the reaction.

The reduction of automotive emissions and the reformulation of gasoline composition require a better understanding of the combustion mechanism, in particular aiming at the determination of the influential reactions which are responsible for the onset of knock in spark ignition engines. We have studied the oxidation mechanism of two hydrocarbons of different research octane number: n-pentane (62) and cyclopentane (100). This work follows a previous study on the oxidation of n-heptane and isooctane. The experimental study was performed at 873 K in a jet-stirred flow reaction vessel. The reaction mechanisms of n-pentane and cyclopentane were analysed on a purely kinetic basis, derived from our experimental results, and were finally modelled by using a programme of simulation of reaction mechanisms. The different behaviour of these two hydrocarbons with respect to autoignition phenomena is mainly dependent on the relative concentration of resonance-stabilized radicals in the reaction medium. Keywords: oxidation reaction, n-pentane, cyclopentane, modelling, autoignition.