Inhibition of the gas phase oxidation of ethylene by various solids and influence of their addition on the catalytic properties of lanthanum oxide towards the oxidative coupling of methane

Abstract

Ethylene oxidation has been studied in an empty clean quartz reactor in the absence and in the presence of Li/MgO and Li 2CO 3 catalysts. It is shown that the gas phase oxidation of ethylene is inhibited by these solids, suggesting that one of the role of the catalyst in oxidative coupling of methane is to inhibit ethylene oxidation into CO x by trapping very reactive chain-carriers. Furthermore, a series of flame retardant, including phosphates and halides of alkali and alkaline earth metals are shown to inhibit the gas phase oxidation of ethylene into CO x. Blending these compounds (5 % wt) with La 2O 3 (physical mixtures) improves selectivity towards C 2+ hydrocarbons without change of the ethylene/ethane ratio. This is interpreted assuming that additives interfere with the early stages of the reaction which involve methyl radicals, rather than invoking the inhibition of secondary reactions such as ethylene oxidation.