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

Ethylene oxidation has been studied in an empty clean quartz reactor in the absence and in the presence of Li/MgO and L2CO3 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 COX 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 COX. Blending, these compounds (5% wt) with La2O3 (physical mixtures) improves selectivity towards C2+ 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.