Oxidative coupling of methane: catalytic behaviour assessment via comprehensive microkinetic modelling

Abstract A comprehensive microkinetic model, including catalyst descriptors, that accounts for thermal, homogeneous and catalytic, heterogeneous reaction steps in the oxidative coupling of methane has been used in the assessment of kinetic data acquired on different catalysts. The applicability of the model was extended from alkali magnesia catalysts represented by Li/MgO and Sn–Li/MgO, to a new class of materials, namely alkaline earth-promoted lanthana catalysts, represented by Sr/La 2 O 3 . To simulate adequately the large experimental dataset, acquired with the latter catalyst, the surface reaction network of the microkinetic model was expanded. The resulting model succeeded in adequately simulating the C 2 , that is, ethane and ethene, production, both individually and as a lump during regression. It was found that the activity of Sr/La 2 O 3 , in terms of methane conversion, is 33 and five times higher than that of Li/MgO and Sn–Li/MgO, respectively. This is attributed mainly to the higher stability of adsorbed hydroxyl, the higher stability of adsorbed oxygen, and the higher active density of Sr/La 2 O 3 . The selectivity toward C 2 products was found to depend on the methyl radical sticking coefficient and the stability of the adsorbed oxygen and was the highest on the Sn-promoted LiMgO catalyst, that is, 70% at about 5% methane conversion at 1023 K, 190 kPa, and inlet molar CH 4 /O 2 ratio of 4.