Application of a simple kinetic model for the oxidative coupling of methane to the design of effective catalysts

Former research on the kinetics and/or mechanisms of the oxidative coupling of methane (OCM) was reviewed and given the following classification: (A) spectroscopic studies of O− species and the reaction with methane, (B) kinetic simulation of gas phase reactions, (C) kinetic simulation of both gas phase and surface reactions, (D) kinetics integrating many radical reactions of single or several reactions, (E) surface kinetics focusing on methane consumption, and (F) power rate law expression of C2 (ethane and ethene) and C1 (CO and CO2) formation. Each kinetic model has its own purpose; however, a method proposed by Iwamatsu and Aika (I–A model), belonging to the (D) classification, was chosen as a convenient model to relate the kinetics with the chemical or morphological nature of OCM catalysts. The I–A model was used to analyze the reaction over Na- or Li-doped oxide catalysts, which have been reported as effective catalysts, and the role of the catalyst components is discussed. The effect of alkali metal sulfates on the kinetics was also studied. Finally the selectivity and productivity of C2 compounds under high pressure (200 kPa) over these catalysts were simulated using the kinetic parameters obtained. Na2CO3/CaO, LiNO3/La2O3–MgO, and three transition-based catalysts (MnO/Na2WO4/SiO2, LiOH/NiTiO3, and Na2CO3/NiTiO3) were found to be effective under these industrial conditions.