Optimization of process parameters and catalyst compositions in carbon dioxide oxidative coupling of methane over CaO-MnO/CeO₂ catalyst using response surface methodology

The optimization of process parameters and catalyst compositions for the CO₂ oxidative coupling of methane (CO₂-OCM) reaction over CaO-MnO/CeO₂ catalyst was developed using Response Surface Methodology (RSM). The relationship between the responses, i.e. CH₄ conversion, C₂ hydrocarbons selectivity or yield, with four independent variables, i.e. CO₂/CH₄ ratio, reactor temperature, wt.% CaO and wt.% MnO in the catalyst, were presented as empirical mathematical models. The maximum C₂ hydrocarbons selectivity and yields of 82.62% and 3.93%, respectively, were achieved by the individual-response optimization at the corresponding optimal process parameters and catalyst compositions. However, the CH₄ conversion was a saddle function and did not show a unique optimum as revealed by the canonical analysis. Moreover pertaining to simultaneous multi-responses optimization, the maximum C₂ selectivity and yield of 76.56% and 3.74%, respectively, were obtained at a unique optimal process parameters and catalyst compositions. It may be deduced that both individual- and multi-responses optimizations are useful for the recommendation of optimal process parameters and catalyst compositions for the CO₂-OCM process.