MvK mechanism dominated methane combustion over Ni-CeO2 derived from MOF by flame pyrolysis

Abstract

Methane catalytic combustion is a significant technique in the fields of enhanced combustion, methane removal, and methane detection with the development of the natural gas industry and the demand for low-carbon combustion. Here, using a facile flame pyrolysis technique, two different types of Ni-CeO2 catalysts for methane combustion were synthesized from metal-organic framework (MOF) and metal salt (MS). Moreover, the Mars–van Krevelen (MvK) mechanism was investigated by combining kinetics with density functional theory (DFT) calculation. The performance shows that Ni-CeO2(BTC) catalysts give high activity owing to the large surface area, abundant Ni cations, and adsorbed oxygen. The high intrinsic activity is also related to a large number of oxygen vacancies which are essential for the MvK mechanism. In terms of kinetic analysis, the methane concentration determines the catalysis, and a redox MvK mechanism shows a good description of the experimental results. DFT calculations further clarify that, according to the MvK mechanism, the reduction of the active site is via dissociative adsorption of CH of CH4 on the catalytic site NiOCe, resulting in the formation of an oxygen vacancy, followed by dissociation of gas-phase oxygen on the oxygen vacancy to reoxidize the active site. Summarily, the MvK mechanism dominates the methane heterogeneous combustion over Ni-CeO2 and provides insight into the catalyst design for strengthening combustion.