Progress in the mechanism of CH4 and CO2 co-conversion reactions

This review provides a comprehensive overview of the reaction pathways involved in the coconversion of CH4 and CO2to produce syngas, acetic acid, and C2 hydrocarbons. The focus is on elucidating the key reaction steps, intermediates, and the influencing factors on reaction selectivity. For the production of syngas, the activation and dissociation of CO2 and CH4 are identified as key steps. The mechanism depends on the acidity of the catalyst support. Acidic or neutral support follow a mono-functional mechanism, where both CH4 and CO2 are activated at the same active center. In contrast, a basic support leads to a bi-functional mechanism, involving the activation of CH4 and CO2 at different active centers. For acetic acid production, the C-C coupling process assumes to be significant. Two mechanisms are considered: the direct insertion of gas-phase CO2 into the M—CH3 bond (Eley-Rideal mechanism), and the prior adsorption of CO2 followed by insertion (Langmuir-Hinshelwood mechanism), with a lower reaction energy barrier for the latter. For producing C2 hydrocarbons, reactive oxygen species are considered to be key intermediates in the reaction, which may be derived from the activation and dissociation of lattice oxygen or CO2 in the catalyst. To enhance the catalytic performance, constructing multiple active sites on the catalyst surface for the co-catalysis of CH4 and CO2 is regarded as a promising catalyst modification strategy. Furthermore, advanced simulation calculation methods and in-situ characterization techniques can help to reveal the dynamic evolution of reaction process and the catalytic mechanism, thus providing the theoretical guidance for the design of catalysts in the CH4 and CO2 co-conversion reaction. © 2024 Chemical Industry Press Co., Ltd.. All rights reserved.