Abstract:

This review provides a comprehensive overview of the reaction pathways involved in the co-conversion of CH₄ and CO₂ to 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 CO₂co-conversion reaction.

Key words: methane, carbon dioxide, reaction mechanism, syngas, acetic acid, C₂ hydrocarbons

摘要：

综述了CH₄和CO₂共转化生成合成气、乙酸和C₂烃3种反应路径的反应步骤、关键中间体及反应产物选择性的影响因素。当生成合成气时，CH₄与CO₂的活化解离是关键步骤，催化剂载体表面为酸性或中性时反应遵循单功能机理，CH₄和CO₂在同一活性中心被活化，当载体为表面碱性时，CH₄和CO₂遵循双功能机理，在不同活性中心被活化，通常双功能机理的催化效率更高。当生成乙酸时，C-C耦合过程应被重点关注，该过程中气相CO₂可能直接插入M—CH₃键（Eley-Rideal机理）或先被吸附活化后再插入（Langmuir-Hinshelwood机理），后者反应能垒更低。当生成C₂烃时，活性氧物种被认为是反应过程中的关键中间体，其可能来源于催化剂中的晶格氧或CO₂的活化与解离。因此，在催化剂表面构建多个独立活性位点，以分别对CH₄和CO₂进行多位点协同催化被认为是良好的催化剂改性策略。另外，先进的模拟计算方法和原位表征手段能够深入揭示反应过程中催化剂和反应中间体的动态演变过程及机理，从而为真实CH₄和CO₂共转化反应过程中催化剂的设计提供理论指导。

关键词: 甲烷, 二氧化碳, 反应机理, 合成气, 乙酸, C₂烃