甲烷-合成气两步梯阶反应合成乙酸的反应机理

In NSFC, a set of metal catalyst models and methods has been established, including the mechanisms of CHx interaction with metal surface, CHx interaction with CO2, as well as the effect of CHx overfall on two-step reactions, which can be applied to accurately describe the reaction thermodynamics and kinetics for CH4-CO2 two-step synthesis to form acetic acid. Moreover, the most suitable metal catalysts for two-step synthesis to acetic acid have been obtained; further, these catalysts have been experimentally verified with good catalytic properties, suggesting that our research results can provide more accurate prediction schemes for the filtration and design of new catalysts. According to the results of NSFC, sixteen papers indexed by SCI have been published. Meanwhile, an interesting result in NSFC shows that the interaction of CO2 with H can easily generate CO, combining with the experimental fact that CO has not been detected in products, as a result, it is thought that CO involves in the two-step reaction to form acetic acid, in which CHx interacts with CO and OH to form an intermediate CHxCOOH, then, the hydrogenation of CHxCOOH leads to CH3COOH; therefore, the idea of methane-synthesis gas by two-step methods to produce acetic acid is proposed. By using quantum chemical DFT theoretical calculations combining with experimental methods, the reaction mechanisms of methane-synthesis gas by two-step method to produce acetic acid are well illustrated from the structure-activity relationship of catalyst, thermodynamic and kinetic aspects. The results are expected to filtrate and obtain the appropriate metal catalysts for two-step reaction of methane-synthesis gas to form acetic acid.

青年科学基金已确定了一套能够准确描述CH4-CO2两步梯阶反应合成乙酸热力学、动力学的金属催化剂反应模型及方法，包括CHx与金属表面、CHx和H分别与CO2作用以及CHx溢流对两步梯阶反应的影响；并获得等温下两步梯阶反应合成乙酸适宜的金属催化剂，且部分催化剂已被实验证实具有较好催化性能，研究结果可为新型催化剂的筛选和设计提供比较准确的指导方案；依据青年科学基金研究结果，发表SCI收录论文16篇。同时，青年科学基金研究表明CO2与H作用容易生成CO和OH，结合实验产物没有检测到CO这一事实，认为CO插入CHx并与OH作用形成CHxCOOH，进而加氢生成乙酸；因此，本项目提出甲烷-合成气两步梯阶反应合成乙酸的研究，采用量子化学计算和实验相结合的方法，从催化剂构效关系、反应热力学和动力学方面阐明金属催化剂作用下甲烷-合成气两步梯阶反应合成乙酸的反应机理，为实验筛选并提出适宜的金属催化剂。

本项目提出具有全新反应机理的甲烷-合成气两步梯阶反应合成乙酸的新工艺路线，采用量子化学DFT计算和实验相结合的方法，从催化剂构效关系、反应热力学和动力学等方面阐明金属催化剂作用下甲烷-合成气两步梯阶反应合成乙酸的反应机理。具体研究内容包括：确定金属催化剂反应模型、两步梯阶反应中表面物种在金属表面吸附的微观结构及性质、甲烷-合成气催化转化反应体系中CHx来源、甲烷-合成气合成乙酸反应机理，以及适宜金属催化剂筛选和确定。研究结果在电子-分子水平上阐明了甲烷-合成气合成乙酸反应中不同金属催化剂表面上物种CHx来源、成因、类型和分布，明确了金属催化剂类型、表面结构、组成、活性组分结构大小和金属-载体相互作用等结构因素与催化性能之间的构效关系；确定了反应路径和基元反应序列，反应物种热力学和动力学参量，重要过渡态和中间体结构；获得了甲烷-合成气合成乙酸的催化反应机理以及不同结构特点的金属催化剂对反应机理的影响。同时，筛选并确定了适宜于甲烷-合成气合成乙酸反应的金属催化剂类型，其需要促进CHx生成和CO插入CHx生成C2氧化物前驱体CHxCO，以及/或者抑制CH3OH和CH4生成，从而实现催化剂对C2氧化物合成反应的催化性能调控；其中，第二金属助剂Rh掺杂改性的Cu基催化剂能够明显促进CH3生成，且抑制CH3OH和乙醇的生成，进而提高反应体系中乙酸选择性，该反应体系中需要补入部分水蒸气实现反应中OH的充分供应。在工艺方法上，基于甲烷和合成气与催化剂表面吸附作用强度差异较大，提出甲烷和合成气交替进样的“交替脉冲反应新工艺”，并搭建了反应装置对催化剂的催化性能进行了初步评价。