CO2加氢制甲醇模型催化剂的构建及其表界面结构调控与反应特性的研究

Aiming at the negative effects of product water, controversial active site microstructures on catalyst surface and interface and the disagreement on catalytic mechanism of CO2 hydrogenation to methanol, this project constructs two novel and highly active model catalysts, ZnO plate, exposed large amount of highly active polar surface, supported Cu as well as Cu doped ZnO plate. According to the real catalytic system, various pretreatment conditions are designed, enabling the research of the microstructures of model catalyst surface and interface without any interference due to their clear structures. Then, the accurate design and construction rules of the catalyst local surface and interface atom and electron structures can be established. Combined with the catalyst performance, the active site microstructures on catalyst surface and interface can be revealed. Further, the interaction mechanisms between the catalyst surface and interface and the adsorbed species, reactive intermediate species and products will be investigated through operando characterization techniques, disclosing the CO2 activation mechanism and its directional transformation mechanism, developing a novel method to improve the catalytic properties through the regulation of the structure of the catalyst surface and interface, realizing CO2 hydrogenation to methanol with high efficiency and low energy consumption. In comparison with the catalyst model in surface science and theory simulation, the model catalysts in this project effectively eliminate the material gap and pressure gap, reducing the deviation between “theory and practice” effectively. The project results will help to further understand the similarities and differences between the active sites of the catalyst surface and interface and the reaction mechanism in the methanol synthesis from CO2 and syngas, provide a new idea for the search of highly efficient and robust catalysts and the study of the catalytic mechanisms and also offer fundamental support and technical guidance to commercialize CO2-to-methanol technology.

针对碳基小分子CO2加氢制甲醇过程中水的副作用、催化剂表界面活性位结构及反应机理有争议等问题，项目构建了两种新型高活性模型催化剂，富含高活性极性面盘状ZnO负载的Cu及Cu掺杂的薄盘状ZnO；结合实际催化体系，设计相关处理条件，排除干扰对比研究模型催化剂表界面微观结构的变化，建立催化剂表界面局域原子和电子结构的精准设计与构建规律；结合催化性能，获得催化剂表界面活性位的微观结构；通过原位-动态表征揭示CO2活化与定向转化机制，发展通过催化剂表界面结构调控以提高催化特性的新方法，实现CO2低能高效转化制甲醇。模型催化剂的构建可有效消除表面科学与理论模拟中的物质鸿沟、压力鸿沟，有效减少“理论与实际”之间的偏差。研究成果有助于进一步认识CO2与合成气制甲醇中催化剂表界面结构与反应机理的异同点，为寻求高效、稳定的催化剂和催化机理研究提供一种新思路，为CO2制甲醇的工业化提供理论支撑与技术指导。

商业合成甲醇的Cu/ZnO/Al2O3催化剂用于CO2加氢制甲醇时由于热力学平衡的限制和逆水煤气变换反应使CO2的转化率偏低、甲醇的选择性也很低，甲醇的收率因此也很低。目前主流观点认为Cu-ZnO催化剂中甲醇的生成位点是催化剂经H2还原时体相ZnO迁移至金属Cu纳米颗粒表面形成的ZnOx-CuNP-ZnO界面；但是该界面中甲醇的生成是通过CO2直接加氢，还是通过逆水煤气反应生成CO然后进一步加氢生成，目前并不清楚。此外，在负载型Cu-ZnO基催化剂中必然存在直接接触的Cu-ZnO界面，此界面是否会产生甲醇、发生逆水煤气变换反应也不清楚。为探究这两种界面上甲醇的生成以及逆水煤气反应的性能，设计了Cu掺杂的盘状ZnO（ZnO:Cu）用以模拟直接接触的Cu-ZnO界面和负载型Cu/盘状ZnO模型催化剂用于模拟直接接触的Cu-ZnO界面和ZnOx-CuNP-ZnO界面，对比研究了两种模型催化剂用于高压制甲醇以及常压下的逆水煤气变换反应性能，以其揭示直接接触的Cu-ZnO界面和ZnOx-CuNP-ZnO界面上两种反应性能的差别，阐明Cu-ZnO基催化剂用于CO2加氢制甲醇时选择性较低的原因。研究成果主要体现在三个方面：Cu/ZnO基催化剂对CO2加氢制甲醇的催化性能具有明显的Cu NPs形貌依赖性； Cu、Zn合金的生成不利于CO2加氢至甲醇；对比研究两种模型催化剂发现甲醇生成主要发生在ZnOx-CuNP-ZnO界面，直接接触的Cu-ZnO界面和ZnOx-CuNP-ZnO界面均会发生RWGS反应，导致Cu-ZnO基催化剂催化CO2加氢制甲醇时选择性较低。