CuZnAl催化CO加氢制乙醇碳链增长机理研究

The catalytic conversion of syngas is a key link for chemical utilization of non-petroleum carbon resources, which involved in the problem of carbon chain growth is also the core of syngas chemistry research. For a long time, the selectivity of catalyst is challenged since the study of carbon chain growth mainly focused on metal components with F-T synthesis properties and alkalis. However, in our previous work, it was found that the syngas could be catalyzed to ethanol over CuZnAl catalyst without these elements, which implied that we do not understand enough about the mechanism of carbon chain growth. In this project, the catalytic mechanism of each metal species and their corresponding fine structures will be investigated through changing the atomic ratio of metals and regulating the Cu+/Cu0, the size of Cu, and AlOOH crystal plane as well as the characterizations of XRD, TPR, XPS, TEM and CO/H2-TPD. Meanwhile, the microcosmic nature of ethanol synthesis will be discussed using situ characterizations and quantum chemical calculations by studying on the conversion process of carbon species on catalyst surface and their active intermediates. Finally, combine with the structure-activity relationship, the carbon chain growth mechanism of CO hydrogenation to ethanol over CuZnAl catalyst will be clarified. This project can not only inject new ideas into the related chain growth research, but also provide guidance for the development of high-efficiency catalysts.

合成气转化是非石油基含碳资源化学利用的关键环节，其所涉及的碳链增长问题也是合成气化学研究的核心。长期以来，碳链增长研究大都集中在具有F-T合成性能的金属组元及碱金属上，催化剂的选择性存在很大挑战。我们前期工作发现CuZnAl催化剂在没有添加这些组元的情况下可催化CO加氢实现碳链增长获得乙醇，这暗示我们对碳链增长机理认识不足。本项目拟通过改变CuZnAl金属原子比和调控Cu+/Cu0、Cu晶粒尺寸和AlOOH晶面等催化剂精细结构，并借助XRD、TPR、XPS、TEM和CO/H2-TPD等多种表征手段探讨催化剂各金属组分及其相应精细结构的催化机制。同时利用原位表征技术和量子化学计算手段研究催化剂表面碳物种及其活性中间体的转化历程，探讨乙醇合成的微观本质。最后结合构效关系，阐明CuZnAl催化CO加氢制乙醇碳链增长机理，为相关链增长研究注入新的思路，也为后续高效催化剂的开发提供指导。

合成气是煤、生物质和天然气等含碳资源化学利用的关键环节，其转化过程中所涉及的碳链增长问题也是合成气化学研究的核心。长期以来，碳链增长研究大都集中Fe、Co、Rh等金属组元及碱金属上，催化剂的选择性存在很大挑战。本项目基于团队自主研发的完全液相技术制备的CuZnAl催化剂具有明显的乙醇合成能力这一事实，深入研究Cu、Zn、Al 三者及其精细结构催化CO加氢制乙醇碳链增长研究，为后续廉价高性能催化剂的开发提供指导的同时丰富C1化学的理论认识。.项目以完全液相技术为基础制备了不同Cu含量、Al含量、双金属CuZn以及单金属Cu和单金属Zn等催化剂，对比了商业甲醇合成催化剂和完全液相技术制备催化剂的结构差异；借助XRD、TEM、SEM-EDX、CO-TPD、H2-TPR、Raman、XPS以及in-situ DRIFTS等表征手段，系统研究了Cu、Zn、Al三者及其精细结构在CO加氢制乙醇/高级醇中的作用机制。研究表明，单金属Cu和Zn均能促进CO加氢生成乙醇，主要是大颗粒的Cu和Zn抑制了CHxO*中间体加氢，延长了其在催化剂表面的停留时间，随后CHxO*解离成CHn*，CHn*和CHxO*耦合生成CHnCHxO*，或CO*插入到CHn*生成CHnCO*实现碳链增长，并最终加氢得到乙醇。 Cu+和AlOOH的存在分别促进了加氢和C-O键的解离过程，从而有利于高选择性的得到乙醇/高级醇。本项目的研究成果澄清了不含碱金属及F-T组元的CuZnAl催化剂上乙醇合成的碳链增长机理，拓展了C1化学碳链增长的理论认识。催化剂的稳定性得到了极大的提升，反应500 h后总醇选择性约25%左右，乙醇及C2+OH在总醇中占比可分别保持在25%与50%。在此基础上完成了百公斤级浆状乙醇合成催化剂的放大制备，获得了与实验室制备相当的活性结果，定型了规模制备设备、工艺过程和工艺条件，扫除了浆态床合成气直接合成乙醇的核心障碍，为规模化合成气一步法合成乙醇奠定了扎实的基础。