纳米结构铜催化剂在CO转化反应过程中的原位动态研究

Copper catalysts supported on oxides are industrially used in large-scale processes of methanol synthesis and low-temperature water-gas shift; however, they are still challenged for further improving the catalytic activities, especially at lower operation temperatures. Because the size and morphology of copper particles and the copper-support interface, which typically show dynamic behaviors under realistic reaction conditions, are generally viewed as the active components, the design and development of highly active copper catalyst would require having an in-depth understanding of the microstructure of the active sites or domains at their functionalities. Recent rapid progress on catalyst characterization techniques, including both visualizing and spectroscopic ones, has now enabled to monitor the electronic and structural features of the working catalysts, at least partially. This proposal is aimed to develop a fundamental understanding of the relationship between the nanostructure properties of copper catalysts and the activities under methanol synthesis and low-temperature water gas shift conditions. More specifically, it starts with the fabrication of copper-oxide (CeO2, ZnO and MgO) catalysts with tunable size and shape at the nanometer level for both components, and then focus on in situ characterizations of the dynamic behavior of copper nanoparticles or clusters as well copper-oxide interfaces under reactive atmosphere and at elevated temperatures, mainly by using environmental transmission electron microscopy (ETEM) and near ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). Also, the overall catalytic performance and reaction kinetics of these nanostructured copper catalysts will be tested for methanol synthesis and low-temperature water gas shift reaction. This, to correlate the dynamic observations of the nanostructured copper catalysts with their activities for methanol synthesis and the water gas shift reaction, will allow establishing a more realistic structure-reactivity relationship of nanostructured copper catalysts and deepening the mechanistic understanding of CO activation and conversion.

氧化物负载的铜催化剂广泛应用于合成甲醇、低温水气变换等大型能源化工过程，提高其低温催化活性是该领域所面临的主要挑战。活性位结构和化学状态的表征和精细调控是研制新型高效铜催化剂的的科学基础，其中的关键科学问题是通过原位、动态表征催化剂组成和表界面结构，构建构效关系。本项目通过构筑具有特定尺寸和表界面结构的氧化物（氧化铈、氧化锌、氧化镁）负载的铜纳米粒子和原子簇，在纳米尺度上实现铜催化剂的尺寸、形貌、界面结构的精细调控，利用载体与铜的空间和电子作用提高铜基催化剂的低温催化活性；主要利用球差校正高分辨ETEM和AP-XPS 技术，结合其它原位谱学技术，在纳米尺度研究铜催化剂表面结构、尺寸、形貌、配位环境、电子结构等的动态演变行为；探讨反应物分子与催化剂表面相互作用的化学机制，揭示接近真实反应条件下催化剂的活性位结构及催化作用机理，深化对CO活化的科学认知。

氧化物负载的铜催化剂广泛应用于合成甲醇、低温水气变换等大型能源化工过程，提高其低温催化活性是该领域所面临的主要挑战。活性位结构和化学状态的表征和精细调控是研制新型高效铜催化剂的的科学基础，其中的关键科学问题是通过原位、动态表征催化剂组成和表界面结构，构建构效关系。项目执行期间，在纳米尺度上实现了铜催化剂的尺寸、形貌、界面结构的精细调控，并在催化剂的原位动态表征、催化反应条件下的催化反应机制等方面取得重要进展。发现同时暴露{111}和{100}晶面的氧化铈纳米棒较主要暴露{100}镜面的纳米立方体对铜具有更好的分散度，在CO氧化、水气变换、甲醇合成等CO活化相关反应中表现更好的催化活性。首次在原子尺度表征了铜氧化铈界面结构，发现氧化铈纳米棒上铜主要以双层铜的形式存在，其表层铜为金属态，底层铜为正价，与氧化铈表面Ce3+通过氧空穴相连，构成Cu+-Ov-Ce3+结构，结合低温水气变换反应条件下的原位漫反射红外光谱研究，发现Cu+-Ov-Ce3+为水气变换反应的活性位，揭示了Cu/CeO2催化剂活性位的原子结构；为通过调控金属-氧化物相互作用方式研制高活性催化剂提供了实验和理论基础。项目还考察了氧化镁形貌对Cu-MgO相互作用及其催化丙酮加氢催化反应性能的影响，采用ETEM研究了CO2加氢逆水气变换反应条件下铜-氧化锌界面结构的动态行为，探讨了反应物分子与催化剂表面相互作用的化学机制，揭示接近了真实反应条件下催化剂的活性位结构及催化作用机理，深化了对CO活化的科学认知。并撰写综述文章，系统总结了近期金属催化剂活化以及反应条件下动态结构变化的最新研究进展。目前，本项目的主要预定研究内容已顺利完成，在Nat. Catal.、Angew. Chem. Inter. Ed.、Nano Today等期刊上发表SCI论文7篇，其中第一作者论文2篇，共通讯作者论文4篇；参加国际/国内会议2人次，另有部分相关研究成果正在整理待发表阶段。