Key Laboratory for Advanced Materials, Feringa Nobel Prize Scientist Joint Research Center, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai, 200237, P. R. China.
Key Laboratory for Advanced Materials, Research Institute of Industrial Catalysis, School of Chemistry and Molecular Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, P. R. China.
Adv Mater. 2023 Jun;35(25):e2208504. doi: 10.1002/adma.202208504. Epub 2023 Apr 29.
Precise determination of the structure-property relationship of zeolite-based metal catalysts is critical for the development toward practical applications. However, the scarcity of real-space imaging of zeolite-based low-atomic-number (LAN) metal materials due to the electron-beam sensitivity of zeolites has led to continuous debates regarding the exact LAN metal configurations. Here, a low-damage high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging technique is employed for direct visualization and determination of LAN metal (Cu) species in ZSM-5 zeolite frameworks. The structures of the Cu species are revealed based on the microscopy evidence and also proved by the complementary spectroscopy results. The correlation between the characteristic Cu size in Cu/ZSM-5 catalysts and their direct oxidation of methane to methanol reaction properties is unveiled. As a result, the mono-Cu species stably anchored by Al pairs inside the zeolite channels are identified as the key structure for higher C1 oxygenates yield and methanol selectivity for direct oxidation of methane. Meanwhile, the local topological flexibility of the rigid zeolite frameworks induced by the Cu agglomeration in the channels is also revealed. This work exemplifies the combination of microscopy imaging and spectroscopy characterization serves as a complete arsenal for revealing structure-property relationships of the supported metal-zeolite catalysts.
精确确定沸石基金属催化剂的结构-性能关系对于朝着实际应用的发展至关重要。然而，由于沸石对电子束敏感，基于沸石的低原子数 (LAN) 金属材料的实空间成像稀缺，导致关于确切的 LAN 金属构型的持续争论。在这里，采用低损伤高角度环形暗场扫描透射电子显微镜 (HAADF-STEM) 成像技术直接可视化和确定 ZSM-5 沸石骨架中的 LAN 金属 (Cu) 物种。基于显微镜证据揭示了 Cu 物种的结构，并通过互补的光谱结果得到了证明。揭示了 Cu/ZSM-5 催化剂中特征 Cu 尺寸与它们直接氧化甲烷为甲醇反应性能之间的相关性。结果表明，稳定锚定在沸石通道内 Al 对中的单 Cu 物种是提高 C1 含氧化合物产率和甲醇选择性的关键结构，用于直接氧化甲烷。同时，还揭示了通道中 Cu 聚集引起的刚性沸石骨架的局部拓扑灵活性。这项工作例证了显微镜成像和光谱表征的结合可作为揭示负载金属-沸石催化剂的结构-性能关系的完整手段。
