Oh Kyung-Ryul, Lee Hyunjoon, Yun Gwang-Nam, Yoo Changho, Yoon Ji Woong, Awad Ali, Jeong Hyun-Wook, Hwang Young Kyu
Research Center for Nanocatalysts, Korea Research Institute of Chemical Technology, Daejeon 34114, Korea.
Fuel Cell Laboratory, Korea Institute of Energy Research, Daejeon 34129, Korea.
ACS Appl Mater Interfaces. 2023 Feb 13. doi: 10.1021/acsami.2c20240.
Bimetallic zeolitic imidazolate frameworks (ZIFs) containing two different metal ions can exhibit superior performances when applied in heterogeneous catalysis. Herein, we present a facile one-pot synthesis method for PdCo-ZIFs with various Pd/Co ratios, where Pd(II) ions are successfully incorporated into the Co node sites of the ZIF structure. The local structure of the bimetallic ZIFs was comprehensively investigated by pore-structure, X-ray absorption fine structure, and in situ CO adsorption Fourier transform infrared analyses. The results demonstrated that the framework comprises different coordination geometries of Co (tetrahedral) and Pd (square planar) ions connected by the benzimidazolate ligand. Notably, the inherently nonporous, 2D Co-ZIF structure was transformed into a hierarchical porous structure, and the PdCo-ZIFs exhibited a significantly increased concentration of defects and distorted Co sites. Based on these results, the catalytic performances of the synthesized ZIFs in the cycloaddition of CO to epoxides were evaluated under a cocatalyst and solvent-free conditions. The PdCo-ZIFs exhibited significantly higher catalytic activity (maximum turnover frequency, TOF = 2501 h) than Co-ZIF (TOF = 65 h) and Pd-ZIF (no activity), which revealed that the undercoordinated Co sites with distorted structure are the active sites rather than the incorporated Pd ions. This study provides a facile one-pot method for synthesizing bimetallic ZIFs with mixed-coordination modes, hierarchical porous structures, and modified defect concentrations, which would expand the library of structurally diverse bimetallic ZIFs toward various applications.
含有两种不同金属离子的双金属沸石咪唑酯骨架材料（ZIFs）在多相催化中应用时可展现出优异性能。在此，我们提出了一种简便的一锅法合成具有不同钯/钴比例的PdCo-ZIFs的方法，其中Pd(II)离子成功地掺入到ZIF结构的钴节点位点中。通过孔结构、X射线吸收精细结构和原位CO吸附傅里叶变换红外分析对双金属ZIFs的局部结构进行了全面研究。结果表明，该骨架由通过苯并咪唑酯配体连接的钴（四面体）和钯（平面正方形）离子的不同配位几何结构组成。值得注意的是，原本无孔的二维Co-ZIF结构转变为分级多孔结构，并且PdCo-ZIFs的缺陷浓度和扭曲的钴位点显著增加。基于这些结果，在无共催化剂和无溶剂条件下评估了合成的ZIFs在CO与环氧化物环加成反应中的催化性能。PdCo-ZIFs表现出比Co-ZIF（TOF = 65 h⁻¹）和Pd-ZIF（无活性）显著更高的催化活性（最大周转频率，TOF = 2501 h⁻¹），这表明结构扭曲的低配位钴位点是活性位点而非掺入的钯离子。本研究提供了一种简便的一锅法来合成具有混合配位模式、分级多孔结构和改性缺陷浓度的双金属ZIFs，这将扩大结构多样的双金属ZIFs库以用于各种应用。
