Zhang Renqin, McEwen Jean-Sabin
The Gene and Linda Voiland School of Chemical Engineering and Bioengineering , Washington State University , Pullman , Washington 99164 , United States.
Department of Physics and Astronomy , Washington State University , Pullman , Washington 99164 , United States.
J Phys Chem Lett. 2018 Jun 7;9(11):3035-3042. doi: 10.1021/acs.jpclett.8b00675. Epub 2018 May 22.
Cu K-edge X-ray absorption near-edge spectra (XANES) have been widely used to study the properties of Cu-SSZ-13. In this Letter, the sensitivity of the XANES features to the local environment for a Cu cation with a linear configuration and a Cu cation with a square-linear configuration in Cu-SSZ-13 is reported. When a Cu cation is bonded to HO or NH in a linear configuration, the XANES has a strong peak at around 8983 eV. The intensity of this peak decreases as the linear configuration is broken. As for the Cu cations in a square-planar configuration with a coordination number of 4, two peaks at around 8986 and 8993 eV are found. An intensity decrease for both peaks at around 8986 and 8993 eV is found in an NH_4_ZCu model as the N-Cu-N angle changes from 180 to 100°. We correlate these features to the variation of the 4p state by PDOS analysis. In addition, the feature peaks for both the Cu cation and Cu cation do not show a dependence on the Cu-N bond length. We further show that the feature peaks also change when the coordination number of the Cu cation is varied, while these feature peaks are independent of the zeolite topology. These findings help elucidate the experimental XANES features at an atomic and an electronic level.
铜 K 边 X 射线吸收近边光谱（XANES）已被广泛用于研究 Cu-SSZ-13 的性质。在本信函中，报道了 Cu-SSZ-13 中具有线性构型的铜阳离子和具有方形-线性构型的铜阳离子的 XANES 特征对局部环境的敏感性。当一个铜阳离子以线性构型与 HO 或 NH 键合时，XANES 在约 8983 eV 处有一个强峰。随着线性构型被破坏，该峰的强度降低。对于具有 4 配位的平面正方形构型的铜阳离子，在约 8986 和 8993 eV 处发现两个峰。在 NH₄_ZCu 模型中，当 N-Cu-N 角从 180°变为 100°时，在约 8986 和 8993 eV 处的两个峰的强度均降低。通过态密度（PDOS）分析，我们将这些特征与 4p 态的变化相关联。此外，铜阳离子和铜阳离子的特征峰均不显示对 Cu-N 键长有依赖性。我们进一步表明，当铜阳离子的配位数改变时，特征峰也会改变，而这些特征峰与沸石拓扑结构无关。这些发现有助于在原子和电子层面阐明实验 XANES 特征。
