Development of Operando Polarization-Dependent Total Reflection Fluorescence X-ray Absorption Fine Structure Technique for Three-Dimensional Structure Determination of Active Metal Species on a Model Catalyst Surface under Working Conditions

作者：Bang Lu, Daiki Kido, Yuta Sato, Haoran Xu, Wang‐Jae Chun, Kiyotaka Asakura, Satoru Takakusagi · 发表于：The Journal of Physical Chemistry C · 年份：2021 · DOI：10.1021/acs.jpcc.1c02913 · 被引用次数：8 · 研究领域：Advanced Chemical Physics Studies、X-ray Spectroscopy and Fluorescence Analysis、Catalytic Processes in Materials Science

A novel operando X-ray absorption fine structure (XAFS) technique was developed that we have called the operando polarization-dependent total reflection fluorescence (PTRF)-XAFS technique, which can provide information on the valence state (XANES) and three-dimensional (3D) structure (EXAFS) of active metal species dispersed on a well-defined single-crystal surface during catalytic reactions. A new compact vacuum chamber, termed an operando PTRF-XAFS cell, was designed with an internal volume of 216 cm 3 for PTRF-XAFS measurements of deposited metal species at high temperatures (<800 K) in the presence of reactant gases (up to atmospheric pressure). Product gas analysis in the cell can be simultaneously conducted with a quadrupole mass spectrometer (QMS) during the PTRF-XAFS measurements. The developed operando PTRF-XAFS technique was applied to a Pt/α-Al 2 O 3 (0001) model catalyst during the CO oxidation reaction. Pt clusters that favor an icosahedral Pt 55 structure were formed on the α-Al 2 O 3 (0001) surface after Pt deposition at room temperature, while they were converted to larger cuboctahedral clusters (Pt 147 ) under the CO oxidation reaction at 493 K. The turnover frequency (TOF) of the CO oxidation activity at 493 K was also estimated to be 0.06 s –1 from simultaneous QMS and XAFS measurements. Thus, operando PTRF-XAFS has enabled the relationship between the 3D structure of a metal species on a well-defined oxide surface and its catalytic activity to be determine...