Utilizing a customized in situ/operando cell designed for X-ray spectroscopy in the tender X-ray range, an investigation is reported that unraveled the interactions between the noble metal, support, and reactive molecules throughout the catalytic bed. The in situ/operando cell allows the study of dynamic structural changes in heterogeneous catalysts, in this example case in the field of emission control catalysis.

Abstract

The design and commissioning of a cell suitable for operando studies using high-energy-resolution fluorescence-detected X-ray absorption near-edge structure (HERFD-XANES) spectroscopy in the tender X-ray regime is reported. The cell is optimized for measurements within the energy range of 1.5 keV to 4.5 keV. It has a plug-flow geometry and can be used for sieved powder samples, analogous to reactors employed for laboratory tests. The functionality of the spectroscopic cell is demonstrated in the area of emission control using CO oxidation as target reaction over 1 wt.% Rh/γ-Al₂O₃ as catalyst. We show how HERFD-XANES at the Rh L₃-edge captures variations in the noble metal structure resulting from the interaction with the support material and reactant molecules. Moreover, distinct structural changes were identified along the catalyst bed as a function of temperature and local gas mixture.