Rh K-Edge High-Energy-Resolution Fluorescence-Detected X-ray Absorption Near-Edge Structure Spectroscopy Reveals Deactivated RhAlO x Structure in Aged Rh/γ-Al2O3 Catalyst

Rh K-edge high-energy-resolution fluorescence-detected (HERFD) X-ray absorption near-edge structure (XANES) spectroscopy was used to investigate the deactivated structure in an aged Rh/gamma-Al2O3 catalyst for automotive gas purification, which has been difficult to identify using conventional XANES spectroscopy. HERFD-XANES spectroscopy uncovered the distinct spectral features of the deactivated structure in the aged Rh/gamma-Al2O3 catalyst, which differed from those of supported Rh2O3 and Rh metal species. Spectral simulations of possible deactivated structures revealed the formation of Rh3+ doped in gamma-Al2O3 or rhodium aluminate with octahedral coordination (octahedral RhAlO x ) as the deactivated structure. The spectrum of octahedral RhAlO x was extracted from the measured spectra of fresh and aged Rh/gamma-Al2O3 samples before and after H2 treatment at 600 degrees C using linear combination fitting analysis, thereby enabling the quantification of the fraction of octahedral RhAlO x present in the aged Rh/gamma-Al2O3 catalyst. This study not only demonstrates the identification and quantification of octahedral RhAlO x in aged Rh/Al2O3 using Rh K-edge HERFD-XANES spectroscopy but also highlights the potential of HERFD-XANES spectroscopy to deepen our understanding of catalyst structures and consequently facilitate catalyst development.