Operando NAP-XPS Studies of a Ceria-Supported Pd Catalyst for CO Oxidation

Supported Pd/CeO2 catalytic systems have been widely investigated in the low-temperature oxidation of CO (LTO CO) due to unique oxygen storage capacity and redox properties ceria support, which highly influence structural, chemical electronic state Pd species. Herein, operando near-ambient pressure XPS (NAP-XPS) technique has allowed study a conventional catalyst surface during reaction under experimental conditions closer actual reaction, unfeasible with other science techniques that demand UHV conditions. SEM, HRTEM XRD analyses powder catalyst, prepared by incipient wetness impregnation, reveal uniformly CeO2-loaded NPs less than 2 nm size, generated an increase vacancies concomitant reduction, as indicated H2-TPR Raman measurements. Adsorbed peroxide (O22?) species on could also be detected spectra. Operando NAP-XPS results obtained at ALBA Synchrotron Light Source revealed two kinds conditions, namely PdOx PdII ions PdxCe1?xO2?? solution, latter one appearing crucial for oxidation. By means non-destructive depth profile analysis using variable synchrotron excitation energies, location role these palladium clarified: was found prevail upper layers metallic supported CO, while mixture it rapidly depleted from surface, leaving greater amount subsurface (7% vs. 12%, respectively). On contrary, phase, created Pd–CeO2 interface contact gas environment, appeared predominant catalyst. Its presence evolution, acting route through active transferred