In situ probing of the near-surface properties of heterogeneous catalysts under reaction conditions: An introduction to total electron-yield XAS

Over the last two years, our understanding of gas-flow total electron-yield (TEY) detection for in situ X-ray absorption spectroscopy (XAS) has rapidly progressed. A short summary of recent developments is presented with a particular view to applications in the field of heterogeneous catalysis. For the first time, true in situ TEY data (of Ni- and Cu-based systems) acquired in reactive gas atmospheres and at pressures up to 40 atm are presented. The salient physical principles underlying the formation of the TEY signal are briefly introduced. Previously unexplained 'self-absorption' distortions in the TEY signal are explained by photoelectrons excited by fluorescent photons. The possibilities and limitations of in situ TEY XAS studies are highlighted.