Real-time X-ray photoelectron spectroscopy of surface reactions

The experimental determination of the composition and structure of gas–solid surface interface at different stages of surface reactions is a crucial point in elucidating the reaction mechanism. This requires a quantitative surface sensitive technique, providing information on how the substrate surface, adsorbed species and their bonding configuration evolve at the time scale of the surface processes. The present review illustrates how the high performance levels achieved in X-ray photoelectron spectroscopy at the third generation synchrotron facilities, in particular the reduced data acquisition time down to a second range, have made possible studies of surface processes in real time. The article summarizes the wealth of knowledge that has been gained using representative examples of adsorption systems, where the relation between adsorption–desorption rate, adsorbate coverage, bonding configuration and interconversion between adsorption sites was established, and simple reaction systems, where the effects of the substrate structure and of the changes in the adsorbate layer under non-linear reaction conditions were probed.