Stroboscopic operando spectroscopy of the dynamics in heterogeneous catalysis by event-averaging

Heterogeneous catalyst surfaces are highly dynamic entities that respond rapidly to changes in their local gas environment, and the dynamics of the response is a decisive factor for the catalysts’ action and activity. Few probes are able to map catalyst structure and local gas environment simultaneously under reaction conditions at the time scales of the dynamic changes. Here we use the CO oxidation reaction over a Pd(100) surface exposed to pressures of 3 and 100 mbar of a CO + O2 gas mixture to demonstrate how such studies can be performed by time-resolved ambient pressure photoelectron spectroscopy. Central elements of the method are cyclic gas pulsing and software-based event-averaging by image recognition of spectral features. For the CO oxidation reaction over Pd(100) our main finding is that that all surface phases – the CO-covered Pd surface, a surface oxide and a thick PdOx phase – catalyse the CO oxidation reaction, in dependence on the supply of gas phase reactants.