X-Ray Photoelectron Spectroscopy for Investigation of Heterogeneous Catalytic Processes

X-ray photoelectron spectroscopy (XPS) is commonly applied for the characterization of surfaces in ultrahigh vacuum apparatus, but the application of XPS at elevated pressures has been known for more than 35 years. This chapter is a description of the development of XPS as a novel method to characterize surfaces of catalysts under reaction conditions. This technique offers opportunities for determination of correlations between the electronic surface structures of active catalysts and the catalytic activity, which can be characterized simultaneously by analysis of gas-phase products. Apparatus used for XPS investigations of samples in reactive atmospheres is described here; the application of synchrotron radiation allows the determination of depth profiles in the catalyst, made possible by changes in the photon energy. The methods are illustrated with examples including methanol oxidation on copper and ethene epoxidation on silver. Correlations between the abundance of surface oxygen species and yields of selective oxidation products are presented in detail. Further examples include CO adsorption and methanol decomposition on palladium and CO oxidation on ruthenium.