Abstract
<jats:p>X-ray photoelectron spectroscopy (XPS), characterised by a high surface sensitivity with a typical information depth of the order of a few nanometres is one of the most suitable techniques for the investigation of heterogeneous catalysts. As largely documented in the literature, the XPS technique can provide qualitative, quantitative and sometimes morphological information on the most external layer of a material in a non-destructive way. A drawback however is represented by the so-called ‘pressure gap’ between the high vacuum conditions required by the XPS technique and the high pressure or ambient pressure of the catalytic reaction. Nevertheless, to get around this problem, most XPS investigations are performed on the catalyst before and after catalytic reaction. Over the past two decades, advancements in technical aspects have enabled XPS measurements to be conducted under near ambient pressure conditions (NAP-XPS). In the present chapter some of the XPS investigations of the most recurrent catalytic materials used in heterogeneous catalysis will be described. The chapter intends to demonstrate the unique information that is derived from the technique. Three types of materials will be considered: (i) supported metal catalysts; (ii) supported oxide catalysts and (iii) sulfur-based catalysts. Some of the case studies will include application of ‘ambient pressure XPS’ to investigate catalytic processes under more realistic conditions.</jats:p>