Quantitative surface analysis by XPS: Application to hydrotreating catalysts

XPS is an ideal technique to provide the chemical composition of the ex-ti-erne surface of solid materials, vastly applied to the study of catalysts. In this article, we will show that a quantitative approach, based upon fundamental expression of the the XPS signal, has enabled us to obtain a consistent set of response factors for the elements of the periodic table. In-depth spadework has been necessary, to know precisely the transmission function of the spectrometer used at IFP. The set of response factors obtained enables to perform, on a routine basis, a quantitative analysis with approximately 20% relative accuracy: which is quite acceptable for an analysis of such a nature. While using this quantitative approach, we have developed an analytical method specific to hydrotreating catalysts that allows obtaining the sulphiding degree of molybdenum quite reliably and reproducibly. The usage of this method is illustrated by two examples for which XPS spectroscopy has provided with information sufficiently accurate and quantitative to help understand the reactivity differences between certain MoS2/Al2O3 or NiMoS/Al2O3-type hydrotreating catalysts.