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 fund amental expression of the the XPS signal, has enabled us to obtain a consis tent set of response factors for the elements of the periodic table. In-dep th spadework has been necessary, to know precisely the transmission functio n of the spectrometer used at IFP. The set of response factors obtained ena bles to perform, on a routine basis, a quantitative analysis with approxima tely 20% relative accuracy: which is quite acceptable for an analysis of su ch a nature. While using this quantitative approach, we have developed an analytical met hod specific to hydrotreating catalysts that allows obtaining the sulphidin g degree of molybdenum quite reliably and reproducibly. The usage of this m ethod is illustrated by two examples for which XPS spectroscopy has provide d with information sufficiently accurate and quantitative to help understan d the reactivity differences between certain MoS2/Al2O3 or NiMoS/Al2O3-type hydrotreating catalysts.