QUANTITATIVE XPS STUDIES OF A NATURAL CATALYST

The surface characterization by X-ray photoelectron spectroscopy (XPS) of a natural mineral found in the Venezuelan Andes is reported. We pr esent XPS studies for the natural mineral (sample ULA2) and for the mi neral after it has served as a catalyst (sample ULA1) in a Fischer-Tro psch reaction for three months. The effect of different treatments on these samples is also investigated. Both samples exhibit a differentia l charge effect which is present once their surfaces have interacted w ith hydrogen. The quantitative XPS results allow us to advance the com position of these samples. The presence of a negatively charged hydrog en species in our samples is discussed based on our XPS results and su pported by work function measurements.