Application of ultraviolet photoelectron spectroscopy (UPS) in the surface characterisation of polycrystalline oxide catalysts. I. Methodics and analytical potential

Polycrystalline oxide surfaces have been investigated by a combination of photoemission and ion-scattering techniques (UPS, XPS, ISS) to assess the analytical potential of UPS for the surface characterisation of real polycrystalline oxide catalysts. UP spectra can be obtained from a number of binary and ternary oxides when the measurement is performed at appropriate temperatures in order to ensure sample conductivity sufficient to avoid surface charging. Where applicable, UPS provides enhanced surface sensitivity (as compared to XPS) and chemical sensitivity permitting the identification of surface structures and adsorbates. The benefit of enhanced surface sensitivity has been demonstrated by the detection of V4+ species in the outmost surface layer(s) of V2O5 The use of the chemical sensitivity for the identification of chemical compounds on a fingerprint basis has been shown by a study of bismuth molybdate surfaces. The chemical sensitivity with respect to adsorbates has been demonstrated by the detection of N-containing species formed in the interaction of V2O5 with NH3.