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

Polycrystalline oxide surfaces have been investigated by a combination of p hotoemission and ion-scattering techniques (UPS, XPS, ISS) to assess the an alytical potential of UPS for the surface characterisation of real polycrys talline oxide catalysts. UP spectra can be obtained from a number of binary and ternary oxides when the measurement is performed at appropriate temper atures in order to ensure sample conductivity sufficient to avoid surface c harging. Where applicable, UPS provides enhanced surface sensitivity (as co mpared to XPS) and chemical sensitivity permitting the identification of su rface structures and adsorbates. The benefit of enhanced surface sensitivit y has been demonstrated by the detection of V4+ species in the outmost surf ace layer(s) of V2O5 The use of the chemical sensitivity for the identifica tion of chemical compounds on a fingerprint basis has been shown by a study of bismuth molybdate surfaces. The chemical sensitivity with respect to ad sorbates has been demonstrated by the detection of N-containing species for med in the interaction of V2O5 with NH3.