TOF‐SIMS characterization of an aluminovanadate oxide catalyst

Time‐of‐flight Secondary Ion Mass Spectrometry (TOF‐SIMS) has been employed to characterize the surface physical and chemical state of aluminovanadate oxide catalyst precursors (‘V? Al? O’) precipitated at different pH values in the range of 5.5…10. The reference oxide V₂O₅ has also been studied for comparison purposes. It is shown that the analysis of molecular ion emission yields valuable information on the surface elemental and phase composition. Increasing pH values while precipitating from aqueous precursor solutions are found to result in a monotonic variation of the surface composition, in a progressive hydroxylation of aluminium and vanadium and in an increasing dispersion of vanadium oxide species. SIMS data evaluated on the basis of Plog's valence model of molecular ion emission reveal reduced V⁴⁺ states, the fraction of which is dependent on the pH value. The SIMS results are supported by XPS data. The enhancement of the catalytic activity in oxidative propane dehydrogenation over V? Al? O prepared at high precipitation pH is in good correlation with the measured surface characteristics. Copyright © 2007 John Wiley & Sons, Ltd.