DEFECT STRUCTURE OF CLEAN AND CHLORINATED ALUMINUM-OXIDE FILMS PROBED BY METHANOL CHEMISORPTION

We have shown that clean gamma- and alpha-Al2O3 films, prepared under relatively high pressure oxidation conditions, display methanol chemisorption properties and reactivity that are typical of powder alumina catalysts. Detailed vibrational and electronic information can be obtained for adsorbates on these thin-film oxides and is consistent with the surface chemistry expected of traditional powder oxides. The low activity toward dissociation of methanol and the low methoxy stability characteristic of our alumina films are in contrast to the highly active nature of UHV-oxidized aluminum surfaces, which have been used extensively to model alumina surfaces. Because high activation energies for dissociative chemisorption on oxides hinder traditional UHV approaches, we have studied methanol reactions effectively under higher pressure conditions. Reaction in several Torr of methanol at 425 K produced the stable formate species, which shows the similarity of our alumina films to powdered alumina surfaces. Chlorinated Al2O3 films, however, stabilized the methoxy species under similar conditions. A Fourier de-Poissonization technique, which removed oxide multiple and combination losses, significantly improved identification of adsorbate features in the HREELS data. There is a substantial opportunity for further examination of the stability and decomposition pathways of methoxy and related intermediates formed under such reaction conditions.