Surface Science Studies of Model Supported Vanadia Catalysts

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Abstract - Vohs 9712774 Professor John M. Vohs, of University of Pennsylvania, will investigate the structure and reactivity of model vanadia catalysts supported on single crystal titania, ceria, zirconia, and magnesia. This fundamental research is of relevance to various industrial processes, such as selective oxidation and ammoxidation of hydrocarbons and alcohols, reduction of nitrogen oxides by ammonia and hydrocarbons, and hydrotreatment of heteroaromatics. HREELS, Auger, RBS, XPS, LEEDS, STM/AFM; TPD of methanol, formic acid, water, ammonia and ethylamine; reaction kinetics of the atmospheric pressure oxidation of methanol; and reduction of NOx with NH3 will be the primary techniques to characterize structure and reactivity. The distinctive feature of this investigation is the vapor deposition of uniform (possibly epitaxial) vanadia overlayers and the determination of the strength of the support-O-V bonds -- to which the selectivity of supported vanadia is usually attributed. Such strength will be correlated with local structure and probe molecule reactivity, and will be varied by the composition and structure of the support. The vibrational characteristics of both supported vanadia and chemisorbed probe molecules will be determined with an HREELS technique having spectral resolution as low as 8 cm-1. In addition, the author will study the surface-O stretching modes, and the O-V-O bending modes, which are more indicative of support interaction than the V=O mode. Surface species (hydroxyl, amino, nitrosyl, methoxy) will be produced by chemisorption and desorbed by TPD. The steady state reactions (methanol oxidation or NOx SCR with NH3) will be carried out on a side microreactor chamber to which samples can be transferred without air exposure.