An investigation of the reaction mechanism for the promotion of propane oxidation over Pt/Al2O3 by SO2

Total oxidation of propane with oxygen in the absence and the respective pr esence of SO2 in the feed gas was studied over 1 wt% Pt on gamma -Al2O3 usi ng transient experiments with TAP (temporal analysis of products) and in si tu DRIFT spectroscopy. The TAP experiments confirm the promoting role of SO 2 on the conversion of propane and, moreover, show an inhibiting effect fro m SO2 on the conversion of the intermediate products propene and CO. In sit u DRIFT spectroscopy reveals the formation of sulphate species on the catal yst surface and indicates the formation of an allylic intermediate in the a bsence of SO2 only. Interaction between hydrocarbon intermediates and the s ulphate species is confirmed by the appearance of thiol fragments in the ma ss spectra. The transient experiments show that propane in the first step i s irreversibly adsorbed at the surface. Analysis of the surface residence t imes of the products formed at the propane pulse in pump-probe experiments provides information about the reaction pathways. Without S02 in the feed g as, propane reacts consecutively in the sequence propane --> propene -->. e thane --> CO --> CO2. In the presence of SO2 the first step of the main rou te is the breaking of a C-C bond in propane producing ethane and a C-1 frag ment, which then form CO and eventually CO2. It is suggested that the promo ting effect by SO2 on the conversion of propane is due to the formation of an acidic site at the Pt/Al2O3/SO42- interface. (C) 2001 Academic Press.