NEXAFS studies of the reaction of SO2 with TiO2(100)-(1x1) and -(1x3)

S K-edge NEXAFS has bean used to monitor the thermally-activated reaction of SO2 with TiO2(100)-(1x3) and TiO2(100)-(1x1) in order to investigate the influence of surface structure and oxygen vacancies on the reactivity. In each case SO2 chemisorbs at 110 K, reacting further to form a sulphite-like intermediate species at higher temperatures (110-400 K). This intermediate transforms to a sulphate-like species as the temperature is further increased (130-500 K). The polarisation dependence of the NEXAFS for the sulphate-like species on both substrates at 130-220 K evidences a lowering of the expected T-d molecular symmetry. Overall, the data indicate that the mesoscopic morphology of the substrate has little influence on the adsorption site or reaction pathway for SO2. In addition, the only discernable effect of oxygen vacancies on the reaction is that 0.03 ML of sulphide is formed on TiO2(100)-(1x3) following SO2 exposure.