NEXAFS studies of the reaction of SO₂ with TiO₂(100)-(1 × 1) and -(1 × 3)

S K-edge NEXAFS has been used to monitor the thermally-activated reaction of SO₂ with TiO₂(100)-(1 × 3) and TiO₂(100)-(1 × 1) in order to investigate the influence of surface structure and oxygen vacancies on the reactivity. In each case SO₂ chernisorbs 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)-(1 × 3) following SO₂ exposure.