A fast XPS study of sulphate promoted propene decomposition over Pt{111}

SO₂ oxidation has been followed by Fast XPS over Pt{111}. Preadsorbed oxygen reduces the low temperature saturation coverage of SO2 with respect to the clean surface. Heating a mixed O₂/SO₂ adlayer results in efficient oxidation of both upright and flat-lying SO₂ molecules to surface-bound SO₄. Sulphate decomposes above room temperature liberating gas-phase SO₂ and SO₃. Propene adsorbs molecularly at 100 K over clean Pt{111} and dehydrogenates above 250 K to form a stable propylidyne adlayer, which in turn decomposes above 400 K to form graphitic carbon. Preadsorbed surface sulphate enhances the sticking probability of propene via formation of an alkyl-sulphate complex. Thermal decomposition of this complex accounts for low temperature propene combustion and is accompanied by atomic sulpur deposition. Propylidyne forms as on clean Pt but is less reactive undergoing partial oxidation above 450 K with residual surface oxygen.