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Abstract

The adsorption and temperature-dependent decomposition of SO₂ on Ni(110) has been studied by core-level photoemission and X-ray absorption fine structure measurements. The analysis shows that on adsorption at 160 K SO₂ partly decomposes, leaving SO₃ and atomic S on the surface. Two different, nearly flat-lying SO₂ species are observed which correspond to long-bridge and short-bridge S sites. The S atoms of co-adsorbed atoms of SO₃ occupy short-bridge sites with the C₃ axis of SO₃ being oriented approximately perpendicular to the surface, whereas atomic S is located in two-fold hollow sites. The average S–Ni bond length of all S-containing species measures 2.30±0.04 Å. On heating this co-adsorption phase to room temperature, SO₂ completely disappears from the surface, the coverages of adsorbed SO₃ and S increase and small amounts of atomic O show up. On further heating, SO₃ decomposes completely, increasing the amounts of atomic S and O on the surface while SO₂ is observed in the gas phase. At still higher temperatures, only atomic S remains adsorbed in a quasi five-fold coordinated site with an average S–Ni bond length of 2.26±0.04 Å.