XPS analysis for sulfur on noble metals

摘要

It is well known that the sulfur included in automobile exhaust deactivates the exhaust catalysts, and that the sulfur affects the Pt and Pd catalysts more than the Rh catalyst. The adsorptive state of the sulfur atom on polycrystalline noble metals has been studied with X-ray photoelectron spectroscopy (XPS). The sulfur atom adsorbed on the Pt, Pd and Rh staied on the surface in a vacuum up to 800°C. Under low pressure O{sub}2 conditions (10{sup}(-2)～10{sup}(-1)Pa), the sulfur on the Rh disappeared from the surface at a lower O{sub}2 pressure and temperature than the sulfur on the Pt and Pd. The reaction of sulfur and oxygen on the Pd and Rh in 10{sup}(-6) Pa O{sub}2 has been studied by temperature programmed XPS(TPXPS). On the Pd, the adsorbed sulfur decreased at temperatures between 200°C and 250°C for only a low initial sulfur coverage of less than 0.5 ML. On the Rh, the adsorbed sulfur disappeared from the surface at about 300°C irrespective of sulfur coverage. The activation energy for the SO{sub}2 recombination on the Pd and Rh derived from the Arrhenius plots were 57±16, 32±6kJ/mol, respectively.