Chemisorption on platinum and tungsten

Abstract

Adsorption of H₂S, H₂Se, SO₂ and CS₂ has been studied on metal films of platinum and tungsten in the temperature range –80 to about 250°C. Fast dissociative chemisorption of H₂S and H₂Se occurred on platinum film at –80°C and with increasing surface coverage H₂ appeared in the gas phase. Extensive adsorption of H₂Se occurred on a W film at –80°C without H₂ evolution. There was a further, but slow, dissociative adsorption of H₂S and H₂Se on a Pt film above 30°C with activation energies of 46 and 24 kJ mol^–1 respectively. On a W film, the slow dissociative chemisorption of H₂Se began above 60°C with an activation energy of 29 kJ mol^–1.

Adsorption of SO₂ and CS₂ on Pt at –80°C was molecular and completely reversible. No further interaction was detected on the film at any temperature up to 250°C. There were two possible modes of chemisorption on the W film-one rapid, mostly weak, and tending to predominate at low temperatures (–80°C), the other slow, stronger and predominating at high temperatures. Furthermore, while a substantial fraction of the adsorption at the low temperature was reversible, high temperature adsorption was completely irreversible and occurred with activation energies of 93 and 125 kJ mol^–1 for SO₂ and CS₂ respectively.