III International Conference

PP-I-55MOLECULAR MECHANISM OF LOW TEMPERATURE DECOMPOSITION OFHYDROGEN SULFIDE INTO HYDROGEN AND ELEMENTAL SULFURVoroshina O.V., Bauman Yu.I., Zakharov I.I., Startsev A.N.Boreskov Institute of Catalysis SB RAS, Novosibirsk, RussiaE-mail: Voroshin@catalysis.nsk.suA new pathway of low temperature catalytic decomposition of hydrogen sulfide intohydrogen and sulfur is found. The reaction occurs at ambient temperature over sulfidecatalysts in the following elementary steps: molecular adsorption of two molecules ofhydrogen sulfide on two adjacent atoms of Co III with d 6 electronic configuration ⇒ adissociative chemisorption of hydrogen sulfide ⇒ the formation of S–S bond in the surfaceintermediate 2Co III -μ(S 2 ) a following the release of the first hydrogen molecule into the gasphase ⇒ the release of the second hydrogen molecule into the gas phase ⇒ the formation ofthe cyclooctasulfur in the surface reaction (4 S 2 → S 8 ). The first three steps can occurspontaneously without an activation energy. The thermodynamic driving force of the overallreaction appears to be the S–S bond formation inside the surface key intermediate togetherwith the release of the dihydrogen molecule into the gas phase. The catalytic cycle isterminated with recombination (oligomerization) of molecular sulfur S 2 into cyclooctasulfurS 8 and removal of the second hydrogen molecule into the gas phase.Experiments on the catalytic decomposition of hydrogen sulfide into hydrogen andelemental sulfur were carried out both in flow regime at room temperature. The sulfidecatalyst was additionally sulfided in situ in a flow of H 2 S at 400 o C, cooled down to 200 o Cand flushed out with argon or helium. Hydrogen was detected both by a thermal conductivityand thermochemical detectors. H 2 S was passed through a catalyst bed at room temperaturewith concentration in helium (argon) ranged from 0.018 to 6 vol. %. After saturation of thecatalyst surface with adsorbed H 2 S, the catalyst was isolated and the closed system washeated to 40-70 o C to avoid sublimation of elemental sulfur from the catalyst surface. In thegas phase only hydrogen was detected. The cycles H 2 S adsorption ⇒ heating were repeatedfor several times until the catalyst surface was blocked with elemental sulfur. To removesulfur, the catalyst was heated to 100-200 o C.AcknowledgementsThe paper is supported by Russian Foundation of Basic Research, Grant No 04-03-32188.104