The molecular mechanism of low-temperature decomposition of hydrogen sulfide under conjugated chemisorption-catalysis conditions

Abstract

The molecular mechanism of interaction of two hydrogen sulfide molecules with the ( Co III − H o ) 2 S 2 ( SH 2 ) 4 model active center containing occluded hydrogen was studied by the density functional theory method with the B3P86 hybrid exchange-correlation functional. The reaction was found to occur in the following elementary steps: molecular adsorption of hydrogen sulfide ⇒ dissociative chemisorption ⇒ S-S bond formation in the surface intermediate { 2 Co III - ( µ - S 2 ) + 2H(ads)} with the release of the first hydrogen molecule into the gas phase c 2 (g) ⇒ the release of the second hydrogen molecule into the gas phase c 2 (g) ⇒ the formation of cyclooctasulfur in the reaction 4 S 2 (ads) S 8 (ads). The first three steps occur spontaneously at room temperature, the thermodynamic driving force of the process being the stoichiometric reaction of S-S bond formation at the stage of conjugated chemisorption of two hydrogen sulfide molecules on two adjacent metal ions with the release of the first hydrogen molecule into the gas phase. The catalytic cycle is terminated by the recombination of molecular sulfur S 2 into cyclooctasulfur S 8 in the adsorption layer and the release of the second hydrogen molecule into the gas phase.