Журнал термодинамики и катализа
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The Reaction Mechanisms of H2S Decomposition into Hydrogen and Sulfur: Application of Classical and Biological Thermodynamics

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Four possible pathways of H₂S decomposition into hydrogen and elemental sulfur are considered. In the thermal reversible process, H₂S dissociation results in the formation of diatomic both hydrogen and sulfur in the singlet state according to the rule of spin conservation:

(i)

On the surface of sulfide catalysts, irreversible H₂S splitting proceeds at low temperature through the stage of disulfane, H₂S₂ formation as a key surface intermediate, followed by its decomposition due to release of hydrogen into the gas phase and recombination of the adsorbed singlet sulfur into cyclooctasulfur:

(ii)

On metal catalysts, irreversible H₂S decomposition occurs at low temperature through the stage of H₂S dissociation into the adsorbed atomic surface species resulted in the formation of both diatomic reaction products in the ground electronic state -the singlet hydrogen and the triplet diatomic sulfur:

(iii)

The reactions (ii) and (iii) are considered to be realized under the principles of biological thermodynamics, in the absence of catalyst both reactions are thermodynamically prohibited in the gas phase. The mechanism of H₂S assimilation by sulfur bacteria is suggested to occur in the processes of chemosynthesis resulted in the formation of colorless sulfur globules and activated hydrogen:

(iv)

Similar to the bacterial process, the hydrogen production from H₂S is realized with the efficiency of 99.6% on metal catalysts immersed into the liquid which is capable well-dissolving H₂S.