The crucial role of catalysts in the reaction of low temperature decomposition of hydrogen sulfide: Non-equilibrium thermodynamics of the irreversible process in an open system

Abstract

The reaction mechanisms of low-temperature H2S decomposition on sulfide and metal catalysts are considered in the framework of thermodynamics of non-equilibrium irreversible biological processes for open systems, since these reactions occur at room temperature without supplying thermal energy from the outside owing to the internal energy of substrate molecules – hydrogen sulfide. On sulfide catalysts the irreversible process of H2S decomposition proceeds through the stage of formation of hydrogen disulfide (disulfane), H2S2, as a key intermediate, and the reaction products are hydrogen and solid sulfur. The reaction occurs through a sequence of consecutive exothermic stages of dissociation of H2S molecules, in which the entropy of the system is reduced due to its dissipation into environment as the bound (waste) energy TΔS. The remaining part of the free energy ΔG is accumulated on the catalyst surface and is used for the implementation of the energy-intensive step of decomposition of the adsorbed intermediate. Similarly, the metal catalyst provides capture and accumulation of energy from the exothermic processes of adsorption and dissociation of the initial H2S molecules in the atomic adsorbed species of hydrogen and sulfur. The stored energy is used for chemical conversion of adsorbed intermediates into the final reaction products – molecular hydrogen and diatomic triplet sulfur, followed by it does desorption into the gas phase. When H2S is decomposed on metal catalysts at room temperature, along with hydrogen, previously unknown diatomic gaseous sulfur in the ground triplet state is obtained, the existence of which is predicted by quantum chemistry. Some properties of the triplet sulfur and the white globular hexagonal sulfur obtained from its saturated aqueous solutions (which is also a previously unknown allotrope of solid sulfur) are considered. Similarity of the morphology of hydrophilic white sulfur globules and bacterial colorless sulfur S0 obtained by sulfur bacteria in the processes of chemosynthesis of organic matter from CO2 and H2S, allowed to develop an alternative hypothesis about the nature of bacterial sulfur S0 and possible mechanism of chemosynthesis of carbohydrates with the participation of sulfur bacteria. Apparently, the low-temperature catalytic decomposition of hydrogen sulfide is the first example in heterogeneous catalysis, when the principles of non-equilibrium biological thermodynamics in open systems are used to justify the possibility implementing a heterogeneous catalytic reaction.