Mechanisms for interactions of H2S and Hg0 with oxygen carrier LaMnO3 during chemical looping combustion: a DFT study

Abstract

Mercury (Hg⁰) and hydrogen sulphide (H₂S) inevitably coexist during chemical looping combustion (CLC) of coal or coal-derived syngas. Their interactions with oxygen carriers are critical to understanding mercury transformation and removal. In this study, density functional theory (DFT) calculations were conducted to investigate the reaction mechanisms among Hg⁰, H₂S, and the LaMnO₃(010) surface (a Mn-based perovskite with excellent redox properties and thermal stability). Results show that H₂S, HS, and S chemisorb on the surface via stable S-Mn bonding, while HgS forms through parallel adsorption involving both Hg-Mn and S-Mn bonds. The preferred H₂S decomposition pathway involves simultaneous dehydrogenation to produce S* and H*, with H* subsequently forming H₂ or H₂O. Among the examined reaction routes, Hg⁰ reacts most favourably with S* via the Eley-Rideal mechanism, exhibiting the lowest energy barrier of 2.939 eV. These findings offer atomic-level insight into Hg-S interactions on LaMnO₃ surfaces and provide a theoretical foundation for the rational design of perovskite-based oxygen carriers (OCs) capable of efficient simultaneous mercury capture and sulphur stabilization, thereby advancing integrated Hg⁰ and HgS removal strategies in CLC systems.