Mechanistic insights into the formation of sulphur-containing pollutants over LaMnO3 oxygen carriers in coal chemical looping combustion

In coal or coal-derived syngas chemical looping combustion (CLC), the formation of sulphur-containing pollutants is a key factor influencing efficient and clean energy conversion. Elucidating the reaction mechanisms of sulphur species on oxygen carriers is essential for understanding sulphur conversion and removal. In this study, density functional theory (DFT) calculations were performed to investigate the microscopic mechanisms of sulphur conversion on LaMnO 3 (010) during CLC. The adsorption of key sulphur-containing species (SO 2 , S 2 , COS, and CS 2 ) was first examined, revealing that all species can be chemisorbed on the LaMnO 3 surface. The formation pathways of these products were then explored, considering 17 possible reaction routes. The results show that SO 2 preferentially forms via S* reaction with O 2 (1.135 eV), followed by COS via S* reaction with CO (1.646 eV), CS 2 via COS* reaction with S* (2.931 eV), and S 2 via S* dimerization (3.361 eV). The activation energies indicate the relative ease of formation follows the order: SO 2 > COS > CS 2 > S 2 . This mechanistic study of sulphur conversion could provide guidance for developing strategies to control sulphur emissions in large-scale CLC systems. Novelty and significance statement Sulphur chemistry in chemical looping combustion (CLC) remains poorly understood at the atomistic level, despite its critical role in pollutant formation and oxygen carrier performance. This work provides the first comprehensive DFT-based mechanistic analysis of sulphur conversion on the LaMnO 3 (010) surface under CLC-relevant conditions. By systematically examining the adsorption and formation pathways of SO 2 , COS, CS 2 , and S 2 across 17 reaction routes, this study establishes a clear kinetic hierarchy among competing sulphur-containing products. The identified energetically preferred pathways elucidate how surface-bound sulphur intermediates evolve toward distinct gaseous species, offering fundamental insight into sulphur transformation mechanisms on perovskite oxygen carriers (OCs). These findings advance the microscopic understanding of sulphur behaviour in solid-fuel CLC and provide a mechanistic basis for rational strategies to mitigate sulphur-related emissions in advanced combustion systems.