A new insight into SO2 low-temperature catalytic oxidation in porous carbon materials: non-dissociated O2 molecule as oxidant

Abstract

SO₂ oxidation is the rate-determining step during the process of low-temperature SO₂ conversion to high-value H₂SO₄ in porous carbon materials. Non-dissociated O₂ molecules and chemisorbed O atoms from O₂ dissociation are possible oxidants for SO₂ oxidation. While the pathways of oxidation reactions in which chemisorbed O atoms participate have been previously studied via density functional theory calculation, the possible SO₂ oxidation pathways by non-dissociated O₂ remain to be investigated. Inspired by the mechanism in which a non-dissociated O₂ molecule oxidizes other molecules such as CO and NO, we elucidate the detailed pathways for SO₂ oxidation by non-dissociated O₂ using density functional theory calculation assisted by SO₂ removal experiment validation. Computational results show that non-dissociated O₂ can be activated at the active sites of porous carbon, generating a C–O–O structure. By low-barrier O transfer processes, the formed C–O–O structure can directly oxidize gaseous SO₂ to SO₃ without the need of the SO₂ chemisorption process. Transient response experiments further validate that the oxidant for SO₂ conversion to SO₃ in porous carbon materials is non-dissociated O₂. This work reveals the role of non-dissociated O₂ in directly oxidizing non-chemisorbed SO₂ to SO₃ at low temperature, providing a new understanding for SO₂ conversion to SO₃ in porous carbon materials.