Carbon materials doped with nitrogen have long been used for SO 2 removal from flue gases for the benefits of the environment. The role of water is generally regarded as hydration of SO 3 which is formed through the oxidization of SO 2 . However, the hydration of SO 2 , especially on the surface of N-doped carbon materials, was almost ignored. In this study, the hydration of SO 2 was investigated in detail on the pyridinic nitrogen (PyN)-doped graphene (GP) surfaces. It is found that, compared with the homogeneous hydration of SO 2 assisted with NH 3 in gas phase, the heterogeneous hydration is much more thermodynamically and kinetically favourable. Specifically, when a single H 2 O molecule is involved, the energy barrier for SO 2 hydration is as low as 0.15 eV, with 0.59 eV released, indicating the hydration of SO 2 can occur at rather low water concentration and temperature. Thermodynamic integration molecular dynamics results show the feasibility of the hydrogenated substrate recovery and the immobilized N acting as a catalytic site for SO 2 hydration. Our findings show that the heterogeneous hydration of SO 2 should be universal and potentially uncover the puzzling reaction mechanism for SO 2 catalytic oxidation at low temperature by N-doped carbon materials.
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