Enhanced heterogenous hydration of SO2 through immobilization of pyridinic-N on carbon materials.

Carbon materials doped with nitrogen have long been used for SO2 removal from flue gases for the benefits of the environment. The role of water is generally regarded as hydration of SO3 which is formed through the oxidization of SO2. However, the hydration of SO2, especially on the surface of N-doped carbon materials, was almost ignored. In this study, the hydration of SO2 was investigated in detail on the pyridinic nitrogen (PyN)-doped graphene (GP) surfaces. It is found that, compared with the homogeneous hydration of SO2 assisted with NH3 in gas phase, the heterogeneous hydration is much more thermodynamically and kinetically favourable. Specifically, when a single H2O molecule is involved, the energy barrier for SO2 hydration is as low as 0.15 eV, with 0.59 eV released, indicating the hydration of SO2 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 SO2 hydration. Our findings show that the heterogeneous hydration of SO2 should be universal and potentially uncover the puzzling reaction mechanism for SO2 catalytic oxidation at low temperature by N-doped carbon materials.