Enhanced heterogenous hydration of SO(2) through immobilization of pyridinic-N on carbon materials

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.