Oxidation of SO2 and NO by epoxy groups on graphene oxides: the role of the hydroxyl group

Abstract

Simultaneous catalytic removal of SO₂ and NO_x at low temperature (<150 °C) has long been recognized as a challenge for the treatment of coal-burned flue gases. Density functional theory corrected with dispersion was used to investigate the potential of graphene oxides (GOs) for the catalytic oxidation of SO₂ and NO_x. It is found that both the SO₂ and NO_x can be oxidized by epoxy groups of GO nearly at room temperature. The hydroxyl groups on the GO surface enhance the adsorption and oxidation of SO₂, and of NO as well, but in quite different ways. For the case of SO₂, the promotion is derived from the formation of charge transfer channels, which are fabricated by the hydroxyl group, the adsorbed SO₂ and the epoxy group. The promotion is enhanced by the introduction of more hydroxyl groups as more charge transfer channels are formed. However, for NO, the hydroxyl group leads to a strong N–C covalent interaction between the adsorbed NO molecules and the GO surface, through which the NO is activated and oxidized with a much lower barrier. These results provide a mechanistic explanation of the low temperature catalytic oxidation of SO₂ and NO by carbon materials and insights into designing new carbon-based catalysts.