Reaction mechanism of heterogeneous reduction of NO₂ on carbonaceous surface

Based on the quantum chemical density functional theory(DFT), the mechanism of heterogeneous reduction of NO₂ on carbonaceous surface was studied. For zigzag and armchair carbonaceous surfaces, M06-2X method and 6-311G(d) basis set were used to optimize the geometry configuration and energy of all stagnation points under different reaction paths, and the reaction paths were analyzed and compared from thermodynamics and kinetics. The role of CO in the heterogeneous reduction of NO₂ was deeply investigated, and the effects of carbon surface and reaction temperature on the heterogeneous reaction were also investigated. The results show that the heterogeneous reduction process of NO₂ on the carbon surface can be divided into two stages: the reduction stage of NO₂ and the desorption stage of carbon oxide. By comparing the reactions without CO molecules, it can be seen that the CO molecules involved in the reaction can reduce the reaction energy barrier of each stage and accelerate the reaction rate of each stage. In the presence of CO molecule, the reaction energy barrier at the reduction stage of NO₂ is reduced, which promotes the heterogeneous reaction process of NO₂ reduction to NO. CO molecules participating in the reaction can combine with the residual oxygen atoms on the surface to form and release CO₂ molecules, which reduces the reaction energy barrier in the release stage of carbon oxides, thus promoting the overall reduction reaction. In addition, the energy barrier of NO₂ heterogeneous reduction reaction on zigzag surface is lower and the reaction rate is faster than that on armchair surface, which indicates that the heterogeneous reduction reaction of NO₂ is easier on Zigzag carbonaceous surface. Finally, the reaction kinetics analysis shows that the reaction rate of each stage increases with the increase of temperature, which indicates that increasing temperature can promote the heterogeneous reduction of NO₂ on the carbonaceous surface.