Research progress in density functional theory study of char-NO heterogeneous reduction

The nitrogen oxides (NO_x) produced by the high-temperature combustion of coal in coal-fired power plants cause serious pollution to the environment, and the control of NO_x pollutant emission has become a common action around the world. The char-NO heterogeneous reduction reaction that occurs in the reburning zone of the boiler is common during coal combustion process. However, because of the complex chemical structure and composition of char as well as the gas-solid composition in the combustion reaction, the mechanism of the char-NO heterogeneous reduction reaction is not yet clear. In this paper, the research on the char-NO heterogeneous reduction reaction by the density functional theory was summarized. The mechanism of the char-NO reaction was reviewed based on the char model, NO adsorption methods, reaction pathways and the different intermediates produced in reaction pathways. The influence mechanism of CO and minerals on NO heterogeneous reduction was also analyzed. It is pointed out that the oxygen groups and active sites on the edge of the char model are beneficial to NO reduction reaction. The intermediates such as HCN, N₂O and NH₃ are produced by different reaction pathways. CO and catalytic metals can promote the char-NO reaction by increasing the reactive sites, reducing the reaction energy barrier and increasing the reaction rate, which provides a theoretical basis for the improvement of NO heterogeneous reduction reaction mechanism and the control of NO_x emission.