Microscopic insights into the effect of oxygen on the NO reduction during ammonia co-firing with pulverized coal

The co-firing of ammonia (NH3) and coal provides a feasible solution for reducing CO2 emissions in power plants, leaving behind problems associated with NOx emissions. In this study, the heterogeneous reduction of NO by NH3 and coal char was systematically investigated by combining density functional theory (DFT) and canonical variational transition-state theory (CVT) methods, elucidating the atomic-level mechanisms of O2 influence. Two char models modified with the Fe contribute to a better representation of the catalytic effect of minerals. In view of two forms of oxidation, the adsorption characteristics and microscopic pathways were characterized for NH3-NO reactions, which go some way toward lending credit to the experimental results. The results show that the Eley-Rideal mechanism governs the process of NO reduction by NH3, no matter whether O2 is present or not. Thermodynamic and kinetic analyses reveal that the presence of O2 inhibits NO reduction primarily through the formation of NO2 and its subsequent interaction with NH3. The presence of the oxygen-containing functional group improves the surface activity of char, suppressing the adverse impact of O2 in N2 release at high temperatures. These results contribute to the understanding of the NH3/coal co-firing mechanisms, making further efforts to reduce NO emissions.