The crucial role of oxygen in NO heterogeneous reduction with NH3 at high temperature

Abstract

The high-temperature ammonia-injected technology is acknowledged as a promising denitrification method with great NOx reduction potential. In this work, char reduction experiments and density functional theory (DFT) calculations were conducted to investigate the heterogeneous reduction mechanism of NO by ammonia (NH3) synergism with char, focusing on the role of O2. Experimental results indicate that O2 has an inhibition effect on the NO reduction efficiency, whose detailed mechanisms can be inferred from a molecular perspective. Theoretical results reveal that both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms exist in the NH3-injected denitrification reactions, presenting significant differences in N2, N2O, and H2O evolution. By comparison, the E-R mechanism governs the NH3–NO reactions, which reduces barriers by up to 14.5 %. The presence of O2 can lead to a significant increase in the energy barriers with a concomitant decrease in reaction rates within a certain temperature range, which however does not change the dominant mechanism governing the NH3 and NO interactions. Although some controversies are found in the kinetic analysis when the temperature increases, the results here shed light on the NO heterogeneous reduction mechanisms with NH3 at high temperature, which also guides the coal/NH3 co-firing investigations.