Theoretical insights into the effect of CO on the heterogeneous reduction of N2O on char

BACKGROUND The role of CO and adsorption sequence of CO and N2O in the adsorption and reduction of N2O on char was investigated based on density functional theory at the M06-2X/6-311G(d) theoretical level. This study lays a foundation for reaction mechanisms of the influence of CO on heterogeneous N2O reduction on char. RESULTS Zigzag and armchair models were used as char models. The first adsorption of CO increases the limiting-step energy barrier of the reaction by 44.5 kJ center dot mol(-1) compared with the first adsorption of N2O for zigzag char. However, the adsorption sequence does not have an effect for armchair char. The rate-limiting steps of the overall reaction for zigzag and armchair char models occur in the stages of N2O adsorption and N2O reduction, respectively. The introduction of CO has little effect on the N2O adsorption stage but increases the energy barrier of the N2O reduction stage. During the reduction of N2O on coal char, zigzag char releases greater heat than armchair char; moreover, zigzag char has a much lower activation energy than armchair char. CONCLUSION In the simultaneous presence of CO and N2O, the char model prefers to adsorb N2O. The rate-limiting step of the two char models are located in different reaction stages, and CO mainly affects the N2O reduction stage. The presence of CO hinders the reduction of N2O on the surface of both zigzag and armchair char models. A rise of temperature can promote the reduction of N2O by char. Zigzag char is superior to armchair char in both thermodynamics and kinetics. (C) 2023 Society of Chemical Industry (SCI).

Automated summary

In this study, the adsorption and reduction of N2O on char in the presence of CO were investigated using density functional theory. It was found that CO affects the reduction of N2O and the rate-limiting steps occur at different stages for different char models.