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ABSTRACT
The mechanism of N2O homogeneous and heterogeneous reactions with CO were investigated using density functional theory (DFT). The M06-2X method with the 6–311 G(d) basis set were adopted for geometry optimization and energy calculations of each configuration (reactants, intermediates, transition states and products). Thermodynamic and kinetic analyzes were also conducted to study the influence of temperature on the reaction process. Calculation results showed that there are two channels for the homogeneous reaction between N2O and CO. In addition, the heterogeneous reduction reaction of N2O and CO has two possible reaction pathways due to the different adsorption configurations of CO on char surface. From thermodynamic analysis, the enthalpy difference (ΔH) and Gibbs free energy difference (ΔG) of the homogeneous and heterogeneous reactions are both negative, which indicates that the reaction of N2O and CO is an exothermic process and can take place spontaneously. For the both homogeneous and heterogeneous reactions between N2O and CO, the equilibrium constant of the N2O and CO reaction is always higher than 105 at 800 ~ 1800 K, suggesting that the reaction can be carried out completely. From the kinetic analysis, activation energy of the heterogeneous reaction (137.26 kJ/mol) is much lower than that of the homogeneous reactions (224.53 kJ/mol and 215.89 kJ/mol), which indicates that the reduction reaction of N2O with CO is more likely to take place on char surface. The calculation results explain the reaction mechanism of N2O and CO, which can provide a theoretical foundation for N2O emission.
Acknowledgments
The financial support from the National Natural Science Foundation of China (51906070) is gratefully acknowledged.