Application of density functional theory on the NO-char heterogeneous reduction mechanism in the presence of CO2

Abstract

In order to obtain the mechanism of the effect of CO2 on the NO heterogeneous reduction, density functional theory (DFT) was adopted to investigate the interactions between char and NO with the participation of CO2. The armchair configuration composed with several aromatic ring clusters was selected as the carbonaceous surfaces. Geometric optimizations were carried out at the B3LYP-D3/6-31G(d) level. Energies of optimized geometries were calculated at the B3LYP-D3/def2-TZVP level. The results show that, the surface carbonyl groups produced by the adsorption of CO2 combine with the adsorbed NO to desorb CO2, thereby providing adjacent carbon active sites for subsequent NO adsorption and N2 desorption. Thermodynamic studies show that the exothermic heat of this reaction is 853.9 kJ/mol, and the highest energy barrier is 297.0 kJ/mol without the participation of CO2, but the exothermic heat of this reaction is 593.7 kJ/mol, and the highest energy barrier is 214.1 kJ/mol with the participation of CO2. Kinetic studies show that over the temperature range of 298.15–1800 K, the reaction rate constants of rate-limiting steps are calculated with conventional transition state theory. The rate constant with the participation of CO2 is higher than that without the participation of CO2. In summary, CO2 plays a promoting role in interacting with NO and char and reducing energy barrier to form N2 directly.