Theoretical and experimental insights into the effects of CO2 on the heterogeneous NO reduction over char surface: Gasification and CO2-mediated oxygen rearrangement

Nitrogen oxides are the major pollutants in solid fuel/waste combustion processes, which can be reduced by unburned or additive chars. The surface char–NO reaction is significantly influenced by CO 2 , whereas the impact mechanism is far from conclusive. Herein, fixed-bed experiments and computational methods were adopted to elucidate the role of CO 2 on char–NO reaction. Experimentally, CO 2 exhibited an inhibitive impact on NO reduction at 873 K but a promotive influence at 1023 K and 1173 K. According to the detection of outlet CO, characterization of char, and density function theory (DFT) calculations, CO and gasified char derived from char–CO 2 gasification are both responsible for the promotive effect at 1173 K, which offers a clear image of the gasification mechanism conjectured in previous work. More importantly, a CO 2 -mediated oxygen rearrangement (CO 2 -MOR) mechanism has been found and confirmed for the first time, which can well explain the experimental results observed at 873 K and 1023 K. The adsorbed CO 2 can intervene in the oxygen rearrangement on the char surface to alter the NO reduction behaviors. The present study offers a comprehensive insight into the roles of CO 2 in the heterogeneous reduction of NO on char surface.