Abstract
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 CO2, whereas the impact mechanism is far from conclusive. Herein, fixed-bed experiments and computational methods were adopted to elucidate the role of CO2 on char–NO reaction. Experimentally, CO2 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–CO2 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 CO2-mediated oxygen rearrangement (CO2-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 CO2 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 CO2 in the heterogeneous reduction of NO on char surface.
Published Version
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