Exploration of the NO-char reaction pathway by in-situ DRIFTS and isotope gas tracing techniques

Abstract

For NO abatement by carbon-based material (for example, char), many studies have been performed on the reactions between carbon and NO. Oxygen is believed to play a key role during the denitrification process: not only positive, but also negative. Some specific intermediates are worth investigating, and reaction routes are needed to be clarified in order to reveal and explain the mechanism of the concerned reactions. To account for the reaction scheme, chemical evolution information of both solid surface side and gaseous side are collected and analyzed by means of in-situ DRIFTS analysis and isotopic gas tracing, respectively. In combination with experimental results of the NO-char reaction in a fixed bed, possible reaction pathway is proposed. The in-situ DRIFTS analysis shows that C(N) and thermodynamically active C = O complexes are produced during NO adsorption on coal char. The presence of O2 promotes the chemisorption of NO molecules. Oxygen combines with carbon to generate not only thermodynamically stable C-O complexes but active C = O complexes. Step response experiments using isotope gas tracing technique demonstrate that CO and CO2 are produced by C = O desorption and the combination between C-O and C = O complexes, respectively. N2 is generated by the reaction of C(N) complexes on the coal char surface with NO molecules in gas phase. The stable C-O complexes promote NO adsorption and dissociation by reaction with C = O complexes and subsequently producing new active sites.