Effect Mechanisms of Sodium on NO Heterogeneous Reduction by Nitrogen-Containing Char: Experimental and DFT Investigation

Abstract

NO heterogeneous reduction by char has great potential in reducing NOx emission. Herein, the Zhundong demineralization coal , the macroscopic and microscopic effects of Na contents and nitrogen-containing functional groups on the heterogeneous reduction by char in the reduction zone or reburning zone of staged combustion were studied by fixed bed experiment and density functional theory (DFT). Experimental results indicated that adding less NaCl(≤1wt.%) could improve the adsorption capacity and reduction rate of NO by char, and the catalytic effect of 0.6wt.% was the best, which was 4.96 and 1.22 times of demineralization coal char, respectively. When the loading amount is ≥ 2wt.%, Na inhibited the adsorption and reduction of NO. The N-6 contents of char were positively correlated with the NO adsorption capacity. Na promoted the adsorption and reduction of NO by increasing the N-6 contents on the char surface . Theoretical calculation further revealed that the single Na atom increased the NO chemisorption heat by 42.4 kJ/mol , and the largest reaction energy barrier decreased by 35.7 kJ/mol , which promoted the adsorption and reduction of NO in the micro-level. While two Na atoms blocked the active sites on the char surface to inhibit the reaction. The reduction of NO to N 2 was accompanied by the release of CO. Na promoted the formation of CO in the reduction zone or reburning zone by promoting the decomposition of the C (O) complexes in heterogeneous reduction.

Keywords: Na, NO heterogeneous reduction, Pyridine, Char(N), Density functional theory