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

NO heterogeneous reduction by char has a great potential in reducing NOx emission. Notably, Na has a considerable effect on heterogeneous reduction. Herein, the Zhundong demineralization coal and the NaCl addition coal were taken as research objects. The char sample structure is characterized by BET surface area analysis, XRD, and XPS. Experimental and density functional theory were used to explore the macroscopic and microscopic effects of the Na contents on NO heterogeneous reduction by nitrogen-containing char in the reduction zone of staged combustion. The results showed that the properties of char are not the key factors, which affect NO heterogeneous by char at high temperature. Na promoted the adsorption and reduction of NO by improving NO chemisorption energy and reducing the largest reduction energy barrier. The catalytic NO heterogeneous activity depended on the contents of Na. While the 0.6 wt.% NaCl addition had the best catalytic effect, the adsorption capacity and reduction rate of NO were 4.96 times and 1.22 times than DC char, respectively. However, a large amount of Na will cover the active centers on char surface to inhibit NO chemisorption and reduction. The reduction of NO to N2 was accompanied by CO release. According to the simulation results, Na can reduce the largest reaction energy barrier of C(O) complexes desorption to promote the formation of CO.