Theoretical insight into NO formation and reduction at biochar N-sites: Influence of different oxygen-containing functional groups

• Published in: Journal of environmental chemical engineering 2024-08, Vol.12 (4), p.113147, Article 113147
• Main Authors: Liu, Ji, Xia, Yuan-gu, Sun, Huai-de, Hu, Bin, Wu, Yang-wen, Li, Ji-hong, Lu, Qiang
• Format: Article
• Language: English
• Subjects: Biochar; N-site; NO management; Oxygen-containing functional group
• ISSN: 2213-3437
• DOI: 10.1016/j.jece.2024.113147

Biochar is a cost-efficient and promising porous carbonaceous material for the efficient removal of flue gas NOx. The N-site located at the edge of biochar can be a crucial gateway for NO reduction to N2 or for NO formation by oxidation, which can be significantly affected by the oxygen-containing functional groups (OFGs) on the biochar edge. However, the roles of different OFGs in N-site-involved reactions remain elusive. Based on the biochar characterization results, reasonable theoretical models of biochar with different N-sites and OFGs were constructed. Subsequently, the effects of distinct OFGs on the interaction between NO and N-sites as well as the NO liberation from N-sites were elucidated, by employing density functional theory (DFT) and electronic structure analysis. The results reveal that all OFGs, encompassing -CHO, -COOH, and -OH, manifest their roles through the direct inherent electrostatic properties of O/H in OFGs (O*/H*) or altering the reactivity of edge atoms indirectly. For pyridinic nitrogen (N-6) at the zigzag edge, unsaturated (-CHO, -COOH)/saturated (-OH) OFGs inhibit/enhance NO reduction with N-6 by electrostatic properties of O*/H*, and all OFGs inhibit NO generation from N-6. Besides, all OFGs enhance the NO reduction with pyrrolic nitrogen (N-5) at the armchair edge while inhibiting the release of NO, by influencing the edge activity. The present study gives a mechanism insight into the roles of distinct OFGs in reactions involving biochar N-sites. [Display omitted] •The role of oxygenated groups in NO formation/reduction at N-sites was studied.•Oxygenated groups play distinct roles in the interaction between O/H and N-sites.•Oxygenated groups have different effects on edge electron redistribution.•Hydroxyl in biochar is conducive to NO removal.