Developing a novel high-efficiency coal combustion technology with ultra-low NOx emission is urgently needed to sustain the good ecological environment. Here, the targeted regulation of local microenvironment around fuel-N, such as functional groups, radicals, molecular configurations, and reaction atmosphere, is realized by the selective oxidation. The molecular configurations, including pore networks and microcrystalline structure in coal, are well characterized through synchrotron radiation-induced SAXS (small angle X-ray scattering) and WAXS (wide angle X-ray scattering) simultaneously. Furthermore, by combining density functional theory (DFT) and experiments, the effects of the local microenvironment on the nitrogen transformation and NO evolution during the thermal conversion are focused on. The results indicate that for the PPA oxidation, the H radicals attack the adjacent carbon to pyrrole/pyridine nitrogen, promoting the conversion of fuel-N to HCN. On the other hand, for the HO oxidation, disrupting the π bond electron cloud by the CO and C = O on the ortho carbon of pyrrole/pyridine dominates the NH generation. Additionally, the increased (average graphene layer extent), (average interlayer spacing), (standard deviation of interlayer spacing) and (standard deviation of the first-neighbor distribution) induce massive smaller pores, promoting the generation of abundant reaction defects inside the particles. Importantly, the intensified adsorption on abundant active sites lead to the decreased HCN and increased NH evolution, which is adverse for the interaction between homogeneous and heterogeneous NO reduction. Interestingly, the PAA selective oxidation can reduce NO emission by 31.72 % - 34.30 % during the air combustion, which is far better than the HO oxidation. Overall, the attack of free radicals on nitrogen-containing heterocycles promotes the conversion of fuel-N to HCN, the adsorption of which on char surfaces can further enhance the heterogeneous reduction in a lean oxygen atmosphere. The work here provides a novel route for developing high-efficiency and low-NOx combustion technologies.

中文翻译：

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基于局部微环境定向调控的新型超低NOx燃煤技术第 1 部分. 选择性氧合

为了维持良好的生态环境，迫切需要开发一种新型高效、超低NOx排放的燃煤技术。这里，通过选择性氧化实现了对燃料-N周围的局部微环境（如官能团、自由基、分子构型和反应气氛）的定向调控。通过同步辐射诱导的 SAXS（小角 X 射线散射）和 WAXS（广角 X 射线散射）同时对煤中的分子结构（包括孔隙网络和微晶结构）进行了很好的表征。此外，结合密度泛函理论（DFT）和实验，重点研究了局部微环境对热转化过程中氮转化和NO释放的影响。结果表明，对于 PPA 氧化，H 自由基攻击与吡咯/吡啶氮相邻的碳，促进燃料-N 转化为 HCN。另一方面，对于 H2O 氧化，吡咯/吡啶邻位碳上的 CO 和 C = O 破坏 π 键电子云主导了 NH 的生成。此外，增加的（平均石墨烯层范围）、（平均层间距）、（层间距标准差）和（第一邻分布标准差）会导致大量较小的孔隙，促进颗粒内部大量反应缺陷的产生。重要的是，丰富的活性位点上的强化吸附导致HCN减少和NH释放增加，这不利于均相和非均相NO还原之间的相互作用。有趣的是，PAA选择性氧化可以将空气燃烧过程中NO的排放量减少31.72%~34.30%，远远优于H2O氧化。总体而言，自由基对含氮杂环的攻击促进了燃料-N向HCN的转化，HCN在炭表面的吸附可以进一步增强贫氧气氛中的非均相还原。这项工作为开发高效、低氮氧化物燃烧技术提供了一条新途径。