Research progress in density functional theory study of char-NO heterogeneous reduction
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摘要: 燃煤电站中煤炭高温燃烧时产生的氮氧化物(NOx)对环境产生严重污染,控制NOx污染物排放成为全世界的共同行动。焦炭-NO异相还原反应在燃煤过程中普遍存在,但由于焦炭复杂的化学结构和成分以及燃烧反应中气固成分,焦炭-NO异相还原反应的机理尚不明晰。本研究通过总结焦炭-NO异相还原反应机理的密度泛函理论方面的研究,从焦炭模型、NO吸附方式、反应路径和反应路径中产生的不同中间体等方面对焦炭-NO异相还原反应的机理进行综述,还分析了CO和矿物质对NO异相还原反应的影响机制,指出焦炭模型边缘的含氧官能团和活性位点对NO还原有利,不同反应路径会产生HCN、N2O和NH3等中间体,CO和催化金属能通过增加反应活性位点、降低反应能垒和提高反应速率等方式促进焦炭-NO异相还原反应,为完善NO异相还原反应机理,控制NOx排放提供理论依据。Abstract: The nitrogen oxides (NOx) produced by the high-temperature combustion of coal in coal-fired power plants cause serious pollution to the environment, and the control of NOx pollutant emission has become a common action around the world. The char-NO heterogeneous reduction reaction that occurs in the reburning zone of the boiler is common during coal combustion process. However, because of the complex chemical structure and composition of char as well as the gas-solid composition in the combustion reaction, the mechanism of the char-NO heterogeneous reduction reaction is not yet clear. In this paper, the research on the char-NO heterogeneous reduction reaction by the density functional theory was summarized. The mechanism of the char-NO reaction was reviewed based on the char model, NO adsorption methods, reaction pathways and the different intermediates produced in reaction pathways. The influence mechanism of CO and minerals on NO heterogeneous reduction was also analyzed. It is pointed out that the oxygen groups and active sites on the edge of the char model are beneficial to NO reduction reaction. The intermediates such as HCN, N2O and NH3 are produced by different reaction pathways. CO and catalytic metals can promote the char-NO reaction by increasing the reactive sites, reducing the reaction energy barrier and increasing the reaction rate, which provides a theoretical basis for the improvement of NO heterogeneous reduction reaction mechanism and the control of NOx emission.
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Key words:
- NO /
- heterogeneous reduction /
- char /
- density functional theory
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表 1 矿物质对焦炭-NO还原反应的催化活性
Table 1 Catalytic activity of minerals in char-NO reaction
Mineral element Activation energy of char-NO
reaction/(kJ·mol−1)Catalytic activation energy of char-NO
reaction/(kJ·mol−1)Reference Na 245.10 107.90 [45] K 245.10 82.00 [45] Li
Na
K245.07
245.07
245.07124.96
82.05
81.84[46]
[46]
[46]Ca 245.35 109.82 [48] Li 503.90 516.50 [47] Na 503.90 530.60 [47] K 503.90 576.70 [47] Na 148.50 139.50 [49] Ca 124.40 91.90 [50] Ca 76.34 51.78 [51] Na 121.04 100.62 [52] Ca 79.84 50.30 [54] Fe2O3 199.99 49.04 [57] Cr2O3 199.99 61.54 [57] FeCrO3 199.99 15.38 [57] Cu 132.85 83.69 [56] -
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