The mechanism of heterogeneous reduction reaction of NO by moderate gasification char
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摘要: 采用量子化学密度泛函理论结合热力学和动力学研究了中度气化的锯齿形煤焦异相还原NO的反应机理。分析了中度气化煤焦异相还原NO的反应路径、异相还原过程中的能量变化以及热力学和动力学分析。结果表明，中度气化煤焦更易于NO的吸附，IM2→IM3的开环过程为整个反应的决速步，所需克服能垒最大（398.03 kJ/mol）。中度气化煤焦异相还原NO的反应在煤燃烧系统中为可自发的放热反应，且为单向反应。根据决速步理论，反应的进行需克服较大活化能（389.83 kJ/mol），同时根据阿伦尼乌斯公式，总体反应速率受温度影响较大，温度越高反应速率越快，越利于NO还原。Abstract: Zigzag carbonaceous model was applied to investigate the heterogeneous reduction mechanism of NO by moderate gasification char through the density functional theory in quantum chemistry method combined with thermodynamics and kinetics. The reaction path of heterogeneous reduction of NO by moderate gasification char were analyzed, and the energy change during heterogeneous reduction, thermodynamic and kinetic analysis were conducted. Research results show that the moderate gasification char is prone to adsorb NO. The process of CO desorption, which provides active sites for NO reduction, is a reaction rate determining step, and need to overcome the maximum barrier(398.03 kJ/mol). The reduction reaction is spontaneous and exothermic reaction in the coal combustion system and takes place in one direction. According to the theory of reaction rate determining step, the progress of the reaction need to overcome the larger activation energy(389.83 kJ/mol), and according to Arrhenius expression, the overall reaction rate is greatly affected by temperature. The higher the temperature is, the faster the reaction rate is, and the more favorable for NO reduction.
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图 2 中度气化的锯齿形煤焦异相还原NO过程中各驻点结构
Figure 2 Geometrical structures of stationary points in the heterogeneous reduction of NO by moderate gasification char
图 3 反应过程能量的变化
Figure 3 Geometrical structures and relative energies of the stationary points
图 6 NO与中度气化煤焦反应速率常数的计算
Figure 6 Calculated thermal rate constants for the reaction between NO and moderate gasification char
表 1 IM5轨道分析
Table 1 Orbital analysis of IM5
Species HOMO/eV LUMO/eV Gap/eV IM5 -4.843 -3.589 1.254 
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表 2 由NBO计算的一些重要原子的自然居群
Table 2 Natural population of some important atoms calculated by NBO
Atom Species Charge Valence C5 IM6 0.11055 1.87912 IM7 0.15988 1.82292 O* IM6 -0.14716 3.14068 IM7 -0.31445 3.30572 N* IM6 0.04322 2.44465 IM7 -0.05353 2.53722 N^ IM6 0.12199 3.15905 IM7 0.05894 2.42765
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表 3 各步反应动力学参数
Table 3 Kinetic parameters for reaction steps
Reaction A Ea IM1→IM2 6.09×1013 294.9 IM2→IM3 2.5×1015 407.4 IM3→IM4 6.0×1014 212.76 IM4→IM5 2.5×1015 259.8 IM5+NO→IM6 - - IM6→IM7 4.1×1013 291.17 IM7→IM8 1.4×1015 408.8 IM8→P 6×1014 212.76
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