Abstract:

Two different simplified models of coal char were applied to investigate heterogeneous reduction mechanism of N₂O by char through density functional theory in quantum chemistry method.Structure and energy of reactants, intermediates and transition states were calculated so as to determine reaction process, and thermodynamic and kinetic analysis were conducted to reveal heterogeneous reaction mechanism.The results showed that the single carbon atom was not suitable as the model of heterogeneous reaction mechanism of N₂O by char due to it cannot reflect the adsorption and desorption of N₂O molecule in char surface.While the heterogeneous reaction mechanism of N₂O by char can be well studied by six rings carbonaceous cluster model.Through three transition states and two intermediates, N₂O was reduced to N₂, and energy barrier of N₂O adsorption on char surface was 51.01 kJ·mol^-1, indicating that adsorption process was easy to happen.In addition, the heterogeneous reduction of N₂O by char was exothermic and spontaneous reaction at temperature range of 298.15-1500 K, and reaction can take place in one direction owing to reaction equilibrium constant of greater than 10⁵.Furthermore, the reaction was fast at temperature range of 298.15-1500 K, and reaction activation energy was 43.55 kJ·mol^-1 with Arrhenius expression of 1.24×10¹⁰exp(-5238.15/T).

Key words: char, heterogeneous reduction, N₂O, adsorption, thermodynamics, reaction kinetic

摘要：

采用两种不同的简化煤焦模型，利用量子化学密度泛函理论研究了煤焦异相还原N₂O的反应机理。通过计算反应物、中间体以及过渡态的结构和能量明确了反应的过程，并通过热力学分析和动力学分析深入分析煤焦异相还原N₂O的反应机理。研究结果表明：单个碳原子无法体现N₂O分子在煤焦表面的吸附和脱附过程，不适于作为煤焦模型研究煤焦异相还原N₂O的反应，六环苯环簇碳基模型可以成功地研究煤焦异相还原N₂O的反应。煤焦异相还原N₂O的反应共经历三个过渡态和两个中间体将N₂O还原成N₂，N₂O分子在煤焦表面的吸附反应的活化能为51.01 kJ·mol^-1，煤焦表面吸附N₂O的过程容易进行。煤焦异相还原N₂O的反应在所研究的温度范围（298.15~1500 K）内为放热反应，可以自发发生，反应平衡常数大于10⁵，可以完全进行，认为是单向反应。煤焦异相还原N₂O的反应在所研究的温度范围（298.15~1500 K）内反应速率较快，反应活化能为43.55 kJ·mol^-1，Arrhenius表达式为1.24×10¹⁰exp（-5238.15/T）。

关键词: 煤焦, 异相还原, N₂O, 吸附, 热力学, 反应动力学