采用armchair结构的焦炭模型,对焦炭异相还原NO的机理进行了分子水平上的模拟研究.在B3LYP/3-21G*计算水平上优化得到各反应路径上的反应物、产物、中间体和过渡态的几何构型.在B3LYP/6-31G(d)水平上计算优化所得结构的单点能.计算得到两个不同的反应路径,分别对应已提出的两个异相还原反应机理.NO分子与预先吸附在焦炭表面的碳氮组分C(N)结合释放出N2的反应路径中最大能垒为128.8kJ/mol;两个表面碳氮组分结合释放出N2的反应路径中需翻越的最大势垒为141.1 kJ/mol.NO在焦炭表面异相还原生成N2的反应为放热反应.采用经典过渡态理论计算得到各中间反应的反应速率常数,在典型再燃温度1 473 K时,路径1的反应速率决定步的速率常数为6.12×109,路径2的反应速率决定步的反应速率常数为1.50×1011.%Density functional theory calculations were carried out to investigate heterogeneous reduction mechanisms of NO on the surface of char by using a simplified char model with armchair configuration. Both intermediate stable species and transition state geometries were optimized at B3LYP/3_21G* calculation level, and their single-point energies were calculated at B3LYP/6-31G (d) level. Two different reaction pathways were obtained for heterogeneous reactions between NO molecules and char model with armchair configuration, which corresponded to the two different mechanisms proposed. The highest energy barriers were 128.8 kJ/mol for the reaction of surface nitrogen species with one NO molecule, and 141.1 kj/mol for the recombination of two surface nitrogen species. The overall reactions are exothermic reactions, which are in agreement with the experiment results. Rate constants for intermediate reactions were calculated by transition state theory and fitted to 2-parameter Arrhenius expressions. The rate constants of rate-determining steps for pathway 1 and pathway 2 are 6.12 × 109 and 1.50 × 1011 at 1 473 K respectively.
展开▼
