O2氧化含氮焦炭释放CO和NO的量子化学研究

选用简化的含氮焦炭模型，在分子水平上对O₂氧化含氮焦炭释放出CO和NO的异相反应机理进行研究。采用B3LYP/6-31G(d)密度泛函理论方法优化了反应路径上的反应物、产物、中间体和过渡态的几何构型，得到各结构的相对能量，进而得到整个反应的势能面。研究表明，O₂氧化含氮焦炭的第1步为在焦炭表面的吸附，吸附反应释放出414.5 kJ/mol的热量。CO和NO从O₂吸附产物中释放所需克服的最大能垒分别为397.4 kJ/mol和197.0 kJ/mol。CO从O₂吸附产物释放后生成的产物可经吸热反应释放出NO、经放热反应转化为五元含氮杂环或六元含氮杂环。NO从O₂吸附产物释放后生成的产物可经吸热反应进一步释放出CO、转化为五元环酮结构或六元环吡喃结构。

A quantum chemistry study of CO and NO desorption from oxidation of nitrogen-containing char by oxygen

A comprehensive molecular modeling study was carried out to clarify mechanisms for CO and NO desorption from heterogeneous oxidation of nitrogen containing char by O2 with a simplified char model.Geometry optimizations of reactants,intermediates,transition states and products were carried out by using density functional theory at the B3LYP/6-31G(d) level.Based on analysis of reaction pathways,energies of optimized geometries were calculated and corrected with zero point energy.The potential energy surfaces were worked out then.The results show that the first step of oxidation is O2 adsorption on the surface of nitrogen containing char,which is 414.5 kJ/mol exothermic.Highest energy barriers for CO and NO desorption from O2 adsorption product are 397.4 kJ/mol and 197.0 kJ/mol,respectively.The product after CO desorption can release NO by endothermic reactions or convert to five or six member nitrogen containing heterocycles by exothermic reactions.Three possible reaction pathways for the product after NO desorption from O2 adsorption product are desorption of CO with char left,formation of a five member cyclic ketone and conversion to a six member pyran,all of which are endothermic reactions.