Zigzag煤焦表面异相还原N_2O反应

采用Zigzag型煤焦表面模型,利用量子化学密度泛函理论研究了煤焦异相还原N_2O的反应机理。首先分析了Zigzag和Armchair碳基模型的差异本质,然后通过热力学分析和动力学分析研究了煤焦异相还原N_2O的反应机理,最后对比分析了Zigzag和Armchair两模型计算结果。研究表明,煤焦异相还原N_2O的反应包括吸附、还原及脱附3个过程,N2的脱附过程是整个反应的决速步。煤焦异相还原N_2O的反应在循环流化床炉温范围内是可自发的放热反应,反应平衡常数大于105,可认为是单向反应。根据决速步理论,Zigzag模型下的反应活化能为66.28 k J/mol,阿累尼乌斯表达式为1.07×1014exp(-7 972.4/T),Armchair模型下的反应活化能为160.99 k J/mol,阿累尼乌斯表达式为3.99×1015exp(-19 364.0/T)。Zigzag模型下的还原反应活化能小,反应速率常数大,反应更为活跃。两模型计算差异主要是由于Zigzag模型存在未成对电子,化学性质活跃导致的。在涉及碳基反应的理论计算时,应充分考虑计算模型对反应过程研究的影响。

Heterogeneous reduction reaction of N2O by char based on Zigzag carbonaceous model

Zigzag char surface model was applied to investigate the heterogeneous reduction mechanism of N2O by char through the density functional theory in quantum chemistry method.Firstly,the fundamental differences between Zigzag and Armchair char model were analyzed,and then the thermodynamic and kinetic analysis were conducted to reveal the heterogeneous reaction mechanism of N2O by char.Finally,the calculated results of Zigzag and Armchair models were compared and analyzed.Research results show that the heterogeneous reduction of N2O by char includes adsorption,reduction and desorption process,and the desorption process of N2 is a reaction rate determining step.The reduction reaction is spontaneous and exothermic reaction,and takes place in one direction owing to that the reaction equilibrium constant is greater than 105 in the circulating fluidized bed furnace temperature range.According to the theory of reaction rate determining step,the reaction activation energies are 160.99 kJ/mol and 66.28 kJ/mol for Armchair and Zigzag model,as well as Arrhenius expressions are 3.99×1015exp(-19 364.0/T) and 1.07×1014exp(-7 972.4/T),respectively.Reaction activation energy is smaller and rate constant is greater in Zigzag model than Armchair,which indicates the reaction is more active under Zigzag model.Additionally,since there are lone pairs in Zigzag model,the chemical properties of Zigzag model is more active,which makes a different calculated results comparing with Armchair model.Thus,the effect of different calculated models on studying reaction process should be considered in the carbon-based theoretical calculation.