煤焦催化HCN还原NO的反应机理

摘要

通过量子化学密度泛函理论研究了均相和煤焦催化的HCN还原NO反应机理,计算了反应动力学参数.结果表明,均相还原反应的活化能为306kJ/mol,而煤焦催化的NO还原反应的活化能为136 kJ/mol.典型再燃温度1 400K下,HCN异相还原NO的反应速率略小于煤焦异相还原NO的反应速率;HCN参与下的煤焦异相还原NO反应较CO参与下的煤焦异相促还原NO反应更易发生.各组分的吸附顺序对HCN异相还原NO的反应有明显的影响;在典型再燃温度下,NO先吸附时煤焦表面的异相还原反应速率常数为5.28×1010,比HCN先吸附时最快反应路径的反应速率常数大一个数量级.煤焦对NO还原具有显著的催化作用;煤焦表面作为NO的还原反应位点,对反应气体具有明显的活化作用.%The reaction mechanism of homogeneous and char-catalyzed heterogeneous NO reduction with HCN were investigated by density functional theory (DFT) of quantum chemistry;the reaction kinetic parameters were determined according to classical transition state theory (TST).The results indicate that the activation energy of homogeneous NO reduction is 306 kJ/mol,much higher than that of heterogeneously catalytic reduction of NO;the later can be as low as 136 kJ/mol.Under the typical reburning temperature (1 400 K),the reaction rate of heterogeneous reduction of NO with HCN is slightly lower than that of heterogeneous reduction catalyzed by char;in comparison with the heterogeneous NO reduction by CO,the heterogeneous NO reduction by HCN over char is more likely to occur.The adsorption sequence of various components has a significant effect on the heterogeneous NO reduction by HCN;the reaction rate coefficient of NO adsorbed on char surface with HCN is 5.28×10t0,which is an order larger than that of the surface adsorbed HCN with NO.Char exhibits a significant catalytic effect on the NO reduction with HCN;char provides surface reaction sites for NO reduction which can effectively activate the reaction gas.