单空缺石墨烯负载的Pd单原子催化剂上NO还原的密度泛函理论研究

DFT study on reduction of NO over Pd atom anchored on single-vacancy graphene

采用密度泛函理论(DFT)方法对单空缺石墨烯负载的Pd单原子(Pd/SVG)催化剂上H_(2)还原NO的反应进行了研究,探究了Pd/SVG上NO还原生成N_(2)和NH_(3)的路径。在Pd/SVG上NO容易加氢形成HNO,需要的活化能为67.0 kJ·mol^(-1),显示了极高的催化活性。N_(2)生成的有利路径为NO活化生成HNO后,HNO继续加氢生成中间体NH_(2)O和NH_(2)OH,然后NH_(2)OH解离生成NH_(2)和OH,生成的NH_(2)中间体结合NO形成NH_(2)NO,然后NH_(2)NO异构化形成的NHNOH再经解离生成N_(2)与H_(2)O,这个过程中的决速步骤为NH_(2)NO分子内氢转移生成NHNOH,能垒为144.3 kJ·mol^(-1)。对于NH_(3)的生成,从NO的活化到中间体NH_(2)的形成与N_(2)的形成过程相同,最后NH_(2)加氢即可形成NH_(3),这个过程中的决速步骤为NH_(2)O加氢生成NH_(2)OH,能垒为86.4 kJ·mol^(-1)。比较生成N_(2)和NH_(3)的决速步能垒可见,Pd/SVG催化剂上NO经H_(2)还原更容易形成NH_(3)。本研究为石墨烯负载型Pd基催化剂上H_(2)还原NO的实验及工业应用提供理论参考。

The mechanism of NO reduction with H_(2)on Pd atom anchored on single-vacancy graphene(Pd/SVG)was studied by the density functional theory(DFT)method.The formation pathways of N_(2)and NH_(3)by NO reduction on Pd/SVG were explored.The activation of NO to HNO on Pd/SVG is more likely to occur,and the energy barrier is 67.0 kJ·mol^(-1),showing a very high catalytic activity.The mechanisms of NO reduction with H_(2)to N_(2)and NH_(3)on Pd/SVG were clarified.The favorable formation route of N_(2)is that the hydrogenation of NO leads to HNO,HNO continues to hydrogenate through intermediates NH_(2)O and NH_(2)OH,and then NH_(2)OH dissociates to generate NH_(2)and OH.The generated NH_(2)intermediate combines with NO to form NH_(2)NO,and then NHNOH was formed by the isomerization of NH_(2)NO,finally NHNOH was dissociated to N_(2)and H_(2)O.From NO activation to the formation of intermediate NH_(2),the favorable route of NH_(3)is the same as that of N_(2),and then NH_(2)hydrogenation leads to NH_(3).The energy barriers of rate-determining steps for the formation of N_(2)and NH_(3)are 144.3 and 86.4 kJ·mol^(-1),respectively.In addition,Pd/SVG catalyst shows higher selectivity to NH_(3)than N_(2),indicating that NH_(3)is the main product.This study will provide a theoretical reference for the experiment and industrial application of H_(2)reduction of NO on graphene-supported Pd-based catalysts.