Abstract:

The mechanism of NO reduction with H₂ on Pd atom anchored on single-vacancy graphene (Pd/SVG) was studied by the density functional theory (DFT) method. The formation pathways of N₂ and NH₃ 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 H₂ to N₂ and NH₃ on Pd/SVG were clarified. The favorable formation route of N₂ is that the hydrogenation of NO leads to HNO, HNO continues to hydrogenate through intermediates NH₂O and NH₂OH, and then NH₂OH dissociates to generate NH₂ and OH. The generated NH₂ intermediate combines with NO to form NH₂NO, and then NHNOH was formed by the isomerization of NH₂NO, finally NHNOH was dissociated to N₂ and H₂O. From NO activation to the formation of intermediate NH₂, the favorable route of NH₃ is the same as that of N₂, and then NH₂ hydrogenation leads to NH₃. The energy barriers of rate-determining steps for the formation of N₂ and NH₃ are 144.3 and 86.4 kJ·mol^-1, respectively. In addition, Pd/SVG catalyst shows higher selectivity to NH₃ than N₂, indicating that NH₃ is the main product. This study will provide a theoretical reference for the experiment and industrial application of H₂ reduction of NO on graphene-supported Pd-based catalysts.

Key words: Pd single atom catalyst, reactivity, SCR, hydrogen, density functional theory

摘要：

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H₂还原NO的反应进行了研究，探究了Pd/SVG上NO还原生成N₂和NH₃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。N₂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NH₂O和NH₂OH，然后NH₂OH解离生成NH₂和OH，生成的NH₂中间体结合NO形成NH₂NO，然后NH₂NO异构化形成的NHNOH再经解离生成N₂与H₂O，这个过程中的决速步骤为NH₂NO分子内氢转移生成NHNOH，能垒为144.3 kJ·mol^-1。对于NH₃的生成，从NO的活化到中间体NH₂的形成与N₂的形成过程相同，最后NH₂加氢即可形成NH₃，这个过程中的决速步骤为NH₂O加氢生成NH₂OH，能垒为86.4 kJ·mol^-1。比较生成N₂和NH₃的决速步能垒可见，Pd/SVG催化剂上NO经H₂还原更容易形成NH₃。本研究为石墨烯负载型Pd基催化剂上H₂还原NO的实验及工业应用提供理论参考。

关键词: Pd单原子催化剂, 活性, 选择催化还原, H₂, 密度泛函理论