氧化锰基催化剂低温NH_3选择性还原NO_x反应及其机理

Reactions and Mechanisms of Low-Temperature Selective Catalytic Reduction of NO_x by NH_3 over Manganese Oxide-Based Catalysts

近年来,氧化锰基催化剂由于在低温氨选择性催化还原(NH3-SCR)NOx反应中表现出优良的催化活性得到了广泛的关注。本文综述了氧化锰基催化剂低温NH3-SCR反应的研究进展,分别分析了氧化锰的氧化态、晶体结构和表面结构以及掺杂离子和载体类型等因素对其催化性能的影响:高氧化态的锰和高比表面积的催化剂有利于低温NH3-SCR反应;金属离子如铈、铬、铁、铜和锡等的掺杂可以提高NOx的转化率和/或N2选择性;具有独特性能的载体如TiO2或硅铝分子筛等可以进一步提高氧化锰基催化剂的抗湿和抗硫性能等。本文同时分别对活化NH3、NO或同时活化NO和NH3的低温NH3-SCR反应机理进行了详细总结。根据不同的反应条件,在氧化锰基催化剂上的很多低温NH3-SCR反应,Eley-Rideal、Langmuir-Hinshelwood以及Marsvan Krevelen机理可能是同时存在的。本文最后论证和指出了氧化锰基催化剂低温NH3-SCR反应研究的主要发展方向。

More attention to manganese oxide-based catalysts has been paid due to their excellent catalytic activities in low-temperature selective catalytic reduction of NOx by NH3（NH3-SCR） in recent years. The progress of low-temperature NH3-SCR on manganese oxide-based catalysts is reviewed in this paper. The effects of oxidation states,bulk and surface structures of manganese oxides together with the nature of the doping cations and the supports on catalytic activities are extensively analyzed,and according to these results,the general conclusions can be drawn that both higher oxidation state of manganese and higher surface areas favor the reaction of NH3-SCR at low temperatures,the doping cations such as Ce^4 ＋ ,Cr^3 ＋ ,Fe^3 ＋ ,Cu^2 ＋ and Sn4 ＋ can enhance NOx conversion and / or N2 selectivity of manganese oxide-based catalysts in low-temperature NH3-SCR,and the supports with excellent features like TiO2 and silicon-aluminum zeolites can facilitate the improvements of hydrophobic ability and sulfurresistant performance. Meanwhile,the mechanisms of low-temperature NH3-SCR according to activations of NH3 and NO alone or both are systematically discussed,and depending on the reaction conditions,Eley-Rideal and Langmuir-Hinshelwood mechanisms as well as Mars-van Krevelen one possibly simultaneously occur in low- temperature NH3-SCR reactions over manganese oxide-based catalysts. Finally,the general proposal for developing highly active manganese oxide-based catalysts in low-temperature NH3-SCR is put forward.