Mn基低温脱硝催化剂性能优化研究进展

Progress of performance optimization for Mn-based SCR catalysts at low temperature

氮氧化物(NO_(x))是我国首要大气污染物,主要采用选择性催化还原(SCR)技术进行排放控制.研发高效、稳定的低温脱硝催化剂可避免高能耗的烟气再热,具有显著的节能降碳效益.锰氧化物(MnO_(x))因多变的化学态和丰富的晶格缺陷而表现出优良的氧化还原性能,并具有极强的表面酸性,在催化还原NO_(x)反应中表现出良好的低温活性,但N_(2)选择性低、抗H_(2)O/SO_(2)性能差,难以实现长期的高效稳定脱硝.近年来,改性提升Mn基催化剂的研究十分广泛,加快了Mn基催化剂工业应用的步伐.本文从低温活性、N_(2)选择性和稳定性三个方面,总结了Mn基催化剂的脱硝反应机理、元素掺杂改性、催化剂结构设计等最新研究进展,指出了当前的研究重点和难点,可为下一步研究提供参考.

The emission of nitrogen oxides(NO_(x)),the primary air pollutant in China,reached 8.96 million tons in 2022,considerably higher than the emissions of volatile organic compounds,particulate matter,and sulfur dioxide(SO_(2)).NO_(x) emission control is the focus and challenge with respect to air pollution management in China.Selective catalytic reduction(SCR)is widely employed to control the emission of NO_(x) in industrial flue gas because of its high efficiency and stability,and it can be used to realize ultralow NO_(x) emission.A catalyst is a vital factor of the SCR technology.Commercial V_(2)O_(5)/TiO_(2) catalysts have satisfactory tolerance to poisoning factors such as SO_(2) and H_(2)O,and the operating temperature is generally in the high-temperature range of 300-420℃.Although the catalysts can be more effectively adapted to the medium-temperature range of 200-300℃ by increasing the loading amount of V_(2)O_(5),their low-temperature activity is poor at temperatures less than 200℃.The development of efficient and stable catalysts for SCR at low temperatures can prevent the high energy consumption associated with flue gas reheating,resulting in considerable energy saving and carbon reduction benefits.Manganese oxides(MnO_(x))exhibit remarkable redox properties due to variable chemical states and abundant lattice defects,and they have considerably strong surface acidity,showing satisfactory low-temperature activity in the reaction of catalytic reduction of NO_(x).However,Mn-based catalysts suffer poor resistance to H_(2)O/SO_(2),making it difficult to achieve efficient and stable denitrification(i.e.,deNO_(x))over an extended period of time.They have poor N_(2) selectivity and are prone to catalytic conversion of NO_(x) into the greenhouse gas N_(2)O.Modification and enhancement of Mn-based catalysts have been extensively researched in recent years,which has expedited the pace of their industrial application.This study summarizes the latest research progress on reaction mechanism,elemental doping,and structure design of Mn-based catalysts in the aspects of low-temperature activity,N_(2) selectivity,and stability.Elemental doping modification is the primary method for optimizing the N_(2) selectivity and H_(2)O/SO_(2) tolerance of these catalysts.In terms of comprehensive low-temperature activity,N_(2) selectivity,and stability,the doping components should have satisfactory oxygen storage-release ability to provide abundant oxygen vacancies and high stability to disperse MnO_(x) and increase the tolerance to H_(2)O and SO_(2);appropriate structural design can block the poisoning of H_(2)O and SO_(2);in particular,surface hydrophobic modification can weaken the promotion effect of H_(2)O on poisoning of SO_(2).In conclusion,this study indicates the ongoing research focuses and difficulties,which can provide references for future research.