摘要
Vanadium-titanium-based catalysts are the most widely used industrial materials for NO_x removal from coal-fired power plants. Owing to their relatively poor low-temperature deNO_x activity, low thermal stability, insufficient Hg^0 oxidation activity, SO_2 oxidation, ammonia slip, and other disadvantages,modifications to traditional vanadium-titanium-based selective catalytic reduction（SCR）catalysts have been attempted by many researchers to promote their relevant performance. This article reviewed the research progress of modified vanadium-titanium-based SCR catalysts from seven aspects, namely,（1） improving low-temperature deNO_x efficiency,（2） enhancing thermal stability,（3） improving Hg^0 oxidation efficiency,（4） oxidizing slip ammonia,（5） reducing SO_2 oxidation,（6） increasing alkali resistance, and（7） others. Their catalytic performance and the influence mechanisms have been discussed in detail. These catalysts were also divided into different categories according to their modified components such as noble metals（e.g., silver, ruthenium）, transition metals（e.g., manganese, iron, copper, zirconium, etc.）, rare earth metals（e.g., cerium, praseodymium）,and other metal chlorides（e.g., calcium chloride, copper chloride） and non-metals（fluorine,sulfur, silicon, nitrogen, etc.）. The advantages and disadvantages of these catalysts were summarized.Based on previous studies and the author＇s point of view, doping the appropriate modified components is beneficial to further improve the overall performance of vanadium-titanium-based SCR catalysts. This has enormous development potential and is a promising way to realize the control of multiple pollutants on the basis of the existing flue gas treatment system.
钒钛基选择性催化还原催化剂是目前燃煤电厂应用最为广泛的脱硝催化剂.由于传统钒钛基催化剂存在低温脱硝效率低、热稳定性差、单质汞氧化效率低、二氧化硫氧化、氨逃逸、碱金属中毒等问题,人们开始尝试通过对传统SCR催化剂进行改性,以期改善其综合性能.本文从(1)拓宽催化剂的反应温度窗口,尤其是向低温区扩展,(2)提高催化剂的热稳定性,(3)协同氧化单质汞,(4)控制氨逃逸,(5)降低SO_2至SO_3的转化率和(6)提高催化剂抗碱金属中毒性能等方面综述了改性钒钛基SCR催化剂的研究进展,总结了其催化性能和相关影响机理.研究表明,某些金属及非金属的改性可以增加钒钛基SCR催化剂的表面酸度、活性位点及氧化还原性能,非金属的掺杂还可以抑制TiO_2载体由锐钛矿向金红石型转化、增加表面氧空位,从而改善了钒钛基催化剂的低温脱硝性能;硅、钨、钡和稀土金属等的添加也可抑制TiO_2的金红石化过程,锆、钾则改变了钒氧化物的存在形态,抑制其高温聚合,提高了钒钛基催化剂的热稳定性;贵金属、过渡金属、金属氯化物及非金属的改性改变了钒钛基催化剂的汞氧化机制,均可有效促进低氯甚至无氯条件下钒钛基催化剂对单质汞的氧化;贵金属钌及助剂钼添加的钒钛基催化剂可在维持较高脱硝效率的同时,实现单质汞及逃逸氨的高效去除,在SCR尾部将逃逸氨选择性氧化生成无害的氮气和水;被铜、氧化钡、氧化硅等物质改性后,更多的钒以低价态存在,使催化剂的氧化还原性能降低,并抑制了二氧化硫的吸附,从而减少了三氧化硫的生成;由于具有高储氧能力和氧化还原特性,还可降低碱金属的吸附量,铈的掺杂可提高钒钛基催化剂的抗碱金属中毒性能.此外,本文还汇总了包括贵金属(如银、钌)、过渡金属(如锰、铁、铜、锆等)、稀土金属(铈、镨)等金属、金属氯化物(如氯化铜、氯化钙)及非金属(氟、硫、硅等)改性钒钛基SCR催化剂的优缺点.基于前人研究及作者观点,改性组分的掺杂有利于进一步提高钒钛基催化剂的综合性能,具有巨大的发展潜力,也是在现有基础上实现多污染物控制的方法之一.
基金
supported by the Science and Technology Plan Project of Hebei Province of China(16273703D)
the Fundamental Research Funds for the Central Universities(2015ZD24,2017XS123)~~
