柴油车选择性催化还原和氨逃逸催化研究进展

Advances in selective catalytic reduction and ammonia slip catalyst for diesel fuelled vehicles

为了进一步提升国Ⅵ柴油车的污染物净化能力,开发更有效的机外净化体系,系统性地回顾了选择性催化还原和氨逃逸催化技术研究进展和应用现状。探讨选择性催化还原反应和氨逃逸催化反应过程中的反应机理,并介绍了2种技术的不同催化器类型和应用优势,重点阐述了催化器类型、载体,系统结构和反应条件等对选择性催化还原催化器中NO_(x)还原活性、N_(2)O排放和NH_(3)逃逸的影响以及其对氨逃逸催化器中NH_(3)转化率和N_(2)选择性的影响。结果表明:对于2种选择性催化还原催化器,铜基比钒基具有更宽的活性温度窗口和优异的催化活性,但铜基催化器同样面临着N_(2)O生成和NH_(3)逃逸等挑战;对于3种氨逃逸催化器,贵金属型具有较高的NH_(3)氧化活性但N_(2)选择性较低,而分子筛型与金属型的性能相反,综合两者优势的双涂层型可以在较宽温度范围内同时实现较高的NH_(3)转化率和N_(2)选择性,但三者都面临N_(2)O排放控制问题。因此,铜基催化器是最具应用前景的选择性催化还原催化器,而双涂层氨逃逸催化器则能够更高效降低随之增加的NH_(3);这2种技术均可实现现阶段柴油车排放达标,但现有技术仍存在不足,需要进一步解决催化过程中N_(2)O生成的问题;未来的发展将主要集中在2种技术的耦合研究,联合开发控制系统以保证同时获得更高的催化效率。

In order to further improve the pollutant removal capability of the ChinaⅥdiesel vehicles and develop a more effective after-treatment system,the advances and application status in selective catalytic reduction(SCR)and ammonia slip catalyst(ASC)were reviewed.The reaction mechanisms of SCR and ASC were discussed,and various catalysts of the two technologies and their application advantages were introduced.In addition,the influence of catalyst type,carrier,structure,and reaction conditions on NO_(x)reduction activity,N_(2)O emission and NH_(3)slip of SCR,NH_(3)conversion and N_(2)selectivity of ASC were introduced.The results show that as to the two SCR catalysts,the Cu-zeolite catalyst has wider activity temperature window and excellent catalytic activity than V-based catalyst.However,it also faces the challenges of N_(2)O generation and NH_(3)slip.As to the three kinds of ASC,the noble-metal catalyst has a higher NH_(3)oxidation activity,but lower N_(2)selectivity while zeolite catalyst shows the opposite behavior.Combining the two advantages,the dual-layer catalyst can simultaneously achieve high NH_(3)conversion and N_(2)selectivity over wider temperature range.But all three catalysts are limited by the N_(2)O emission problem.Therefore,the Cu-zeolite catalyst is the most promising catalytic converters for SCR,while the double-coated ASC catalyst can more efficiently reduce the increased NH_(3)caused by the Cu-zeolite catalyst.Although both of these technologies can meet current diesel vehicle emissions standards,there are still shortcomings in existing technologies.It is necessary to further solve the N_(2)O generation problems in the catalytic process.The future development of SCR and ASC research will be mainly focused on the coupling of the two technologies,and the joint development of control systems to achieve the high SCR and ASC performance at the same time.3 tabs,9 figs,78 refs.