稀土改性负载型锰基复合氧化物低温SCR催化剂及其作用机理

The current catalytic system for selective catalytic reduction of NO with NH3 (NH3-SCR) needs to be operated at relatively higher and narrow temperature window of 300~400 ℃, and is easy to be deactived due to high concentrations of ash, water vapor and SO2 emmited from the outlet of flue gas, where regular the activity of normal NH3-SCR catalyst can be maintained. Developing new low temperature (80~180oC) SCR catalysts placed downstream of electrostatic precipitator and the desulfurizer are considered to be hopeful to solve problems mentioned above. In our previous study, a series of novel Mn based mix-oxides catalysts with specific crystal structures exibiting well catalystic performance have been developed, but, their resistance ability for H2O and SO2 should be enhanced. In this project, Mn based mix-oxides possessing specific crystal structures loaded on a series of porous materials and modified by rare earth will be investigated for the development of catalytic systems with stable denitrification activity and enhanced sulfur and water resistance. At the same time, in situ techniques will be adopted for the tracking of the surface reaction processes to obtain both catalytic process and deactivation meachanisms of low temperature SCR catalytic system, which is also capable of providing reference for catalyst designation and industrial application in the issue of low temperature of SCR.

应用于现行NH3-SCR技术的催化剂体系活性温度高且范围窄（300～400℃），置于烟道气出口的催化床层易受飞灰、水及SO2的影响而存在非常严重的堵塞、毒化及失活等问题。开发新型低温（80～180 oC）SCR催化剂体系而将催化剂床层置于除尘与脱硫单元之后，有望解决上述问题。课题组前期发展的具有特定晶相结构的系列新型锰基复合金属氧化物催化剂具有较高低温SCR脱NOx活性，但尚存在抗硫耐水能力弱等问题。本申请项目拟将具有特定晶相结构的系列锰基复合氧化物进行负载化并对其进行稀土金属的掺杂改性，构建既具有稳定的脱氮活性，又兼顾较强的抗硫及耐水蒸气能力的稀土改性负载型Mn基复合金属氧化物催化剂体系；同时，采用原位技术对系列催化剂表面反应过程进行跟踪，获取关于低温SCR催化体系的催化过程与其中毒失活机理，为新型低温SCR催化剂的设计及工业化提供参考。

采用多种方法制备了系列锰基复合氧化物催化剂，并用稀土元素改性，获得了具有优异脱除NOx性能，又兼具耐硫耐水性能的催化剂体系。并对其组成、结构与其催化性能及反应过程因素之间的关联规律以及催化过程机理及中毒失活机理进行了研究。.发现采用柠檬酸法制备的负载型Cr-Mn催化剂和FeMnOx具有较好的低温选择性催化还原NOx的性能，前者140 oC时脱氮效率可达83%，当温度超过180 oC，NOx转化率接近100%,后者在80 oC下NOx的转化率达到90.5%。Ce改性可提高催化剂活性和耐硫性，Ce(12.5)-FeMnOx在空速为30, 000 h-1，90 oC时的转化率高达97.4%；在120 oC下，50 ppm SO2存在下，通入SO2达到12 h时，活性仍在90%以上。中毒失活后的催化剂Cr5%Mn/γ-Al2O3中CrMn1.5O4结构遭到破坏，说明SO2中毒催化剂表面形成的硫酸盐占据了催化剂表面。.Raman和XPS分析结果表明所制备的CrMn/γ-Al2O3催化剂中含有Cr6+，吸附氧在催化剂表面的富集促进了低温下NO向NO2氧化，从而使CrMn/γ-Al2O3系列催化剂具有较好的低温SCR活性。EDS分析发现Cr16%Mn/γ-Al2O3在SO2存在的条件下反应4 h后，催化剂表面检测到了S元素，表明生成了硫酸盐。XRD结果表明CeO2与活性相Fe3Mn3O8之间存在强的相互作用，适量Ce的添加可以促进活性相Fe3Mn3O8在催化剂表面的分散，降低结晶度。Ce(12.5)-FeMnOx催化剂表面具有最大的Mn4+/Mn3+比值，最高表面Ce4+浓度和晶格氧浓度，这些都很好地解释了该催化剂具有最好低温活性；而Ce4+和SO2反应，抑制Fe3Mn3O8的硫化和毒化，从而使该催化剂表现出最佳的抗硫性能。研究结果可为相关催化剂设计开发提供理论依据和指导。