多金属复合氧化物低温SCR脱NOx及其抗硫-耐水性能协同作用机制研究

Current NH3-SCR technology is undertaken at relatively high temperature, within a narrow thermal range. However, this means that the catalyst has to be placed prior to the electrostatic precipitator and desulphurization devices. But, the presence of dust, SO2 and H2O in the flue gas have a pronounced effect on the catalysts lifetime, due to, competitive adsorption and eventual modification/blockage of the active metal and/or catalyst support. It is believed that this may be solved by developing low temperature (80-180 oC) SCR technology and constructing the reactor after the flue gas decontamination devices. Previously, two low temperature SCR catalysts with unique crystal structures have been developed by our group (CrMnOx and FeMnOx mixed oxides), which exhibit suitable catalytic activity and reasonable SO2/H2O resistance, respectively. Hence, in this project, a series of novel multi-metal mixed oxides composed from the two unique crystal structures found previously, CrMn1.5O4 and Fe3Mn3O8, will be modified via selective addition of suitable metal ions, to attain improved catalytic performance and poisoning resistance. Simultaneously, the synergistic effect between catalyst structure and corresponding change in resistance and performance will be extensively examined, making use of in-situ and ex-situ characterization techniques, in an effort to determine structure-activity relationships. Such features will prove to be of use in determining mechanistic aspects of the reaction and aid endeavors toward the rational design of a novel low temperature deNOx process.

现行NH3-SCR脱NOx技术的催化剂体系活性温度高且范围窄，置于烟道气出口的催化床层易受飞灰、水及SO2的影响而存在严重的堵塞、毒化及失活等问题。低温(80～180 oC)SCR技术将催化剂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铬-锰及铁-锰复合氧化物分别具有较高的低温SCR脱NOx活性及抗硫耐水性能。本项目拟通过精细调节各金属前驱物之间的比例，制备出同时包含铬基(CrMn1.5O4)及铁基(Fe3Mn3O8)两种特定晶相结构的系列多金属复合氧化物。构建既具有稳定的脱硝活性，又兼顾较强的抗硫及耐水性能的多金属复合氧化物催化剂体系。同时，采用原位技术等对多金属复合氧化物催化剂体系各组分在脱NOx活性及抗硫耐水性能方面的协同催化作用机制进行研究，有望获得新型高效低温SCR脱NOx催化体系的催化过程机理，为新型低温SCR催化剂的设计及工业化提供参考

选择性催化还原SCR催化剂的低温活性低、N2选择性低以及其抗水、抗硫性差，是导致该类型催化剂处理尾气过程中低温适用范围窄、易失活和易被毒化等技术难点的关键科学问题。本项目在国家自然科学基金的支持下，通过改变各催化剂活性组分和制备方法，设计并制备了系列具有较高活性和选择性，以及较宽活性温度窗口的催化剂，实现了催化剂的抗水和抗硫性能；同时揭示了催化剂体系各催化性能的协调控制与优化，并在一定程度上实现了多组分污染物分子的催化同步脱除。研究发现，催化剂焙烧温度和时间的改变，主要作用在于调变了酸性位点密度，催化剂的面积比活性与酸性位点密度呈现正相关的线性关联。催化剂表面的活性组分的氧化还原能力及存在状态与催化剂掺杂组分含量呈现火山型规律，同时催化活性也遵循类似趋势和规律，这说明较高的氧化还原能力或元素价态会增加反应分子的活化，促进催化活性。此外，掺杂不同助剂可调变中间体的活化和生成类型，进而影响催化活性和选择性；利用反向活性位点掺杂修饰，则显著增强催化剂的抗水抗硫性能。基于上述结果，我们通过调变催化剂活性组分的物相构成、氧化还原能力以及化学态，实现了氮氧化物（NOx）、硫氧化物（SO2）以及一氧化碳（CO）等小分子污染物催化同步脱除。在NOx、SO2以及CO催化同步脱除过程中，主要涉及到氧化还原机理和COS机理；在CO与NO同步脱除过程中，低温阶段则主要以硝酸盐或者亚硝酸盐与CO反应，而在高温阶段则遵循NCO与CO反应路径。基于上述成果，项目组在Applied Catalysis B: Environmental、Industrial & Engineering Chemistry Research、ACS Omega等本领域权威杂志上发表研究论文3篇，申请中国发明专利4项，出站博士后1名，培养博士生2名（已毕业1名），硕士生6名（已毕业4名）。相关研究成果可为低温选择性催化还原技术的实际应用提供理论借鉴与技术支撑。