Ce-MnO_x/TiO_2-ZrO_2低温选择催化还原NO活性和抗毒性研究

Study on the NO removal activity and poison resistance of Ce-MnO_x/TiO_2-ZrO_2 at low-temperature

采用溶胶-凝胶法制备TiO_2-ZrO_2载体,以硝酸锰为前驱体采用柠檬酸溶液浸渍法制备Ce(n)-MnO_x/TiO_2-ZrO_2复合催化剂。通过XRD、SEM-EDS、XPS等测试方法对催化剂的物化性能进行表征分析,并进行NH_3选择性催化还原NO实验,考察其在低温下的活性及抗水抗硫性能。结果表明,Ce-Mn氧化物和TiO_2-ZrO_2载体间发生了相互作用,后者结晶度发生变化。与MnO_x/TiO_2-ZrO_2比较,Ce(n)-MnO_x/TiO_2-ZrO_2中Mn^(4+)的含量提高。Ce元素以Ce^(4+)、Ce^(3+)存在于Ce(n)-MnO_x/TiO_2-ZrO_2中,在催化反应中能起到传递电子、离子和储氧的作用,提高催化剂的氧化还原能力,同时Ce元素的电离能和电负性要远小于Mn元素,优先于Mn发生化学反应,保护Mn元素的活性。Ce(0.2)-MnO_x/TiO_2-ZrO_2的颗粒分散均匀、粒径达到20nm左右。制备的Ce(n)-MnO_x/TiO_2-ZrO_2催化剂的低温活性和抗毒性都优于MnO_x/TiO_2-ZrO_2,其中Ce(0.2)-MnO_x/TiO_2-ZrO_2在80℃时脱硝效率为94%;100℃时脱硝效率达到100%,在同时通入5%H2O和100mg/m3 SO_2后,脱硝效率缓慢下降,反应210min降到85%后趋于稳定。

Using the sol-gel prepared TiO2-ZrO2 carrier,Ce（n）-MnOx/TiO2-ZrO2 composite catalysts were syn-thesized with critic acid solution impregnation method with manganese nitrate as MnOx precursor.The physical and chemical properties of catalysts were characterized with XRD,SEM-EDS and XPS.Meanwhile,its low-temperature catalytic activities as well as sulfur and water resistance were evaluated with selective catalytic re-duction （SCR）of NO by NH3 .The results show that there is an interaction between Ce-Mn oxide and TiO2-ZrO2 carrier,which leads to a crystallinity change in carrier.Comparing to the MnOx/TiO2-ZrO2 ,there is a higher Mn4＋ content in Ce（n）-MnOx/TiO2-ZrO2 .Furthermore,Ce in the Ce（n）-MnOx/TiO2-ZrO2 exists as Ce4＋,Ce3＋ state,which has the effect of transmission electron,ion and oxygen storage in the catalytic reac-tion,and then it improves the redox ability of catalysts.And ionization energy and electronegativity of Ce are much less than Mn.Therefore,Ce takes chemical reactions in preference to Mn.So the activity of Mn could be protected.The low temperature activity and antitoxic performance of Ce（n）-MnOx/TiO2-ZrO2 are superior to MnOx/TiO2-ZrO2 .Among the prepared five catalysts with different molar ratios of Ce/Mn,Ce（0.2）-MnOx/TiO2-ZrO2 demonstrates the best performance owing to the best particle dispersion and the small particle size about 20 nm,and a 94% denitrification efficiency can be achieved at 80 ℃ and 100% at 100 ℃.When 5% H2 O and 100 mg/m3 SO2 are simultaneously added,the denitrification efficiency decreases slowly and stabilizes at 8 5% after 2 1 0 min.