Cr--MnOx/TiO2--ZrO2低温选择催化还原NO的活性及抗毒性能

采用溶胶凝胶法制备TiO2-ZrO2载体,然后采用柠檬酸溶液浸渍法制备Cr-MnOx/TiO2-ZrO2复合催化剂.通过X射线衍射、比表面积测试( BET)、扫描电镜、X射线光电子能谱等测试方法对催化剂的物化性能进行表征分析,并进行NH3选择性催化还原NO实验,考察催化剂在低温下的活性及抗硫抗水性能. Cr元素介入到MnOx 中,形成了新型的CrMn1.5 O4活性物相,其中的Mn元素多以Mn3+和Mn4+存在.高价态的Cr5+使Mn元素由Mn3+向高氧化态的Mn4+转化,有利于低温选择性催化还原反应的进行.鉴于Cr元素第一电离能和电负性均低于Mn元素,能优先于Mn与SO2-4和SO2-3结合,保护MnOx 不被硫酸化,从而提高Cr-MnOx/TiO2-ZrO2催化剂的抗毒性能.制备的五种不同Cr/(Cr+Mn)摩尔比的催化剂中,Cr(0.4)-MnOx/TiO2-ZrO2的性能最优,其颗粒分散均匀,具有较大比表面积,在180℃时脱硝效率能够达到95.8%,同时通入5% H2 O和10-4 SO2,脱硝效率缓慢下降,反应8 h后,下降到73%,并保持稳定.

Activity and antitoxic properties of Cr--MnOx/TiO2--ZrO2 for low-temperature selective catalytic reduction of NO

Using a sol-gel prepared TiO2- ZrO2 carrier, Cr- MnOx/TiO2- ZrO2 composite catalysts were synthesized by a critic acid solution impregnation method. The physical and chemical properties of the catalysts were characterized by X-ray diffraction, specific surface area determination ( BET) , scanning electron microscopy and X-ray photoelectron spectroscopy. Meanwhile, the low-temperature catalytic activity and the sulfur and water resistance were evaluated with selective catalytic reduction ( SCR) of NO by NH3. The introduction of Cr element to MnOx yields a new CrMn1.5O4 active phase, in which Mn primarily exists as Mn3+ and Mn4+. The Cr5+ valence state facilitates the transformation of Mn3+ to high oxidation state Mn4+, which is beneficial to the low temperature SCR reaction. Because of lower first ionization energy and electronegativity, Cr preferentially reacts with SO2-4 and SO2-3 than Mn, thus protecting MnOx not to be sulphatized and resulting in the enhanced antitoxic performance of Cr-MnOx/TiO2-ZrO2 . Among the prepared five catalysts with different molar ratios of Cr/(Cr+Mn), Cr(0. 4)- MnOx/TiO2- ZrO2 demonstrates the best performance owing to the largest surface area and the best particle dispersion, and a 95. 8% denitrification efficiency can be achieved at 180℃. When 5% H2 O and 10 -4 SO2 are simultaneously added, the denitrification efficiency decreases slowly and stabilizes at 73% after 8 h reaction.