Mn-CeOx/钛基层柱粘土(Ti-PILCs)低温选择性催化还原催化剂的钙中毒研究

摘要

以钛基层柱粘土(Ti-PILCs)为载体,制备了Mn-Ceox/Ti-PILCs低温选择性催化还原(SCR)催化剂,采用浸溃法模拟了催化剂钙中毒,研究了不同含钙量对催化剂活性的影响,并运用NH3-程序升温脱附(TPD)、H2-程序升温还原(TPR)及X射线光电子能谱(XPS)表征,分析了钙对催化剂的失活作用.结果表明:(1)钙中毒前后催化剂活性均随温度的升高而加强;钙中毒催化剂活性的下降程度随含钙量的提高而加强;钙中毒催化剂最高脱硝率所对应的温度往高温处推移.(2)钙对催化剂活性具有较大阻碍作用,而且失活程度与含钙量及温度有关.(3)在160～260℃,钙中毒引起了催化剂L酸的上升,L酸可能在较高温度区间开始发挥作用,因此该温度区间的钙中毒催化剂的失活程度减弱.(4)钙中毒催化剂中金属氧化能力下降,进而影响了催化剂在SCR反应中的氧化还原能力,使其活性下降.(5)钙中毒前后催化剂表面的锰氧化物都以Mn2O3为主要形式存在,但钙中毒催化剂出现了其他形态的锰氧化物,可能进一步影响催化剂活性;钙中毒前后催化剂表面的铈氧化物都以CeO2为主要存在形式,钙的引入基本没有影响铈的主要价态.(6)催化剂表面吸附氧量的降低可能是造成钙中毒的直接原因.%Mn-CeOx/Ti-PILCs catalyst was prepared for low-temperature selective catalytic reduction (SCR) of NO. The catalyst was poisoned by impregnating alkali metal calcium on its surface. The effect of calcium content on NO removal efficiency was investigated. The poisoned catalysts were characterized by NH3-TPD, H2-TPR and XPS.Results indicated that calcium had a negative effect on the activity of the catalysts, and the deactivation depended on the content of calcium and the temperature of SCR system. Poisoning did not lead to much change on the surface acidity of the catalyst, with Br⊕nsted acid sites decreasing slightly while Lewis ones increasing. Calcium could influence the valence distribution of manganese and reduce adsorption oxygen on the surface of the catalyst, thus lowering the redox ability of the catalyst, and hampering the low-temperature.NH3-SCR in a certain extent.