改性ZrO_2-MnO_2基整体式催化剂上NH_3选择性催化还原NO

Selective Catalytic Reduction of NO with NH_3 on Modified ZrO_2-MnO_2 Monolithic Catalysts

采用共沉淀法制备了ZrO2-MnO2催化剂,考察了CeO2,MoO3和WO3的添加对ZrO2-MnO2整体式催化剂上NH3选择性催化还原(NH3-SCR)NOx的影响,并利用低温N2吸附-脱附、X射线衍射、X射线光电子能谱、NH3和NO程序升温脱附等方法对催化剂进行了表征.结果表明催化剂物相为Mn0.2Zr0.8O1.8固溶体,CeO2和WO3分散在其中;添加MoO3或WO3后,样品中出现了新的中强酸位,强吸附的NO物种增加,从而有利于催化剂中高温活性的提高.另外,Mn和Ce物种主要分别以Mn4+和Ce4+形式存在.在NH3-SCR反应中,CeO2的添加提高了ZrO2-MnO2催化剂的低温活性,但反应温度窗口较窄;继续添加MoO3或WO3后,催化剂表现出良好的低温活性和宽的反应温度窗口,其中WO3/CeO2/ZrO2-MnO2催化剂上NO的起燃温度为176oC,且反应温度在240～424oC范围内,NOx转化率大于90%,具有良好的低温活性和宽的温度窗口.

A ZrO2-MnO2 catalyst was prepared by the co-precipitation method,and modified with CeO2,MoO3,and WO3 by impregnation. The catalytic activity of the monolithic catalysts for selective catalytic reduction of NOx with NH3（NH3-SCR） was studied. All the catalysts were characterized by low temperature nitrogen adsorption-desorption,X-ray diffraction,X-ray photoelectron spectroscopy,and NH3/NO-temperature-programmed desorption. The results show that the phase of the catalysts is Mn0.2Zr0.8O1.8 solid solution,and CeO2 and WO3 are well dispersed in catalysts. When adding MoO3 or WO3 into the catalyst,some medium-strength acid sites and the strongly adsorbed NO species that are beneficial to the elevated temperature catalytic activity increase. Mn and Ce exist as Mn4＋ and Ce4＋. The low temperature SCR activity is improved by the modification with CeO2,but the temperature window of the reaction is relatively narrow. When MoO3 or WO3 is introduced into CeO2/ZrO2-MnO2,the catalyst exhibits better catalytic performance and wider temperature window. The light-off temperature of WO3/CeO2/ZrO2-MnO2 is 176 oC,and the NOx conversion is over 90% in the temperature range of 240–424 oC,and it has good low-temperature activity and wide temperature window.