共沉淀法制备Cr-Mn复合氧化物及其低温催化还原NO_x性能

Preparation of Cr-Mn Mixed Oxide by Coprecipitation and Its Performancefor Low-Temperature Selective Catalytic Reduction of NO_x

采用共沉淀法制备了一系列具有CrMn1.5O4晶相的新型Cr-Mn复合氧化物催化剂并用于低温有氧条件下氨选择性催化还原(SCR)NOx.结果表明,NOx转化率随着Cr/(Cr+Mn)摩尔比从0.1到0.4的增加而升高.其中Cr(0.4)-MnOx具有较高的低温活性,在140oC,空速为30000h-1的条件下,NOx转化率可高达90%.利用N2吸附法,X射线衍射及X射线光电子能谱对系列催化剂进行了表征,发现通过添加Cr元素,可形成新型CrMn1.5O4活性物相;由于Cr元素对催化剂表面电子性能具有调变作用,Mn元素主要以高氧化态形式Mn4+及Mn3+富集,不仅可以促进对NO的氧化,而且有利于对NH3的吸附和活化,从而使该催化剂具有较好的低温SCR活性.

A series of Cr-Mn mixed-oxide catalysts comprising a novel CrMnl.504 crystal phase were prepared by the coprecipitation method and applied to low-temperature selective catalytic reduction （SCR） of NOx with NH3 in the presence of O2. The experimental results showed that the NOx conversion increased with the increase of Cr content and peaked at the Cr（0.4）-MnOx catalyst with the molar ratio of Cr/（Mn＋Cr） = 0.4, which yielded nearly 90% NOx conversion at 140 ~C with a high space velocity of 30 000 h-1. The characterization of N2 adsorption, X-ray diffraction, and X-ray photoelectron spectroscopy indicated that the addition of Cr generated the novel CrMnl.504 crystal phase and adjusted the surface electronic properties, leading to the enrichment of higher oxidation states Mn4＋ and Mn3＋ on the surface. This promotes the oxidation of NO and is helpful for the adsorption of NH3, so that the catalyst exhibits higher low-temperature SCR activity.