WO3 Modification of MnOx/TiO2 Catalysts for Low Temperature Selective Catalytic Reduction of NO with Ammonia

A series of WO3-modified MnOx/TiO2 catalysts were prepared by three different impregnation methods and were investigated by specific surface area measurement, X-ray diffraction, laser Raman spectroscopy, H2 temperature-programmed reduction, high-resolution transmission electron microscopy, and in situ Fourier transform infrared spectroscopy. The three-component catalysts obtained with the one-step impregnation exhibited the best catalytic activity. The characterization data revealed that a synergism between tungsten and manganese oxide existed in the catalysts when tungsten was loaded either prior to or simultaneously with manganese, which made the active components better dispersed and blocked the transformation of TiO2 from the anatase to rutile structure. The manganese oxide existed in the form of Mn2O3 on all the samples but was accompanied by a small amount of MnO2 for 15%MnOx−5%WO3/TiO2. WO3 improved the reducibility and enhanced the amount and strength of the surface acid sites, especially the Brönsted acid sites and promoted the formation of the active intermediate ((NH2). Lewis acid sites had the major role in the low temperature selective catalytic reduction reaction while surface (NH2 was an important intermediate species.

摘要采用 3 种不同的浸渍过程制备了系列 WO3 改性 MnOx/TiO2 催化剂, 并采用 BET 比表面积测试 X 射线衍射 拉曼光谱 H2 程序升温还原 高分辨扫描电镜和原位红外光谱等技术进行表征. 结果显示, 一步浸渍法和先钨后锰的分布浸渍法制备的催化剂中, Mn 和 W 的协同作用提高了活性组分的分散状态, 并阻止了钛载体的转晶; 在所有的 Mn 基催化剂中, Mn 物种主要以 Mn2O3 形式存在, 但在 15%MnOx-5%WO3/TiO2 中出现了少量的 MnO2; WO3 的加入大大增强了催化剂的还原能力, 提高了其表面酸位尤其是 B 酸的数量与强度, 并促进了活性中间物 (-NH2) 的生成. 表面 Lewis 酸在低温 SCR 反应起主要作用, 并且发现-NH2 也是活性很高的物种. 在 NH3 低温催化还原 NO 的反应中, 一步浸渍法制备的催化剂活性最高.

WO3 addition improved the reducibility and enhanced the amount and strength of the surface acid sites of a Mn-based catalyst synthesized by a one-step impregnation method, and it showed excellent activity.Figure optionsDownload as PowerPoint slide