Influence of Mn/(Mn+Ce) Ratio of MnOx-CeO2/WO3-ZrO2 Monolith Catalyst on Selective Catalytic Reduction of NOx with Ammonia

Abstract

A series of monolith MnO x -CeO 2 /WO 3 -ZrO 2 catalysts with different mass ratios of Mn/(Mn+Ce) were prepared and used for the selective catalytic reduction (SCR) of NO x with NH 3 in the presence of excess O 2 . The catalysts were characterized by N 2 adsorption, oxygen storage capacity, X-ray diffraction, X-ray photoelectron spectroscopy, NH 3 /NO temperature-programmed desorption, and H 2 temperature-programmed reduction. The best catalyst had the mass ratio of Mn/(Mn+Ce) = 0.5. It gave 90% NO x conversion in the range of 173-355 °C at the gas hourly space velocity of 10000 h −1 , and characterization results showed that a higher oxidation activity of NO to NO 2 , more surface Ce and Mn with a larger Ce 3+ /Ce 4+ ratio, lower NH 3 and NO desorption temperatures, and excellent redox ability were together responsible for its best NH 3 -SCR performance. 制备了一系列不同 Mn/(Mn+Ce) 质量比的 MnO x -CeO 2 /WO 3 -ZrO 2 整体式催化剂用于富氧条件下的 NH 3 选择性催化还原 NO x (NH 3 -SCR), 并采用 N 2 吸脱附、储氧量、X 射线衍射、X 光电子能谱、NH 3 /NO 程序升温脱附以及 H 2 程序升温还原等手段对催化剂进行表征. 结果表明, 当 Mn/(Mn+Ce) 质量比为 0.5 时, 整体式催化剂具有较好的 NH 3 -SCR 性能, 在空速 10000 h −1 和 173–355 ºC 条件反应下, NO x 转化率达 90% 以上. 这是由于该 MnO x -CeO 2 /WO 3 -ZrO 2 催化剂具有更高的 NO 氧化活性、更高的表面 Ce 和 Mn 原子浓度以及 Ce 3+ /Ce 值较低的 NH 3 和 NO 脱附温度以及优异的氧化还原性能所致. A monolithic 10%MnO x –10%CeO 2 /WO 3 -ZrO 2 catalyst was active at low temperature and gave over 90% NO conversions at 173–355 °C.