Ceria Modified MnOx/TiO2-Pillared Clays Catalysts for the Selective Catalytic Reduction of NO with NH3 at Low Temperature

Abstract

Titania-pillared clays (TiO 2 -PILC) were synthesized by ion exchange and manganese was introduced as the active phase. The catalytic behavior of the x Mn/TiO 2 -PILC catalysts was studied for the low-temperature selective catalytic reduction (SCR) of NO with NH 3 . A series of Ce-doped 8%Mn- y Ce/TiO 2 -PILC catalysts were prepared and evaluated for their performance in the low-temperature SCR of NO with NH 3 , their resistance to water vapor (H 2 O), and their resistance to sulfur dioxide (SO 2 ). It was found that the NO conversion properties of the 8%Mn/TiO 2 -PILC catalysts could be significantly improved by adding Ce and all the catalysts gave high resistance to H 2 O but were sensitive to SO 2 . The catalyst with a Ce loading of 2% gave 95% NO conversion at 220 °C and exhibited a moderate SO 2 -poisoning resistance compared with the other catalysts. X-ray diffraction, N 2 adsorption-desorption, temperature-programmed desorption of NH 3 , X-ray photoelectron spectroscopy, and temperature-programmed reduction of H 2 were used to characterize the properties of the catalysts. The addition of Ce improved the diffusion of Mn on the surfaces of the catalysts, which enhanced the surface acidity and improved the reduction properties of the catalysts and these were the main influencing factors for the low-temperature SCR. 采用离子交换法制备了钛基层柱粘土 (TiO 2 -PILC), 并应用浸渍法将 Mn 负载于其上制得不同 Mn 含量的 x Mn/TiO 2 -PILCs 催化剂, 考察了催化剂低温 NH 3 选择性催化还原 NO (NH 3 -SCR) 活性, 研究了添加 Ce 对 8%Mn/TiO 2 -PILC 催化剂活性及其抗水蒸气抗 SO 2 特性的影响. 结果发现, TiO 2 -PILC 负载的锰基催化剂具有良好的抗水蒸气性能, 但在水蒸气和 SO 2 共存时失活严重. Ce 的添加对催化剂活性以及抗 SO 2 能力均有所提高, 其中 8%Mn-2%Ce/TiO 2 -PILC 在 200 o C 时 NO 去除率达到 95%, 同时 SO 2 失活速率明显比其他催化剂低. 采用 N 2 吸附-脱附、X 射线衍射、NH 3 程序升温脱附、H 2 程序升温还原和 X 射线光电子能谱等技术对催化剂结构和性质进行了表征. 结果表明, 所制备催化剂具有丰富的中孔结构和较大的比表面积; Ce 的添加使 Mn 在催化剂表面分散性更好, 提高了催化剂表面酸性和催化剂氧化还原性能, 从而使其活性和抗硫性能增加. The addition of Ce to 8%Mn/TiO 2 -pillared clays (PILC) catalysts significantly improved NO conversion during the SCR and the resistance to SO 2 during low temperature selective catalytic reduction. The higher catalytic activity of the 8%Mn-2%Ce/TiO 2 -PILC catalyst is due to its better reduction behavior at low temperature and its higher number of acid sites.