富氧条件下Fe-Mn/Beta选择性催化丙烯还原氮氧化物

以Beta分子筛为载体,采用等体积浸渍法制备Fe-Mn/Beta催化剂,并对其在富氧条件下丙烯选择性催化还原NO性能进行了研究。通过N₂吸附-脱附、X射线衍射（XRD）、X射线光电子能谱（XPS）、透射电子显微镜（TEM）、程序升温还原（H₂-TPR）和原位漫反射傅里叶变换红外光谱（in-situ DRIFTS）等研究手段对催化剂进行表征,考察Mn组分对催化剂的物理化学性质、C₃H₆-SCR反应活性和反应中间产物的影响。结果表明,引入Mn物种可以显著提高Fe-Mn/Beta催化剂的低温催化活性,1.5Fe1.0Mn/Beta催化剂NO还原效率350℃最高可达99.4%,在250-400℃反应温度下显示出很高的反应活性和N₂选择性。原位红外光谱研究表明,分子筛离子交换位上孤立的铁离子是丙烯选择性氧化的主要活性位,分散良好的MnO₂物种不能提高催化剂对丙烯的活化能力,但有助于促进形成NO₂吸附物种,从而提升了Fe-Mn/Beta催化剂的低温C₃H₆-SCR性能。经高温水热老化处理后,Fe-Mn/Beta催化剂脱硝活性明显下降,这与孤立的Fe³⁺离子迁移形成Fe_xO_y团聚物种有关。

Selective catalytic reduction of nitric oxide with propylene in excess oxygen over Fe-Mn/Beta catalysts

Fe-Mn/Beta catalysts were prepared by incipient wet-impregnation methods and used for selective catalytic reduction of nitric oxide with propylene in excess oxygen. The catalysts were characterized using N₂-physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), H₂-temperature programmed reduction (H₂-TPR) and in-situ diffuse reflectance infrared Fouier transform spectroscopy (in-situ DRIFTS) techniques. The effects of Mn component on the physicochemical properties, C₃H₆-SCR activity and reaction intermediates of catalysts were also investigated. The results showed that C₃H₆-SCR activity of Fe-Mn/Beta catalysts at low temperature could be significantly improved by introducing Mn species. 1.5Fe1.0Mn/Beta catalyst achieved the highest activity with a nitrogen oxide conversion of 99.4% at 350℃, which possessed high catalytic performance and N₂ selectivity within the temperature window of 250-400℃. Based on the in-situ DRIFT studies, the isolated Fe³⁺ ions at the ion-exchange sites were the main active sites for selective oxidation of propylene. Although the well-dispersed MnO₂ species could not improve the activation ability of the catalysts for propylene, they would enhance the formation of NO₂ adsorption species, then promoted C₃H₆-SCR activity at the low temperature. The significant decrease of SCR activity after hydrothermal aging of Fe-Mn/Beta catalysts might be due to the migration of isolated Fe³⁺ ions into oligomeric clusters.