制备方法对Mn-Ce/ZSM-5催化剂低温选择性催化还原NO性能的影响

采用浸渍法、氨水共沉淀法和机械混合法制备了Mn-Ce/ZSM-5催化剂, 并研究了其对氨选择性催化还原(NH-3-SCR)NO反应的催化性能. 结果表明, 采用氨水共沉淀法制备的Mn-Ce/ZSM-5催化剂显示出优越的NH₃-SCR催化活性, 不仅具有好的低温催化活性和宽的反应温度窗口, 而且具有高的热稳定性. 铈的含量对催化活性也存在着明显的影响. 采用X射线衍射(XRD)、 X射线光电子能谱(XPS)和等离子体发射光谱(ICP)等技术对不同方法制备的Mn-Ce/ZSM-5催化剂的体相和表面结构进行了表征. 结果发现, Mn-Ce/ZSM-5催化剂中Ce主要以Ce⁴⁺的形态出现, 并与锰有较强的协同作用. Mn以多种氧化物的形态共存, 采用氨水共沉淀法制备更有利于低价态的锰氧化物Mn₂O₃, Mn₃O₄等的形成, 并且更易于氧物种(O_1s)在催化剂表面富集, 这可能是导致氨水共沉淀法所制备的Mn-Ce/ZSM-5样品活性最佳的原因.

Effect of Preparation Methods on Performance of Mn-Ce/ZSM-5 Catalyst for Low-temperature Selective Catalytic Reduction of NO

Mn-Ce/ZSM-5 catalysts for selective catalytic reduction(SCR) of nitric oxide with NH3 were prepared by co-impregnation(CI), co-precipitation(CP) and physical mixture(PM) methods. The Mn-Ce/ZSM-5 catalyst prepared by co-precipitation method exhibited excellent SCR performance, it had not only good SCR activity and broad temperature window, but also high thermal stability. The effect of Ce content on SCR activity of Mn-Ce/ZSM-5 catalyst was obvious. The structure and phase of the Mn-Ce/ZSM-5 catalysts prepared by different methods were investigated. The results show that Ce exist mainly in Ce4+ in Mn-Ce/ZSM-5 catalyst, and CeO2 may strongly interact with MnOx. Many kinds of Mn phases exist in Mn-Ce/ZSM-5 catalyst. The sample prepared by co-precipitation method possesses more MnOx phases of lower bond valence such as Mn2O3 and Mn3O4. It can make oxygen species(O1s) easily enriched on the surface of the Mn-Ce/ZSM-5 catalyst. These factors may lead to the best catalytic activity of the Mn-Ce/ZSM-5 prepared by co-precipitation.