制备方法对氧化锰八面体分子筛的NH_3选择性催化还原NO_x性能的影响

采用不同方法制备了一系列氧化锰八面体分子筛(OMS-2)催化剂,考察了制备方法对其低温NH3-SCR催化性能的影响,并采用BET、XRD、Raman、H2-TPR、XPS和TEM等手段对催化剂的物化性质进行表征。结果表明,OMS-2催化剂在50~150℃时其低温SCR活性明显优于MnOx催化剂,OMS-2催化剂在120℃时NOx转化率接近100%。此外,不同的制备方法对OMS-2催化剂的SCR脱硝活性影响明显。其中,固相法制备的OMS-2催化剂的SCR活性最佳。H2-TPR测试结果表明,OMS-2更容易发生氧化还原反应,MnOx还原峰对应的温度较高。XRD、TEM和XPS分析结果表明,低结晶度和高分散性的无定形催化剂有利于低温SCR反应,较高的表面晶格氧和无定形MnO2物种是OMS-2催化剂具有优异低温SCR活性的主要原因。

Effect of preparation methods on selective catalytic reduction of NOx with NH3 over manganese oxide octahedral molecular sieves

A series of manganese oxide octahedral molecular sieves (OMS-2) were prepared by different methods for the purpose of investigating the effect of the preparation methods on their catalytic properties in selective catalytic reduction (SCR) of NO_x with NH₃. These samples were characterized with BET, XRD, Raman, H₂-TPR, XPS and TEM techniques. It was found that all the samples showed higher NO_x conversions than MnO_x in the temperature range from 50 to 150 ℃ due to their easier reduction behavior, and the NO_x conversion reached about 100% at 120 ℃. Nonetheless, the preparation methods have a great effect on the catalytic activity of OMS-2. The sample prepared by the solid-state method shows the highest catalytic activity. The BET, XRD, TEM and XPS results reveal that this because it has lower crystallinity but higher dispersion as result of the presence of larger amounts of surface lattice oxygen and less crystalline MnO₂ species.