摘要
关于载Ni丝光沸石上Ni的还原态,Naiayanan曾指出:还原态NiM沸石上,位于结合能为855.6eV附近的Ni2p峰可能是Ni+或Ni（OH）2。孟中岳等研究载Ni的Y-和ZSM-5型沸石的结果表明,还原态Ni以Ni0形态存在,部分未还原Ni2+以NiO,Ni（OH）2或NiAl2O4物种存在。为此,本文用XPS、EPR技术对载Ni丝光沸石上Ni的还原态进行进一步的研究,并在指定条件下,观察其氧化-还原的“可逆”性。 所用原料NaM的SiO2/Al2O3=10.0。脱铝方法参见文献[3]。
The reduced Ni-containing mordenite zeolites prepared by ion exchanged and by impregnation methods were characterized by XPS and EPR techniques. Under given reduction conditions (450℃, H2, cutting off from air), there exists Ni?in the surface layer of mordenite zeolites, and no Ni+ ion is observed in EPR spectrum. However, at lower reduction temperature (250℃), for exchanged NiNaM sample, the weak EPR signal shows the presence of Ni+,which g values are g1 =2.04 and g2 =2.49-2.54 respectively. But for acidic NiHM samples, EPR signal of Ni+ is not observed,it is possible that the presence of acidic protons of the sample enables the Ni+ to be unstable. Exposed the reduced samples to the dry air for a long time at room temperature, the surface metallic nickel particles decrease markedly, and Ni2+ states increase showing that Ni?is not stable. The redox cycle of Ni is not completely reversible.
基金
国家自然科学基金
