摘要
采用多种手段证明了Ga处在所合成的ZSM-5型镓硅分子筛骨架中。XRD表明Ga取代AI导致了沸石晶胞参数增大;IR表明Ga取代后骨架振动特征峰向低频方向迁移。^(71)Ga MASNMR显示Ga以四面体单元GaO_4的形式存在,未检测到六配位的Ga。^(29)Si MASNMR显示Ga在Si原子周围只有Si(0Ga)和Si(1Ga)两种分布方式。XPS和EMPA表明镓硅分子筛中Ga呈+3价,分布大体均匀。
Isomorphous substitution of Ga for Al in MFI type zeolites has been characterized using Ga-ZSM-5 samples made by ourselves. XRD pattern of Ga-ZSM-5 is similar to that of ZSM-5, with the cell parameters expanding markedly compared with those of ZSM-5. Characteristic IR bands in framework vibration region, especially the band at ea. 1210 cm-1, shift considerably to lower frequency when Al in MFI zeolite is substituted by Ga and when the Ga content in Ga-ZSM-5 increases. Ga is in the form of GaO4 tetrahedron,corresponding to the line at +154 ppm in 71Ga MASNMR, with the existence of two silicon unit , Si ( oGa) and Si(1Ga), corresponding to the resonances at -112.3 and -104.0 ppm in 28Si MASNMR respectively. No Al can be detected inside or outside the framework of Ga-ZSM-5 by 27A1 MASNMR. In addition, Ga in Ga-ZSM -5 can hardly be removed from the zeolite by acid exchange. All these suggest that Ga is situated in the framework of Ga-ZSM-5 . XPS and EMPA indicate that Ga in Ga-ZSM-5 is in +3 oxidative state and is nearly well-distributed, with a slight Ga abundance in the bulk.
