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应用多晶X射线衍射法,在400℃时测定了含三价镧离子的杂原子(Si)AlPO_4-5型分子筛的结构,并经Rietveld法修正。从结构的测定得出,该分子筛的骨架几何构型与AlPO_4-5基本一致,但骨架中磷、铝、硅有序度较低。La~(3+)位于六方柱中心,与三个O(2)及六个O(4)相配位。由此可推论出分子筛为H型时,B酸的中心可能机遇地分布在O(2)和O(4)附近,而O(2)处于十二元环直通道的内壁,因此分子筛的活性中心位置应机遇地分布在O(2)附近。由于每个晶胞仅为阳离子提供四个位置,因此杂原子APO-5型分子筛的骨架最高负电荷将不超过4。
The structure of the heteroatom (Si) AlPO_4-5 molecular sieve containing trivalent lanthanum ions was determined by polycrystalline X-ray diffraction at 400 ℃ and corrected by Rietveld method. According to the structure determination, the framework geometry of the molecular sieve is basically the same as that of AlPO_4-5, but the order of the phosphorus, aluminum and silicon in the framework is relatively low. La ~ (3+) is located in the center of the hexagonal column and coordinates with three O (2) and six O (4). It can be deduced that when the molecular sieve is H type, the center of B acid may be located in the vicinity of O (2) and O (4), and the O (2) is in the inner wall of twelve- The center location should be opportunistically distributed around O (2). Since each unit cell provides only four positions for the cation, the highest negative charge of the framework of the heteroatom APO-5 molecular sieve will not exceed 4.