物理化学学报 >> 1988, Vol. 4 >> Issue (05): 516-522.doi: 10.3866/PKU.WHXB19880515

研究论文 上一篇    下一篇

SAPO-5分子筛结构和酸性的研究

韦承谦; 郑香苗; 尹维真; 刘振义; 王定一; 张婉静; 林炳雄;   

  1. 北京大学物理化学研究所; 广西大学化学系; 广西民族学院化学系

  • 收稿日期:1987-08-08 修回日期:1988-03-23 发布日期:1988-10-15
  • 通讯作者: 张婉静

STRUCTURAL AND ACIDIC STUDIES ON SAPO-5 MOLECULAR SIEVES

Wei Chengqian; Zheng Xiangmiao; Yin Weizheng; Liu Zhenyi; Wang Dingyi; Zang Wanjing*; Lin Bihgxiong   

  1. Institute of Physical Chemistry; Peking University
    Deparment of Chemistry; Guangxi University
    Deparsment of Chemistry; Guangxi National Academy
  • Received:1987-08-08 Revised:1988-03-23 Published:1988-10-15
  • Contact: Zang Wanjing

摘要: 以三乙胺为模板剂, 在一定的实验条件下, 合成了一系列以硅原子非等比取代APO-5分子筛骨架中的磷和铝或选择取代磷的SAPO-5分子筛。它的酸性取决于硅取代磷, 铝原子的差值。对于差值为1.86的样品,在TPD实验中NH_3脱附峰面积是APO-5的7.4倍。
应用多晶x射线衍射法在400 ℃测定了非等比取代和选择取代的NaSAPO-5的结构, 并经Rietveld法修正。其骨架与APO-5相似。空间群C_(6v)~2-P_6cc。结果说明, 非等比取代和选择取代SAPO-5分子筛的骨架中, 磷和铝的排列有较高的有序度。
非等比取代和选择取代SAPO-5具有开口直径为0.8 nm左右的12元环直通道。由于阳离子位于六方柱中心, 则可认为HSAPO-5中的质子酸中心, 应机迂地分布在12元环直通道内壁上的O(2)附近。因此, 其晶内仅存在一类质子酸中心或活性中心。在NH_3-TPD曲线上只应出现一个NH_3脱附峰。这一推断与实验结果是一致的。

Abstract: The non-proportion substitutive SAPO-5 and the selective substitutive SAPO-5 were synthesized by taking triethylamine as the template under certain experimental conditions. They result from substituting Si for P, Al in non-proportion and partly replacing of P with Si in the framework of APO-5 respectively. The compositions are as follows:
H_(y-x) (Al_(12-x)Si_x) (P_(12-y)Si_y) O_(48)·zH_2O y-x=0.5~2.01 y+x=1.3~3.09 H_xAl_(12)(P_(12_x)Si_x) O_(48)·zH_2O x=0.7~2.66
The charge in framework and the acidity enhances considerably with the difference between P and Al in the framework. The area of NH_3-TPD of the sample of the difference 1.86 is 7.4 times as that of APO-5.
The crystal structures of two SAPO-5 containing Na~+ were determineted by powder X-ray diffraction at 400 ℃. Then the structure parameters were refined by Rietveld method. The unit cells of the two SAPO-5 contain Na_(y-x) (Al_(12-x)Si_x) and (P_(12-y)Si_y)O_(48) and Na_xAl_(12) (P_(12-x)Si_y)O_(48), respectively. The constructions of their framework are quite similar to APO-5. The space group is C_(6v)~2-P6cc. The lattice parameters: a=b=1.3761(5) nm, c=0.8402(3) nm; a=b=1.3805(7) nm, c=0.8428(4) nm respectively. The “Goodness of fit” is shown in Table 1. The average bod lengths of P(Si)-O, Al(Si)-O are 1.494A, 1.695A respectively and their difference equals 0.196A for the non-proportional substitutive SAPO-5. The average bond lengths of P(Si)-O, Al-O are 1.504A, 1.702A respectively and their difference equals 0.198A for the selective substitutive SAPO-5. Both of the differences are much larger than that of the disordered APO-5 and the proportional substitutiue sAPO-5. It is concluded that the ordered degree of P and Al is fairly hight in the two frameworks of SAPO-5.
There is a 12-ring straight channel ca. 0.8 nm in diameter and Na~+ are located at center of the hexagonal prism in the framework. The Brönsted center or activative center in SAPO-5 and the unique disabsorption peak of NH_3 appears in TPD spectra.