金属元素对Y沸石的液固相类质同晶取代

用(NH_4)_2TiF_6、(NH_4)_3ZrF_7和(NH_4)_3FeF_6为取代剂研究了Ti、Pe和Zr等杂原子对Y沸石的液固相类质同晶取代规律,发现Ti、Fe和Zr主要取代Y沸石中的A1,其取代程度取决于溶液中M/A1比,最高允许M/A1比与杂原子的半径和氟配合物的稳定常数有关。用XRD、IR、DTA和TPR表征了相对结晶度大于80％的杂原子Y沸石。Ti、Fe和Zr等杂原子进入Y沸石后,沸石的晶胞参数增大,热稳定性下降,红外反对称伸缩振动频率红移,且变化的程度与取代原子的半径和取代量有明显的对应关系,说明杂原子以四面体形式进入Y沸石骨架。

Isomorphous Substitution of Metallic Elements for Zeolite Y in Aqueous Solution

The substitution of Ti, Fe and Zr into zeolite Y in aqueous solution of(NH4)2TiF6, (NH4)3ZrF7 and (NH4)3FeF6 is investigated systematically. It is found that Al in the framework was replaced by the metallic elements and the extent of substitution depends on the M/Al ratio of the solution. The maximum allowable M/Al ratio of the aqueous solution is related with the radius of M atom and the stability constant of the MFam-complex. The substituted, zeolite samples with crystallinity > 80% were characterized with XRD, IR, DTA and TPR . The incorporation of Ti, Fe and Zr into the zeolite leads to an increase in unit cell parameter, a lowering of thermal stability and a red shift of the asymmetric stretch frequency. The extent of these changes is correlated with the ionic radius of the metallic element and the degree of substitution. Results of various characterization methods show that the heteroatoms are substituted readily into the zeolite framework using this preparation method.