改性Y沸石的孔结构与催化性能

测定了不同方法改性的Y沸石样品的N_2吸附和脱附等温线, 并计算了样品的微孔、大孔和二次孔的孔容和表面积, 以及样品的二次孔分布, 证实改性方法对样品的孔结构有显著的影响。同时, 还考察了不同尺码探针分子在改性Y沸石样品上的酸催化反应活性, 将所得数据与样品的酸量、酸强度和二次孔容相关联, 取得了满意的结果。说明对大尺码反应分子, 改性过程中生成的大孔径二次孔, 对提高沸石催化剂的反应活性是有利的。

PORE STRUCTURE AND CATALYTIC BEHAVIOR OF MODIFIED Y ZEOLITES

The N_2 adsorption and desorption isotherms of Y zeolites modified by hydrothermal treatment (HUSY), H_4EDTA dealumination (HEY) and (NH_4)_2SiF_6 isomorphous substitution (HSY) were measured and compared with that of the original NaY and HY zeolites. The size and the shape of the hysteresis loops on the isotherms are different, which shows that the secondary pore systems of these zeolites vary with the modification procedures. The sequence of the secondary pore volumes of the samples is as follows HY (2.6)2.0 nm and <2.0 nm as well.Reactant with various molecular sizes such as propanol, cumene and 1,3,5-tritert-butylbenzene were used as probes to study the catalytic behavior of the modified zeolite samples. The catalytic activities of the probe molecules on the zeolite were correlated with the data of the acidity and the secondary pore volume. It is clear that for larger molecules as cumene and 1,3,5-tri-tert-butylbenzene the presence of secondary mesopores in the zeolite structure promotes the cracking reactions considerably.