不同方法制备的脱铝Y沸石的孔结构

Y沸石脱铝有多种方法。由于在脱铝过程中发生水解、聚合、重排等反应,分子筛的孔结构将发生很大的变化,如形成空穴,甚至可导致骨架结构单元的崩塌,形成二次孔。由于不同的脱铝方法的脱铝机理不同,即使它们的脱铝程度一致,产生的孔结构也将不同,这必将导致它们的酸性质和催化性能的差异。目前关于Y沸石孔结构的研究报导还很少,尤其对SSY,US-SSY沸石孔结构的报导更为鲜见。本文用低温N_2吸附-脱附等温线和层厚t等方法,对四种不同方法制备的脱铝Y沸石(USY,DAY,SSY和US-SSY)的微孔、二次孔及其孔径分布(2.0～60.0nm)进行了初步研究,得到了一些有用的信息,为进一步研究其酸性质和催化性能打下了基础。

POROUS STRUCTURE OF DEALUMINATED Y ZEOLITES PREPARED BY DIFFERENT METHODS

The adsorption-desorption isotherms of N2 and t-plot were used to study the porous structure of dealuminated Y zeolites prepared by different methods. It is found that the formation of secondary mesopore is closely related to the dealumination method and the mechanism of filling aluminium vacancies by silicon. These results showed that the secondary mesopore volume of SSY zeolite treated with (NH4)2SiF6 and US-SSY zeolite (SSY further treated by steam) was not related to their depth of dealumination. But for DAY and USY zeolites, which were treated by deup-bed calcination, their crystallinity, secondary pore volume and mi-cropore volume were closely related to the depth, of dealumination. From the comparison of the four dealuminated Y zeolites, a common rule is found that the higher the crystallinity of the dealuminated zeolite is, the more is its micropore volume and the fewer its mesopore volume.