Desilication by Alkaline Treatment and Increasing the Silica to Alumina Ratio of Zeolite Y

Abstract

The framework silica to alumina ratio, the porosity, and the acidity properties of ultrastable Y zeolites prepared by ‘steaming’ and by the ‘sequential alkaline treatment and steaming’ of NaY zeolites are compared. The adaptability of the combined alkaline treatment method and steaming toward the type of starting NaY zeolites was studied. By comparison with single steaming treatment the combination of sequential alkaline treatment and steaming affords products with an obviously increased mesopore volume. The level of framework ultrastabilization and acidity of the final products were not affected. The mesopore volume of the ultrastable Y zeolite prepared by steaming dealumination only was no more than 0.14 cm3/g. The mesopore volume of the final product prepared by sequential desilication and dealumination was 0.22 cm3/g. The sequential desilication and dealumination method is suitable for the NaY zeolite with a high framework silica to alumina ratio. A small increase in the mesopore volume and severe micropore damage were evident when the NaY zeolite with a relatively low silica to alumina ratio (SiO2/Al2O3 = 4.8, determined by nuclear magnetic resonance) was used as the starting material for the combined desilication and dealumination treatment. 考察了 “水热处理”以及“碱处理+水热处理”两种方法所制得的超稳 Y 分子筛的骨架硅铝比、孔结构特征以及酸量, 并探讨了“碱处理+水热处理”方法对起始 NaY 分子筛的适应性. 结果表明, 在水热处理前, 对 NaY 分子筛进行碱处理脱硅可在不改变最终样品的骨架超稳化水平和酸量的同时, 样品的介孔体积显著增加. 直接水热处理 NaY 分子筛所得样品介孔体积不超过 0.14 cm3/g, 而先碱处理后水热处理, 所得样品介孔体积可达 0.22 cm3/g. 该法适用于制备骨架硅铝比高的 NaY 分子筛. 起始原料的骨架硅铝比较低时, 所得样品的介孔体积增幅小, 而且微孔受损严重.