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.

Key words: zeolite Y, desilication by alkaline treatment, dealumination by steaming, silica to alumina ratio, ultrastabilization treatment, mesopore