Creation of mesostructured hollow Y zeolite by selective demetallation of an artificial heterogeneous Al distributed zeolite crystal

Abstract

Hollow zeolites have gained great interest in the last decade because of their broad applications in catalysis, drug delivery, and as membranes. Here, we demonstrate that a low silica hollow Y zeolite with mesoporous walls can be prepared by a sequential demetallation (SiCl₄, HCl and NaOH) strategy without using any organic templates. It has been found that the design of a Y crystal with a Si-rich surface and an Al-rich core introduced by SiCl₄ treatment is a critical factor. The inhomogeneous Al distribution structure guides the sequent HCl and NaOH treatment to the selective demetallation for the generation of a hollow cavity and mesoporous shell. The resultant hollow Y zeolite with a 200 nm shell shows an extremely high hierarchy factor (0.18), higher than that of the conventional steamed USY zeolite (0.08), due to the larger BET surface area (844.4 vs. 620.3 m² g⁻¹), and in particular the significantly increased mesopore surface area (415.6 vs. 76.6 m² g⁻¹). As such, the catalytic cracking performance in 1,3,5-triisopropylbenzene and the vacuum gas oil conversion of the hollow mesoporous Y zeolite outperforms the conventional steamed USY zeolite in terms of catalytic activity, product selectivity, and catalyst lifetime.