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The synthesized nanoscale beta zeolites (SiO2/Al2O3 = 25, nanocrystals of 50 nm) were treated by two different sequential procedures called acid-steaming and acid-calcination treatment: that is, dilute HCl aq. solution (less than 1 mol/L) treatment followed by either steaming or calcination. These successive treatments were applied two times. The effect of both acid-steaming and acid-calcination treatment of beta zeolite on framework Al at different T-sites, extra-framework Al (EFAL) of different types, and acidity was studied. It was found that nearly 70% of Al was removed in these processes, the location and state of Al in zeolite beta are regulated by different combinations of treatments. 27Al (MQ) MAS NMR, IR, XPS, and XRF data showed that steaming dominated dealumination in the acid-steaming treatment, and Al atoms on T2, T5, T6, and T7 sites were almost completely removed. More EFAL species were formed and migrated to external surfaces of zeolite beta. In acid-calcination treatment, dealumination was completed stepwise by calcination and acid treatment, framework Al atoms on T5, T6, and T9 sites were removed, and more monomeric EFAL species were formed, leading to a more homogeneous Al distribution. The resultant zeolites beta treated by acid calcination and by acid steaming show similar bulk SiO2/Al2O3 ratios but different acidity distributions. Acid-calcination treatment results in more Bronsted acid sites and stronger Bronsted acidity than acid-steaming treatment, leading to higher conversion in n-octane catalytic cracking and higher gasoline yield in vacuum gas oil catalytic cracking.

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.

Mesoporous ultra-stable Y zeolite with outstanding performance for heavy oil cracking was prepared through the combination of desilication and dealumination. Atomic removal of silicon atoms from the starting NaY zeolite framework during desilication was reported. Nucleation and propagation of mesopores in the following dealumination process was studied. Si(0Al) and Si(1Al) atoms are selectively removed from zeolite framework by desilication. Consequently, silanol nests and unique hydroxyl nests with framework associated Al-OH were created in the framework of the desilicated zeolite. The artificial defects effect the initiation of mesopores in crystal parts where used to be rich in framework silicon and unfavorable for mesopore formation and promote the propagation and coalescence of mesopores. Catalytic studies revealed improved activity and lifetime in the crack of 1,3,5-triisopropylbenzene and showed increased gasoline and light cycle oil selectivity when the conversion of a heavy oil was compared. (C) 2012 Elsevier Inc. All rights reserved.