Understanding and direct strategy to synthesize hydrothermally stable micro-mesoporous aluminosilicates with largely enhanced acidity

• Mesoporous aluminosilicate with acidity and hydrothermal stability was developed.
• Hydrothermal stability was improved by Beta zeolite precursors in zeolite walls.
• Al was introduced into the mesophases, and thus the acidity was improved.
• Bimodal zeolites demonstrated superior catalytic properties for heavy oil FCC.

A general synthetic route of bimodal micro-mesoporous aluminosilicates with strong acidity and excellent hydrothermal stability has been developed. This method is built on the understanding that mesoporous aluminosilicates with high hydrothermal stability can be obtained via assembly of zeolite precursors in acidic conditions by copolymer templates, and the acidity can be improved by the introduction of Al species in neutral and alkaline systems. It is proposed that in order to obtain the mesoporous aluminosilicates with simultaneously strong acidity and excellent hydrothermal stability, an important requirement is that the paradox between stability and acidity must be harmonized. In this article, the crystallization of the resulting aluminosilicates was significantly improved by taking advantage of the Beta zeolite precursors in acidic media. When the mesostructure was basically formed, the pH of the reaction system was adjusted from strong acid to neutral, followed by a second hydrothermal crystallization, during which a large amount of Al could be introduced into the mesophases. XRF and Al NMR show that BPs possessed a high tetrahedrally coordinated Al loading. Py-IR results reveal that the total amount of Brønsted and Lewis acid sites increases 7.23 times. Such bimodal micro-mesoporous aluminosilicates demonstrated superior catalytic properties for heavy crude oil catalytic cracking, because of the increased hydrothermal stability and acidity. Our achievements have added new contributions to understanding the preparation of mesoporous aluminosilicates with strong acidity and excellent hydrothermal stability, which sheds a light on the practical application of mesoporous zeolites in petrochemical industry.

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