Abstract
The article reviews different strategies towards obtaining mesoporous zeolites Y: desilication; surfactant templating and assembly of zeolite crystals. The impact of those methods on physicochemical properties is covered, with a special focus on the acidity of the samples measured with infrared (IR) spectroscopy. The methods of characterization of acidity are presented. Quaternary ammonium cations used for desilication lead to obtaining crystalline; mesoporous and highly acidic zeolites. Si-OH-Al groups of extremely high acidity can be produced by calcination in a humid atmosphere. When the conditions are optimized, post-synthetic surfactant templating allows crystalline mesoporous zeolite to be obtained with no loss of material. All mesoporous zeolites Y proved to be active catalysts in liquid phase isomerization, catalytic cracking, and other reactions.
Highlights
Zeolites are well-known catalysts of high surface area, high hydrothermal and thermal stability, structural pores of molecular dimensions, and containing strong Brønsted acid sites
As most of the catalytic reactions catalysed by hierarchical zeolites are catalysed by acid sites the characterization of acidity of zeolites is essential for catalytical applications
The results concerning acidity and catalytic activity of desilicated zeolites Y presented above were obtained for zeolite Y of Si/Al = 31 which was treated at room temperature with NaOH/TBAOH
Summary
Zeolites are well-known catalysts of high surface area, high hydrothermal and thermal stability, structural pores of molecular dimensions, and containing strong Brønsted acid sites. Carbon particles [12,13,14,15,16] or template micelles [17,18,19,20,21,22] were incorporated into zeolite crystals, during the synthesis, and these were burned off producing the additional mesopores. Most of the studies concerning hierarchical zeolites Y, including those that obtained them by incorporation of template micelles and by desilication, presented the results of structural and textural studies, as well as of catalytic tests.
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