The Hydrothermal Synthesis of Zeolites: History and Development from the Earliest Days to the Present Time

The hydrothermal synthesis of zeolites: precursors, intermediates and reaction mechanism

This review focuses on the synthesis, crystallization mechanism, and application of colloidal zeolites. The synthesis formulations and features of different zeolite-type structures prepared in nanosized form are summarized. Special attention is paid to zeolites prepared as stable colloidal suspensions. Next, new insights into zeolite crystallization mechanism gained by using colloidal zeolites as model systems are discussed. Further, the methods for deposition of zeolite nanocrystals from suspensions onto supports of different shapes and compositions used for the fabrication of zeolite films and membranes are reviewed. The use of colloidal zeolites for the fabrication of hierarchical macrostructures is also described. Other uses of nanozeolites for the preparation of functionalized materials, for the synthesis of mesoporous silicas of improved hydrothermal stability, and as seeds for zeolite syntheses are illustrated. The emerging applications of nanozeolites in sensing, optoelectronics, and medicine cons...

Nanozeolites: Synthesis, Crystallization Mechanism, and Applications

Porous nanosized particles: preparation, properties, and applications.

New stories of zeolite structures: their descriptions, determinations, predictions, and evaluations.

Synthesis of zeolite MCM-22 under rotating and static conditions

Further comments on the role of autocatalytic nucleation in hydrothermal zeolite syntheses

The interest in zeolites is due to their extensive commercial uses as molecular sieves in highly selective catalysts, adsorbents, ion exchangers, and separators. These properties enabled the development of a large number of chemical and petrochemical processes. Zeolites are crystalline aluminosilicates. Independent control of product composition, morphology and the control of defect concentrations during crystallization of zeolites from reactive aluminosilicate gels are difficult. Modifications in synthesis conditions aimed at modifying crystal size and shape also effect the chemistry of the reactions and the nucleation and growth in the gel. It is hypothesized that with the control of the nucleation event, varying defect concentrations and size can be obtained in the microgravity environment on the space shuttle. Experimental results from previous flight samples (STS‐50, STS‐57) and their terrestrial counterparts indicated that crystal size is increased around 25 percent for zeolite A and 50 percent for zeolite X. The theoretical Si/Al ratio was obtained in several on‐orbit samples for zeolite A. The results for a number of different zeolite systems of commercial interest will be discussed.

Zeolite crystal growth in microgravity

The extensive use of zeolites and their impact on the world’s economy has resulted in many efforts to characterize their structure and improve the knowledge base for nucleation and growth of these crystals. The zeolite crystal growth (ZCG) experiment on USML-2 aimed to enhance the understanding of nucleation and growth of zeolite crystals, while attempting to provide a means of controlling the defect concentration in microgravity. Zeolites A, X, and Silicalite were grown during the 16-day USML-2 mission. The solutions where the nucleation event was controlled yielded larger and more uniform crystals of better morphology and purity than their terrestrial/control counterparts.

Investigating the nucleation and growth of zeolite crystals in space

The extensive use of zeolites and their impact on the world's economy has resulted in many efforts to characterize their structure, and improve the knowledge base for nucleation and growth of these crystals. The zeolite crystal growth (ZCG) experiment on USML-2 aimed to enhance the understanding of nucleation and growth of zeolite crystals, while attempting to provide a means of controlling the defect concentration in microgravity. Zeolites A, X, Beta, and Silicalite were grown during the 16 day - USML-2 mission. The solutions where the nucleation event was controlled yielded larger and more uniform crystals of better morphology and purity than their terrestrial/control counterparts. The external surfaces of zeolite A, X, and Silicalite crystals grown in microgravity were smoother (lower surface roughness) than their terrestrial controls. Catalytic studies with zeolite Beta indicate that crystals grown in space exhibit a lower number of Lewis acid sites located in micropores. This suggests fewer structural defects for crystals grown in microgravity. Transmission electron micrographs (TEM) of zeolite Beta crystals also show that crystals grown in microgravity were free of line defects while terrestrial/controls had substantial defects.

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Ipek Guray

Papers

Synthesis of zeolite MCM-22 under rotating and static conditions

Further comments on the role of autocatalytic nucleation in hydrothermal zeolite syntheses

Zeolite crystal growth in microgravity

Investigating the nucleation and growth of zeolite crystals in space

Zeolite Crystal Growth (Zcg) Flight on Usml-2