This book entitled Zeolites is a collection of papers recently published in the journal Crystals, focusing on zeolites as a group of hydrated aluminosilicates with unique physical and chemical ...properties that can have numerous and important applications. The collection opens with works related to the geological documentation of the newest deposits of natural zeolites. The second part of the book describes a variety of synthesis methods and characterizes the resulting products. Finally, some recent advances in their applications in different fields are presented at the end of the book.
This book is a special collection of articles dedicated to the preparation and characterization of nanoporous materials, such as zeolitic-type materials, mesoporous silica (SBA-15, MCM-41, and ...KIT-6), mesoporous metallic oxides, metal–organic framework structures (MOFs), and pillared clays, and their applications in adsorption, catalysis, and separation processes. This book presents a global vision of researchers from international universities, research centers, and industries working with nanoporous materials and shares the latest results on the synthesis and characterization of such materials, which have given rise to the special interest in their applications in basic and industrial processes.
High‐silica zeolite Y is a desired catalytic material for oil refining and the petrochemical industry. However, its direct synthesis remains a symbolic challenge in the field of zeolite synthesis, ...with a limited improvement of the framework SiO2/Al2O3 ratio (SAR) from ≈5 to 9 over the past 60 years. Here, the synthesis of highly siliceous zeolite Y with tunable SAR up to 15.6 through a cooperative strategy is reported, which involves the use of FAU nuclei, a bulky organic structure‐directing agent (OSDA), and a gel system with low alkalinity (named NOA‐co strategy). A series of quaternary alkylammonium ions is discovered as effective OSDAs based on the NOA‐co strategy, and the relevant crystallization mechanism is elucidated. Moreover, the high‐silica products are demonstrated to have greatly improved (hydro)thermal stability, high concentration of strong acid sites, and uniform acid distribution, which lead to superior catalytic performance in the cracking of bulky hydrocarbons. It is anticipated that this synthetic strategy will benefit the synthesis and development of zeolitic catalysts in a wide range of reaction processes.
High‐silica zeolite Y with tunable SiO2/Al2O3 ratio up to 15.6 is synthesized through a cooperative strategy that involves the use of FAU nuclei, a bulky organic structure‐directing agent (OSDA), and a gel system with low alkalinity. The obtained materials show greatly improved (hydro)thermal stability, high concentration of strong acid sites, and superior catalytic cracking performance.
Siting of Al atoms in the framework T sites, in zeolite rings and channel/cavity system, and the distribution of Al atoms between single Al atoms and close Al atoms in various Al-O-(Si-O)
n
-Al ...sequences in Si-rich zeolites represent key parameters controlling properties of counter ion species. Framework Al siting and distribution is not random or controlled by simple rules and depends on the conditions of the zeolite synthesis. Al in Al-O-(Si-O)
2
-Al in one 6-MR and single Al atoms predominate in Si-rich zeolites and their population can be varied to a large extent. The siting and distribution of framework Al atoms dramatically affect catalytic activity/selectivity both of protonic and transition metal ion-containing zeolite catalysts.
CO 2 adsorption in amine-grafted zeolite 13X Bezerra, Diôgo P.; Silva, Francisco W.M. da; Moura, Pedro A.S. de ...
Applied surface science,
09/2014, Letnik:
314
Journal Article
The preparation of nanosized zeolites is critical for applications where mass‐transport limitations within microporous networks hinder their performance. Often the ability to generate ultrasmall ...zeolite crystals is dependent upon the use of expensive organics with limited commercial relevance. Herein, we report the generation of zeolite L crystals with uniform sizes less than 30 nm using a facile, organic‐free method. Time‐resolved analysis of precursor assembly and evolution during nonclassical crystallization highlights key differences among silicon sources. Our findings reveal that a homogenous dispersion of potassium ions throughout silicate precursors leads to the formation of a metastable nonporous phase, which undergoes an intercrystalline transformation to zeolite L. The generation of highly interdispersed alkali‐silicate precursors is seemingly critical to enhancing the rate of nucleation and facilitating the formation of ultrasmall crystal.
Highway to L: A new method of preparing nanosized zeolite L crystals from silicates composed of highly interdispersed potassium ions reveals that a uniform distribution of inorganic structure‐directing agents can alter the pathway of zeolite crystallization and dramatically reduce synthesis time.
In this work, the concept of zeolite (zeolitic) membrane is discussed from a practical perspective. We consider the limitations of the existing synthesis methods and speculate on new opportunities of ...zeolites and zeolite-type materials such as metal organic frameworks for the production of membranes. This paper focuses on the barriers that need to be eliminated before the commercialization of these membranes becomes attractive. Additional opportunities for commercialization may arise in the shape either of mixed matrix membranes, taking advantage of composites with polymers, or as zeolite coatings useful for a plethora of new applications.
Multi-quaternary ammonium surfactants can assemble co-operatively with silicate anions to generate MFI zeolite nanosheets, where the ammonium acts as a structure-directing agent for the microporous ...zeolite, while the surfactant tails assemble into a lamellar micelle. The two-level structure-directing effects have been investigated for various molecules with the formula of tail-N+(CH3)2–{spacer–N+ R 2} n−1–R*. Here, n is varied over 1–4. The tail is selected among linear alkyl chains (C m H2m+1, m = 6–22). The spacer is an alkylene bridge (−C i H2i –, i = 3, 6 and 8). R and R* are alkyl groups (C j H2j+1, j = 1–6). The result highlights that the surfactant molecule should be equipped with at least 2 suitable ammonium groups for the formation of zeolite structure, in addition to the amphiphilic nature and micelle packing ability. Moreover, the thickness of the nanosheets can be increased and tailored according to the number of the ammonium groups. Detailed consideration of the effects of template molecular features may be useful for the design of hierarchically structure-directing surfactants for nanomorphic zeolites.
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