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)
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-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)
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-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.
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•Hierarchical zeolite for biofuel production from biomass is discussed.•Several major reaction routes from different biomass sources are elaborated.•The presence of hierarchical ...porosity significantly enhances the catalytic performance.•It is vital to incorporate hierarchical zeolite in the upscale production of biofuel.•There is plenty of room for improvement to increase the efficiency.
The development of biofuel production from biomass has become a promising breakthrough and could tremendously enhance the potential of industrial technology. In this case, zeolites have emerged as suitable materials for catalyzing biomass conversion due to their outstanding catalytic properties, including the presence of the intrinsic acid sites, shape-selectivity properties, and high thermal stability. However, the sole micropores in zeolite cause diffusional limitation issues, especially for the bulky molecules involved in biomass feedstocks. For instance, many oxygenate molecules are too large to enter the micropores, so they cannot be converted into the product. In this case, hierarchical porosity could facilitate these molecules to access the acid site within the zeolite crystals. Research on synthetic strategies, modifications, and evaluations of their catalytic properties has consistently grown every year. This article reviews the recent development of hierarchical zeolite catalysts for biomass conversion to biofuel. Numerous strategies of hierarchical zeolite fabrication (bottom-up, top-down methods, and green synthesis approaches) and its modification (metals and functionalization with organic materials) and their characteristics are comprehensively reviewed. The key point in the fabrication of hierarchical zeolites is the development of notable mesopores while preserving the intrinsic micropores. Moreover, the role of hierarchical zeolites in various biofuel and bio-based chemicals for biofuel and biofuel additives production reactions, i.e., pyrolysis, hydrolysis, esterification and transesterification, isomerization, condensation, upgrading of bio-oil, and catalytic cracking reactions, are discussed in detail. Finally, the remaining challenges and insight that can be considered for further improvement are provided.
Hierarchical core–shell zeolite–zeolite composite was fabricated by Y overgrown with a thin layer of nano-β: The extracted aluminum species by depolymerizing NaY zeolite crystals react with the ...silicon species near the interface of the NaY zeolite core and the precursor yielding the β zeolite layers, which induces and promotes the growth of β zeolite crystals over the core zeolite. Steric hindrance provoked by the concurrently growing crystals in the shell gives the β zeolite phase in the composite a relatively smaller size; A hierarchical pore system resulted from alkaline etching of the core Y and intercrystalline void of nano-β in the shells is introduced into the as-synthesized zeolite–zeolite composites.
•Zeolite composite is fabricated by which Y is overgrown with a thin layer of nano-β.•Incompatibility of core and shell is circumvented using core as nutrients for growth of shell.•Hierarchical pore system contributes to enhancing the accessibilities of Brönsted-acid site.•Depolymerization of core contributes to transmission of Al-species from cores to shell layers.•A high-efficiency hydrocracking catalyst of heavy oil producing good liquid yield.
Zeolite–zeolite composites composed of Y zeolite cores and polycrystalline β zeolite shells were prepared, in which Y zeolite was overgrown with a thin layer of nano-β zeolite. The incompatibility of the cores and the shells with different zeolite structure types, chemical compositions and crystallization conditions was circumvented by using Y zeolite as the nutrients for the growth of β zeolite crystals since the dissolution of the core zeolites was inevitable during the formation of the shell layers. The structural, crystalline, and textural properties of the as-synthesized samples were characterized by XRD, SEM, TEM, EDS, SAED, N2 adsorption–desorption, FT-IR, in situ IR spectra of pyridine and di-tert-butyl pyridine. The performances of the as-synthesized zeolite–zeolite composite supported by Ni–Mo active components were investigated during the hydrocracking of Iran VGO oil. The results displayed that the core–shell structured composites with a high-silicon β zeolite shell displayed a better performance in terms of conversion of VGO oil and yield of jet fuel, middle distillate yields and middle distillate selectivity than the reference catalyst and the composite catalyst with a low-silicon β zeolite shell.
The objective of this review is to highlight the need for further investigation of microbial toxicity caused by desorption of surfactant from Surfactant Modified Zeolite (SMZ). SMZ is a low cost, ...versatile permeable reactive media which has the potential to treat multiple classes of contaminants. With this combination of characteristics, SMZ has significant potential to enhance water and wastewater treatment processes. Surfactant desorption has been identified as a potential issue for the ongoing usability of SMZ. Few studies have investigated the toxicity of surfactants used in zeolite modification towards microorganisms and fewer have drawn linkages between surfactant desorption and surfactant toxicity. This review provides an overview of natural zeolite chemistry, characteristics and practical applications. The chemistry of commonly used surfactants is outlined, along with the kinetics that drive their adsorption to the zeolite surface. Methodologies to characterise this surfactant loading are also described. Applications of SMZ in water remediation are highlighted, giving focus to applications which deal with biological pollutants and where microorganisms play a role in the remediation process. Studies that have identified surfactant desorption from SMZ are outlined. Finally, the toxicity of a commonly used cationic surfactant towards microorganisms is discussed. This review highlights the potential for surfactant to desorb from the zeolite surface and the need for further research into the toxicity of this desorbed surfactant towards microorganisms, including pathogens and environmental microbes.
•Water remediation applications for Surfactant Modified Zeolite (SMZ) are reviewed.•Desorption of surfactant from SMZ highlighted as a potential environmental issue.•Quantifying desorbed surfactant toxicity crucial to understanding SMZ's useability.•Toxicity of desorbed surfactants towards microorganisms requires further research.
