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Zeolites and Related Porous Materials: Design, Synthesis, and Applications

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Published Papers

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Physical Chemistry".

Deadline for manuscript submissions: closed (21 September 2019) | Viewed by 15242

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Special Issue Editors

Prof. Dr. Carlos Otero Arean

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Guest Editor

Department of Chemistry, University of the Balearic Islands, E-07122 Palma, Spain
Interests: zeolites; nanostructured materials; gas adsorption; gas–solid interaction; heterogeneous catalysis; reactivity of solids, environmental science
Special Issues, Collections and Topics in MDPI journals

Dr. Montserrat Rodriguez Delgado

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Guest Editor

Department of Chemistry, University of the Balearic Islands, E-07122 Palma, Spain
Interests: zeolites; periodic porous solids; gas adsorption; gas–solid interaction; nanodrug delivery; water purification; absorption
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

As an introduction to this Special Issue of Molecules, let us briefly summarize the involved research field by defining zeolites as being three-dimensional aluminosilicates (tectosilicates) bearing an ordered array of channels and cavities (up to 50% of the total volume), which show a characteristic spatial arrangement and dimensions for each particular structure type. Zeolites can thus be regarded as being the archetype of periodic porous solids, as opposed to non-periodic porous materials, such as non-structured active carbons, xerogels and aerogels. The periodicity of the pore layout and regular pore size endows zeolites and related porous solids with the potential to act as molecular sieves and size-selective catalysts, and it also facilitates the engineering of a range of molecular superstructures in zeolite-based host–guest composites with applications in nano-photonic devices and chemical sensors (to name only a couple of examples). Aside from aluminosilicates, both natural and synthetic, several other porous materials merit consideration herein; among them, purely siliceous materials such as silicalite and nanoporous MCM-41 silica, as well as several aluminophosphates and silicoaluminophosphates.

The main applications of zeolites and related porous solids span such fields of use as: heterogeneous catalysts in the petrochemical industry; biomass upgrading and the production of fine chemicals; water softening and purification; environmental pollution control; gas separation, purification and storage; agriculture and aquaculture; medicine and biotechnology; as well as nano-photonic and nano-sensor devices. Research reports making a relevant contribution to any of these (or related) fields will be welcome in this Special Issue of Molecules. Also welcome are reports on novel methods of synthesis, which could be needed to optimize particle size, crystallinity or dimensionality for some specialized applications of zeolites.

Prof. Dr. Carlos Otero Arean
Dr. Montserrat Rodriguez Delgado
Guest Editors

Manuscript Submission Information

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Keywords

Aluminophosphates
Biotechnology
Catalysis
Environmental pollution
Gas adsorption
Gas separation and purification
Gas storage
Host-guest nanosystems
Low dimensional zeolites
MCM-41
Medicine
Nanotechnology
Novel synthesis methods
Zeolites
Water purification

Published Papers (5 papers)

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Research

12 pages, 1437 KiB

Open AccessArticle

IR and NMR Studies of the Status of Al and Acid Sites in Desilicated Zeolite Y

by Mariusz Gackowski, Jerzy Podobiński, Ewa Broclawik and Jerzy Datka

Molecules 2020, 25(1), 31; https://doi.org/10.3390/molecules25010031 - 20 Dec 2019

Cited by 21 | Viewed by 2966

Abstract

The desilication of zeolite Y (of Si/Al = 31) that was previously dealuminated by steaming and acid treatment was studied. Desilication of zeolites of high Si/Al module in alkali solutions extracts both Si and Al from zeolite crystals, but while Si remains in solution, Al is reinserted into the zeolite grain. The main goal of our study was to follow the status of Al reinserted into zeolite during the desilication procedure, and its role in the formation of acid sites of the Brønsted and Lewis types. The properties of Al were followed by ²⁷Al MAS NMR spectroscopy (for parent samples and zeolites treated either with NaOH or NaOH/tetrabutylammonium hydroxide), whereas the acid sites generated in the final stages were studied by IR spectroscopy with NH₃ and CO as probe molecules. In non-desilicated zeolite, most of the Al was in a typically zeolitic tetrahedral coordination, while both NMR and quantitative IR studies of NH₃ sorption evidenced that Al that was extracted by desilication and was subsequently reinserted had a tetrahedral coordination similar to amorphous aluminosilicates and showed an ion exchange ability. After the exchange of Na⁺ to NH₄⁺ and decomposition of NH₄⁺ ions, reinserted Al forms generated protonic sites from which some condensed at higher temperatures producing Lewis acid sites (with stoichiometry typical for zeolites i.e., the condensation of two protonic sites produces one Lewis site) but some other kept their character. Full article

(This article belongs to the Special Issue Zeolites and Related Porous Materials: Design, Synthesis, and Applications)

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15 pages, 4333 KiB

Open AccessArticle

Comprehensive Analysis of the Copper Exchange Implemented in Ammonia and Protonated Forms of Mordenite Using Microwave and Conventional Methods

by Marina G. Shelyapina, Ekaterina A. Krylova, Yurii M. Zhukov, Irina A. Zvereva, Inocente Rodriguez-Iznaga, Vitalii Petranovskii and Sergio Fuentes-Moyado

Molecules 2019, 24(23), 4216; https://doi.org/10.3390/molecules24234216 - 20 Nov 2019

Cited by 14 | Viewed by 2598

Abstract

This article presents the results of a comprehensive study of copper-exchanged mordenite samples prepared from its ammonia and protonated forms (Si/Al = 10) using two different ion exchange methods: conventional and microwave (MW)-assisted. The protonated H-MOR-10 sample was obtained by calcination of commercial NH₄-MOR-10; in this case, a slight degradation of the mordenite framework was observed, but the resulting defects were partially restored after the first ion-exchange procedure of protons for copper ions. The level of copper exchange in the studied materials was found to be limited to 70%. Regardless of the exchange procedure, the replacement of ammonium or proton ions with copper led to a linear increase in the a/b ratio of cell parameters in accordance with an increase in the level of copper exchange, which means that all Cu²⁺ cations are ion-exchangeable and enter the main mordenite channel. Thermal analysis indicated a correlation between the replacement of various ammonium and hydroxyl groups by copper ions during the exchange treatment and their dehydroxylation energy during thermal decomposition. As a conclusion: MW-assisted treatment proved itself as an efficacious method for the synthesis of copper-exchanged mordenites, which not only significantly reduces preparation time but leads to a systematically higher copper exchange level. Full article

(This article belongs to the Special Issue Zeolites and Related Porous Materials: Design, Synthesis, and Applications)

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17 pages, 3851 KiB

Open AccessArticle

The Exchange Mechanism of Alkaline and Alkaline-Earth Ions in Zeolite N

by Monireh Khosravi, Vinuthaa Murthy and Ian D R Mackinnon

Molecules 2019, 24(20), 3652; https://doi.org/10.3390/molecules24203652 - 10 Oct 2019

Cited by 5 | Viewed by 2897

Abstract

Zeolite N is a synthetic zeolite of the EDI framework family from the more than 200 known zeolite types. Previous experimental laboratory and field data show that zeolite N has a high capacity for exchange of ions. Computational modelling and simulation techniques are effective tools that help explain the atomic-scale behaviour of zeolites under different processing conditions and allow comparison with experiment. In this study, the ion exchange behaviour of synthetic zeolite N in an aqueous environment is investigated by molecular dynamics simulations. The exchange mechanism of K⁺ extra-framework cations with alkaline and alkaline-earth cations NH₄⁺, Li⁺, Na⁺, Rb⁺, Cs⁺, Mg²⁺ and Ca²⁺ is explored in different crystallographic directions inside the zeolite N structure. Moreover, the effect of different framework partial charges on MD simulation results obtained from different DFT calculations are examined. The results show that the diffusion and exchange of cations in zeolite N are affected by shape and size of channels controlling the ion exchange flow as well as the nature of cation, ionic size and charge density. Full article

(This article belongs to the Special Issue Zeolites and Related Porous Materials: Design, Synthesis, and Applications)

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14 pages, 4299 KiB

Open AccessArticle

A Facile Strategy to Prepare Shaped ZSM-5 Catalysts with Enhanced Para-Xylene Selectivity and Stability for Toluene Methylation: The Effect of In Situ Modification by Attapulgite

by Yiren Wang, Yang Chang, Min Liu, Anfeng Zhang and Xinwen Guo

Molecules 2019, 24(19), 3462; https://doi.org/10.3390/molecules24193462 - 24 Sep 2019

Cited by 14 | Viewed by 3263

Abstract

A general strategy for preparing shaped toluene methylation catalysts with enhanced para-selectivity and stability is developed by extruding ZSM-5 zeolite with attapulgite as a binder. The novel attapulgite/ZSM-5 extrudate exhibited significantly higher para-selectivity and stability in comparison to the conventional alumina-bound ZSM-5 extrudate. The catalyst samples have been characterized by in situ X-ray diffraction, scanning electron microscope (SEM), NH₃ temperature programmed desorption (TPD), thermogravimetric analysis (TGA) as well as n-hexane/cyclohexane physical adsorption. The enhanced catalytic performance of attapulgite/ZSM-5 extrudate is correlated with the in-situ modification of acid sites in the catalyst by mobile alkaline species, which is introduced via extrusion with attapulgite. Moreover, a higher para-selectivity was obtained over attapulgite-bound modified ZSM-5 extrudate. Such facile and universal strategy of extruding ZSM-5 catalysts with attapulgite as binder could pave a way for preparation of shaped zeolite-base catalyst with enhanced catalytic performance. Full article

(This article belongs to the Special Issue Zeolites and Related Porous Materials: Design, Synthesis, and Applications)

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10 pages, 2372 KiB

Open AccessArticle

Studying Proton Mobility in Zeolites by Varying Temperature Infrared Spectroscopy

by Pit Losch, Hrishikesh Joshi, Niklas Stegmann, Olena Vozniuk and Wolfgang Schmidt

Molecules 2019, 24(17), 3199; https://doi.org/10.3390/molecules24173199 - 03 Sep 2019

Cited by 4 | Viewed by 2780

Abstract

We report a varying temperature infrared spectroscopic (VTIR) study with partial deuterium isotopic exchange as a method for characterizing proton mobility in acidic materials. This VTIR technique permits the estimation of activation energies for proton diffusion. Different acidic materials comprising classical proton-conducting materials, such as transition metal phosphates and sulfonated solids, as well as different zeolites, are tested with this new method. The applicability of the method is thus extended to a vast library of materials. Its underlying principles and assumptions are clearly presented herein. Depending on the temperature ranges, different activation energies for proton transfer are observed irrespective of the different materials. In addition to the well-studied transition metal phosphates, Si-rich zeolites appear to be promising proton-transfer materials (with E_act < 40 kJ mol⁻¹) for application in high-temperature (>150 °C) PEM fuel cells. They significantly outperform Nafion and sulfonated silica, which exhibit higher activation energies with E_act ~ 50 and 120 kJ mol⁻¹, respectively. Full article

(This article belongs to the Special Issue Zeolites and Related Porous Materials: Design, Synthesis, and Applications)

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