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4 pages, 172 KiB

Open AccessEditorial

Zeolitic Microporous Materials and Their Applications

by Susana Valencia

Molecules 2021, 26(3), 730; https://doi.org/10.3390/molecules26030730 - 31 Jan 2021

Cited by 8 | Viewed by 2268

Abstract

Research in the field of zeolites is a very active and relevant area, since these materials are still widely used as catalysts and adsorbents in many industrial applications, despite the appearance of other fascinating microporous materials with excellent properties [...] Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

Research

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14 pages, 1330 KiB

Open AccessFeature PaperArticle

Nitrogen as a Probe Molecule for the IR Studies of the Heterogeneity of OH Groups in Zeolites

by Łukasz Kuterasiński, Mariusz Gackowski, Jerzy Podobiński, Dorota Rutkowska-Zbik and Jerzy Datka

Molecules 2021, 26(20), 6261; https://doi.org/10.3390/molecules26206261 - 16 Oct 2021

Cited by 3 | Viewed by 1876

Abstract

One of the methods of IR studies of the heterogeneity of Si–OH–Al groups in zeolites is the investigation of the frequency shift of the band of free OH bands restored upon the adsorption of ammonia and subsequent desorption at increasing temperatures. We extended [...] Read more.

One of the methods of IR studies of the heterogeneity of Si–OH–Al groups in zeolites is the investigation of the frequency shift of the band of free OH bands restored upon the adsorption of ammonia and subsequent desorption at increasing temperatures. We extended this method by following the shift of the band of the OH group interacting by hydrogen bonding with nitrogen. The advantage of nitrogen, compared with CO, which has been commonly used as a probe molecule in studies on hydrogen bonding, is that for nitrogen the frequency shift is smaller than for CO and therefore there is no overlapping of shifted OH band with the bands of ammonium ions. For zeolites NaHY, HMFI, and HBEA, the frequency shift of IR bands of both free and hydrogen-bonded Si–OH–Al with the increase of ammonia desorption temperature evidences the heterogeneity of these hydroxyls. On the other hand, in zeolite HFAU of Si/Al = 31, Si–OH–Al were found to be homogeneous. Heterogeneity of OH groups may be explained both by the presence of Si–OH–Al of various number of Al near the bridge and of Si–OH–Al of various geometry. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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15 pages, 3373 KiB

Open AccessArticle

Understanding the Deactivation Phenomena of Small-Pore Mo/H-SSZ-13 during Methane Dehydroaromatisation

by Miren Agote-Arán, Anna B. Kroner, David S. Wragg, Wojciech A. Sławiński, Martha Briceno, Husn U. Islam, Igor V. Sazanovich, María E. Rivas, Andrew W. J. Smith, Paul Collier, Inés Lezcano-González and Andrew M. Beale

Molecules 2020, 25(21), 5048; https://doi.org/10.3390/molecules25215048 - 30 Oct 2020

Cited by 7 | Viewed by 3017

Abstract

Small pore zeolites have shown great potential in a number of catalytic reactions. While Mo-containing medium pore zeolites have been widely studied for methane dehydroaromatisation (MDA), the use of small pore supports has drawn limited attention due to the fast deactivation of the [...] Read more.

Small pore zeolites have shown great potential in a number of catalytic reactions. While Mo-containing medium pore zeolites have been widely studied for methane dehydroaromatisation (MDA), the use of small pore supports has drawn limited attention due to the fast deactivation of the catalyst. This work investigates the structure of the small pore Mo/H-SSZ-13 during catalyst preparation and reaction by operando X-ray absorption spectroscopy (XAS), in situ synchrotron powder diffraction (SPD), and electron microscopy; then, the results are compared with the medium pore Mo/H-ZSM-5. While SPD suggests that during catalyst preparation, part of the MoO_x anchors inside the pores, Mo dispersion and subsequent ion exchange was less effective in the small pore catalyst, resulting in the formation of mesopores and Al₂(M_OO₄)₃ particles. Unlike Mo/H-ZSM-5, part of the Mo species in Mo/H-SSZ-13 undergoes full reduction to Mo⁰ during MDA, whereas characterisation of the spent catalyst indicates that differences also exist in the nature of the formed carbon deposits. Hence, the different Mo speciation and the low performance on small pore zeolites can be attributed to mesopores formation during calcination and the ineffective ion exchange into well dispersed Mo-oxo sites. The results open the scope for the optimisation of synthetic routes to explore the potential of small pore topologies. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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13 pages, 4412 KiB

Open AccessArticle

Preparation of Continuous Highly Hydrophobic Pure Silica ITQ-29 Zeolite Layers on Alumina Supports

by Miguel Palomino, Hideki Ono, Susana Valencia and Avelino Corma

Molecules 2020, 25(18), 4150; https://doi.org/10.3390/molecules25184150 - 10 Sep 2020

Cited by 5 | Viewed by 2830

Abstract

The preparation of continuous layers of highly hydrophobic pure silica ITQ-29 zeolite, potentially applicable as hydrophobic membranes for separation of molecules based on their polarity, has been investigated. Continuous layers of intergrown ITQ-29 zeolite crystals were successfully grown on porous alumina supports by [...] Read more.

The preparation of continuous layers of highly hydrophobic pure silica ITQ-29 zeolite, potentially applicable as hydrophobic membranes for separation of molecules based on their polarity, has been investigated. Continuous layers of intergrown ITQ-29 zeolite crystals were successfully grown on porous alumina supports by optimization of the synthesis conditions, such as the appropriate selection of the seeds, the procedure for the gel preparation, and the calcination conditions. This resulted in the formation of all silica ITQ-29 zeolite layers without the presence of germanium required in previously reported ITQ-29 membranes, with the subsequent improvement in quality and stability, as verified by the absence of cracks after calcination. We have proved that the incorporation of aluminum from the support into the zeolite layer does not occur, neither during the secondary growth nor through migration of aluminum species during calcination. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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20 pages, 4563 KiB

Open AccessArticle

Effect of Alkali-Free Synthesis and Post-Synthetic Treatment on Acid Sites in Beta Zeolites

by Kinga Mlekodaj, Joanna E. Olszowka, Venceslava Tokarova, Edyta Tabor, Ales Kasparek, Jana Novakova, Gabriela Stavova, Olga Gonsiorova, Lenka Peliskova, Jiri Brus, Radim Pilar, Petr Klein and Jiri Dedecek

Molecules 2020, 25(15), 3434; https://doi.org/10.3390/molecules25153434 - 28 Jul 2020

Cited by 7 | Viewed by 2622

Abstract

Beta zeolites with Si/Al around 14 were prepared using three new alkali-free synthesis methods based on the application of amorphous aluminosilicate precursor and calcined in ammonia or air. All samples exhibit structural and textural properties of standard beta zeolite. Comprehensive study by ²⁷ [...] Read more.

Beta zeolites with Si/Al around 14 were prepared using three new alkali-free synthesis methods based on the application of amorphous aluminosilicate precursor and calcined in ammonia or air. All samples exhibit structural and textural properties of standard beta zeolite. Comprehensive study by ²⁷Al and ²⁹Si MAS NMR, together with FTIR adsorption of d₃-acetonitrile and pyridine were used to characterize the influence of both the synthesis and calcination procedure on the framework Al atoms and related Brønsted and Lewis acid sites. While calcination in ammonia preserves all framework Al atoms, calcination in air results in 15% release of framework Al, but without restrictions of the accessibility of the beta zeolite channel system for bulky pyridine molecules. Terminal (SiO)₃AlOH groups present in the hydrated zeolites were suggested as a precursor of framework Al-Lewis sites. Surprisingly, the mild dealumination of the air-calcined zeolites result in an increase of the concentration of Brønsted acid sites and a decrease of the total concentration of Lewis sites with the formation of the extra-framework ones. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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9 pages, 3227 KiB

Open AccessArticle

Combining Soft- and Hard-Templating Approaches in MWW-Type Zeolites

by Anderson Joel Schwanke, Jaíne Fernandes Gomes, Katia Bernardo-Gusmão and Sibele Pergher

Molecules 2020, 25(15), 3335; https://doi.org/10.3390/molecules25153335 - 23 Jul 2020

Cited by 5 | Viewed by 2930

Abstract

A combination of hard-templating (HT) and soft-templating (ST) approaches was studied to obtain MWW-type materials with intermediate physicochemical properties. The HT methodology involved the introduction of carbon particles as hard templates during gel synthesis to obtain a layered zeolitic precursor (LZP) with particles [...] Read more.

A combination of hard-templating (HT) and soft-templating (ST) approaches was studied to obtain MWW-type materials with intermediate physicochemical properties. The HT methodology involved the introduction of carbon particles as hard templates during gel synthesis to obtain a layered zeolitic precursor (LZP) with particles possessing a microspherical morphology. The LZP obtained was treated with surfactants as soft templates to expand the layers of the LZP, followed by a pillaring procedure. The materials were characterized by X-ray diffraction, transmission and scanning electron microscopy, elemental analysis and N₂ adsorption. The results demonstrate that the obtained material possesses intermediate properties from both approaches, with interparticle mesopores/macropores and pore sizes between 18 and 46 Å. However, the ST procedure causes a partial disruption of some microspheres, forming small crystallite aggregates, and results in a decrease in the number of interparticle mesopores/macropores previously formed by the HT method. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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15 pages, 4765 KiB

Open AccessArticle

High-Silica Zeolites as Sorbent Media for Adsorption and Pre-Concentration of Pharmaceuticals in Aqueous Solutions

by Elena Sarti, Tatiana Chenet, Claudia Stevanin, Valentina Costa, Alberto Cavazzini, Martina Catani, Annalisa Martucci, Nicola Precisvalle, Giada Beltrami and Luisa Pasti

Molecules 2020, 25(15), 3331; https://doi.org/10.3390/molecules25153331 - 22 Jul 2020

Cited by 18 | Viewed by 3267

Abstract

The present work focused on the use of high-silica commercial zeolites as sorbent media for pharmaceuticals in an aqueous matrix. As drug probes, ketoprofen, hydrochlorothiazide, and atenolol were selected, because of their occurrence in surface waters and effluents from wastewater treatment plants. Pharmaceuticals [...] Read more.

The present work focused on the use of high-silica commercial zeolites as sorbent media for pharmaceuticals in an aqueous matrix. As drug probes, ketoprofen, hydrochlorothiazide, and atenolol were selected, because of their occurrence in surface waters and effluents from wastewater treatment plants. Pharmaceuticals adsorption was evaluated for two Faujasite topology zeolites with Silica/Alumina Ratio 30 and 200. The selected zeolites were demonstrated to be efficient sorbents towards all investigated pharmaceuticals, thanks to their high saturation capacities (from 12 to 32% w/w) and binding constants. These results were corroborated by thermal and structural analyses, which revealed that adsorption occurred inside zeolite’s porosities, causing lattice modifications. Finally, zeolites have been tested as a pre-concentration media in the dispersive-solid phase extraction procedure. Recoveries higher than 95% were gained for ketoprofen and hydrochlorothiazide and approximately 85% for atenolol, at conditions that promoted the dissolution of the neutral solute into a phase mainly organic. The results were obtained by using a short contact time (5 min) and reduced volume of extraction (500 µL), without halogenated solvents. These appealing features make the proposed procedure a cost and time saving method for sample enrichment as well as for the regeneration of exhausted sorbent, rather than the more energetically expensive thermal treatment. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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16 pages, 2263 KiB

Open AccessArticle

Conversion of the Propane–Butane Fraction into Arenes on MFI Zeolites Modified by Zinc Oxide and Activated by Low-Temperature Plasma

by Vladimir I. Erofeev, Sofiya N. Dzhalilova, Mikhail V. Erofeev, Vasilii S. Ripenko and Vladimir P. Reschetilowski

Molecules 2020, 25(11), 2704; https://doi.org/10.3390/molecules25112704 - 11 Jun 2020

Cited by 4 | Viewed by 2802

Abstract

The effect of modification of MFI zeolite 1–5 wt.% ZnO activated by plasma on acid and catalytic properties in the conversion of the propane–butane fraction into arenes was investigated. The high-silica zeolites with silicate module 45 were synthesized from alkaline alumina–silica gels in [...] Read more.

The effect of modification of MFI zeolite 1–5 wt.% ZnO activated by plasma on acid and catalytic properties in the conversion of the propane–butane fraction into arenes was investigated. The high-silica zeolites with silicate module 45 were synthesized from alkaline alumina–silica gels in the presence of an ‘X-oil’ organic structure-forming additive. The modification of the zeolite with zinc was carried out by impregnating the zeolite granules in the H-form with an aqueous solution of Zn(NO₃)₂. The obtained zeolites were characterized by X-ray phase analysis and IR spectroscopy. It is shown that the synthesized zeolites belong to the high-silica MFI zeolites. The study of microporous zeolite-containing catalysts during the conversion of C₃-C₄ alkanes to aromatic hydrocarbons made it possible to establish that the highest yield of aromatic hydrocarbons is observed on zeolite catalysts modified with 1 and 3% ZnO and amount to 63.7 and 64.4% at 600 °C, respectively, which is 7.7–8.4% more than on the original zeolite. The preliminary activation of microporous zeolites modified with 1–5% ZnO and plasma leads to an increase in the yield of aromatic hydrocarbons from the propane–butane fraction; the maximum yield of arenes is observed in zeolite catalysts modified with 1 and 3% ZnO and activated by plasma, amounting to 64.9 and 65.5% at 600 °C, respectively, which is 8.9–9.5% more than on the initial zeolite. The activity of the zeolite catalysts modified by ZnO and activated by plasma show good agreement with their acid properties. Activation of the zeolites modified by 1 and 3% ZnO and plasma leads to an increase in the concentration of the weak acid sites of the catalyst to 707 and 764 mmol/g in comparison with plasma-inactivated 1 and 3% ZnO/ZKE-XM catalysts at 626 and 572 mmol/g, respectively. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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13 pages, 1983 KiB

Open AccessArticle

Freeze Granulated Zeolites X and A for Biogas Upgrading

by Kritika Narang and Farid Akhtar

Molecules 2020, 25(6), 1378; https://doi.org/10.3390/molecules25061378 - 18 Mar 2020

Cited by 14 | Viewed by 4858

Abstract

Biogas is a potential renewable energy resource that can reduce the current energy dependency on fossil fuels. The major limitation of utilizing biogas fully in the various applications is the presence of a significant volume fraction of carbon dioxide in biogas. Here, we [...] Read more.

Biogas is a potential renewable energy resource that can reduce the current energy dependency on fossil fuels. The major limitation of utilizing biogas fully in the various applications is the presence of a significant volume fraction of carbon dioxide in biogas. Here, we used adsorption-driven CO₂ separation using the most prominent adsorbents, NaX (faujasite) and CaA (Linde Type A) zeolites. The NaX and CaA zeolites were structured into hierarchically porous granules using a low-cost freeze granulation technique to achieve better mass transfer kinetics. The freeze granulation processing parameters and the rheological properties of suspensions were optimized to obtain homogenous granules of NaX and CaA zeolites 2–3 mm in diameter with macroporosity of 77.9% and 68.6%, respectively. The NaX and CaA granules kept their individual morphologies, crystallinities with a CO₂ uptake of 5.8 mmol/g and 4 mmol/g, respectively. The CO₂ separation performance and the kinetic behavior were estimated by breakthrough experiments, where the NaX zeolite showed a 16% higher CO₂ uptake rate than CaA granules with a high mass transfer coefficient, 1.3 m/s, compared to commercial granules, suggesting that freeze-granulated zeolites could be used to improve adsorption kinetics and reduce cycle time for biogas upgrading in the adsorption swing technology. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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13 pages, 6081 KiB

Open AccessArticle

Natural Mordenite from Spain as Pozzolana

by Leticia Presa, Jorge L. Costafreda, Domingo A. Martín and Isabel Díaz

Molecules 2020, 25(5), 1220; https://doi.org/10.3390/molecules25051220 - 9 Mar 2020

Cited by 9 | Viewed by 3541

Abstract

This work deals with anomalous concentrations of natural mordenite in the southeast of Spain. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies evidenced that the samples contain mainly monomineral zeolitic phase of mordenite (70% to 74%), usually accompanied by smectite (montmorillonite), [...] Read more.

This work deals with anomalous concentrations of natural mordenite in the southeast of Spain. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies evidenced that the samples contain mainly monomineral zeolitic phase of mordenite (70% to 74%), usually accompanied by smectite (montmorillonite), the principal component of bentonite. A study of the applicability of these zeolites is presented to establish the potential use as pozzolanic cements. For comparative purposes, synthetic commercial mordenite is also characterized and tested. The initial mixtures were prepared using cement and mordenite at a 75:25 ratio. Chemical analysis and a pozzolanicity test showed the high pozzolanic character. These mixtures were further added to sand and water, yielding the cement specimens to be used as concrete. Mechanical test results showed that the mechanical compression at 7 and 28 days fall into the range of 19.23 to 43.05 MegaPascals (MPa) for the cement specimens built with natural mordenites. The obtained results fall in the same range of cement specimens prepared with natural clinoptilolite, using mixtures within the European requirement for commercial concretes. Thus, these results and the low cost of natural mordenite of San José de los Escullos deposit supports the potential use of natural mordenite as pozzolanic cement. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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14 pages, 3226 KiB

Open AccessArticle

Evaluation of the Textural Parameters of Zeolite Beta in LDPE Catalytic Degradation: Thermogravimetric Analysis Coupled with FTIR Operando Studies

by Kamila Pyra, Karolina A. Tarach, Ewa Janiszewska, Dorota Majda and Kinga Góra-Marek

Molecules 2020, 25(4), 926; https://doi.org/10.3390/molecules25040926 - 19 Feb 2020

Cited by 17 | Viewed by 3798

Abstract

Zeolite-based catalysts are globally employed in many industrial processes, such as crude-oil refining and bulk chemical production. In this work, the cracking of low-density polyethylene (LDPE) was thoroughly followed in a FTIR operando study to examine the catalytic efficiency of purely microporous zeolites [...] Read more.

Zeolite-based catalysts are globally employed in many industrial processes, such as crude-oil refining and bulk chemical production. In this work, the cracking of low-density polyethylene (LDPE) was thoroughly followed in a FTIR operando study to examine the catalytic efficiency of purely microporous zeolites of various textural characteristics. To provide complementary and valuable information on the catalytic activity of the zeolite studied, the thermogravimetric analysis results were compared with yields of the products generated under operating conditions. The reaction products were analyzed via GC–MS to determine the hydrocarbon chain distribution in terms of paraffin, olefins, and aromatics. The individual impact of textural and acidic parameters on catalytic parameters was assessed. The accumulation of bridging hydroxyls of high strength in the zeolite benefited the decrease in polymer decomposition temperature. Through a strategic comparison of purely microporous zeolites, we showed that the catalytic cracking of LDPE is dominated by the acidic feature inherent to the microporous environment. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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10 pages, 2354 KiB

Open AccessCommunication

Preparation of Aluminosilicate Ferrierite Zeolite Nanosheets with Controllable Thickness in the Presence of a Sole Organic Structure Directing Agent

by Hao Xu, YuXia Yu, LongFeng Zhu, ChaoQun Bian, HangLing Zhai, JianYing Tong, HuiZhen Wu and Chao Shen

Molecules 2020, 25(4), 771; https://doi.org/10.3390/molecules25040771 - 11 Feb 2020

Cited by 7 | Viewed by 3642

Abstract

Preparation of aluminosilicate ferrierite (FER) zeolite nanosheets with controllable thickness in the presence of a sole organic ammonium is attractive, but still challenging. In this report, with the employment of N,N-diethyl-cis-2,6-dimethylpiperidinium (DMP) as both a structure directing agent [...] Read more.

Preparation of aluminosilicate ferrierite (FER) zeolite nanosheets with controllable thickness in the presence of a sole organic ammonium is attractive, but still challenging. In this report, with the employment of N,N-diethyl-cis-2,6-dimethylpiperidinium (DMP) as both a structure directing agent and crystal growth inhibitor, aluminosilicate FER zeolite nanosheets, with a variety of crystal thicknesses, ranging from 6 to 200 nm, are successfully synthesized under hydrothermal conditions. Very interestingly, the amount of DMP in the starting gel is the key factor for crystal thickness control of aluminosilicate FER zeolite nanosheets. The obtained FER products, with different thicknesses, are well characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), N₂ sorption, thermogravimetric analysis (TG), inductively coupled plasma (ICP), and magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. This simple strategy might provide a novel avenue for the synthesis of other zeolite nanosheets with controllable thickness. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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13 pages, 3795 KiB

Open AccessArticle

Magnetic Solid-Phase Extraction of Pyrethroid Pesticides from Environmental Water Samples Using Deep Eutectic Solvent-type Surfactant Modified Magnetic Zeolitic Imidazolate Framework-8

by Huifang Liu, Lihua Jiang, Meng Lu, Guangyang Liu, Tengfei Li, Xiaomin Xu, Lingyun Li, Huan Lin, Jun Lv, Xiaodong Huang and Donghui Xu

Molecules 2019, 24(22), 4038; https://doi.org/10.3390/molecules24224038 - 7 Nov 2019

Cited by 39 | Viewed by 4157

Abstract

A simple, sensitive and effective magnetic solid-phase extraction (MSPE) technique was developed for the extraction of pyrethroid pesticides from environmental water samples, followed by gas chromatography tandem triple quadrupole mass spectrometry determination. An adsorbent of magnetic zeolitic imidazolate framework-8@deep eutectic solvent (M-ZIF-8@DES) was [...] Read more.

A simple, sensitive and effective magnetic solid-phase extraction (MSPE) technique was developed for the extraction of pyrethroid pesticides from environmental water samples, followed by gas chromatography tandem triple quadrupole mass spectrometry determination. An adsorbent of magnetic zeolitic imidazolate framework-8@deep eutectic solvent (M-ZIF-8@DES) was prepared using deep eutectic solvent coated on the surface of M-ZIF-8. The features of M-ZIF-8@DES were confirmed by material characterizations, and the results indicated that M-ZIF-8@DES has a good magnetism (61.3 emu g⁻¹), a decent surface area (96.83 m² g⁻¹) and pore volume (0.292 mL g⁻¹). Single factor experiments were carried out to investigate the effect of different conditions on the performance of MSPE. Under the optimal conditions, the developed method performs good linearity (R² ≥ 0.9916) in the concentration range of 1–500 μg L⁻¹. The limits of detection were in the range of 0.05–0.21 μg L⁻¹ (signal/noise = 3/1). The intraday relative standard deviation (RSD) and interday RSD were less than 9.40%. Finally, the proposed technique was applied for the determination of pyrethroid pesticides in environmental water samples. This work shows the potential of DES-modified metal-organic frameworks for different sample pretreatment techniques. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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8 pages, 523 KiB

Open AccessArticle

The Influence of Zeolite (Sokyrnytsya Deposit) on the Physical and Chemical Resistance of a Magnesium Potassium Phosphate Compound for the Immobilization of High-Level Waste

by Svetlana A. Kulikova and Sergey E. Vinokurov

Molecules 2019, 24(19), 3421; https://doi.org/10.3390/molecules24193421 - 20 Sep 2019

Cited by 14 | Viewed by 2669

Abstract

The manuscript presents the results of the development of new material for high-level waste (HLW) management: the magnesium potassium phosphate (MKP) compound. The possibility of using zeolite (Sokyrnytsya deposit) to increase the mechanical, thermal, and hydrolytic resistance of this compound with immobilized HLW [...] Read more.

The manuscript presents the results of the development of new material for high-level waste (HLW) management: the magnesium potassium phosphate (MKP) compound. The possibility of using zeolite (Sokyrnytsya deposit) to increase the mechanical, thermal, and hydrolytic resistance of this compound with immobilized HLW was studied. The main component of the used natural zeolite is a mineral of the clinoptilolite–heulandite series, and quartz, microcline, and clay minerals (illite, sepiolite, and smectite) are present as impurities. The compressive strength of the compound, containing at least 4.2 wt % zeolite, is about 25 MPa. Compound containing 28.6 wt % zeolite retains high compressive strength (at least 9.0 MPa), even after heat treatment at 450 °C. The adding of zeolite to the composition of the compound increases its hydrolytic stability, while the leaching rate of the mobile nuclides ¹³⁷Cs and ⁹⁰Sr decreases up to one order of values. Differential leaching rate of radionuclides from the compound containing 28.6 wt % zeolite is 2.6 × 10⁻⁷ for ¹³⁷Cs, 2.9 × 10⁻⁶ for ⁹⁰Sr, 1.7 × 10⁻⁹ for ²³⁹Pu, and 2.9 × 10⁻⁹ g/(cm²∙day) for ²⁴¹Am. Thus, the properties of the resulting compound correspond to the requirements for solidified HLW in Russia. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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9 pages, 2566 KiB

Open AccessArticle

SYSU-6, A New 2-D Aluminophosphate Zeolite Layer Precursor

by Jiang-Zhen Qiu, Long-Fei Wang and Jiuxing Jiang

Molecules 2019, 24(16), 2972; https://doi.org/10.3390/molecules24162972 - 16 Aug 2019

Cited by 6 | Viewed by 3205

Abstract

Two-dimensional aluminophosphate is an important precursor of phosphate-based zeolites; a new Sun Yat-sen University No. 6 (SYSU-6) with |Hada|₂[Al₂(HPO₄)(PO₄)₂] has been synthesized in the hydrothermal synthesis with organic structure-directing agent (OSDA) of N [...] Read more.

Two-dimensional aluminophosphate is an important precursor of phosphate-based zeolites; a new Sun Yat-sen University No. 6 (SYSU-6) with |Hada|₂[Al₂(HPO₄)(PO₄)₂] has been synthesized in the hydrothermal synthesis with organic structure-directing agent (OSDA) of N,N,3,5-tetramethyladamantan-1-amine. In this paper, SYSU-6 is characterized by single-crystal/powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, transmission electron microscopy, infrared and UV Raman spectroscopy, solid-state ²⁷Al, ³¹P and ¹³C magic angle spinning (MAS) NMR spectra, and elemental analysis. The single-crystal X-ray diffraction structure indicates that SYSU-6 crystallized in the space group P2₁/n, with a = 8.4119(3), b = 36.9876(12), c = 12.5674(3), α = 90°, β = 108.6770(10)°, γ = 90°, V = 3704.3(2) Å³, Z = 4, R = 5.12%, for 8515 observed data (I > 2σ(I)). The structure has a new 4,12-ring layer framework topology linked by alternating AlO₄ and PO₄ tetrahedra. The organic molecules reside between the layers and are hydrogen-bonded to the inorganic framework. The new type of layer provides a greater opportunity to construct zeolite with novel topology. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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Review

Jump to: Editorial, Research

19 pages, 1844 KiB

Open AccessReview

Pervaporation Zeolite-Based Composite Membranes for Solvent Separations

by Roberto Castro-Muñoz and Grzegorz Boczkaj

Molecules 2021, 26(5), 1242; https://doi.org/10.3390/molecules26051242 - 25 Feb 2021

Cited by 22 | Viewed by 3653

Abstract

Thanks to their well-defined molecular sieving and stability, zeolites have been proposed in selective membrane separations, such as gas separation and pervaporation. For instance, the incorporation of zeolites into polymer phases to generate composite (or mixed matrix) membranes revealed important advances in pervaporation. [...] Read more.

Thanks to their well-defined molecular sieving and stability, zeolites have been proposed in selective membrane separations, such as gas separation and pervaporation. For instance, the incorporation of zeolites into polymer phases to generate composite (or mixed matrix) membranes revealed important advances in pervaporation. Therefore, the goal of this review is to compile and elucidate the latest advances (over the last 2–3 years) of zeolite applications in pervaporation membranes either combining zeolites or polymers. Here, particular emphasis has been focused on relevant insights and findings in using zeolites in pervaporative azeotropic separations and specific aided applications, together with novel concepts of membranes. A brief background of the pervaporation process is also given. According to the findings of this review, we provide future perspectives and recommendations for new researchers in the field. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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24 pages, 2850 KiB

Open AccessReview

Acid Properties of Hierarchical Zeolites Y

by Mariusz Gackowski and Jerzy Datka

Molecules 2020, 25(5), 1044; https://doi.org/10.3390/molecules25051044 - 26 Feb 2020

Cited by 25 | Viewed by 5720

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. [...] Read more.

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. Full article

(This article belongs to the Special Issue Zeolitic Microporous Materials and Their Applications)

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