Research

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16 pages, 1250 KiB

Open AccessArticle

High Reactivity of Dimethyl Ether Activated by Zeolite Ferrierite within a Fer Cage: A Prediction Study

by Xiaofang Chen, Pei Feng and Xiujie Li

Molecules 2024, 29(9), 2000; https://doi.org/10.3390/molecules29092000 - 26 Apr 2024

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The zeolite-catalyzed conversion of DME into chemicals is considered environmentally friendly in industry. The periodic density functional theory, statistical thermodynamics, and the transition state theory are used to study some possible parallel reactions about the hydrogen-bonded DME over zeolite ferrierite. The following are [...] Read more.

The zeolite-catalyzed conversion of DME into chemicals is considered environmentally friendly in industry. The periodic density functional theory, statistical thermodynamics, and the transition state theory are used to study some possible parallel reactions about the hydrogen-bonded DME over zeolite ferrierite. The following are the key findings: (1) the charge separation probably leads to the conversion of a hydrogen-bonded DME into a dimethyl oxonium ion (i.e., DMO⁺ or (CH₃)₂OH⁺) with a positive charge of about 0.804 e; (2) the methylation of DME, CH₃OH, H₂O, and CO by DMO⁺ at the T2O6 site of zeolite ferrierite shows the different activated internal energy (∆E^≠) ranging from 18.47 to 30.06 kcal/mol, implying the strong methylation ability of DMO⁺; (3) H-abstraction by DMO⁺ is about 3.94–15.53 or 6.57–18.16 kcal/mol higher than DMO⁺ methylation in the activation internal energy; (4) six DMO⁺-mediated reactions are more likely to occur due to the lower barriers, compared to the experimental barrier (i.e., 39.87 kcal/mol) for methyl acetate synthesis; (5) active intermediates, such as (CH₃)₃O⁺, (CH₃)₂OH⁺, CH₃CO⁺, CH₃OH₂⁺, and CH₂=OH⁺, are expected to appear; (6) DMO⁺ is slightly weaker than the well-known surface methoxy species (ZO-CH₃) in methylation; and (7) the methylated activity declines in the order of DME, CH₃OH, H₂O, and CO, with corresponding rate constants at 463.15 K of about 3.4 × 10⁴, 1.1 × 10², 0.18, and 8.2 × 10⁻² s⁻¹, respectively. Full article

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

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14 pages, 6566 KiB

Open AccessArticle

A Polyzwitterionic@MOF Hydrogel with Exceptionally High Water Vapor Uptake for Efficient Atmospheric Water Harvesting

by Jian Yan, Wenjia Li, Yingyin Yu, Guangyu Huang, Junjie Peng, Daofei Lv, Xin Chen, Xun Wang and Zewei Liu

Molecules 2024, 29(8), 1851; https://doi.org/10.3390/molecules29081851 - 18 Apr 2024

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Abstract

Atmospheric water harvesting (AWH) is considered a promising strategy for sustainable freshwater production in landlocked and arid regions. Hygroscopic salt-based composite sorbents have attracted widespread attention for their water harvesting performance, but suffer from aggregation and leakage issues due to the salting-out effect. [...] Read more.

Atmospheric water harvesting (AWH) is considered a promising strategy for sustainable freshwater production in landlocked and arid regions. Hygroscopic salt-based composite sorbents have attracted widespread attention for their water harvesting performance, but suffer from aggregation and leakage issues due to the salting-out effect. In this study, we synthesized a PML hydrogel composite by incorporating zwitterionic hydrogel (PDMAPS) and MIL-101(Cr) as a host for LiCl. The PML hydrogel was characterized using various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The swelling properties and water vapor adsorption-desorption properties of the PML hydrogel were also assessed. The results demonstrate that the MIL-101(Cr) was uniformly embedded into PDMAP hydrogel, and the PML hydrogel exhibits a swelling ratio of 2.29 due to the salting-in behavior. The PML hydrogel exhibited exceptional water vapor sorption capacity of 0.614 g/g at 298 K, RH = 40% and 1.827 g/g at 298 K, RH = 90%. It reached 80% of its saturated adsorption capacity within 117 and 149 min at 298 K, RH = 30% and 90%, respectively. Additionally, the PML hydrogel showed excellent reversibility in terms of water vapor adsorption after ten consecutive cycles of adsorption-desorption. The remarkable adsorption capacity, favorable adsorption-desorption rate, and regeneration stability make the PML hydrogel a potential candidate for AWH. This polymer-MOF synergistic strategy for immobilization of LiCl in this work offers new insights into designing advanced materials for AWH. Full article

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

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14 pages, 6302 KiB

Open AccessArticle

Study of CHF₃/CH₂F₂ Adsorption Separation in TIFSIX-2-Cu-i

by Shoudong Wang, Lei Zhou, Hongyun Qin, Zixu Dong, Haoyuan Li, Bo Liu, Zhilu Wang, Lina Zhang, Qiang Fu and Xia Chen

Molecules 2024, 29(8), 1721; https://doi.org/10.3390/molecules29081721 - 11 Apr 2024

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Abstract

Hydrofluorocarbons (HFCs) have important applications in different industries; however, they are environmentally unfriendly due to their high global warming potential (GWP). Hence, reclamation of used hydrofluorocarbons via energy-efficient adsorption-based separation will greatly contribute to reducing their impact on the environment. In particular, the [...] Read more.

Hydrofluorocarbons (HFCs) have important applications in different industries; however, they are environmentally unfriendly due to their high global warming potential (GWP). Hence, reclamation of used hydrofluorocarbons via energy-efficient adsorption-based separation will greatly contribute to reducing their impact on the environment. In particular, the separation of azeotropic refrigerants remains challenging, such as typical mixtures of CH₂F₂ (HFC-23) and CHF₃ (HFC-32), due to a lack of adsorptive mechanisms. Metal–organic frameworks (MOFs) can provide a promising solution for the separation of CHF₃–CH₂F₂ mixtures. In this study, the adsorption mechanism of CHF₃–CH₂F₂ mixtures in TIFSIX-2-Cu-i was revealed at the microscopic level by combining static pure-component adsorption experiments, molecular simulations, and density-functional theory (DFT) calculations. The adsorption separation selectivity of CH₂F₂/CHF₃ in TIFSIX-2-Cu-i is 3.17 at 3 bar under 308 K. The existence of similar TiF₆²⁻ binding sites for CH₂F₂ or CHF₃ was revealed in TIFSIX-2-Cu-i. Interactions between the fluorine atom of the framework and the hydrogen atom of the guest molecule were found to be responsible for determining the high adsorption separation selectivity of CH₂F₂/CHF₃. This exploration is important for the design of highly selective adsorbents for the separation of azeotropic refrigerants. Full article

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

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11 pages, 2245 KiB

Open AccessArticle

Morphology Regulation of Zeolite MWW via Classical/Nonclassical Crystallization Pathways

by Wenwen Zi, Zejing Hu, Xiangyu Jiang, Junjun Zhang, Chengzhi Guo, Konggang Qu, Shuo Tao, Dengran Tan and Fangling Liu

Molecules 2024, 29(1), 170; https://doi.org/10.3390/molecules29010170 - 27 Dec 2023

Viewed by 776

Abstract

The morphology and porosity of zeolites have an important effect on adsorption and catalytic performance. In the work, simple inorganic salts, i.e., Na salts were used to synthesize MWW zeolite using the organic compound 1-Butyl-2,3-dimethyl-1H-imidazol-3-ium hydroxide as a structure-directing agent and the morphology [...] Read more.

The morphology and porosity of zeolites have an important effect on adsorption and catalytic performance. In the work, simple inorganic salts, i.e., Na salts were used to synthesize MWW zeolite using the organic compound 1-Butyl-2,3-dimethyl-1H-imidazol-3-ium hydroxide as a structure-directing agent and the morphology was regulated by the alkali metals. The sample synthesized without Na salts shows a dense hexagon morphology, while different morphologies like ellipsoid, wool ball, and uniform hexagon appear when using NaOH, Na₂CO₃, and NaHCO₃, respectively. Moreover, the impact of Na salts on the induction, nucleation, and the evolution of crystal growth was studied. Different kinds of Na salts have a different impact on the crystalline induction time in the order of NaHCO₃ (36 h) < Na₂CO₃ (72 h) = NaOH (72 h). Meanwhile, the crystalline mechanism with the cooperation of inorganic salts and the organic SDAs is proposed. NaOH- and Na₂CO₃-MWW zeolite crystallized with a network of hydrogel via the nonclassical pathway in the system; however, the product is synthesized via a classical route in the NaHCO₃ environment. This work provides information about MWW zeolite crystallization and modulating diverse morphologies by adjusting the process. Full article

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

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15 pages, 2389 KiB

Open AccessArticle

Simulating Crystal Structure, Acidity, Proton Distribution, and IR Spectra of Acid Zeolite HSAPO-34: A High Accuracy Study

by Xiaofang Chen and Tie Yu

Molecules 2023, 28(24), 8087; https://doi.org/10.3390/molecules28248087 - 14 Dec 2023

Cited by 28 | Viewed by 779

Abstract

It is a challenge to characterize the acid properties of microporous materials in either experiments or theory. This study presents the crystal structure, acid site, acid strength, proton siting, and IR spectra of HSAPO-34 from the SCAN + rVV10 method. The results indicate: [...] Read more.

It is a challenge to characterize the acid properties of microporous materials in either experiments or theory. This study presents the crystal structure, acid site, acid strength, proton siting, and IR spectra of HSAPO-34 from the SCAN + rVV10 method. The results indicate: the crystal structures of various acid sites of HSAPO-34 deviate from the space group of

R \bar{3}

; the acid strength inferred from the DPE value likely decreases with the proton binding sites at O(2), O(4), O(1),and O(3), contrary to the stability order in view of the internal energy; the calculated ensemble-averaged DPE is about 1525 kJ/mol at 673.15 K; and the proton siting and the proton distribution are distinctly influenced by the temperature: at low temperatures, the proton is predominantly located at O(3), while it prefers O(2) at high temperatures, and the proton at O(4) assumedly has the least distribution at 273.15–773.15 K. In line with the neutron diffraction experiment, a correction factor of 0.979 is needed to correct for the calculated hydroxyl stretching vibration (ν(O-H)) of HSAPO-34. It seems that the SCAN meta-GGA method, compensating for some drawbacks of the GGA method, could provide satisfying results regarding the acid properties of HSAPO-34. Full article

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

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15 pages, 10564 KiB

Open AccessArticle

Efficient Selective Capture of Carbon Dioxide from Nitrogen and Methane Using a Metal-Organic Framework-Based Nanotrap

by Junjie Peng, Chengmin Fu, Jiqin Zhong, Bin Ye, Jing Xiao, Chongxiong Duan and Daofei Lv

Molecules 2023, 28(23), 7908; https://doi.org/10.3390/molecules28237908 - 02 Dec 2023

Cited by 1 | Viewed by 947

Abstract

Selective carbon capture from exhaust gas and biogas, which mainly involves the separation of CO₂/N₂ and CO₂/CH₄ mixtures, is of paramount importance for environmental and industrial requirements. Herein, we propose an interesting metal-organic framework-based nanotrap, namely ZnAtzCO [...] Read more.

Selective carbon capture from exhaust gas and biogas, which mainly involves the separation of CO₂/N₂ and CO₂/CH₄ mixtures, is of paramount importance for environmental and industrial requirements. Herein, we propose an interesting metal-organic framework-based nanotrap, namely ZnAtzCO₃ (Atz⁻ = 3-amino-1,2,4-triazolate, CO₃²⁻ = carbonate), with a favorable ultramicroporous structure and electrostatic interactions that facilitate efficient capture of CO₂. The structural composition and stability were verified by FTIR, TGA, and PXRD techniques. Particularly, ZnAtzCO₃ demonstrated high CO₂ capacity in a wide range of pressures, with values of 44.8 cm³/g at the typical CO₂ fraction of the flue gas (15 kPa) and 56.0 cm³/g at the CO₂ fraction of the biogas (50 kPa). Moreover, ultrahigh selectivities over CO₂/N₂ (15:85, v:v) and CO₂/CH₄ (50:50, v:v) of 3538 and 151 were achieved, respectively. Molecular simulations suggest that the carbon atom of CO₂ can form strong electrostatic C^δ+···^δ−O-C interactions with four oxygen atoms in the carbonate ligands, while the oxygen atom of CO₂ can interact with the hydrogen atoms in the triazolate ligands through O^δ−···^δ+H-C interactions, which makes ZnAtzCO₃ an optimal nanotrap for CO₂ fixation. Furthermore, breakthrough experiments confirmed excellent real-world separation toward CO₂/N₂ and CO₂/CH₄ mixtures on ZnAtzCO₃, demonstrating its great potential for selective CO₂ capture. Full article

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

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10 pages, 1563 KiB

Open AccessArticle

Exquisitely Constructing a Robust MOF with Dual Pore Sizes for Efficient CO₂ Capture

by Yanxi Li, Yuhua Bai, Zhuozheng Wang, Qihan Gong, Mengchen Li, Yawen Bo, Hua Xu, Guiyuan Jiang and Kebin Chi

Molecules 2023, 28(17), 6276; https://doi.org/10.3390/molecules28176276 - 28 Aug 2023

Cited by 2 | Viewed by 1210

Abstract

Developing metal–organic framework (MOF) adsorbents with excellent performance and robust stability is of critical importance to reduce CO₂ emissions yet challenging. Herein, a robust ultra-microporous MOF, Cu(bpfb)(bdc), with mixed ligands of N, N′-(1,4-phenylene)diisonicotinamide (bpfb), and 1,4-dicarboxybenzene (bdc) was delicately constructed. Structurally, this [...] Read more.

Developing metal–organic framework (MOF) adsorbents with excellent performance and robust stability is of critical importance to reduce CO₂ emissions yet challenging. Herein, a robust ultra-microporous MOF, Cu(bpfb)(bdc), with mixed ligands of N, N′-(1,4-phenylene)diisonicotinamide (bpfb), and 1,4-dicarboxybenzene (bdc) was delicately constructed. Structurally, this material possesses double-interpenetrated frameworks formed by two staggered, independent frameworks, resulting in two types of narrow ultra-micropores of 3.4 × 5.0 and 4.2 × 12.8 Å², respectively. The above structural properties make its highly selective separation at 273~298 K with a CO₂ capacity of 71.0~86.2 mg/g. Its adsorption heat over CO₂ and IAST selectivity were calculated to be 27 kJ/mol and 52.2, respectively. Remarkably, cyclic breakthrough experiments corroborate its impressive performance in CO₂/N₂ separation in not only dry but also 75% RH humid conditions. Molecular simulation reveals that C-H···O_CO2 in the pores plays a pivotal role in the high selectivity of CO₂ adsorption. These results point out the huge potential application of this material for CO₂/N₂ separation. Full article

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

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13 pages, 6561 KiB

Open AccessArticle

A Microporous Zn(bdc)(ted)_0.5 with Super High Ethane Uptake for Efficient Selective Adsorption and Separation of Light Hydrocarbons

by Feng Xu, Yilu Wu, Juan Wu, Daofei Lv, Jian Yan, Xun Wang, Xin Chen, Zewei Liu and Junjie Peng

Molecules 2023, 28(16), 6000; https://doi.org/10.3390/molecules28166000 - 10 Aug 2023

Cited by 2 | Viewed by 823

Abstract

Separating light hydrocarbons (C₂H₆, C₃H₈, and C₄H₁₀) from CH₄ is challenging but important for natural gas upgrading. A microporous metal-organic framework, Zn(bdc)(ted)_0.5, based on terephthalic acid (bdc) and [...] Read more.

Separating light hydrocarbons (C₂H₆, C₃H₈, and C₄H₁₀) from CH₄ is challenging but important for natural gas upgrading. A microporous metal-organic framework, Zn(bdc)(ted)_0.5, based on terephthalic acid (bdc) and 1,4-diazabicyclo[2.2.2]octane (ted) ligands, is synthesized and characterized through various techniques, including powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and porosity analysis. The adsorption isotherms of light hydrocarbons on the material are measured and the isosteric adsorption heats of CH₄, C₂H₆, C₃H₈, and C₄H₁₀ are calculated. The prediction of C2–4/C1 adsorption selectivities is accomplished using ideal adsorbed solution theory (IAST). The results indicate that the material exhibits exceptional characteristics, including a Brunauer-Emmett-Teller (BET) surface area of 1904 m²/g and a pore volume of 0.73 cm³/g. Notably, the material demonstrates remarkable C₂H₆ adsorption capacities (4.9 mmol/g), while CH₄ uptake remains minimal at 0.4 mmol/g at 298 K and 100 kPa. These findings surpass those of most reported MOFs, highlighting the material’s outstanding performance. The isosteric adsorption heats of C₂H₆, C₃H₈, and C₄H₁₀ on the Zn(bdc)(ted)_0.5 are higher than CH₄, suggesting a stronger interaction between C₂H₆, C₃H₈, and C₄H₁₀ molecules and Zn(bdc)(ted)_0.5. The molecular simulation reveals that Zn(bdc)(ted)_0.5 prefers to adsorb hydrocarbon molecules with richer C-H bonds and larger polarizability, which results in a stronger dispersion force generated by an adsorbent-adsorbate induced polarization effect. Therefore, the selectivity of C₄H₁₀/CH₄ is up to 180 at 100 kPa, C₃H₈/CH₄ selectivity is 67, and the selectivity of C₂H₆/CH₄ is 13, showing a great potential for separating C2–4 over methane. Full article

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

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Review

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25 pages, 1335 KiB

Open AccessReview

Zeolite Properties, Methods of Synthesis, and Selected Applications

by Natalia Kordala and Mirosław Wyszkowski

Molecules 2024, 29(5), 1069; https://doi.org/10.3390/molecules29051069 - 29 Feb 2024

Cited by 1 | Viewed by 1754

Abstract

Zeolites, a group of minerals with unique properties, have been known for more than 250 years. However, it was the development of methods for hydrothermal synthesis of zeolites and their large-scale industrial applications (oil processing, agriculture, production of detergents and building materials, water [...] Read more.

Zeolites, a group of minerals with unique properties, have been known for more than 250 years. However, it was the development of methods for hydrothermal synthesis of zeolites and their large-scale industrial applications (oil processing, agriculture, production of detergents and building materials, water treatment processes, etc.) that made them one of the most important materials of the 20th century, with great practical and research significance. The orderly, homogeneous crystalline and porous structure of zeolites, their susceptibility to various modifications, and their useful physicochemical properties contribute to the continuous expansion of their practical applications in both large-volume processes (ion exchange, adsorption, separation of mixture components, catalysis) and specialized ones (sensors). The following review of the knowledge available in the literature on zeolites aims to present the most important information on the properties, synthesis methods, and selected applications of this group of aluminosilicates. Special attention is given to the use of zeolites in agriculture and environmental protection. Full article

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

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