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14 pages, 44406 KiB

Open AccessArticle

Engineering In-Co₃O₄/H-SSZ-39(OA) Catalyst for CH₄-SCR of NO_x: Mild Oxalic Acid (OA) Leaching and Co₃O₄ Modification

by Guanyu Chen, Weixin Zhang, Rongshu Zhu, Yanpeng Chen, Minghu Zhao and Mei Hong

Molecules 2024, 29(16), 3747; https://doi.org/10.3390/molecules29163747 - 7 Aug 2024

Cited by 1 | Viewed by 883

Abstract

Zeolite-based catalysts efficiently catalyze the selective catalytic reduction of NO_x with methane (CH₄-SCR) for the environmentally friendly removal of nitrogen oxides, but suffer severe deactivation in high-temperature SO₂- and H₂O-containing flue gas. In this work, SSZ-39 [...] Read more.

Zeolite-based catalysts efficiently catalyze the selective catalytic reduction of NO_x with methane (CH₄-SCR) for the environmentally friendly removal of nitrogen oxides, but suffer severe deactivation in high-temperature SO₂- and H₂O-containing flue gas. In this work, SSZ-39 zeolite (AEI topology) with high hydrothermal stability is reported for preparing CH₄-SCR catalysts. Mild acid leaching with oxalic acid (OA) not only modulates the Si/Al ratio of commercial SSZ-39 to a suitable value, but also removes some extra-framework Al atoms, introducing a small number of mesopores into the zeolite that alleviate diffusion limitation. Additional Co₃O₄ modification during indium exchange further enhances the catalytic activity of the resulting In-Co₃O₄/H-SSZ-39(OA). The optimized sample exhibits remarkable performance in CH₄-SCR under a gas hourly space velocity (GHSV) of 24,000 h⁻¹ and in the presence of 5 vol% H₂O. Even under harsh SO₂- and H₂O-containing high-temperature conditions, it shows satisfactory stability. Catalysts containing Co₃O₄ components demonstrate much higher CH₄ conversion. The strong mutual interaction between Co₃O₄ and Brønsted acid sites, confirmed by the temperature-programmed desorption of NO (NO-TPD), enables more stable N_xO_y species to be retained in In-Co₃O₄/H-SSZ-39(OA) to supply further reactions at high temperatures. Full article

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

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Effects of oxalic acid concentration, etching time, and etching temperature in acid etching post-treatment on the (a–c) NOx conversion, (d–f) CH4 conversion, and (g–i) CH4 selectivity of the resulting catalysts for dry CH4-SCR. Reaction conditions: [NO] = 400 ppm, [CH4] = 600 ppm, [O2] = 10 vol%, Ar balance, GHSV = 24,000 h−1. Full article ">Figure 2
Effect of the Co3O4 to H-SSZ-39(OA) mass ratio on the (a) NOx conversion and (b) CH4 conversion of the resulting catalysts under wet conditions. Reaction conditions: [NO] = 400 ppm, [CH4] = 600 ppm, [O2] = 10 vol%, [H2O] = 5 vol%, Ar balance, GHSV = 24,000 h−1. (c) Recyclability test of In-Co3O4/H-SSZ-39(OA) under harsh H2O- and SO2-containing conditions. Reaction conditions: [NO] = 400 ppm, [CH4] = 600 ppm, [O2] = 10 vol%, [H2O] = 5 vol%, [SO2] = 50 ppm, Ar balance, GHSV = 12,000 h−1. (d) Stability test of In-Co3O4/H-SSZ-39(OA) under harsh H2O- and SO2-containing conditions. Reaction conditions: [NO] = 400 ppm, [CH4] = 600 ppm, [O2] = 10 vol%, [H2O] = 5 vol%, [SO2] = 50 ppm, Ar balance, GHSV = 12,000 h−1, T = 600 °C. Full article ">Figure 3
SEM images of (a) Pristine H-SSZ-39, (b) In/H-SSZ-39(OA), and (c) In-Co3O4/H-SSZ-39(OA). HRTEM images of (d) Pristine H-SSZ-39, (e) In/H-SSZ-39(OA), and (f) In-Co3O4/H-SSZ-39(OA). (g) PXRD patterns, (h) N2 adsorption–desorption isotherms, and (i) NLDFT PSD curves of samples. Full article ">Figure 4
(a) 27Al MAS SSNMR and (b) 29Si MAS SSNMR of Pristine H-SSZ-39 and In/H-SSZ-39(OA). Full article ">Figure 5
High-resolution XPS spectra of (a) In 3d region and (b) Co 2p region. Full article ">Figure 6
(a) NH3-TPD profiles and (b) NO-TPD profiles of samples. Full article ">

15 pages, 2677 KiB

Open AccessArticle

Adsorption of Bichromate and Arsenate Anions by a Sorbent Based on Bentonite Clay Modified with Polyhydroxocations of Iron and Aluminum by the “Co-Precipitation” Method

by Bakytgul Kussainova, Gaukhar Tazhkenova, Ivan Kazarinov, Marina Burashnikova, Aisha Nurlybayeva, Gulnaziya Seitbekova, Saule Kantarbayeva, Nazgul Murzakasymova, Elvira Baibazarova, Dinara Altynbekova, Assem Shinibekova and Aidana Bazarkhankyzy

Molecules 2024, 29(15), 3709; https://doi.org/10.3390/molecules29153709 - 5 Aug 2024

Cited by 1 | Viewed by 968

Abstract

The physicochemical properties of natural bentonite and its sorbents were studied. It has been established the modification of natural bentonites using polyhydroxoxides of iron (III) (mod.1_Fe_5-c) and aluminum (III) (mod.1_Al_5-c) by the “co-precipitation” method led to changes in their chemical composition, structure, and [...] Read more.

The physicochemical properties of natural bentonite and its sorbents were studied. It has been established the modification of natural bentonites using polyhydroxoxides of iron (III) (mod.1_Fe_5-c) and aluminum (III) (mod.1_Al_5-c) by the “co-precipitation” method led to changes in their chemical composition, structure, and sorption properties. It was shown that modified sorbents based on natural bentonite are finely porous (nanostructured) objects with a predominance of pores of 1.5–8.0 nm in size. The modification of bentonite with iron (III) and aluminum compounds by the “co-precipitation” method also leads to an increase in the sorption capacity of the obtained sorbents with respect to bichromate and arsenate anions. A kinetic analysis showed that, at the initial stage, the sorption process was controlled by an external diffusion factor, that is, the diffusion of the sorbent from the solution to the liquid film on the surface of the sorbent. The sorption process then began to proceed in a mixed diffusion mode when it limited both the external diffusion factor and the intra-diffusion factor (diffusion of the sorbent to the active centers through the system of pores and capillaries). To clarify the contribution of the chemical stage to the rate of adsorption of bichromate and arsenate anions by the sorbents under study, kinetic curves were processed using equations of chemical kinetics (pseudo-first-order, pseudo-second-order, and Elovich models). It was found that the adsorption of the studied anions by the modified sorbents based on natural bentonite was best described by a pseudo-second-order kinetic model. The high value of the correlation coefficient for the Elovich model (R² > 0.9) allows us to conclude that there are structural disorders in the porous system of the studied sorbents, and their surfaces can be considered heterogeneous. Considering that heterogeneous processes occur on the surface of the sorbent, it is natural that all surface properties (structure, chemical composition of the surface layer, etc.) play an important role in anion adsorption. Full article

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

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22 pages, 3957 KiB

Open AccessArticle

Encapsulation of Imidazole into Ce-Modified Mesoporous KIT-6 for High Anhydrous Proton Conductivity

by Agata Tabero, Aldona Jankowska, Adam Ostrowski, Ewa Janiszewska, Jolanta Kowalska-Kuś, Agnieszka Held and Stanisław Kowalak

Molecules 2024, 29(13), 3239; https://doi.org/10.3390/molecules29133239 - 8 Jul 2024

Cited by 1 | Viewed by 905

Abstract

Imidazole molecules entrapped in porous materials can exhibit high and stable proton conductivity suitable for elevated temperature (>373 K) fuel cell applications. In this study, new anhydrous proton conductors based on imidazole and mesoporous KIT-6 were prepared. To explore the impact of the [...] Read more.

Imidazole molecules entrapped in porous materials can exhibit high and stable proton conductivity suitable for elevated temperature (>373 K) fuel cell applications. In this study, new anhydrous proton conductors based on imidazole and mesoporous KIT-6 were prepared. To explore the impact of the acidic nature of the porous matrix on proton conduction, a series of KIT-6 materials with varying Si/Al ratios and pure silica materials were synthesized. These materials were additionally modified with cerium atoms to enhance their Brønsted acidity. TPD-NH₃ and esterification model reaction confirmed that incorporating aluminum into the silica framework and subsequent modification with cerium atoms generated additional acidic sites. UV-Vis and XPS identified the presence of Ce³⁺ and Ce⁴⁺ in the KIT-6 materials, indicating that high-temperature treatment after cerium introduction may lead to partial cerium incorporation into the framework. EIS studies demonstrated that dispersing imidazole within the KIT-6 matrices resulted in composites showing high proton conductivity over a wide temperature range (300–393 K). The presence of weak acidic centers, particularly Brønsted sites, was found to be beneficial for achieving high conductivity. Cerium-modified composites exhibited conductivity surpassing that of molten imidazole, with the highest conductivity (1.13 × 10⁻³ S/cm at 393 K) recorded under anhydrous conditions for Ce-KIT-6. Furthermore, all tested composites maintained high stability over multiple heating and cooling cycles. Full article

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

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16 pages, 3623 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

Viewed by 888

Abstract

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

Cited by 2 | Viewed by 1682

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

Viewed by 1019

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

Cited by 1 | Viewed by 1388

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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(a) PXRD patterns of the synthesized MCM-22P and the calcined sample. (b) Rietveld refinements of MCM-22 and the structure with SDA inside. (c) TG thermogravimetry of the pure silica MWW zeolite synthesized with the only SDA. Experimental (red) and calculated (black) PXRD patterns as well as the positions of the Bragg reflections shown by the short tick marks (blue). (d) N2 isotherm curve of the calcined pure silicate MCM-22. Full article ">Figure 2
Paragraphs including the SEM, N2 isotherm curves, and TEM images of MCM-22P using SDA directly and using the cooperation of SDA with NaOH, Na2CO3, and NaHCO3 under the same ratio of Na+/Si = 0.1. Full article ">Figure 3
(a) N2 adsorption/desorption isotherms and (b) pore size distribution of the samples with the addition of NaHCO3 under different ratios of HF/Si (a: 0.5, b: 0.65, c: 0.75, d: 1, e: 1.25). Full article ">Figure 4
SEM pictures of the samples synthesized with Na salts at different crystalline time. Full article ">Scheme 1
Two pathways of zeolite crystallization. Full article ">Scheme 2
Crystallization pathways of MWW zeolite: NaOH/Na2CO3-added (i) and NaHCO3-added (ii). Full article ">

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 48 | Viewed by 1401

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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Full article ">Figure 1
Single silicon-doped alumino-phosphates (HSAPO-34): (a) the single-unit cell (1UC) with rhombohedral representation, (b) the expanded lattice structure. Note that the proton is omitted for simplicity. Full article ">Figure 2
The total energy depends on the lattice volume. The proton binding sites of HSAPO-34 are (a) O(1), (b) O(2), (c) O(3), and (d) O(4). Full article ">Figure 3
Schematic diagram for four possible Brönsted acid sites of HSAPO-34. The proton binding sites are (a) O1, (b) O2, (c) O3, and (d) O4. Noting that Al in cycn, Si in blue, P in purple, O in red, and the number in figure is the numbering of O atom. Full article ">Figure 4
The proton distribution of HSAPO-34 depends on the temperature. Full article ">Figure 5
Bader charges on AlO3-O(H)-SiO3 fragment from four possible Brönsted acid sites of HSAPO-34. The proton binding sites are (a) O(1), (b) O(2), (c) O(3), and (d) O(4). Noting that Al in cyan, Si in blue, and O in red. Full article ">Figure 6
Calculated ensemble-averaged DPE (<DPE>) of HSAPO-34 depends on the temperature. Full article ">

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 - 2 Dec 2023

Cited by 2 | Viewed by 1668

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 3 | Viewed by 1976

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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Full article ">Figure 1
(A) The synthesis of PRI-1. (B) PXRD patterns of the simulated and as-synthesized PRI-1, as well as those after various treatments. (C) 195 K CO2 adsorption-desorption isotherms. (D) TGA curve. (E) Comparison of thermal stabilities of PRI-1 and other MOF adsorbents. The distances are in Å. Full article ">Figure 2
(A) CO2 and N2 adsorption isotherms of PRI-1 at 273, 283, and 298 K. (B) Qst of CO2 in PRI-1. (C) Comparison of CO2 Qst for PRI-1 with those of other top-performing MOF adsorbents. (D) Comparison of CO2/N2 (15:85, v/v) IAST selectivity at 298 K and 1 bar and Qst of CO2 under ambient conditions in PRI-1 with those of reported CO2-selective MOFs. Full article ">Figure 3
Calculated preferential binding sites for CO2 (A) and N2 (B) on PRI-1. The distances are in Å. Cu, C, N, O, and H atoms are shown in pink, grey, blue, red, and white, respectively. Full article ">Figure 4
(A) Experimental breakthrough curves of PRI-1 for CO2/N2 (15:85) binary mixture at 298 K and 1 bar. (B) Experimental cycling breakthrough curves of a CO2/N2 (15:85) binary mixture at 298 K and 1 bar. (C) Experimental breakthrough for CO2/N2 (15:85) under both dry and 75% RH humid conditions. C and C0 stand for outlet concentration and inlet concentration of CO2 and N2 in the gas mixture flow, respectively. Full article ">

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 5 | Viewed by 1429

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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Open AccessReview

Zeolite and Neurodegenerative Diseases

by Stefan Panaiotov, Lyubka Tancheva, Reni Kalfin and Polina Petkova-Kirova

Molecules 2024, 29(11), 2614; https://doi.org/10.3390/molecules29112614 - 2 Jun 2024

Cited by 1 | Viewed by 5798

Abstract

Neurodegenerative diseases (NDs), characterized by progressive degeneration and death of neurons, are strongly related to aging, and the number of people with NDs will continue to rise. Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the most common NDs, and the current treatments [...] Read more.

Neurodegenerative diseases (NDs), characterized by progressive degeneration and death of neurons, are strongly related to aging, and the number of people with NDs will continue to rise. Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the most common NDs, and the current treatments offer no cure. A growing body of research shows that AD and especially PD are intricately related to intestinal health and the gut microbiome and that both diseases can spread retrogradely from the gut to the brain. Zeolites are a large family of minerals built by [SiO₄]⁴⁻ and [AlO₄]⁵⁻ tetrahedrons joined by shared oxygen atoms and forming a three-dimensional microporous structure holding water molecules and ions. The most widespread and used zeolite is clinoptilolite, and additionally, mechanically activated clinoptilolites offer further improved beneficial effects. The current review describes and discusses the numerous positive effects of clinoptilolite and its forms on gut health and the gut microbiome, as well as their detoxifying, antioxidative, immunostimulatory, and anti-inflammatory effects, relevant to the treatment of NDs and especially AD and PD. The direct effects of clinoptilolite and its activated forms on AD pathology in vitro and in vivo are also reviewed, as well as the use of zeolites as biosensors and delivery systems related to PD. Full article

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

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25 pages, 1335 KiB

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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 23 | Viewed by 11891

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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