Hierarchical Pore System Research Articles

Investigating antimicrobial behavior of thymol/Zn encapsulated hierarchically structured zeolite and thymol release kinetics

A new bioactive material was proposed by encapsulating thymol molecules and Zn2+ cations within the post-modified intracrystalline voids of hierarchical zeolite X crystals. To enhance the accessibility of thymol molecules within zeolite X crystals, commercial zeolite samples underwent post-synthesis treatment involving consecutive aqueous KCl, NH4Cl, and Na2H2EDTA solutions. The gas adsorption method utilized the encapsulation of both Zn2+ cation and thymol molecules into the resulting hierarchical zeolite X framework, which demonstrated improved antimicrobial activity. While sole thymol-encapsulated zeolite X exhibited no antimicrobial activity against S. aureus, Zn2+ encapsulated zeolite X (ZnX), thymol encapsulated post-treated zeolite X (HX-thy), and both Zn2+ and thymol encapsulated post-treated zeolite X (ZnHX-thy) displayed zone of inhibition values of 18.7 mm, 25.0 mm, and 37.5 mm, respectively. Adding Zn2+ and creating a hierarchical pore system in the zeolite X framework altered the release profiles. The Higuchi kinetic release model has the highest R2 value to describe the process of thymol release from X-thy, whereas the Elovich release model has the best fitting profile of thymol release kinetics from ZnX-thy, HX-thy, and ZnHX-thy. Results indicate that thymol and Zn2+ containing hierarchical porous materials could be beneficial tools for obtaining enhanced antibacterial activity and stability with reduced degradation and volatility of thymol with extended protection against microbial attack due to the controlled release. These findings highlight an innovative approach to designing sustainable and green materials, utilizing modified porous networks that encapsulate natural antibacterial compounds with environmentally benign metal ions.

Kinetic implications of (hierarchical) zeolite fouling during liquid-phase aromatics upgrading

The kinetics of fouling in large pore zeolites (BEA, MOR), including those with hierarchical pore systems, were probed during the Brønsted acid catalyzed reaction of benzyl alcohol (BA) with 1,3,5-trimethylbenzene (TMB) by varying reactant driving force (i.e., [TMB]0/[BA]0; 11–119). In BEA, initial deactivation rate constants (kD,0) decreased exponentially with [TMB]0/[BA]0, highlighting the significance of oxygenates as deactivation precursors. Further, seeding pores with oxygenates completely suppressed measured rates in parent MOR and BEA, while seeding with TMB had no effect. Comparisons of mass accumulations of different organics (low molecular weight reaction species and coke) as functions of ln([TMB]0/[BA]0) revealed that coke (derived from oxygenate-seeded polyalkylation of TMB) disproportionately controlled deactivation rates by damping apparent (diffusion-controlled) and intrinsic (diffusion-corrected) rate constants through proton losses and/or altered molecule confinement within shrinking pores. These kinetic consequences were delayed upon introduction of mesopores, demonstrating how zeolite porosity impacts coke proliferation and behavior in liquid-phase reactions.

Hierarchical Porous Bimetallic FeMn Metal-Organic Framework Gel for Efficient Activation of Peracetic Acid in Antibiotic Degradation.

Effective techniques for eliminating antibiotics from water environments are in high demand. The peracetic acid (PAA)-based advanced oxidation process has recently drawn increasing attention for its effective antibiotic degrading capability. However, current applications of PAA-based techniques are limited and tend to have unsatisfactory performance. An additional catalyst for PAA activation could provide a promising solution to improve the performance of PAA. Bulky metal-organic framework gels (MOGs) stand out as ideal catalysts for PAA activation owing to their multiple advantages, including large surface areas, high porosity, and hierarchical pore systems. Herein, a bimetallic hierarchical porous structure, i.e., FeMn13BTC, was synthesized through a facile one-pot synthesis method and employed for PAA activation in ofloxacin (OFX) degradation. The optimized FeMn MOG/PAA system exhibited efficient catalytic performance, characterized by 81.85% OFX degradation achieved within 1 h owing to the specific hierarchical structure and synergistic effect between Fe and Mn ions, which greatly exceeded the performance of the only PAA-catalyzed system. Furthermore, the FeMn MOG/PAA system maintained >80% OFX degradation in natural water. Quenching experiments, electron spin resonance spectra, and model molecular degradation revealed that the primary reactive oxygen species responsible for the catalytic effect was R-O•, especially CH3C(=O)OO•, with minor contributions of •OH and 1O2. Overall, introduction of the MOG catalyst strategy for PAA activation achieved high antibiotic degradation performance, establishing a paradigm for the design of heterogeneous hierarchical systems to broaden the scope of catalyzed water treatment applications.

A hierarchically porous PEDOT embedded cryogel for in-syringe solid phase extraction of parabens in beverages

A hierarchically porous adsorbent was fabricated using polyethylene dioxythiophene (PEDOT) embedded in a polyvinyl alcohol cryogel. This adsorbent was designed for use in the in-syringe solid-phase extraction (IS-SPE) of parabens present in beverage samples. The creation of a hierarchical pore system was achieved through a reaction between a hydrochloric acid solution and calcium carbonate, strategically introduced during the cryogel synthesis within a needle hub. The porous structure of the cryogel allowed for efficient entrapment of adsorption materials, significantly increasing the number of available adsorption sites. Additionally, PEDOT was incorporated to enhance paraben adsorption through hydrophobic and π-π interactions. High-performance liquid chromatography was employed to quantify the extracted parabens. Under optimized conditions, the developed method exhibited detection limits ranging from 0.15 to 0.25 µg L–1 and quantification limits ranging from 0.50 to 1.0 µg L–1. The technique was successfully applied to assess parabens in various beverage samples, consistently obtaining extraction recoveries between 88.4% and 98.4%, and relative standard deviations (RSDs) below 6%. We conclude that the in-syringe extraction approach offers a straightforward and efficient method, while the composite adsorbent demonstrates ease of preparation and robust reproducibility, allowing for twelve extraction–desorption cycles.

Enabling hydrate-based methane storage under mild operating conditions by periodic mesoporous organosilica nanotubes

Biomethane is a renewable natural gas substitute produced from biogas. Storage of this sustainable energy vector in confined clathrate hydrates, encapsulated in the pores of a host material, is a highly promising avenue to improve storage capacity and energy efficiency. Herein, a new type of periodic mesoporous organosilica (PMO) nanotubes, referred to as hollow ring PMO (HR-PMO), capable of promoting methane clathrate hydrate formation under mild working conditions (273 K, 3.5 MPa) and at high water loading (5.1 g water/g HR-PMO) is reported. Gravimetric uptake measurements reveal a steep single-stepped isotherm and a noticeably high methane storage capacity (0.55 g methane/g HR-PMO; 0.11 g methane/g water at 3.5 MPa). The large working capacity throughout consecutive pressure-induced clathrate hydrate formation-dissociation cycles demonstrates the material’s excellent recyclability (97% preservation of capacity). Supported by ex situ cryo-electron tomography and x-ray diffraction, HR-PMO nanotubes are hypothesized to promote clathrate hydrate nucleation and growth by distribution and confinement of water in the mesopores of their outer wall, along the central channels of the nanotubes and on the external nanotube surface. These findings showcase the potential for application of organosilica materials with hierarchical and interconnected pore systems for pressure-based storage of biomethane in confined clathrate hydrates.

Hierarchical Zeolite Synthesis by Alkaline Treatment: Advantages and Applications

Zeolites are of great interest to the scientific and industrial communities due to their interesting catalytic properties, such as high specific area, shape selectivity, and thermal and hydrothermal stability. For this reason, zeolites have been intensively studied and applied in several reactions of great industrial interest. However, the size of zeolite micropores may hinder the diffusion of bulky molecules in the pore system, limiting the use of zeolites in some reactions/applications that use bulky molecules. One way to address this limitation is to generate secondary porosity (in the range of supermicropores, mesopores and/or macropores) in such a way that it connects with the existing micropores, creating a hierarchical pore system. There are different hierarchical approaches; however, most are not economically viable and are complicated/time-consuming. Alkaline treatment has been highlighted in recent years due to its excellent results, simplicity, speed and low cost. In this review, we highlight the importance of alkaline treatment in the generation of secondary porosity and the parameters that influence alkaline treatment in different zeolitic structures. The properties and catalytic performance of hierarchical zeolites prepared by alkaline treatment are extensively discussed. It is expected that this approach will be useful for understanding how alkaline treatment acts on different hierarchical structures and will thus open doors to achieve other hierarchical zeolites by this method.

Highly thermally stable multi-porous calcium aluminum hydrotalcite catalyst for efficient carbonate synthesis

In the context of a carbon–neutral era, conversion of greenhouse gas CO2via chemical catalysis is a powerful means. Using CO2and petroleum-derived alkylene oxide as the raw materials to produce high-value carbonate substances has been considered a green and economic path for carbon reduction and energy transition. We discovered a multi-porous calcium aluminum hydrotalcite material (Ca-Al HT), and found that it performs excellent catalytic ability on transesterification (an important reaction in the synthesis of carbonates). Being different from homogeneous basic catalysts such as soluble metal hydroxides and organic halide salts, and well-known solid basic catalyst CaO, which are difficult to recycle and suffer severe deactivation in long-term catalytic process, the robust Ca12Al14O33crystal phase in Ca-Al HT catalyst behaves much more stable catalytic performance during 4000 min efficient catalysis (63 % conversion and 100 % selectivity). The special crystal phase structure of Ca12Al14O33remains stable at even a very high temperature of 900 °C. In contrast, CaO as the reference catalyst is very sensitive to trace H2O in catalytic system, and deactivates immediately. The outstanding catalytic ability of Ca-Al HT is attributed to its super-strong alkali strength, large alkali amount, and quick mass transfer originating from the hierarchical pore system.

Highly thermally stable multi-porous calcium aluminum hydrotalcite catalyst for efficient carbonate synthesis

<h2>Abstract</h2> In the context of a carbon-neutral era, conversion of greenhouse gas CO₂ via chemical catalysis is a powerful means. Using CO₂ and petroleum-derived alkylene oxide as the raw materials to produce high-value carbonate substances has been considered a green and economic path for carbon reduction and energy transition. We discovered a multi-porous calcium aluminum hydrotalcite material (Ca-Al HT), and found that it performs excellent catalytic ability on transesterification (an important reaction in the synthesis of carbonates). Being different from homogeneous basic catalysts such as soluble metal hydroxides and organic halide salts, and well-known solid basic catalyst CaO, which are difficult to recycle and suffer severe deactivation in long-term catalytic process, the robust Ca₁₂Al₁₄O₃₃ crystal phase in Ca-Al HT catalyst behaves much more stable catalytic performance during 4000 min efficient catalysis (63% conversion and 100% selectivity). The special crystal phase structure of Ca₁₂Al₁₄O₃₃ maintains stability at even a very high temperature of 900 °C. In contrast, CaO as the reference catalyst is very sensitive to trace H₂O in catalytic system, and deactivates immediately. The outstanding catalytic ability of Ca-Al HT is attributed to its super-strong alkali strength, large alkali amount, and quick mass transfer originating from the hierarchical pore system.

An approach for the pore-centred description of adsorption in hierarchical porous materials

Analysis of metal–organic frameworks featuring hierarchical pore systems is presented and leveraged to understand adsorption in unique pore structures.

Renewable bio-based routes to γ-valerolactone in the presence of hafnium nanocrystalline or hierarchical microcrystalline zeotype catalysts

Different renewable bio-based routes leading to the versatile bioproduct γ-valerolactone (GVL) were studied in integrated fashions, starting from furfural (Fur), α-angelica lactone (AnL) and levulinic acid (LA), in the presence of multifunctional hafnium-containing catalysts, in alcohol media. These routes involved acid and reduction reactions for which multifunctional catalysts were prepared via top-down strategies, namely the nanocatalyst Hf-deAlBeta-n and the hierarchical (intracrystalline micro/mesopores) microcrystalline material Hf-WdeSAlBeta-m. Mechanistic and kinetic modelling studies, molecular-level investigations by solid-state spectroscopic characterization, and catalyst stability studies led to assessments about the catalytic roles and potentialities of the prepared materials for GVL production. The influences of the catalytic reaction conditions and type of transition metal in the catalysts were studied. The best-performing catalyst was the hierarchical zeotype Hf-WdeSAlBeta-m (GVL yields of up to 99% from LA, 91% from AnL, and 73% from Fur, at 180 °C), which correlated with its enhanced acidity and mesoporosity. To the best of our knowledge, this is the first reported hafnium-containing BEA zeotype possessing an intracrystalline hierarchical pore system, and the results highlighted the catalytic potentialities of these types of materials for the integrated production of GVL.

Enhanced activity of a bifunctional Pt/zeolite Y catalyst with an intracrystalline hierarchical pore system in the aqueous-phase hydrogenation of levulinic acid

Mesopores in the range of 4 to 5 nm were introduced into zeolite Y (nSi/nAl = 16) by surfactant-templating. This method using a mixture of octadecyltrimethylammonium hydroxide and bromide (C18TAOH/C18TABr) yields a mesoporous zeolite (Y–C18TAOH) with a higher specific mesopore volume and only a small loss in crystallinity and specific micropore volume. After loading with Pt, the two bifunctional catalysts (2.7Pt/Y and 2.6Pt/Y–C18TAOH) were applied in the aqueous-phase hydrogenation of levulinic acid (LA) to γ–valerolactone (GVL) (pH2 = 2.5 MPa, 393 K). Intraparticle mass–transfer limitations present for the catalyst 2.7Pt/Y were not observed in the LA hydrogenation over the catalyst with the hierarchical pore system 2.6Pt/Y–C18TAOH. Changes in the acid and de-/hydrogenation functionality are shown not to be responsible for the high catalytic activity of 2.6Pt/Y–C18TAOH. The presence of additional mesopores in a bifunctional catalyst based on zeolite Y is proven to enhance the mass-transfer properties and the resulting catalytic activity in the aqueous-phase hydrogenation of LA for the first time.

Kinetic models for sensory response of multicomponent oxide nanomaterials with a hierarchical pore system

A kinetic model for sensory response of multicomponent oxide nanomaterials used as sensing elements of gas sensors and vacuum gauges is proposed. It is shown that gas-sensitive properties of nanomaterials depend both on their qualitative and quantitative composition, and morphostructure to determine the presence of a hierarchical pore system therein.

Tuning Open Metal Site-Free ncb Type of Metal-Organic Frameworks for Simultaneously High Gravimetric and Volumetric Methane Storage Working Capacities.

The design and synthesis of a single metal-organic framework (MOF) material with simultaneously high gravimetric and volumetric methane storage working capacities are still a great challenge. The open metal site (OMS) in MOFs is generally regarded as an advantage to enhance host-guest affinity. However, it is detrimental to the methane storage working capacity to some extent due to the resulting high low-pressure uptake. Moreover, the reported methane storage MOFs are predominately focusing on edge-transitive or low-connected mixed-linker networks. In contrast, high-connected mixed-linker MOFs have been less investigated for methane storage. Herein, three isoreticular nine-connected trinuclear iron-based Fe-ncb-MOFs without OMSs have been judiciously designed and successfully constructed by means of the mixed-linker approach associated with the fixing amide-functionalized pyridyl-carboxylate ligand LP (4-(pyridin-4-ylcarbamoyl)benzoate) and three differing sized dicarboxylate ligands. High-pressure methane adsorption measurements show that, with the isoreticular extension from BDC (1,4-benzenedicarboxylate) to BPDC (4,4'-biphenyldicarboxylate) and ABDC (azobenzene-4,4'-dicarboxylate), three Fe-ncb-MOFs exhibit gradually increasing not only gravimetric but also volumetric storage capacities because of their balancing gravimetric surface area and volumetric surface area, hierarchical pore system, and modest CH4 heats of adsorption. Among them, the Fe-ncb-ABDC demonstrates a rare combination of simultaneously high gravimetric and volumetric CH4 storage working capacities of 0.302/0.37 g g-1 and 196/240 cm3 (STP) cm-3 at 298/273 K and between 80 and 5 bar, respectively, which outperform the 8-c Fe-8T18-ABDC assembled from a shorter pyridyl-carboxylate ligand IN (isonicotinate) and ABDC, due to its limited pore volume, the presence of OMSs, and more confined pore spaces, and place Fe-ncb-ABDC among the best performing MOFs.

Free template synthesis of novel hybrid MFI/BEA zeolite structure used in the conversion of methanol to clean gasoline: Effect of Beta zeolite content

A new type of host–guest composite catalyst, ZSM-5/Beta, with a hierarchical pore system were synthesized by incorporating Beta zeolite into the structure of ZSM-5 zeolite. The crystalline, structural, textural and acid properties of the composite zeolites, as well as the parent ZSM-5, were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), nitrogen adsorption/desorption analyses (BET) and temperature programmed desorption of ammonia (NH3-TPD) techniques. The solid product was employed as a catalyst for methanol to gasoline reaction. Results showed that the binary structure of these catalysts, not only integrates the pore characteristics of ZSM-5 and Beta zeolites but also changes the acid properties and creating new active sites that lead to higher activity. The highest activity, gasoline yield and longer lifetime were obtained over a sample with 30 wt% Beta zeolite due to improved textural and acid properties. Over the optimized sample, selectivity to alkylated aromatics as an octane number boosters increased about 15%, gasoline yield increased by an average of 9% and 65% increase in catalyst lifetime compared to reference ZSM-5 was obtained. In addition, the decline in unfavorable durene selectivity compared to the pristine ZSM-5, from 0.98% to 0.85%, verifies the improvement in gasoline quality.

Bottom-Up Assembly of a Complex Superstructure from a Simple Low-Symmetry Block and Three Ni Nodes

Design and synthesis of a superstructure with a hierarchical pore system from simple building blocks are a great challenge. Herein, we report the assembly of a complex superstructure (termed NTU-81) by using a strategy of bottom-up synthesis with a simple low-symmetry building block (4-(3,5-di(1H-imidazol-1-yl)phenyl)pyridine) and Ni nodes. Single-crystal X-ray diffraction revealed that NTU-81 ([C216H173N60Ni16O54, 2ZrF6·xGuest]) has three kinds of Ni clusters (Ni, Ni2O, and Ni3O) and two kinds of ligand connections (2-c and 3-c), which therefore makes the framework possess an unprecedented structural complexity and attractive hierarchical pore system. Notably, the crystallographically nonequivalent moieties in this monoclinic system fabricate 4-c and 5-c tetrakaidecahedrons, which are then organized into a cage-contained layer with a new topology (point symbol of {4.6.8}2{6.82}). Along with a charged pore surface, coordinated water molecules, and free pyridine N sites, NTU-81 shows highly efficient I2 capture in solution. These effects give rise to not only a new material for highly efficient I2 capture but also, more attractively, a design philosophy that can be extended to the construction of complex superstructures in a one-step reaction for desired applications.

Synthesis of composite zeolites composed of SAPO-5 and SAPO-34 and its application in methanol dehydration to light olefins

In present work, bi-phases composite zeolites consisting of SAPO-5 and SAPO-34 (named as SSC) are prepared by a traditional hydrothermal way, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption–desorption, intelligent gravimetric analyzer (IGA), intrusive mercury technology, and NH3-TPD techniques. The results display that the crystals in the as-synthesized composites have a hierarchical pore system with a size of about 3–130 nm, which displays a butterfly-like pattern on the crystal faces and runs throughout the whole crystal. Catalytic performances of the as-synthesized SSC catalysts are tested during methanol to olefin (MTO). As compared with a microporous composite catalyst, the hierarchical SSC composite catalyst displays excellent catalytic performances with a prolonged catalytic life and an elevated selectivity for light olefins.

A novel strategy combining electrospraying and one-step carbonization for the preparation of ultralight honeycomb-like multilayered carbon from biomass-derived lignin

Despite the great advantages of interconnected porous architectures of three-dimensional carbon as functional materials, apparent common drawbacks restricting their widespread applications are high cost and non-renewable of the carbon precursors and complicated activation procedures. In this study, biomass-derived honeycomb-like multilayered carbon (HMC) is synthesized by electrospraying and direct carbonization for the first time. Poly (methyl methacrylate) (PMMA) is mixed with biomass-derived lignin, the only carbon source, to form lignin/PMMA microspheres and microbowls by electrospraying. One-step carbonization of prepared micromaterials to obtain ultralight HMC, and the microstructures and pore size of carbon materials are controllable by adjusting the applied voltage of electrospraying. The obtained HMC-13 by carbonization of lignin/PMMA microspheres possesses interconnected carbon skeleton, partially graphitized structure and hierarchical pore system composed of macropores, mesopores and micropores. Benefiting from the structural advantages, HMC-13 as electrode of supercapacitor delivers a high specific capacitance of 348 F g−1 at 0.5 A g−1 in aqueous electrolytes. Additionally, the supercapacitor exhibits excellent cycling stability with only 4% capacitance loss after 10 000 cycles. Based on these encouraging results, environmental friendliness and facile synthesis strategy, the biomass-derived ultralight porous carbon material holds great promise for facilitating wasted biomass utilization and developing sustainable energy products.

Two-dimensional zeolites in catalysis: current state-of-the-art and perspectives

ABSTRACT Two-dimensional (2D) zeolites with modifiable structures, can possess great advantages in catalysis compared to three-dimensional (3D) rigid ones. Three kinds of 2D zeolites, including traditional lamellar ones, 2D zeolites induced by oriented growth with specially designed structural-directing agents, and 2D intermediates derived from germanosilicates, are covered in this review. 2D zeolites derived catalysts with higher surface area, larger pore size or hierarchical pore system release the diffusion constrains and enhance the accessibility of active sites, but they may also exhibit different microenvironments to the traditional 3D zeolites. The present review focuses on the complex relationship among pore architectures, location of active sites and the catalytic properties by comparing the 2D zeolite catalysts to 3D ones in the reactions catalyzed by framework Al or other heteroatoms (Ti and Sn), such as alkylation, selective oxidation and isomerization reactions. Last but not least, the challenges for future progress on both the preparation and application of these 2D zeolite catalysts are addressed.

Characterization of Nanoporous Materials.

Detailed analysis of textural properties, e.g., pore size and connectivity, of nanoporous materials is essential to identify correlations of these properties with the performance of gas storage, separation, and catalysis processes. The advances in developing nanoporous materials with uniform, tailor-made pore structures, including the introduction of hierarchical pore systems, offer huge potential for these applications. Within this context, major progress has been made in understanding the adsorption and phase behavior of confined fluids and consequently in physisorption characterization. This enables reliable pore size, volume, and network connectivity analysis using advanced, high-resolution experimental protocols coupled with advanced methods based on statistical mechanics, such as methods based on density functional theory and molecular simulation. If macro-pores are present, a combination of adsorption and mercury porosimetry can be useful. Hence, some important recent advances in understanding the mercury intrusion/extrusion mechanism are discussed. Additionally, some promising complementary techniques for characterization of porous materials immersed in a liquid phase are introduced.

Hierarchically‐Ordered Zeolites: A Critical Assessment

AbstractHierarchically‐ordered zeolites have received increasing attention in the last 15 years due to their outstanding properties, which are explored in catalytic reaction with industrial relevance. Up to now, a large number of different synthetic strategies have been reported that allow to introduce an additional meso‐ or macropore system in addition to the intrinsic microporosity of classical zeolites. Thus, hierarchical zeolites combine the intrinsic (catalytic) properties of conventional zeolites with facilitated access and transport via the additional pore system. In this critical review, the various synthesis pathways reported so far are evaluated, several physico‐chemical methods required for in‐depth characterization of the hierarchical pore system are discussed, and selective applications that are or potentially will be of technical relevance are introduced. The present review provides a critical analysis of the present achievements and discusses future opportunities and challenges for the research on hierarchically‐ordered zeolite in particular with respect to their industrial use.