Hierarchically Structured Zeolites: From Design to Application

Construction of diverse hollow MFI zeolites through regulating the micropore filling agents

Constructing hollow structure into microporous zeolites can improve the accessibility of acid sites located at the inner part and the diffusion property. Hence, the development of an efficient synthesis strategy to acquire zeolites with tunable hollow structures and acidity has attracted much attention. In this work, an innovative tandem synthesis route was proposed to prepare MFI zeolites with diverse hollow structure while maintaining solid yields exceeding 90 %. The substitution of ethanol molecules, which previously occupied the micropores, with tetrapropylammonium cations was proved to be the key factor to construct hollow structure. And a crystallization-driven particle dissolution mechanism was proposed. The dimension of the hollow cavity, particle size, and Si/Al ratio can be flexibly regulated. Interestingly, hollow MFI samples featuring the common cavity structure, "eye-like" cavity structure, or double-cavity structure can be directly synthesized by controlling the dissolution of core parts. In the 1-butene catalytic cracking reactions, a much higher conversion of 67.2 % was acquired over hollow ZSM-5 compared with that over conventional ZSM-5 (35.8 %) after 64 h of reaction. This improvement can be attributed to the eightfold increase of diffusivity in hollow ZSM-5. This facile and efficient synthesis method endows accurate regulation of the hollow structure, which is meaningful for both fundamental research and industrial applications of hollow zeolites.

Rational Design of Fe Single Sites Supported on Hierarchical Zeolites via Atomic Layer Deposition for Few-Walled Carbon Nanotube Production

Metal single-site catalysts have recently played an essential role in catalysis due to their enhanced activity, selectivity, and precise reaction control compared to those of conventional metal cluster catalysts. However, the rational design and catalytic application of metal single-site catalysts are still in the early stages of development. In this contribution, we report the rational design of Fe single sites incorporated in a hierarchical ZSM-5 via atomic layer deposition (ALD). The designer catalysts demonstrated highly dispersed Fe species, predominantly stabilized by oxygen atoms in the zeolite framework at terminal, isolated, and vicinal silanol groups within the micropores and external surfaces of the zeolite. The successful incorporation of highly thermally stable and uniform Fe single sites into hierarchical zeolite through ALD represents a significant advancement in few-walled carbon nanotube production. The inner and outer diameters of produced CNTs are approximately 4.4 ± 2.4 and 8.6 ± 1.8 nm, respectively, notably smaller than those produced via traditional impregnated catalysts. This example emphasizes the concept of rational design of a single Fe site dispersed on a hierarchical ZSM-5 surface, which is anticipated to be a promising catalyst for advancing catalytic applications.

Zeolite-Templated Carbons Supported Rh and Ru Electrocatalysts for Highly Active Hydrogen Evolution Reaction

Here, we report the systematical synthesis of zeolite-templated carbon (ZTC) supported Ru and Rh mono- or bi-metallic electrocatalysts towards hydrogen evolution reaction (HER). The zeolite A or ZSM-5 derived ZTC supports and metal sites were adjusted, and all electrocatalysts outperformed the commercial Pt/C electrocatalyst for HER performance. In particular, the RhRu/(ZTC/ZSM5) sample exhibited superior catalytic performance with the overpotential of 24.8 mV@10 mA ⋅ cm-2, and outstanding stability with 1 mV drop after 20000 cyclic voltammetry circles. This work offers a simple impregnation method for the synthesis of highly performed HER electrocatalysts supported on porous zeolite-templated carbon.

The Current Understanding of Mechanistic Pathways in Zeolite Crystallization

Zeolite catalysts and adsorbents have been an integral part of many commercial processes and are projected to play a significant role in emerging technologies to address the changing energy and environmental landscapes. The ability to rationally design zeolites with tailored properties relies on a fundamental understanding of crystallization pathways to strategically manipulate processes of nucleation and growth. The complexity of zeolite growth media engenders a diversity of crystallization mechanisms that can manifest at different synthesis stages. In this review, we discuss the current understanding of classical and nonclassical pathways associated with the formation of (alumino)silicate zeolites. We begin with a brief overview of zeolite history and seminal advancements, followed by a comprehensive discussion of different classes of zeolite precursors with respect to their methods of assembly and physicochemical properties. The following two sections provide detailed discussions of nucleation and growth pathways wherein we emphasize general trends and highlight specific observations for select zeolite framework types. We then close with conclusions and future outlook to summarize key hypotheses, current knowledge gaps, and potential opportunities to guide zeolite synthesis toward a more exact science.

Structured Catalysts and Catalytic Processes: Transport and Reaction Perspectives

The structure of catalysts determines the performance of catalytic processes. Intrinsically, the electronic and geometric structures influence the interaction between active species and the surface of the catalyst, which subsequently regulates the adsorption, reaction, and desorption behaviors. In recent decades, the development of catalysts with complex structures, including bulk, interfacial, encapsulated, and atomically dispersed structures, can potentially affect the electronic and geometric structures of catalysts and lead to further control of the transport and reaction of molecules. This review describes comprehensive understandings on the influence of electronic and geometric properties and complex catalyst structures on the performance of relevant heterogeneous catalytic processes, especially for the transport and reaction over structured catalysts for the conversions of light alkanes and small molecules. The recent research progress of the electronic and geometric properties over the active sites, specifically for theoretical descriptors developed in the recent decades, is discussed at the atomic level. The designs and properties of catalysts with specific structures are summarized. The transport phenomena and reactions over structured catalysts for the conversions of light alkanes and small molecules are analyzed. At the end of this review, we present our perspectives on the challenges for the further development of structured catalysts and heterogeneous catalytic processes.

Review and perspectives on TS-1 catalyzed propylene epoxidation

Titanium silicate zeolite (TS-1) is widely used in the research on selective oxidations of organic substrates by H2O2. Compared with the chlorohydrin process and the hydroperoxidation process, the TS-1 catalyzed hydroperoxide epoxidation of propylene oxide (HPPO) has advantages in terms of by-products and environmental friendliness. This article reviews the latest progress in propylene epoxidation catalyzed by TS-1, including the HPPO process and gas phase epoxidation. The preparation and modification of TS-1 for green and sustainable production are summarized, including the use of low-cost feedstocks, the development of synthetic routes, strategies to enhance mass transfer in TS-1 crystal and the enhancement of catalytic performance after modification. In particular, this article summarizes the catalytic mechanisms and advanced characterization techniques for propylene epoxidation in recent years. Finally, the present situation, development prospect and challenge of propylene epoxidation catalyzed by TS-1 were prospected.

Fabrication of a ZIF-on-lamella-zeolite architecture as a highly efficient catalyst for aldol condensation

Designing composite catalysts that harness the strengths of individual components while mitigating their limitations is a fascinating yet challenging task in catalyst engineering. In this study, we aimed to enhance the catalytic performance by anchoring ZIF-67 nanoparticles of precise sizes onto lamella Si-MWW zeolite surfaces through a stepwise regrowth process. Co ions were initially grafted onto the zeolite surface using ultrasonication, followed by a seed-assisted secondary growth method. Si-MWW proved to be the ideal zeolite support due to its thin layered structure, large external surface area and substantial lateral dimensions. The abundant Si-OH groups on its surface played a crucial role in securely binding Co ions, limiting size growth and preventing undesirable ZIF-67 aggregation. The resulting ZIF-67/MWW composite with finely dispersed nano-scale ZIF-67 particles exhibited a remarkable catalytic performance and stability in the aldol condensation reactions involving acetone and various aldehydes. This approach holds promise for designing MOF/zeolite composite catalysts.

Selective and Scalable CO2 Electrolysis Enabled by Conductive Zinc Ion-Implanted Zeolite-Supported Cadmium Oxide Nanoclusters

Catalyst supports play an essential role in catalytic reactions, hinting at pronounced metal-support effects. Zeolites are a propitious support in heterogeneous catalysts, while their use in the electrocatalytic CO2 reduction reaction has been limited as yet because of their electrically insulating nature and serious competing hydrogen evolution reaction (HER). Enlightened by theoretical prediction, herein, we implant zinc ions into the structural skeleton of a zeolite Y to strategically tailor a favorable electrocatalytic platform with remarkably enhanced electronic conduction and strong HER inhibition capability, which incorporates ultrafine cadmium oxide nanoclusters as guest species into the supercages of the tailored 12-ring window framework. The metal d-bandwidth tuning of cadmium by skeletal zinc steers the extent of substrate-molecule orbital mixing, enhancing the stabilization of the key intermediate *COOH while weakening the CO poisoning effect. Furthermore, the strong cadmium-zinc interplay causes a considerable thermodynamic barrier for water dissociation in the conversion of H+ to *H, potently suppressing the competing HER. Therefore, we achieve an industrial-level partial current density of 335 mA cm-2 and remarkable Faradaic efficiency of 97.1% for CO production and stably maintain Faradaic efficiency above 90% at the industrially relevant current density for over 120 h. This work provides a proof of concept of tailored conductive zeolite as a favorable electrocatalytic support for industrial-level CO2 electrolysis and will significantly enhance the adaptability of conductive zeolite-based electrocatalysts in a variety of electrocatalysis and energy conversion applications.

Enhanced Adsorption of Trace Ethylene on Ag/NZ5 Modified with Ammonia: Hierarchical Structure and Metal Dispersion Effects

Trace ethylene poses a significant challenge during the storage and transportation of agricultural products, causing over-ripening, reducing shelf life, and leading to food waste. Zeolite-supported silver adsorbents show promise for efficiently removing trace ethylene. Herein, hierarchical Ag/NZ5(X) adsorbents were prepared via different ammonia modifications, which featured enhanced ethylene adsorption ability. Ag/NZ5(2.5) exhibited the largest capacity and achieved near-complete removal at room temperature with prolonged efficacy. Characterization results indicated that the ammonia modification led to the formation of a hierarchical structure in the zeolite framework, reducing diffusion resistance and increasing the accessibility of the active sites. Additionally, desilication effects increased the defectiveness, generating a stronger metal-support interaction and resulting in a higher metal dispersion rate. These findings provide valuable insights into the development of efficient adsorbents for removing trace ethylene, thereby reducing food waste and extending the shelf life of agricultural products.

Unveiling the mechanisms of carboxylic acid esterification on acid zeolites for biomass-to-energy: A review of the catalytic process through experimental and computational studies

In recent years, there has been significant interest from industrial and academic areas in the esterification of carboxylic acids catalyzed by acidic zeolites, as it represents a sustainable and economically viable approach to producing a wide range of high-value-added products. However, there is a lack of comprehensive reviews that address the intricate reaction mechanisms occurring at the catalyst interface at both the experimental and atomistic levels. Therefore, in this review, we provide an overview of the esterification reaction on acidic zeolites based on experimental and theoretical studies. The combination of infrared spectroscopy with atomistic calculations and experimental strategies using modulation excitation spectroscopy techniques combined with phase-sensitive detection is presented as an approach to detecting short-lived intermediates at the interface of zeolitic frameworks under realistic reaction conditions. To achieve this goal, this review has been divided into four sections: The first is a brief introduction highlighting the distinctive features of this review. The second addresses questions about the topology and activity of different zeolitic systems, since these properties are closely correlated in the esterification process. The third section deals with the mechanisms proposed in the literature. The fourth section presents advances in IR techniques and theoretical calculations that can be applied to gain new insights into reaction mechanisms. Finally, this review concludes with a subtle approach, highlighting the main aspects and perspectives of combining experimental and theoretical techniques to elucidate different reaction mechanisms in zeolitic systems.

Integrating Levels of Hierarchical Organization in Porous Organic Molecular Materials

Porous organic molecular materials (POMMs) are an emergent class of molecular-based materials characterized by the formation of extended porous frameworks, mainly held by non-covalent interactions. POMMs represent a variety of chemical families, such as hydrogen-bonded organic frameworks, porous organic salts, porous organic cages, C - H⋅⋅⋅π microporous crystals, supramolecular organic frameworks, π-organic frameworks, halogen-bonded organic framework, and intrinsically porous molecular materials. In some porous materials such as zeolites and metal organic frameworks, the integration of multiscale has been adopted to build materials with multifunctionality and optimized properties. Therefore, considering the significant role of hierarchy in porous materials and the growing importance of POMMs in the realm of synthetic porous materials, we consider it appropriate to dedicate for the first time a critical review covering both topics. Herein, we will provide a summary of literature examples showcasing hierarchical POMMs, with a focus on their main synthetic approaches, applications, and the advantages brought forth by introducing hierarchy.

Highly dispersed Pd-based pseudo-single atoms in zeolites for hydrogen generation and pollutant disposal

Atomically dispersed metal catalysts with excellent activity and stability are highly desired in heterogeneous catalysis. Herein, we synthesized zeolite-encaged Pd-based pseudo-single atoms via a facile and energy-efficient ligand-protected direct H2 reduction method. Cs-corrected scanning transmission electron microscopy, extended X-ray absorption, and pair distribution function measurements reveal that the metal species are close to atomic-level dispersion and completely confined within the intersectional channels of silicalite-1 (S-1) zeolite with the MFI framework. The Pd@S-1-H exhibits excellent activity and stability in methane combustion reactions with a complete combustion temperature of 390 °C, and no deactivation is observed even after 100 h on stream. The optimized bimetallic 0.8Pd0.2Ni(OH)2@S-1-H catalyst exhibits an excellent H2 generation rate from FA decomposition without any additives, affording a superhigh turnover frequency up to 9308 h-1 at 333 K, which represents the top activity among all of the best heterogeneous catalysts under similar conditions. Significantly, zeolite-encaged metal catalysts are first used for Cr(vi) reduction coupled with formic acid (FA) dehydrogenation and show a superhigh turnover number of 2980 mol(Cr2O72-) mol(Pd)-1 at 323 K, surpassing all of the previously reported catalysts. This work demonstrates that zeolite-encaged pseudo-single atom catalysts are promising in efficient hydrogen storage and pollutant disposal applications.

Constructing Intrapenetrated Hierarchical Zeolites with Highly Complete Framework via Protozeolite Seeding

Creation of intrapenetrated mesopores with open highway from external surface into the interior of zeolite crystals are highly desirable that can significantly improve the molecular transport and active sites accessibility of microporous zeolites to afford enhanced catalytic properties. Here, different from traditional zeolite-seeded methods that generally produced isolated mesopores in zeolites, nanosized amorphous protozeolites with embryo structure of zeolites were used as seeds for the construction of single-crystalline hierarchical ZSM-5 zeolites with intrapenetrated mesopores (mesopore volume of 0.51 cm3  g-1 ) and highly complete framework. In this strategy, in contrast to the conventional synthesis, only a small amount of organic structure directing agents and a low crystallization temperature were adopted to promise the protozeolites as the dominant growth directing sites to induce crystallization. The protozeolite nanoseeds provided abundant nucleation sites for surrounding precursors to be crystallized, followed by oriented coalescence of crystallites resulting in the formation of intrapenetrated mesopores. The as-prepared hierarchical ZSM-5 zeolites exhibited ultra-long lifetime of 443.9 hours and a high propylene selectivity of 47.92 % at a WHSV of 2 h-1 in the methanol-to-propylene reaction. This work provides a facile protozeolite-seeded strategy for the synthesis of intrapenetrated hierarchical zeolites that are highly effective for catalytic applications.

Amino-Acid-Assisted Synthesis of Hollow Hierarchical FER Zeolite with Improved Catalytic Performance

Hierarchical zeolites are highly-desired catalysts in the petrochemical industry due to their shorter diffusion length, faster diffusion rate, and better accessibility to active acid sites compared with conventional zeolites. Herein, we report a simple amino-acid-assisted method to synthesize urchin-like hollow hierarchical FER zeolites with abundant mesopores and macroporous inner cavities. An amino acid (i. e. L-lysine) is used to facilitate the agglomeration of primary gel nanoparticles. The preferential nucleation and crystal growth at the external surfaces together with the lagged crystallization of the inner core of the agglomerates results in the formation of hollow inner cavities after the exhaustion of interior materials. Thanks to the unique hierarchical structure and more accessible acid sites, the hollow hierarchical FER zeolite exhibits improved catalytic performance over the conventional one in the skeletal isomerization of 1-butene to isobutene.

Bridging the Gap between Zeolites and Dense Silica Polymorphs: Formation of All-Silica Zeolite with High Framework Density from Natural Layered Silicate Magadiite

A silica zeolite (RWZ-1) with a very high framework density (FD) was synthesized from highly crystalline natural layered silicate magadiite, bridging the gap between the two research areas of zeolites and dense silica polymorphs. Magadiite was topotactically converted into a 3D framework through two-step heat treatment. The resulting structure had a 1D micropore system of channel-like cavities with an FD of 22.1 Si atoms/1000 Å3 . This value is higher than those of all other silica zeolites reported so far, approaching those of silica polymorphs (tridymite (22.6) and α-quartz (26.5)). RWZ-1 is a slight negative thermal expansion material with thermal properties approaching those of dense silica polymorphs. It contributes to the creation of a new field on microporous high-density silica/silicates. Synergistic interactions are expected between the micropores with molecular sieving properties and the dense layer-like building units with different topologies which provide thermal and mechanical stabilities.

Positional Isomers of Covalent Organic Frameworks for Indoor Humidity Regulation

Humidity is one of the most important indicators affecting human health. Here, a pair of covalent organic frameworks (COFs) of positional isomers (p-COF and o-COF) for indoor humidity regulation is reported. Although p-COF and o-COF have the same sql topology and pore size, they exhibit different water adsorption behaviors due to the subtle differences in water adsorption sites. Particularly, o-COF exhibits a steep adsorption isotherm in the range of 45-65% RH with a hysteresis loop, which is perfectly suitable for indoor humidity regulation. In the laboratory experiment, when the humidity of the external environment is 20-75% RH, o-COF can control the humidity of the room in the range of 45-60% RH. o-COF has shown great potential as a dual humidification/dehumidification adsorbent for indoor humidity regulation.

Covalent organic frameworks: linkage types, synthetic methods and bio-related applications

Covalent organic frameworks (COFs) are composed of small organic molecules linked via covalent bonds, which have tunable mesoporous structure, good biocompatibility and functional diversities. These excellent properties make COFs a promising candidate for constructing biomedical nanoplatforms and provide ample opportunities for nanomedicine development. A systematic review of the linkage types and synthesis methods of COFs is of indispensable value for their biomedical applications. In this review, we first summarize the types of various linkages of COFs and their corresponding properties. Then, we highlight the reaction temperature, solvent and reaction time required by different synthesis methods and show the most suitable synthesis method by comparing the merits and demerits of various methods. To appreciate the cutting-edge research on COFs in bioscience technology, we also summarize the bio-related applications of COFs, including drug delivery, tumor therapy, bioimaging, biosensing and antimicrobial applications. We hope to provide insight into the interdisciplinary research on COFs and promote the development of COF nanomaterials for biomedical applications and their future clinical translations.

Study of the diffusion properties of zeolite mixtures by combined gravimetric analysis, IR spectroscopy and inversion methods (IRIS)

We report the development of a new method of investigation of the mass transport properties of acidic zeolite-based materials aiming to overcome the limitations of classical approaches. It consists in hyphenating gravimetric analysis and infrared spectroscopy. The former allows assessing the diffusion from the gas phase to all the porosity, while IR allows for selective assessment of diffusion to the zeolite active sites located in the micropores. Furthermore, the data are processed by an original methodology allowing the recovery of the distribution of diffusion domains by inversion of the integral equations describing the uptake curves or the evolution of the infrared spectra. The combination of gravimetric analysis and IR spectroscopy makes it possible to monitor and distinguish diffusion within the various components of the material. The methodology has been applied to the isooctane uptake in the mechanical mixture of FAU and MFI zeolites. Analysis of both gravimetric uptake curves and evolving infrared spectra allows distinguishing and assigning diffusion domains to the H-FAU and H-MFI components of the mixture, with high and low effective diffusion rate constants, respectively. The advantages and limits of the methodology are discussed.

Boosting the catalysis of cesium phosphomolybdate encapsulated in hierarchical porous UiO-66 by microenvironment modulation for epoxidation of alkenes

The chemical microenvironment of polyoxometalates (POMs) encapsulated in metal-organic frameworks (MOFs) presents a significant influence on their catalytic performance, which can be easily regulated by the linker functional group alteration or metal substitution in MOFs. Herein, a series of cesium phosphomolybdate (CsPM) encapsulated in hierarchical porous UiO-66-X composites (CsPM@HP-UiO-66-X, X = H, 2CH3, or 2OH, where X represents the alterable group grafted onto the linker benzene ring) were successfully synthesized through a one pot modulated solvothermal method. The catalytic performances of the obtained materials were explored in alkene epoxidation reaction with tert-butyl hydroperoxide (t-BuOOH). CsPM@HP-UiO-66-2CH3 showed relatively high catalytic activity, stability, and epoxidation selectivity in cyclooctene epoxidation among the CsPM@HP-UiO-66-X composites. Moreover, CsPM@HP-UiO-66-2CH3 was effective in the epoxidation of numerous alkenes, especially cyclic alkenes. The superior catalytic activity of CsPM@HP-UiO-66-2CH3 is mainly attributed to the modulation of the microenvironment surrounding CsPM active sites by introducing a hydrophobic methyl group. Meanwhile, the size-matched effect, the introduction of cesium cations, and the strong metal-support interactions (SMSIs) between CsPM and HP-UiO-66-2CH3 play a crucial role in the stability of CsPM@HP-UiO-66-2CH3.

Synthetic Control of the Defect Structure and Hierarchical Extra-Large-/Small-Pore Microporosity in Aluminosilicate Zeolite SWY

The SWY-type aluminosilicate zeolite, STA-30, has been synthesized via different routes to understand its defect chemistry and solid acidity. The synthetic parameters varied were the gel aging, the Al source, and the organic structure directing agent. All syntheses give crystalline materials with similar Si/Al ratios (6-7) that are stable in the activated K,H-form and closely similar by powder X-ray diffraction. However, they exhibit major differences in the crystal morphology and in their intracrystalline porosity and silanol concentrations. The diDABCO-C82+ (1,1'-(octane-1,8-diyl)bis(1,4-diazabicyclo[2.2.2]octan)-1-ium)-templated STA-30 samples (but not those templated by bisquinuclidinium octane, diQuin-C82+) possess hierarchical microporosity, consisting of noncrystallographic extra-large micropores (13 Å) that connect with the characteristic swy and gme cages of the SWY structure. This results in pore volumes up to 30% greater than those measured in activated diQuin-C8_STA-30 as well as higher concentrations of silanols and fewer Brønsted acid sites (BASs). The hierarchical porosity is demonstrated by isopentane adsorption and the FTIR of adsorbed pyridine, which shows that up to 77% of the BASs are accessible (remarkable for a zeolite that has a small-pore crystal structure). A structural model of single can/d6r column vacancies is proposed for the extra-large micropores, which is revealed unambiguously by high-resolution scanning transmission electron microscopy. STA-30 can therefore be prepared as a hierarchically porous zeolite via direct synthesis. The additional noncrystallographic porosity and, subsequently, the amount of SiOHs in the zeolites can be enhanced or strongly reduced by the choice of crystallization conditions.

Interplay Between Particle Size and Hierarchy of Zeolite ZSM-5 During the CO2 -to-aromatics Process

The CO2 -to-aromatics process is a chemical reaction that converts carbon dioxide (CO2 ) into valuable petrochemical, i. e., aromatics (especially, benzene, toluene, and xylene) over the metal/zeolite bifunctional catalytic systems. These aromatics are used in producing plastics, fibers, and other industrial products, which are currently exclusively sourced from fossil-derived feedstocks. The significance of this process lies in its potential to mitigate climate change by reducing greenhouse gas emissions and simultaneously producing valuable chemicals. Consequently, these CO2 -derived aromatics can reduce the reliance on fossil fuels as a source of feedstocks, which can help to promote a more sustainable and circular economy. Owing to the existence of a wider straight channel favoring the aromatization process, zeolite ZSM-5 is extensively used to yield aromatics during CO2 hydrogenation over bifunctional (metal/zeolite) catalytic systems. To provide a better understanding of this unique property of zeolite ZSM-5, this work investigates the impact of particle size and hierarchy of the zeolite and how these govern the reaction performance and the overall selectivity. As a result, an improved understanding of the zeolite-catalyzed hydrocarbon conversion process has been obtained.

Intraparticle ripening to create hierarchically porous Ti-MOF single crystals for deep oxidative desulfurization

The catalytic oxidative desulfurization (ODS) technique is able to remove sulfur compounds from fuels, conducive to achieving deep desulfurization for the good of the ecological environment. Ti-based metal-organic frameworks (Ti-MOFs) possessing good affinity to organic reactants and considerable numbers of Ti active sites are promising catalysts for ODS. However, current Ti-MOFs suffer from severe diffusion limitations caused by the size mismatch between sole micropores and bulky sulfur compounds, leading to poor ODS performance. Here, a facile method of intraparticle ripening without any additive is developed to obtain hierarchically meso-microporous Ti-MIL-125 single crystals (Meso-Ti-MIL-125) for the first time. Such Meso-Ti-MIL-125 shows a BET surface area of 1401 m2 g-1 and a mesoporous volume that is 1.7 times as high as that of the conventional Ti-MIL-125. Our novel Meso-Ti-MIL-125 exhibits excellent catalytic performance in the ODS of a series of bulky thiophenic sulfur compounds, completely removing benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (DMDBT) from model fuels, which is, respectively, 2.4 times, 1.5 times, and 6.7 times higher than the removal achieved with conventional Ti-MIL-125. Such a facile synthetic strategy is envisioned to be applied in many kinds of crystalline materials, such as zeolites, for industrial production.

Combinatorial Synthesis of Covalent Organic Framework Particles with Hierarchical Pores and Their Catalytic Application

Precise tailoring of the aggregation state of covalent organic frameworks (COFs) to form a hierarchical porous structure is critical to their performance and applications. Here, we report a one-pot and one-step strategy of using dynamic combinatorial chemistry to construct imine-based hollow COFs containing meso- and macropores. It relies on a direct copolymerization of three or more monomers in the presence of two monofunctional competitors. The resulting particle products possess high crystallinity and hierarchical pores, including micropores around 0.93 nm, mesopores widely distributed in the range of 3.1-32 nm, and macropores at about 500 nm, while the specific surface area could be up to 748 m2·g-1, with non-micropores accounting for 60% of the specific surface area. The particles demonstrate unique advantages in the application as nanocarriers for in situ loading of Pd catalysts at 93.8% loading efficiency in the copolymerization of ethylene and carbon monoxide. The growth and assembly of the copolymer could thus be regulated to form flower-shaped particles, efficiently suppressing the fouling of the reactor. The copolymer's weight-average molecular weight and the melting temperature are also highly improved. Our method provides a facile way of fabricating COFs with hierarchical pores for advanced applications in catalysis.

Hierarchical SAPO-34 Catalysts as Host for Cu Active Sites

Cu-containing hierarchical SAPO-34 catalysts were synthesized by the bottom-up method using different mesoporogen templates: CTAB encapsulated within ordered mesoporous silica nanoparticles (MSNs) and sucrose. A high fraction of the Cu centers exchanged in the hierarchical SAPO-34 architecture with high mesopore surface area and volume was achieved when CTAB was embedded within ordered mesoporous silica nanoparticles. Physicochemical characterization was performed by using structural and spectroscopic techniques to elucidate the properties of hierarchical SAPO-34 before and after Cu introduction. The speciation of the Cu sites, investigated by DR UV-Vis, and the results of the catalytic tests indicated that the synergy between the textural properties of the hierarchical SAPO-34 framework, the high Cu loading, and the coordination and localization of the Cu sites in the hierarchical architecture is the key point to obtaining good preliminary results in the NO selective catalytic reduction with hydrocarbons (HC-SCR).

Recent Developments on the Catalytic and Biosensing Applications of Porous Nanomaterials

Nanoscopic materials have demonstrated a versatile role in almost every emerging field of research. Nanomaterials have come to be one of the most important fields of advanced research today due to its controllable particle size in the nanoscale range, capacity to adopt diverse forms and morphologies, high surface area, and involvement of transition and non-transition metals. With the introduction of porosity, nanomaterials have become a more promising candidate than their bulk counterparts in catalysis, biomedicine, drug delivery, and other areas. This review intends to compile a self-contained set of papers related to new synthesis methods and versatile applications of porous nanomaterials that can give a realistic picture of current state-of-the-art research, especially for catalysis and sensor area. Especially, we cover various surface functionalization strategies by improving accessibility and mass transfer limitation of catalytic applications for wide variety of materials, including organic and inorganic materials (metals/metal oxides) with covalent porous organic (COFs) and inorganic (silica/carbon) frameworks, constituting solid backgrounds on porous materials.

Zeolites and metal-organic frameworks for gas separation: the possibility of translating adsorbents into membranes

Zeolites and metal-organic frameworks (MOFs) represent an attractive class of crystalline porous materials that possesses regular pore structures. The inherent porosity of these materials has led to an increasing focus on gas separation applications, encompassing adsorption and membrane separation techniques. Here, a brief overview of the critical properties and fabrication approaches for zeolites and MOFs as adsorbents and membranes is given. The separation mechanisms, based on pore sizes and the chemical properties of nanochannels, are explored in depth, considering the distinct characteristics of adsorption and membrane separation. Recommendations for judicious selection and design of zeolites and MOFs for gas separation purposes are emphasized. By examining the similarities and differences between the roles of nanoporous materials as adsorbents and membranes, the feasibility of zeolites and MOFs from adsorption separation to membrane separation is discussed. With the rapid development of zeolites and MOFs towards adsorption and membrane separation, challenges and perspectives of this cutting-edge area are also addressed.

Advanced Materials Design for Adsorption of Toxic Substances in Cigarette Smoke

Cigarettes, despite being economically important legal consumer products, are highly addictive and harmful, particularly to the respiratory system. Tobacco smoke is a complex mixture containing over 7000 chemical compounds, 86 of which are identified to have "sufficient evidence of carcinogenicity" in either animal or human tests. Thus, tobacco smoke poses a significant health risk to humans. This article focuses on materials that help reduce the levels of major carcinogens in cigarette smoke; these include nicotine, polycyclic aromatic hydrocarbons, tobacco-specific nitrosamines, hydrogen cyanide, carbon monoxide, and formaldehyde. Specifically, the research progress on adsorption effects and mechanisms of advanced materials such as cellulose, zeolite, activated carbon, graphene, and molecularly imprinted polymers are highlighted. The future trends and prospects in this field are also discussed. Notably, with advancements in supramolecular chemistry and materials engineering, the design of functionally oriented materials has become increasingly multidisciplinary. Certainly, several advanced materials can play a critical role in reducing the harmful effects of cigarette smoke. This review aims to serve as an insightful reference for the design of hybrid and functionally oriented advanced materials.

Methane Oxidation over the Zeolites-Based Catalysts

Zeolites have ordered pore structures, good spatial constraints, and superior hydrothermal stability. In addition, the active metal elements inside and outside the zeolite framework provide the porous material with adjustable acid–base property and good redox performance. Thus, zeolites-based catalysts are more and more widely used in chemical industries. Combining the advantages of zeolites and active metal components, the zeolites-based materials are used to catalyze the oxidation of methane to produce various products, such as carbon dioxide, methanol, formaldehyde, formic acid, acetic acid, and etc. This multifunction, high selectivity, and good activity are the key factors that enable the zeolites-based catalysts to be used for methane activation and conversion. In this review article, we briefly introduce and discuss the effect of zeolite materials on the activation of C–H bonds in methane and the reaction mechanisms of complete methane oxidation and selective methane oxidation. Pd/zeolite is used for the complete oxidation of methane to carbon dioxide and water, and Fe- and Cu-zeolite catalysts are used for the partial oxidation of methane to methanol, formaldehyde, formic acid, and etc. The prospects and challenges of zeolite-based catalysts in the future research work and practical applications are also envisioned. We hope that the outcome of this review can stimulate more researchers to develop more effective zeolite-based catalysts for the complete or selective oxidation of methane.

Application of Hydrogen-Bonded Organic Frameworks in Environmental Remediation: Recent Advances and Future Trends

The hydrogen-bonded organic frameworks (HOFs) are a class of porous materials with crystalline frame structures, which are self-assembled from organic structures by hydrogen bonding in non-covalent bonds π-π packing and van der Waals force interaction. HOFs are widely used in environmental remediation due to their high specific surface area, ordered pore structure, pore modifiability, and post-synthesis adjustability of various physical and chemical forms. This work summarizes some rules for constructing stable HOFs and the synthesis of HOF-based materials (synthesis of HOFs, metallized HOFs, and HOF-derived materials). In addition, the applications of HOF-based materials in the field of environmental remediation are introduced, including adsorption and separation (NH3, CO2/CH4 and CO2/N2, C2H2/C2He and CeH6, C2H2/CO2, Xe/Kr, etc.), heavy metal and radioactive metal adsorption, organic dye and pesticide adsorption, energy conversion (producing H2 and CO2 reduced to CO), organic dye degradation and pollutant sensing (metal ion, aniline, antibiotic, explosive steam, etc.). Finally, the current challenges and further studies of HOFs (such as functional modification, molecular simulation, application extension as remediation of contaminated soil, and cost assessment) are discussed. It is hoped that this work will help develop widespread applications for HOFs in removing a variety of pollutants from the environment.

Zeolites as a Class of Semiconductors for High-Performance Electrically Transduced Sensing

Zeolites are widely used as catalysts and adsorbents in the chemical industry, but their potential for electronic devices has been stunted to date, as they are commonly recognized as electronic insulators. Here, we have for the first time demonstrated that Na-type ZSM-5 zeolites are ultrawide-direct-band-gap semiconductors based on optical spectroscopy, variable-temperature current-voltage characteristics, and photoelectric effect as well as electronic structure theoretical calculations and further unraveled the band-like charge transport mechanism in electrically conductive zeolites. The increase in charge-compensating Na⁺ cations in Na-ZSM-5 decreases the band gap and affects its density of states, shifting the Fermi level close to the conduction band. Remarkably, the semiconducting Na-ZSM-5 zeolites have been first applied for constructing electrically transduced sensors that can sense trace-level (77 ppb) ammonia with unprecedentedly high sensitivity, negligible cross-sensitivity, and high stability under moisture ambient conditions compared with conventional semiconducting materials and conductive metal-organic frameworks (MOFs). The charge density difference shows that the massive electron transfer between NH₃ molecules and Na⁺ cations ascribed to Lewis acid sites enables electrically transduced chemical sensing. This work opens a new era of zeolites in applications of sensing, optics, and electronics.

Advanced zeolite and ordered mesoporous silica-based catalysts for the conversion of CO2 to chemicals and fuels

For many years, capturing, storing or sequestering CO₂ from concentrated emission sources or from air has been a powerful technique for reducing atmospheric CO₂. Moreover, the use of CO₂ as a C1 building block to mitigate CO₂ emissions and, at the same time, produce sustainable chemicals or fuels is a challenging and promising alternative to meet global demand for chemicals and energy. Hence, the chemical incorporation and conversion of CO₂ into valuable chemicals has received much attention in the last decade, since CO₂ is an abundant, inexpensive, nontoxic, nonflammable, and renewable one-carbon building block. Nevertheless, CO₂ is the most oxidized form of carbon, thermodynamically the most stable form and kinetically inert. Consequently, the chemical conversion of CO₂ requires highly reactive, rich-energy substrates, highly stable products to be formed or harder reaction conditions. The use of catalysts constitutes an important tool in the development of sustainable chemistry, since catalysts increase the rate of the reaction without modifying the overall standard Gibbs energy in the reaction. Therefore, special attention has been paid to catalysis, and in particular to heterogeneous catalysis because of its environmentally friendly and recyclable nature attributed to simple separation and recovery, as well as its applicability to continuous reactor operations. Focusing on heterogeneous catalysts, we decided to center on zeolite and ordered mesoporous materials due to their high thermal and chemical stability and versatility, which make them good candidates for the design and development of catalysts for CO₂ conversion. In the present review, we analyze the state of the art in the last 25 years and the potential opportunities for using zeolite and OMS (ordered mesoporous silica) based materials to convert CO₂ into valuable chemicals essential for our daily lives and fuels, and to pave the way towards reducing carbon footprint. In this review, we have compiled, to the best of our knowledge, the different reactions involving catalysts based on zeolites and OMS to convert CO₂ into cyclic and dialkyl carbonates, acyclic carbamates, 2-oxazolidones, carboxylic acids, methanol, dimethylether, methane, higher alcohols (C₂₊OH), C₂₊ (gasoline, olefins and aromatics), syngas (RWGS, dry reforming of methane and alcohols), olefins (oxidative dehydrogenation of alkanes) and simple fuels by photoreduction. The use of advanced zeolite and OMS-based materials, and the development of new processes and technologies should provide a new impulse to boost the conversion of CO₂ into chemicals and fuels.

Metal Organic Framework Cubosomes

We demonstrate a general strategy for the synthesis of ordered bicontinuous-structured metal organic frameworks (MOFs) by using polymer cubosomes (PCs) with a double primitive structure (Im 3 ‾ ${\bar{3}}$ m symmetry) as the template. The filling of MOF precursors in the open channel of PCs, followed by their coordination and removal of the template, generates MOF cubosomes with a single primitive topology (Pm 3 ‾ ${\bar{3}}$ m) and average mesopore diameters of 60-65 nm. Mechanism study reveals that the formation of ZIF-8 cubosomes undergoes a new MOF growth process, which involves the formation of individual MOF seeds in the template, their growth and eventual fusion into the cubosomes. Their growth kinetics follows the Avrami equation with an Avrami exponent of n=3 and a growth rate of k=1.33×10^-4 , indicating their fast 3D heterogeneous growth mode. Serving as a bioreactor, the ZIF-8 cubosomes show high loading of trypsin enzyme, leading to a high catalytic activity in the proteolysis of bovine serum albumin.

Brief History, Preparation Method, and Biological Application of Mesoporous Silica Molecular Sieves: A Narrative Review

It has been more than 30 years since the first ordered mesoporous silica molecular sieve (MCM-41) was reported, but the enthusiasm for exploiting mesoporous silica is still growing due to its superior properties, such as its controllable morphology, excellent hosting capability, easy functionalization, and good biocompatibility. In this narrative review, the brief history of the discovery of mesoporous silica and several important mesoporous silica families are summarized. The development of mesoporous silica microspheres with nanoscale dimensions, hollow mesoporous silica microspheres, and dendritic mesoporous silica nanospheres is also described. Meanwhile, common synthesis methods for traditional mesoporous silica, mesoporous silica microspheres, and hollow mesoporous silica microspheres are discussed. Then, we introduce the biological applications of mesoporous silica in fields such as drug delivery, bioimaging, and biosensing. We hope this review will help people to understand the history of the development of mesoporous silica molecular sieves and become familiar with their synthesis methods and applications in biology.

Ti-MOF single-crystals featuring an intracrystal macro-microporous hierarchy for catalytic oxidative desulfurization

For the first time, we demonstrate a Ti-MOF (Ti-metal organic framework) single-crystal featuring an intracrystal macro-microporous hierarchy (Hier-NTU-9) by a vapor-assisted polymer-templated method. This Hier-NTU-9 possesses macropores (100-1000 nm) derived from polymer templates and enhanced transport ability of bulky molecules, exhibiting almost double the desulfurization activity compared to the conventional NTU-9.

Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

Metal substitution of molecular sieve systems is a major driving force in developing novel catalytic processes to meet current demands of green chemistry concepts and to achieve sustainability in the chemical industry and in other aspects of our everyday life. The advantages of metal-substituted molecular sieves include high surface areas, molecular sieving effects, confinement effects, and active site and morphology variability and stability. The present review aims to comprehensively and critically assess recent advances in the area of tetra- (Ti, Sn, Zr, Hf) and pentavalent (V, Nb, Ta) metal-substituted molecular sieves, which are mainly characterized for their Lewis acidic active sites. Metal oxide molecular sieve materials with properties similar to those of zeolites and siliceous molecular sieve systems are also discussed, in addition to relevant studies on metal-organic frameworks (MOFs) and some composite MOF systems. In particular, this review focuses on (i) synthesis aspects determining active site accessibility and local environment; (ii) advances in active site characterization and, importantly, quantification; (iii) selective redox and isomerization reaction applications; and (iv) photoelectrocatalytic applications.

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.

Carbon-Carbon Linked Organic Frameworks: An Explicit Summary and Analysis

Organic frameworks with carbon-carbon (CC) linkage are an important class of materials owing to their outstanding chemical stability and extended π-electron delocalization resulting in unique optoelectronic properties. In the first part of this review article, the design principles for the bottom-up synthesis of 2D and 3D sp/sp² CC linked organic frameworks are summarized. Representative reaction methodologies, such as Knoevenagel condensation, Aldol condensation, Horner-Wadsworth-Emmons reaction, Wittig reaction, and coupling reactions (Ullmann, Suzuki, Heck, Yamamoto, etc.) are included. This is discussed in the context of their reaction mechanism, reaction dynamics, and whether and why resulting in an amorphous or crystalline product. This is followed by a discussion of different state-of-the art bottom-up synthesis methodologies, like solvothermal, interfacial, and solid-state synthesis. In the second part, the structure-property relationships in CC linked organic frameworks with representative examples of organocatalysis, photo(electro)catalysis, energy storage and conversion, magnetism, and molecular storage and separation are analyzed. The importance of linkage type, building blocks, topology, and crystallinity of the framework material in connection with the structure-property relationship is highlighted. Finally, brief concluding remarks are presented based on the key development of bottom-up synthetic methods and provide perspectives for future development in this field.

The recent development of inverse vulcanized polysulfide as an alternative adsorbent for heavy metal removal in wastewater

Inverse vulcanized polysulfides have been used as low-cost and effective adsorbents to remediate heavy metals in wastewater. Inverse vulcanization introduces sustainable polysulfide synthesis by solving the rapid desulfurization problem of unstable polysulfides, and provides superior performance compared to conventional commercial adsorbents. The review discussed the brief applications of the inverse vulcanized polysulfides to remove heavy metal wastewater and emphasized the modified synthesis processes for enhanced uptake ratios. The characteristics of polysulfide adsorbents, which play a vital role during the removal process are highlighted with a proper discussion of the interaction between metal ions and polysulfides. The review paper concludes with remarks on the future outlook of these low-cost adsorbents with high selectivity to heavy metals. These polysulfide adsorbents can be prepared using a wide variety of crosslinker monomers including organic hydrocarbons, cooking oils, and agro-based waste materials. They have shown good surface area and excellent metal-binding capabilities compared to the commercially available adsorbents. Proper postmodification processes have enabled the benefits of repetitive uses of the polysulfide adsorbents. The improved surface area obtained by appropriate choice of crosslinkers, modified synthesis techniques, and regeneration through post-modification has made inverse vulcanized polysulfides capable of removing.

Covalent organic frameworks (COFs): a promising CO2 capture candidate material

Covalent organic frameworks (COFs) are an emerging kind of porous crystal material.

Zeolites in Adsorption Processes: State of the Art and Future Prospects

Zeolites have been widely used as catalysts, ion exchangers, and adsorbents since their industrial breakthrough in the 1950s and continue to be state-of the-art adsorbents in many separation processes. Furthermore, their properties make them materials of choice for developing and emerging separation applications. The aim of this review is to put into context the relevance of zeolites and their use and prospects in adsorption technology. It has been divided into three different sections, i.e., zeolites, adsorption on nanoporous materials, and chemical separations by zeolites. In the first section, zeolites are explained in terms of their structure, composition, preparation, and properties, and a brief review of their applications is given. In the second section, the fundamentals of adsorption science are presented, with special attention to its industrial application and our case of interest, which is adsorption on zeolites. Finally, the state-of-the-art relevant separations related to chemical and energy production, in which zeolites have a practical or potential applicability, are presented. The replacement of some of the current separation methods by optimized adsorption processes using zeolites could mean an improvement in terms of sustainability and energy savings. Different separation mechanisms and the underlying adsorption properties that make zeolites interesting for these applications are discussed.

Rapid Synthesis of Si-Rich SSZ-13 Zeolite under Fluoride-Free Conditions

Rapid synthesis of Si-rich (SiO₂/Al₂O₃ > 100) SSZ-13 zeolite under fluoride-free conditions is highly desirable but still challenging. Herein, we for the first time report a rapid synthesis of all silica and aluminosilicate (SiO₂/Al₂O₃ > 100) SSZ-13 zeolite without the addition of fluoride species. The crystallization could be fully completed at 160 °C for 4 h when the aging of the starting gel is 3 h at room temperature after the addition of a zeolite seed. The key to success is the formation of more basic building units (4- and 6-membered rings) in the initial gel with the aging time of 3 h after the addition of a zeolite seed, leading to the successful rapid synthesis of Si-rich SSZ-13 zeolite. The obtained Si-rich SSZ-13 zeolite displays high crystallinity, uniform cubic morphology with a nanoparticle feature, and a large surface area. More importantly, the obtained Si-rich SSZ-13 zeolite displays excellent performance in the adsorption of ethanol and methanol-to-olefin reaction.

In Situ Confined Synthesis of a Copper-Encapsulated Silicalite-1 Zeolite for Highly Efficient Iodine Capture

Effective capture of radioactive iodine is highly desirable for decontamination purposes in spent fuel reprocessing. Cu-based adsorbents with a low cost and high chemical affinity for I2 molecules act as a decent candidate for iodine elimination, but the low utilization and stability remain a significant challenge. Herein, a facile in situ confined synthesis strategy is developed to design and synthesize a copper-encapsulated flaky silicalite-1 (Cu@FSL-1) zeolite with a thickness of ≤300 nm. The maximum iodine uptake capacity of Cu@FSL-1 can reach 625 mg g-1 within 45 min, which is 2 times higher than that of a commercial silver-exchanged zeolite even after nitric acid and NOX treatment. The Cu nanoparticles (NPs) confined within the zeolite exert superior iodine adsorption and immobilization properties as well as high stability and fast adsorption kinetics endowed by the all-silica zeolite matrix. This study provides new insight into the design and controlled synthesis of zeolite-confined metal adsorbents for efficient iodine capture from gaseous radioactive streams.

Improving the Hydrothermal Stability of ZSM-5 Zeolites in 1-Octene Aromatization by Sequential Alkali Treatment and Phosphorus Modification

For the aromatization of olefins (in Fischer–Tropsch synthetic oil), especially for the fluidized bed reaction with steam as the fluidized medium, improving the catalytic and hydrothermal stabilities of ZSM-5 catalysts is a research focus because of both fundamental research interests and potential commercial applications. In this work, sequential alkali treatment and phosphorus modification were carried out for ZSM-5 samples. The results obtained from characterization and reaction evaluation show that the introduction of mesopores facilitates the dispersion of phosphorus species into the pores and improves the reaction stability for 1-octene aromatization. After the hydrothermal treatment, the P-0.5A-Z5-ST sample treated with an appropriate concentration of alkali retains the most acid sites and shows the highest aromatic selectivity (22.5%) at TOS = 660 min. Therefore, a moderate distribution of mesopores in a zeolite plays an important role in the diffusions of reactants and products, as well as in the distribution of phosphorus species.