Heterogeneous Catalysis in Zeolites,Mesoporous Silica,and Metal–Organic Frameworks

Crystalline porous materials are important in the development of catalytic systems with high scientific and industrial impact. Zeolites, ordered mesoporous silica, and metal–organic frameworks (MOFs) are three types of porous materials that can be used as heterogeneous catalysts. This review focuses on a comparison of the catalytic activities of zeolites, mesoporous silica, and MOFs. In the first part of the review, the distinctive properties of these porous materials relevant to catalysis are discussed, and the corresponding catalytic reactions are highlighted. In the second part, the catalytic behaviors of zeolites, mesoporous silica, and MOFs in four types of general organic reactions (acid, base, oxidation, and hydrogenation) are compared. The advantages and disadvantages of each porous material for catalytic reactions are summarized. Conclusions and prospects for future development of these porous materials in this field are provided in the last section. This review aims to highlight recent research advancements in zeolites, ordered mesoporous silica, and MOFs for heterogeneous catalysis, and inspire further studies in this rapidly developing field.     

Carbon‐Rich Nanomaterials: Fascinating Hydrogen and Oxygen Electrocatalysts

Hydrogen energy is commonly considered as a clean and sustainable alternative to the traditional fossil fuels. Toward universal utilization of hydrogen energy, developing high‐efficiency, low‐cost, and sustainable energy conversion technologies, especially water‐splitting electrolyzers and fuel cells, is of paramount significance. In order to enhance the energy conversion efficiency of the water‐splitting electrolyzers and fuel cells, earth‐abundant and stable electrocatalysts are essential for accelerating the sluggish kinetics of hydrogen and oxygen reactions. In the past decade, carbon‐rich nanomaterials have emerged as a promising class of hydrogen and oxygen electrocatalysts. Here, the development and electrocatalytic activity of various carbon‐rich materials, including metal‐free carbon, conjugated porous polymers, graphdiyne, covalent organic frameworks (COFs), atomic‐metal‐doped carbon, as well as metal–organic frameworks (MOFs), are demonstrated. In particular, the correlations between their porous nanostructures/electronic structures of active centers and electrocatalytic performances are emphatically discussed. Therefore, this review article guides the rational design and synthesis of high‐performance, metal‐free, and noble‐metal‐free carbon‐rich electrocatalysts and eventually advances the rapid development of water‐splitting electrolyzers and fuel cells toward practical applications.     

Engineering Homochiral Metal‐Organic Frameworks for Heterogeneous Asymmetric Catalysis and Enantioselective Separation

Owing to the potential applications in technological areas such as gas storage, catalysis, separation, sensing and nonlinear optics, tremendous efforts have been devoted to the development of porous metal‐organic frameworks (MOFs) over the past ten years. Homochiral porous MOFs are particularly attractive candidates as heterogeneous asymmetric catalysts and enantioselective adsorbents and separators for production of optically active organic compounds due to the lack of homochiral inorganic porous materials such as zeolites. In this review, we summarize the recent research progress in homochiral MOF materials, including their synthetic strategy, distinctive structural features and latest advances in asymmetric heterogeneous catalysis and enantioselective separation.     

Metalation of Catechol‐Functionalized Defective Covalent Organic Frameworks for Lewis Acid Catalysis

Covalent organic frameworks (COFs) have emerged as a fascinating crystalline porous material and are widely used in the field of catalysis. However, developing simple approaches to fabricate conjugated COFs with specific functional groups remains a significant challenge. In this study, the construction of defective COF‐LZU1 with Lewis acid sites embedded into the frameworks is fulfilled by a facile solvent‐assisted ligand exchange method. A monodentate ligand, protocatechualdehyde, is successfully introduced into the skeleton of COF‐LZU1, which endows the defects in the structure of COF‐LZU1 via replacement of the original coordinated benzene‐1,3,5‐tricarbaldehyde ligand. As‐synthesized defective COF‐LZU1 decorated with protocatechualdehyde is rich of free hydroxy groups for chelating with active metal ions. Specifically, after combining with Fe³⁺, the defective COF‐LZU1 shows excellent activity in catalytic alcoholysis of epoxides under mild conditions. The method reported here will open up the opportunity to incorporate different functional groups into COFs and enrich the strategies for creating new types of porous catalysts.     

Ultrasmall Metal Nanoparticles Confined within Crystalline Nanoporous Materials: A Fascinating Class of Nanocatalysts

Crystalline nanoporous materials with uniform porous structures, such as zeolites and metal–organic frameworks (MOFs), have proven to be ideal supports to encapsulate ultrasmall metal nanoparticles (MNPs) inside their void nanospaces to generate high‐efficiency nanocatalysts. The nanopore‐encaged metal catalysts exhibit superior catalytic performance as well as high stability and catalytic shape selectivity endowed by the nanoporous matrix. In addition, the synergistic effect of confined MNPs and nanoporous frameworks with active sites can further promote the catalytic activities of the composite catalysts. Herein, recent progress in nanopore‐encaged metal nanocatalysts is reviewed, with a special focus on advances in synthetic strategies for ultrasmall MNPs (<5 nm), clusters, and even single atoms confined within zeolites and MOFs for various heterogeneous catalytic reactions. In addition, some advanced characterization methods to elucidate the atomic‐scale structures of the nanocatalysts are presented, and the current limitations of and future opportunities for these fantastic nanocatalysts are also highlighted and discussed. The aim is to provide some guidance for the rational synthesis of nanopore‐encaged metal catalysts and to inspire their further applications to meet the emerging demands in catalytic fields.     

Covalent Organic Framework Electrocatalysts for Clean Energy Conversion

Covalent organic frameworks (COFs) are promising for catalysis, sensing, gas storage, adsorption, optoelectricity, etc. owning to the unprecedented combination of large surface area, high crystallinity, tunable pore size, and unique molecular architecture. Although COFs are in their initial research stage, progress has been made in the design and synthesis of COF‐based electrocatalysis for the oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and CO₂ reduction in energy conversion and fuel generation. Design principles are also established for some of the COF materials toward rational design and rapid screening of the best electrocatalysts for a specific application. Herein, the recent advances in the design and synthesis of COF‐based catalysts for clean energy conversion and storage are presented. Future research directions and perspectives are also being discussed for the development of efficient COF‐based electrocatalysts.     

Rational Design of Catalytic Centers in Crystalline Frameworks

Crystalline frameworks including primarily metal organic frameworks (MOF) and covalent organic frameworks (COF) have received much attention in the field of heterogeneous catalysts recently. Beyond providing large surface area and spatial confinement, these crystalline frameworks can be designed to either directly act as or influence the catalytic sites at molecular level. This approach offers a unique advantage to gain deeper insights of structure–activity correlations in solid materials, leading to new guiding principles for rational design of advanced solid catalysts for potential important applications related to energy and fine chemical synthesis. In this review, recent key progress achieved in designing MOF‐ and COF‐based molecular solid catalysts and the mechanistic understanding of the catalytic centers and associated reaction pathways are summarized. The state‐of‐the‐art rational design of MOF‐ and COF‐based solid catalysts in this review is grouped into seven different areas: (i) metalated linkers, (ii) metalated moieties anchored on linkers, (iii) organic moieties anchored on linkers, (iv) encapsulated single sites in pores, and (v) metal‐mode‐based active sites in MOFs. Along with this, some attention is paid to theoretical studies about the reaction mechanisms. Finally, technical challenges and possible solutions in applying these catalysts for practical applications are also presented.     

Multifunctional Metal–Organic Frameworks for Photocatalysis

Metal–organic frameworks (MOFs) have attracted significant research attention in diverse areas due to their unique physical and chemical characteristics that allow their innovative application in various research fields. Recently, the application of MOFs in heterogeneous photocatalysis for water splitting, CO₂ reduction, and organic transformation have emerged, aiming at providing alternative solutions to address the world‐wide energy and environmental problems by taking advantage of the unique porous structure together with ample physicochemical properties of the metal centers and organic ligands in MOFs. In this review, the latest progress in MOF‐involved solar‐to‐chemical energy conversion reactions are summarized according to their different roles in the photoredox chemical systems, e.g., photocatalysts, co‐catalysts, and hosts. The achieved progress and existing problems are evaluated and proposed, and the opportunities and challenges of MOFs and their related materials for their advanced development in photocatalysis are discussed and anticipated.     

Template Conversion of Covalent Organic Frameworks into 2D Conducting Nanocarbons for Catalyzing Oxygen Reduction Reaction

Progress over the past decades in porous materials has exerted great effect on the design of metal‐free carbon electrochemical catalysts in fuel cells. The carbon material must combine three functions, i.e., electrical conductivity for electron transport, optimal pores for ion motion, and abundant heteroatom sites for catalysis. Here, an ideal carbon catalyst is achieved by combining two strategies—the use of a 2D covalent organic framework (COF) and the development of a suitable template to guide the pyrolysis. The COF produces nanosized carbon sheets that combine high conductivity, hierarchical porosity, and abundant heteroatom catalytic edges. The catalysts achieve superior performance to authentic Pt/C with exceptional onset potential (0 V vs ?0.03 V), half‐wave potentials (?0.11 V vs ?0.16 V), high limit current density (7.2 mA cm^?2 vs 6.0 mA cm^?2), low Tafel slope (110 mV decade^?1 vs 121 mV decade^?1), long‐time stability, and methanol tolerance. These results reveal a novel material platform based on 2D COFs for designing novel 2D carbon materials.     

Electrocatalysts Derived from Metal–Organic Frameworks for Oxygen Reduction and Evolution Reactions in Aqueous Media

Electrochemical energy conversion and storage devices such as fuel cells and metal–air batteries have been extensively studied in recent decades for their excellent conversion efficiency, high energy capacity, and low environmental impact. However, sluggish kinetics of the oxygen‐related reactions at air cathodes, i.e., oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are still worth improving. Noble metals such as platinum (Pt), iridium (Ir), ruthenium (Ru) and their oxides are considered as the benchmark ORR and OER electrocatalysts, but they are expensive and prone to be poisoned due to the fuel crossover effect, and may suffer from agglomeration and leaching after long‐term usage. To mitigate these limits, it is highly desirable to design alternative ORR/OER electrocatalysts with prominent performance. Metal–organic frameworks (MOFs) are a class of porous crystalline materials consisting metal ions/clusters coordinated by organic ligands. Their crystalline structure, tunable pore size and high surface area afford them wide opportunities as catalytic materials. This Review covers MOF‐derived ORR/OER catalysts in electrochemical energy conversion, with a focus on the different strategies of material design and preparation, such as composition control and nanostructure fabrication, to improve the activity and durability of MOF‐derived electrocatalysts.     

Porous Carbon‐Hosted Atomically Dispersed Iron–Nitrogen Moiety as Enhanced Electrocatalysts for Oxygen Reduction Reaction in a Wide Range of pH

As one of the alternatives to replace precious metal catalysts, transition‐metal–nitrogen–carbon (M–N–C) electrocatalysts have attracted great research interest due to their low cost and good catalytic activities. Despite nanostructured M–N–C catalysts can achieve good electrochemical performances, they are vulnerable to aggregation and insufficient catalytic sites upon continuous catalytic reaction. In this work, metal–organic frameworks derived porous single‐atom electrocatalysts (SAEs) were successfully prepared by simple pyrolysis procedure without any further posttreatment. Combining the X‐ray absorption near‐edge spectroscopy and electrochemical measurements, the SAEs have been identified with superior oxygen reduction reaction (ORR) activity and stability compared with Pt/C catalysts in alkaline condition. More impressively, the SAEs also show excellent ORR electrocatalytic performance in both acid and neutral media. This study of nonprecious catalysts provides new insights on nanoengineering catalytically active sites and porous structures for nonprecious metal ORR catalysis in a wide range of pH.     

MOF‐Derived Bifunctional Cu3P Nanoparticles Coated by a N,P‐Codoped Carbon Shell for Hydrogen Evolution and Oxygen Reduction

Metal–organic frameworks (MOFs) have recently emerged as a type of uniformly and periodically atom‐distributed precursor and efficient self‐sacrificial template to fabricate hierarchical porous‐carbon‐related nanostructured functional materials. For the first time, a Cu‐based MOF, i.e., Cu‐NPMOF is used, whose linkers contain nitrogen and phosphorus heteroatoms, as a single precursor and template to prepare novel Cu₃P nanoparticles (NPs) coated by a N,P‐codoped carbon shell that is extended to a hierarchical porous carbon matrix with identical uniform N and P doping (termed Cu₃P@NPPC) as an electrocatalyst. Cu₃P@NPPC demonstrates outstanding activity for both the hydrogen evolution and oxygen reduction reaction, representing the first example of a Cu₃P‐based bifunctional catalyst for energy‐conversion reactions. The high performances are ascribed to the high specific surface area, the synergistic effects of the Cu₃P NPs with intrinsic activity, the protection of the carbon shell, and the hierarchical porous carbon matrix doped by multiheteroatoms. This strategy of using a diverse MOF as a structural and compositional material to create a new multifunctional composite/hybrid may expand the opportunities to explore highly efficient and robust non‐noble‐metal catalysts for energy‐conversion reactions.     

Hybridization of MOFs and COFs: A New Strategy for Construction of MOF@COF Core–Shell Hybrid Materials

The exploration of new porous hybrid materials is of great importance because of their unique properties and promising applications in separation of materials, catalysis, etc. Herein, for the first time, by integration of metal–organic frameworks (MOFs) and covalent organic frameworks (COFs), a new type of MOF@COF core–shell hybrid material, i.e., NH₂‐MIL‐68@TPA‐COF, with high crystallinity and hierarchical pore structure, is synthesized. As a proof‐of‐concept application, the obtained NH₂‐MIL‐68@TPA‐COF hybrid material is used as an effective visible‐light‐driven photocatalyst for the degradation of rhodamine B. The synthetic strategy in this study opens up a new avenue for the construction of other MOF–COF hybrid materials, which could have various promising applications.     

Nanoarchitectured Design of Porous Materials and Nanocomposites from Metal‐Organic Frameworks

The emergence of metal‐organic frameworks (MOFs) as a new class of crystalline porous materials is attracting considerable attention in many fields such as catalysis, energy storage and conversion, sensors, and environmental remediation due to their controllable composition, structure and pore size. MOFs are versatile precursors for the preparation of various forms of nanomaterials as well as new multifunctional nanocomposites/hybrids, which exhibit superior functional properties compared to the individual components assembling the composites. This review provides an overview of recent developments achieved in the fabrication of porous MOF‐derived nanostructures including carbons, metal oxides, metal chalcogenides (metal sulfides and selenides), metal carbides, metal phosphides and their composites. Finally, the challenges and future trends and prospects associated with the development of MOF‐derived nanomaterials are also examined.     

Iron‐Based Metal–Organic Frameworks as Catalysts for Visible Light‐Driven Water Oxidation

The development of earth‐abundant, active, and stable catalysts is important for solar energy conversion. Metal‐organic frameworks (MOFs) have been viewed as a promising class of porous materials, which may have innovative application in photocatalysis. In this paper, three types of Fe‐based MOFs and their aminofunctionalized derivatives have been fabricated and systematically studied as water oxidation catalysts (WOCs) for oxygen evolution under visible light irradiation. MIL‐101(Fe) possesses a higher current density and earlier onset potential and exhibits excellent visible light‐driven oxygen evolution activity than the other Fe‐based catalysts. It speeds up the oxygen evolution reaction rate with the higher initial turnover frequencies value of 0.10 s^?1. Our study demonstrates that Fe‐based MOFs as efficient WOCs are promising candidates for photocatalytic water oxidation process.     

Robust Catalysis on 2D Materials Encapsulating Metals: Concept,Application, and Perspective

Great endeavors are undertaken to search for low‐cost, rich‐reserve, and highly efficient alternatives to replace precious‐metal catalysts, in order to cut costs and improve the efficiency of catalysts in industry. However, one major problem in metal catalysts, especially nonprecious‐metal catalysts, is their poor stability in real catalytic processes. Recently, a novel and promising strategy to construct 2D materials encapsulating nonprecious‐metal catalysts has exhibited inimitable advantages toward catalysis, especially under harsh conditions (e.g., strong acidity or alkalinity, high temperature, and high overpotential). The concept, which originates from unique electron penetration through the 2D crystal layer from the encapsulated metals to promote a catalytic reaction on the outermost surface of the 2D crystal, has been widely applied in a variety of reactions under harsh conditions. It has been vividly described as “chainmail for catalyst.” Herein, recent progress concerning this chainmail catalyst is reviewed, particularly focusing on the structural design and control with the associated electronic properties of such heterostructure catalysts, and also on their extensive applications in fuel cells, water splitting, CO₂ conversion, solar cells, metal–air batteries, and heterogeneous catalysis. In addition, the current challenges that are faced in fundamental research and industrial application, and future opportunities for these fantastic catalytic materials are discussed.     

Porous Organic Frameworks Featured by Distinct Confining Fields for the Selective Hydrogenation of Biomass-Derived Ketones

The asymmetric hydrogenation of biomass-derived molecules for the preparation of single enantiomer compounds is an effective method to reduce the rapid consumption of fossil resources. Porous organic frameworks (POFs) with pure organic surfaces may provide unusual confinement effects for organic substrates in chiral catalysis. Here, a series of POF catalysts are designed with chiral active centers decorated into sharply defined one-dimensional channels with diameters in the range of 1.2–2.9 nm. Due to the synergistic effect originating from the conjugated inner wall, the POF material (aperture size 2.4 nm) concentrates over 90% of aromatic species into the porous architecture, and its affinity is one or two orders of magnitude higher than those of classical porous solids. As determined by PBE+D3 calculation, the phenyl fragment reveals strong π–π interaction for steric hindrance around the metal active site to achieve stronger asymmetric induction. Therefore, this POF catalyst achieves high conversion (>99% yield) and enantioselectivity (>99% ee) for various substrates. The advantages of using the POF platform as a chiral catalyst can provide new perspectives on POF-based solid-state host–guest chemistry and asymmetric heterogeneous catalysis.     

Heterostructures Based on 2D Materials: A Versatile Platform for Efficient Catalysis

The unique structural and electronic properties of 2D materials, including the metal and metal‐free ones, have prompted intense exploration in the search for new catalysts. The construction of different heterostructures based on 2D materials offers great opportunities for boosting the catalytic activity in electo(photo)chemical reactions. Particularly, the merits resulting from the synergism of the constituent components and the fascinating properties at the interface are tremendously interesting. This scenario has now become the state‐of‐the‐art point in the development of active catalysts for assisting energy conversion reactions including water splitting and CO₂ reduction. Here, starting from the theoretical background of the fundamental concepts, the progressive developments in the design and applications of heterostructures based on 2D materials are traced. Furthermore, a personal perspective on the exploration of 2D heterostructures for further potential application in catalysis is offered.     

Tuning Pore Heterogeneity in Covalent Organic Frameworks for Enhanced Enzyme Accessibility and Resistance against Denaturants

Achieving high‐performance biocomposites requires knowledge of the compatability between the immobilized enzyme and its host material. The modular nature of covalent organic frameworks (COFs), as a host, allows their pore geometries and chemical functionalities to be fine‐tuned independently, permitting comparative studies between the individual parameters and the performances of the resultant biocomposites. This research demonstrates that dual pores in COFs have profound consequences on the catalytic activity and denaturation of infiltrated enzymes. This approach enforces a constant pore environment by rational building‐block design, which enables it to be unequivocally determined that pore heterogeneity is responsible for rate enhancements of up to threefold per enzyme molecule. More so, the enzyme is more tolerant to detrimental by‐products when occupying the larger pore in a dual‐pore COF compared to a corresponding uniform porous COF. Kinetic studies highlight that pore heterogeneity facilitates mass transfer of both reagents and products. This unparalleled versatility of these materials allows many different aspects to be designed on demand, lending credence to their prospect as next‐generation host materials for various enzyme biocomposites catalysts.