Metal–organic frameworks (MOFs) are porous crystalline materials constructed from metal ions or clusters and multidentate organic ligands. Recently, the use of MOFs or MOF composites as catalysts for synergistic catalysis and tandem reactions has attracted increasing attention due to their tunable open metal centres, functional organic linkers, and active guest species in their pores. In this review, the applications of MOFs with multiple active sites in synergistic organic catalysis, photocatalysis and tandem reactions are discussed. These multifunctional MOFs can be categorized by the type of active centre as follows: (i) open metal centres and functional organic linkers in the MOF structure, (ii) active guest sites in the pores and active sites in the MOF structure, and (iii) bimetallic nanoparticles (NPs) on MOF supports. The types of synergistic catalysis and tandem reactions promoted by multifunctional MOFs and their proposed mechanisms are presented in detail. Here, catalytic MOFs with a single type of active site and MOFs that only serve as supports to enhance substrate adsorption are not discussed.

Multifunctional metal–organic framework catalysts: synergistic catalysis and tandem reactions

Rapidly increasing atmospheric CO2 concentrations threaten human society, the natural environment, and the synergy between the two. In order to ameliorate the CO2 problem, carbon capture and conversion techniques have been proposed. Metal–organic framework (MOF)-based materials, a relatively new class of porous materials with unique structural features, high surface areas, chemical tunability and stability, have been extensively studied with respect to their applicability to such techniques. Recently, it has become apparent that the CO2 capture capabilities of MOF-based materials significantly boost their potential toward CO2 conversion. Furthermore, MOF-based materials’ well-defined structures greatly facilitate the understanding of structure–property relationships and their roles in CO2 capture and conversion. In this review, we provide a comprehensive account of significant progress in the design and synthesis of MOF-based materials, including MOFs, MOF composites and MOF derivatives, and their application to carbon capture and conversion. Special emphases on the relationships between CO2 capture capacities of MOF-based materials and their catalytic CO2 conversion performances are discussed.

Carbon capture and conversion using metal–organic frameworks and MOF-based materials

Metal–organic frameworks (MOFs), established as a relatively new class of crystalline porous materials with high surface area, structural diversity, and tailorability, attract extensive interest and exhibit a variety of applications, especially in catalysis. Their permanent porosity enables their inherent superiority in confining guest species, particularly small metal nanoparticles (MNPs), for improved catalytic performance and/or the expansion of reaction scope. This is a rapidly developing interdisciplinary research field. In this review, we provide an overview of significant progress in the development of MNP/MOF composites, including various preparation strategies and characterization methods as well as catalytic applications. Special emphasis is placed on synergistic effects between the two components that result in an enhanced performance in heterogeneous catalysis. Finally, the prospects of MNP/MOF composites in catalysis and remaining issues in this field have been indicated.

Metal–organic frameworks meet metal nanoparticles: synergistic effect for enhanced catalysis

More than 95% (in volume) of all of today’s chemical products are manufactured through catalytic processes, making research into more efficient catalytic materials a thrilling and very dynamic rese...

Metal–Organic Frameworks in Heterogeneous Catalysis: Recent Progress, New Trends, and Future Perspectives

Metal-organic frameworks (MOFs) are a class of distinctive porous crystalline materials constructed by metal ions/clusters and organic linkers. Owing to their structural diversity, functional adjustability, and high surface area, different types of MOF-based single metal sites are well exploited, including coordinately unsaturated metal sites from metal nodes and metallolinkers, as well as active metal species immobilized to MOFs. Furthermore, controllable thermal transformation of MOFs can upgrade them to nanomaterials functionalized with active single-atom catalysts (SACs). These unique features of MOFs and their derivatives enable them to serve as a highly versatile platform for catalysis, which has actually been becoming a rapidly developing interdisciplinary research area. In this review, we overview the recent developments of catalysis at single metal sites in MOF-based materials with emphasis on their structures and applications for thermocatalysis, electrocatalysis, and photocatalysis. We also compare the results and summarize the major insights gained from the works in this review, providing the challenges and prospects in this emerging field.

Metal-Organic Framework-Based Catalysts with Single Metal Sites.

A bifunctional imidazolium functionalized zirconium metal–organic framework (Zr-MOF), (I−)Meim-UiO-66 (2), was successfully prepared from the imidazole-containing Zr-MOF Im-UiO-66 (1) by a post-synthetic modification (PSM) method. It was found that the crystal size and pore features of the imidazole-containing 1 could be tuned at the nanoscale. The bifunctional MOF 2, containing Bronsted acid sites and iodide ions, was shown to be an efficient and recyclable heterogeneous catalyst for the cycloaddition of carbon dioxide (CO2) with epoxides, without the use of any co-catalyst, at ambient pressure. The solvent-free synthesis of the cyclic carbonate from CO2 and an epoxide was monitored by in situ Fourier transform infrared spectroscopy (FT-IR) and an acid/base synergistic catalysis mechanism was proposed. We hope that our strategy provides an effective approach for the introduction of functional N-heterocyclic groups into MOFs for potential applications.

https://pubs.rsc.org/en/Content/ArticlePDF/2017/SC/C6SC04357G

Postsynthetic ionization of an imidazole-containing metal–organic framework for the cycloaddition of carbon dioxide and epoxides

It is still a great challenge to achieve high selectivity of CH4 in CO2 electroreduction reactions (CO2 RR) because of the similar reduction potentials of possible products and the sluggish kinetics for CO2 activation. Stabilizing key reaction intermediates by single type of active sites supported on porous conductive material is crucial to achieve high selectivity for single product such as CH4 . Here, Cu2 O(111) quantum dots with an average size of 3.5 nm are in situ synthesized on a porous conductive copper-based metal-organic framework (CuHHTP), exhibiting high selectivity of 73 % towards CH4 with partial current density of 10.8 mA cm-2 at -1.4 V vs. RHE (reversible hydrogen electrode) in CO2 RR. Operando infrared spectroscopy and DFT calculations reveal that the key intermediates (such as *CH2 O and *OCH3 ) involved in the pathway of CH4 formation are stabilized by the single active Cu2 O(111) and hydrogen bonding, thus generating CH4 instead of CO.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.202085262

Highly Selective CO 2 Electroreduction to CH 4 by In Situ Generated Cu 2 O Single-Type Sites on a Conductive MOF: Stabilizing Key Intermediates with Hydrogen Bonding

Rui-Ping Chen

Papers

Postsynthetic ionization of an imidazole-containing metal–organic framework for the cycloaddition of carbon dioxide and epoxides

Highly Selective CO 2 Electroreduction to CH 4 by In Situ Generated Cu 2 O Single-Type Sites on a Conductive MOF: Stabilizing Key Intermediates with Hydrogen Bonding

Water-medium C–H activation over a hydrophobic perfluoroalkane-decorated metal-organic framework platform