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.

It is still a great challenge to achieve high selectivity of CH4 in CO2 electroreduction reactions (CO2RR) 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, Cu2O(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 CO2RR. Operando infrared spectroscopy and DFT calculations reveal that the key intermediates (such as *CH2O and *OCH3) involved in the pathway of CH4 formation are stabilized by the single active Cu2O(111) and hydrogen bonding, thus generating CH4 instead of CO.

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A bifunctional imidazolium functionalized Zr-based metal–organic framework, (I–)Meim-UiO-66, was successfully prepared, which can serve as an efficient heterogeneous catalyst towards the capture and coupling of CO2 with epoxides.

The rational design of highly efficient, low-cost, and durable electrocatalysts to replace platinum-based electrodes for oxygen reduction reaction (ORR) is highly desirable. Although atomically dispersed supported metal catalysts often exhibit excellent catalytic performance with maximized atom efficiency, the fabrication of single-atom catalysts remains a great challenge because of their easy aggregation. Herein, a simple ionothermal method was developed to fabricate atomically dispersed Fe−N x species on porous porphyrinic triazine-based frameworks (FeSAs/PTF) with high Fe loading up to 8.3 wt %, resulting in highly reactive and stable single-atom ORR catalysts for the first time. Owing to the high density of single-atom Fe−N 4 active sites, highly hierarchical porosity, and good conductivity, the as-prepared catalyst FeSAs/PTF-600 exhibited highly efficient activity, methanol tolerance, and superstability for oxygen reduction reaction (ORR) under both alkaline and acidic conditions. This work will bring new inspiration to the design of highly efficient noble-metal-free catalysts at the atomic scale for energy conversion.

The electrocatalytic conversion of CO 2 into valueadded chemicals is apromising approach to realize ac arbonenergy balance.H owever,l ow current density still limits the application of the CO 2 electroreduction reaction (CO 2 RR). Metal-organic frameworks (MOFs) are one class of promising alternatives for the CO 2 RR due to their periodically arranged isolated metal active sites.H owever,t he poor conductivity of traditional MOFs usually results in al ow current density in CO 2 RR. We have prepared conductive two-dimensional (2D) phthalocyanine-based MOF (NiPc-NiO 4 )n anosheets linked by nickel-catecholate,w hichc an be employed as highly efficient electrocatalysts for the CO 2 RR to CO.T he obtained NiPc-NiO 4 has ag ood conductivity and exhibited av ery high selectivity of 98.4 %t oward CO production and al arge CO partial current density of 34.5 mA cm À2 ,o utperforming the reported MOF catalysts.T his work highlights the potential of conductive crystalline frameworks in electrocatalysis.

Herein, an effective tandem catalysis strategy is developed to improve the selectivity of the CO 2 RR towards C 2 H 4 by multiple distinct catalytic sites in local vicinity.A n earth-abundant elements-based tandem electrocatalyst PTF-(Ni)/Cu is constructed by uniformly dispersing Cu nanoparticles (NPs) on the porphyrinic triazine framework anchored with atomically isolated nickel-nitrogen sites (PTF(Ni)) for the enhanced CO 2 RR to produce C 2 H 4 .T he Faradaic efficiency of C 2 H 4 reaches 57.3 %a tÀ1.1 Vv ersus the reversible hydrogen electrode (RHE), whichi sa bout 6t imes higher than the non-tandem catalyst PTF/Cu, whichproduces CH 4 as the major carbon product. The operando infrared spectroscopya nd theoretic density functional theory (DFT) calculations reveal that the local high concentration of CO generated by PTF(Ni)s ites can facilitate the CÀCc oupling to form C 2 H 4 on the nearby Cu NP sites.T he work offers an effective avenue to design electrocatalysts for the highly selective CO 2 RR to produce multicarbon products via atandem route.

Covalent organic frameworks (COFs) are promising candidates for electrocatalytic reduction of carbon dioxide into valuable chemicals due to their porous crystalline structures and tunable single active sites, but the low conductivity leads to unmet current densities for commercial application. The challenge is to create conductive COFs for highly efficient electrocatalysis of carbon dioxide reduction reaction (CO2RR). Herein, a porphyrin‐based COF containing donor–acceptor (D–A) heterojunctions, termed TT‐Por(Co)‐COF, is constructed from thieno[3,2‐b]thiophene‐2,5‐dicarbaldehyde (TT) and 5,10,15,20‐tetrakis(4‐aminophenyl)‐porphinatocobalt (Co‐TAPP) via imine condensation reaction. Compared with COF‐366‐Co without TT, TT‐Por(Co)‐COF displays enhanced CO2RR performance to produce CO due to its favorable charge transfer capability from the electron donor TT moieties to the acceptor Co‐porphyrin ring active center. The combination of strong charge transfer properties and enormous amount of accessible active sites in the 2D TT‐Por(Co)‐COF nanosheets results in good catalytic performance with a high Faradaic efficiency of CO (91.4%, −0.6 V vs reversible hydrogen electrode (RHE) and larger partial current density of 7.28 mA cm−2 at −0.7 V versus RHE in aqueous solution. The results demonstrate that integration of D–A heterojunctions in COF can facilitate the intramolecular electron transfer, and generate high current densities for CO2RR.