Steering CO2 Electroreduction Selectivity U-Turn to Ethylene by Cu-Si Bonded Interface.

Copper (Cu), with the advantage of producing a deep reduction product, is a unique catalyst for the electrochemical reduction of CO2 (CO2RR). Designing a Cu-based catalyst to trigger CO2RR to a multicarbon product and understanding the accurate structure-activity relationship for elucidating reaction mechanisms still remain a challenge. Herein, we demonstrate a rational design of a core-shell structured silica-copper catalyst (p-Cu@m-SiO2) through Cu-Si direct bonding for efficient and selective CO2RR. The Cu-Si interface fulfills the inversion in CO2RR product selectivity. The product ratio of C2H4/CH4 changes from 0.6 to 14.4 after silica modification, and the current density reaches a high of up to 450 mA cm-2. The kinetic isotopic effect, in situ attenuated total reflection Fourier-transform infrared spectra, and density functional theory were applied to elucidate the reaction mechanism. The SiO2 shell stabilizes the *H intermediate by forming Si-O-H and inhibits the hydrogen evolution reaction effectively. Moreover, the direct-bonded Cu-Si interface makes bare Cu sites with larger charge density. Such bare Cu sites and Si-O-H sites stabilized the *CHO and activated the *CO, promoting the coupling of *CHO and *CO intermediates to form C2H4. This work provides a promising strategy for designing Cu-based catalysts with high C2H4 catalytic activity.

Boosting CO2 Electroreduction over a Covalent Organic Framework in the Presence of Oxygen.

Herein, we propose an oxygen-containing species coordination strategy to boost CO2 electroreduction in the presence of O2. A two-dimensional (2D) conjugated metal-covalent organic framework (MCOF), denoted as NiPc-Salen(Co)2-COF that is composed of the Ni-phthalocyanine (NiPc) unit with well-defined Ni-N4-O sites and the salen(Co)2 moiety with binuclear Co-N2O2 sites, is developed and synthesized for enhancing the CO2RR under aerobic condition. In the presence of O2, one of the Co sites in the NiPc-Salen(Co)2-COF that coordinated with the intermediate of *OOH from ORR could decrease the energy barrier of the activation of CO2 molecules and stabilize the key intermediate *COOH of the CO2RR over the adjacent Co center. Besides, the oxygen species axially coordinated Ni-N4-O sites can favor in reducing the energy barrier of the intermediate *COOH formation for the CO2RR. Thus, NiPc-Salen(Co)2-COF exhibits high oxygen-tolerant CO2RR performance and achieves outstanding CO Faradaic efficiency (FECO) of 97.2 % at -1.0 V vs. the reversible hydrogen electrode (RHE) and a high CO partial current density of 40.3 mA cm-2 at -1.1 V in the presence of 0.5 % O2, which is superior to that in pure CO2 feed gas (FECO=94.8 %, jCO=19.9 mA cm-2). Notably, the NiPc-Salen(Co)2-COF achieves an industrial-level current density of 128.3 mA cm-2 in the flow-cell reactor with 0.5 % O2 at -0.8 V, which is higher than that in pure CO2 atmosphere (jCO=104.8 mA cm-2). It is worth noting that an excellent FECO of 86.8 % is still achieved in the presence of 5 % O2 at -1.0 V. This work provides an effective strategy to enable the CO2RR under O2 atmosphere by utilizing the *OOH intermediates of ORR to boost CO2 electroreduction.

Photocoupled Electroreduction of CO2 over Photosensitizer-Decorated Covalent Organic Frameworks.

Introducing an external visible-light field would be a promising strategy to improve the activity of the electrocatalytic CO2 reduction reaction (CO2RR), but it still remains a challenge due to the short excited-state lifetime of active sites. Herein, Ru(bpy)3Cl2 struts as powerful photosensitive donors were immobilized into the backbones of Co-porphyrin-based covalent organic frameworks (named Co-Bpy-COF-Rux, x is the molar ratio of Ru and Co species, x = 1/2 and 2/3) via coordination bonds, for the photo-coupled CO2RR to produce CO. The optimal Co-Bpy-COF-Ru1/2 displays a high CO Faradaic efficiency of 96.7% at -0.7 V vs reversible hydrogen electrode (RHE) and a CO partial current density of 16.27 mA cm-2 at -1.1 V vs RHE under the assistance of light, both of which were far surpassing the values observed in the dark. The significantly enhanced activity is mainly attributed to the incorporation of a Ru(bpy)3Cl2 donor with long excited-state lifetime and concomitantly giant built-in electric field in Co-Bpy-COF-Ru1/2, which efficiently accelerate the photo-induced electron transfer from Ru(bpy)3Cl2 to the cobalt-porphyrin under the external light. Thus, the cobalt-porphyrin active sites have a longer excited-state lifetime to lower the rate-determining steps' energy occurring during the actual photo-coupled electrocatalytic CO2RR process. This is the first work of porphyrin-based COFs for photo-coupled CO2RR, opening a new frontier for the construction of efficient photo-coupled electrocatalysts.

Tandem Photocatalysis of CO2 to C2H4 via a Synergistic Rhenium-(I) Bipyridine/Copper-Porphyrinic Triazine Framework.

The photocatalytic conversion of CO2 into C2+ products such as ethylene is a promising path toward the carbon neutral goal but remains a big challenge due to the high activation barrier for CO2 and similar reduction potentials of many possible multi-electron-transfer products. Herein, an effective tandem photocatalysis strategy has been developed to support conversion of CO2 to ethylene by construction of the synergistic dual sites in rhenium-(I) bipyridine fac-[ReI(bpy)(CO)3Cl] (Re-bpy) and copper-porphyrinic triazine framework [PTF(Cu)]. With these two catalysts, a large amount of ethylene can be produced at a rate of 73.2 µmol g-1 h-1 under visible light irradiation. However, ethylene cannot be obtained from CO2 by use of either component of the Re-bpy or PTF(Cu) catalysts alone; with a single catalyst, only monocarbon product CO is produced under similar conditions. In the tandem photocatalytic system, the CO generated at the Re-bpy sites is adsorbed by the nearby Cu single sites in PTF(Cu), and this is followed by a synergistic C-C coupling process which ultimately produces ethylene. Density functional theory calculations demonstrate that the coupling process between PTF(Cu)-*CO and Re-bpy-*CO to form the key intermediate Re-bpy-*CO-*CO-PTF(Cu) is vital to the C2H4 production. This work provides a new pathway for the design of efficient photocatalysts for photoconversion of CO2 to C2 products via a tandem process driven by visible light under mild conditions.

Thermo-, Electro-, and Photocatalytic CO2 Conversion to Value-Added Products over Porous Metal/Covalent Organic Frameworks.

ConspectusThe continuing increase of the concentration of atmospheric CO2 has caused many environmental issues including climate change. Catalytic conversion of CO2 using thermochemical, electrochemical, and photochemical methods is a potential technique to decrease the CO2 concentration and simultaneously obtain value-added chemicals. Due to the high energy barrier of CO2 however, this method is still far from large-scale applications which requires high activity, selectivity, and stability. Therefore, development of efficient catalysts to convert CO2 to different products is urgent. With their well-engineered pores and chemical compositions, high surface area, elevated CO2 adsorption capability, and adjustable active sites, porous crystalline frameworks including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are potential materials for catalytic CO2 conversion. Here, we summarize our recent work on MOFs and COFs for thermocatalytic, electrocatalytic, and photocatalytic CO2 conversion and describe the structure-activity relationships that could guide the design of effective catalysts.The first section of this paper describes imidazolium-functionalized porous MOFs, including porous liquid and cationic MOFs with nucleophilic halogen ions, which can promote thermocatalytically CO2 cycloaddition reaction with epoxides toward cyclic carbonates at one bar pressure. A porous liquid MOF takes on the role of a CO2 reservoir to tackle the low local CO2 concentrations in gas-liquid-solid heterogeneous reactions. Imidazolium-functionalized MOFs with halogen ions for CO2 cycloaddition could avoid the use of cocatalysts, and this leads to milder and more facile experimental conditions and separation processes.In a section dealing with the electrocatalytic CO2 reduction reaction (CO2RR), we developed a series of conductive porous framework materials with fast electron transmission capabilities, which afford high current densities and outperform the traditional MOF and COF catalysts that have been reported. The intrinsically conductive two-dimensional 2D MOFs and COFs nanosheets based on the fully π-conjugated phthalocyanine motif with excellent electron transport capability were prepared, and strong electron transporters were also integrated into metalloporphyrin-based COFs for CO2RR. Cu2O quantum dots and Cu nanoparticles (NPs) can be uniformly dispersed on porous conductive MOFs/COFs to afford synergistic and/or tandem electrocatalysts, which can achieve highly selective production of CH4 or C2H4 in CO2RR.A third section describes our efforts to facilitate electron-hole separation in CO2 photocatalysis. Our focus is on regulation of coordination spheres in MOFs, fabrication of the architecture of MOF heterojunctions, and engineering MOF films to facilitate photocatalytic CO2 reduction.Finally, we discuss several problems associated with the studies of MOFs and COFs for CO2 conversion and consider some prospects of the fabrication of effective porous frameworks for CO2 adsorption and conversion.

Boosting Electroreduction of CO2 over Cationic Covalent Organic Frameworks: Hydrogen Bonding Effects of Halogen Ions.

We present the first example of charged imidazolium functionalized porphyrin-based covalent organic framework (Co-iBFBim-COF-X) for electrocatalytic CO2 reduction reaction, where the free anions (e.g., F- , Cl- , Br- , and I- ) of imidazolium ions nearby the active Co sites can stabilize the key intermediate *COOH and inhibit hydrogen evolution reaction. Thus, Co-iBFBim-COF-X exhibits higher activity than the neutral Co-BFBim-COF, following the trend of F-

Boosting CO2 Photoreduction via Regulating Charge Transfer Ability in a One-Dimensional Covalent Organic Framework.

Two-dimensional (2D) imine-based covalent organic frameworks (COFs) hold potential for photocatalytic CO2 reduction. However, high energy barrier of imine linkage impede the in-plane photoelectron transfer process, resulting in inadequate efficiency of CO2 photoreduction. Herein, we present a dimensionality induced local electronic modulation strategy through the construction of one-dimensional (1D) pyrene-based covalent organic frameworks (PyTTA-COF). The dual-chain-like edge architectures of 1D PyTTA-COF enable the stabilization of aromatic backbones, thus reducing energy loss during exciton dissociation and thermal relaxation, which provides energetic photoelectron to traverse the energy barrier of imine linkages. As a result, the 1D PyTTA-COF exhibits significantly enhanced CO2 photoreduction activity under visible-light irradiation when coordinated with metal cobalt ion, yielding a remarkable CO evolution of 1003 µmol g-1 over an 8-hour period, which surpasses that of the corresponding 2D counterpart by a factor of 59. These findings present a valuable approach to address in-plane charge transfer limitations in imine-based COFs.

Atomically Precise Copper Nanoclusters for Highly Efficient Electroreduction of CO2 towards Hydrocarbons via Breaking the Coordination Symmetry of Cu Site.

We propose an effective highest occupied d-orbital modulation strategy engendered by breaking the coordination symmetry of sites in the atomically precise Cu nanocluster (NC) to switch the product of CO2 electroreduction from HCOOH/CO to higher-valued hydrocarbons. An atomically well-defined Cu6 NC with symmetry-broken Cu-S2 N1 active sites (named Cu6 (MBD)6 , MBD=2-mercaptobenzimidazole) was designed and synthesized by a judicious choice of ligand containing both S and N coordination atoms. Different from the previously reported high HCOOH selectivity of Cu NCs with Cu-S3 sites, the Cu6 (MBD)6 with Cu-S2 N1 coordination structure shows a high Faradaic efficiency toward hydrocarbons of 65.5 % at -1.4 V versus the reversible hydrogen electrode (including 42.5 % CH4 and 23 % C2 H4 ), with the hydrocarbons partial current density of -183.4 mA cm-2 . Theoretical calculations reveal that the symmetry-broken Cu-S2 N1 sites can rearrange the Cu 3d orbitals with d x 2 - y 2 ${d_{x^2 - y^2 } }$ as the highest occupied d-orbital, thus favoring the generation of key intermediate *COOH instead of *OCHO to favor *CO formation, followed by hydrogenation and/or C-C coupling to produce hydrocarbons. This is the first attempt to regulate the coordination mode of Cu atom in Cu NCs for hydrocarbons generation, and provides new inspiration for designing atomically precise NCs for efficient CO2 RR towards highly-valued products.

A CO2 -Masked Carbene Functionalized Covalent Organic Framework for Highly Efficient Carbon Dioxide Conversion.

Free N-heterocyclic carbenes (NHCs) are generally prepared by treatment of imidazolium precursors with strong alkali reagents, which usually produces inactive NHC dimers. This treatment would destroy porous supports and thus make supported NHC catalysts difficult to recovery and reuse. Herein, we report the first stable CO2 -masked N-heterocyclic carbenes (NHCs) grafted on a porous crystalline covalent organic framework (COF). The stable NHC-CO2 moieties in the COF-NHC-CO2 could be transformed in situ into isolated NHCs by heating, which exhibit superior catalytic performances in hydrosilylation and N-formylation reactions with CO2 . The NHC sites can reversibly form NHC-CO2 and thus can be easily recycled and reused while maintaining excellent catalytic activity. Density functional theory calculations revealed that NHC sites can be fully exposed after removal of CO2 -masks and rapidly react with silanes, which endows COF-NHC with high catalytic activity.

Construction of Donor-Acceptor Heterojunctions in Covalent Organic Framework for Enhanced CO2 Electroreduction.

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 (CO2 RR). 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 CO2 RR 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 CO2 RR.

Self-Assembly of Imidazolium-Functionalized Zr-Based Metal-Organic Polyhedra for Catalytic Conversion of CO2 into Cyclic Carbonates.

Three cationic capsule-shaped Zr-based metal-organic polyhedra (MOPs) with different cavity sizes were successfully constructed through the self-assembly of trinuclear zirconocene clusters and imidazolium-functionalized dicarboxylic ligands. Owing to the imidazolium groups in the MOPs, they show good CO2 adsorption uptake. Moreover, the halogen anions of the imidazolium groups and Brønsted acid sites (-OH) in the Zr-based knots are in close proximity, making these MOPs able to catalyze synergistically the cycloaddition reaction of CO2 with epoxides into cyclic carbonates. This is the first report of using MOPs as catalysts for this reaction without the addition of a cocatalyst.

Highly Selective Tandem Electroreduction of CO2 to Ethylene over Atomically Isolated Nickel-Nitrogen Site/Copper Nanoparticle Catalysts.

Herein, an effective tandem catalysis strategy is developed to improve the selectivity of the CO2 RR towards C2 H4 by multiple distinct catalytic sites in local vicinity. An 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 CO2 RR to produce C2 H4 . The Faradaic efficiency of C2 H4 reaches 57.3 % at -1.1 V versus the reversible hydrogen electrode (RHE), which is about 6 times higher than the non-tandem catalyst PTF/Cu, which produces CH4 as the major carbon product. The operando infrared spectroscopy and theoretic density functional theory (DFT) calculations reveal that the local high concentration of CO generated by PTF(Ni) sites can facilitate the C-C coupling to form C2 H4 on the nearby Cu NP sites. The work offers an effective avenue to design electrocatalysts for the highly selective CO2 RR to produce multicarbon products via a tandem route.

Porous Metal-Organic Framework Liquids for Enhanced CO2 Adsorption and Catalytic Conversion.

The unique applications of porous metal-organic framework (MOF) liquids with permanent porosity and fluidity have attracted significant attention. However, fabrication of porous MOF liquids remains challenging because of the easy intermolecular self-filling of the cavity or the rapid settlement of porous hosts in hindered solvents that cannot enter their pores. Herein, we report a facile strategy for the fabrication of a MOF liquid (Im-UiO-PL) by surface ionization of an imidazolium-functionalized framework with a sterically hindered poly(ethylene glycol) sulfonate (PEGS) canopy. The Im-UiO-PL obtained in this way has a CO2 adsorption approximately 14 times larger than that of pure PEGS. Distinct from a porous MOF solid counterpart, the stored CO2 in Im-UiO-PL can be slowly released and efficiently utilized to synthesize cyclic carbonates in the atmosphere. This is the first example of the use of a porous MOF liquid as a CO2 storage material for catalysis. It offers a new method for the fabrication of unique porous liquid MOFs with functional behaviors in various fields of gas adsorption and catalysis.

Conductive Two-Dimensional Phthalocyanine-based Metal-Organic Framework Nanosheets for Efficient Electroreduction of CO2.

The electrocatalytic conversion of CO2 into value-added chemicals is a promising approach to realize a carbon-energy balance. However, low current density still limits the application of the CO2 electroreduction reaction (CO2 RR). Metal-organic frameworks (MOFs) are one class of promising alternatives for the CO2 RR due to their periodically arranged isolated metal active sites. However, the poor conductivity of traditional MOFs usually results in a low current density in CO2 RR. We have prepared conductive two-dimensional (2D) phthalocyanine-based MOF (NiPc-NiO4 ) nanosheets linked by nickel-catecholate, which can be employed as highly efficient electrocatalysts for the CO2 RR to CO. The obtained NiPc-NiO4 has a good conductivity and exhibited a very high selectivity of 98.4 % toward CO production and a large CO partial current density of 34.5 mA cm-2 , outperforming the reported MOF catalysts. This work highlights the potential of conductive crystalline frameworks in electrocatalysis.

Conductive Phthalocyanine-Based Covalent Organic Framework for Highly Efficient Electroreduction of Carbon Dioxide.

The electroreduction of CO2 to value-added chemicals such as CO is a promising approach to realize carbon-neutral energy cycle, but still remains big challenge including low current density. Covalent organic frameworks (COFs) with abundant accessible active single-sites can offer a bridge between homogeneous and heterogeneous electrocatalysis, but the low electrical conductivity limits their application for CO2 electroreduction reaction (CO2 RR). Here, a 2D conductive Ni-phthalocyanine-based COF, named NiPc-COF, is synthesized by condensation of 2,3,9,10,16,17,23,24-octa-aminophthalocyaninato Ni(II) and tert-butylpyrene-tetraone for highly efficient CO2 RR. Due to its highly intrinsic conductivity and accessible active sites, the robust conductive 2D NiPc-COF nanosheets exhibit very high CO selectivity (>93%) in a wide range of the applied potentials of -0.6 to -1.1 V versus the reversible hydrogen electrode (RHE) and large partial current density of 35 mA cm-2 at -1.1 V versus RHE in aqueous solution that surpasses all the conventional COF electrocatalysts. The robust NiPc-COF that is bridged by covalent pyrazine linkage can maintain its CO2 RR activity for 10 h. This work presents the implementation of the conductive COF nanosheets for CO2 RR and provides a strategy to enhance energy conversion efficiency in electrocatalysis.

Highly Selective CO2 Electroreduction to CH4 by In†Situ Generated Cu2 O Single-Type Sites on a Conductive MOF: Stabilizing Key Intermediates with Hydrogen Bonding.

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.

Encapsulation of Phosphotungstic Acid into Metal-Organic Frameworks with Tunable Window Sizes: Screening of PTA@MOF Catalysts for Efficient Oxidative Desulfurization.

Clean fuels with extremely low sulfur content are highly desirable due to environmental concerns. Herein, three water-stable and eco-friendly metal-organic frameworks with tunable window diameters, denoted as MOF-808X, have been employed as PTA solid supports. An array of PTA@MOF-808X composites were facilely synthesized via the encapsulation strategy. With tunable window sizes and adjustable PTA loading amounts, the obtained PTA@MOF-808X composites were screened for catalytic oxidative desulfurization (ODS) with H2O2 serving as oxidant. The experiments found that 42%PTA@MOF-808A had the highest catalytic ODS activity and could completely remove dibenzothiophene (DBT) in a model fuel with an initial sulfur content of 1000 ppm within 30 min, which falls far below the acceptable limits for fuel standards (10 ppm). Further investigations revealed that this high catalytic activity could be attributed to the cooperative catalysis of metal clusters in the host framework and the guest PTA molecules. Moreover, 42%PTA@MOF-808A could be facilely recovered and reused for at least five runs without loss of catalytic activity. Having a combination of eco-sustainability, high stability, high catalytic activity, and good recyclability, 42%PTA@MOF-808A therefore represents a new benchmark material for catalytic ODS and provides a new perspective for ultradeep desulfurization.

Zinc Porphyrin/Imidazolium Integrated Multivariate Zirconium Metal-Organic Frameworks for Transformation of CO2 into Cyclic Carbonates.

The design and synthesis of metal-organic frameworks (MOFs) enclosed with multiple catalytic active sites is favorable for cooperative catalysis, but is is still challenging. Herein, we developed a sequential postsynthetic ionization and metalation strategy to prepare bifunctional multivariate Zr-MOFs incorporating zinc porphyrin and imidazolium functionalities. Using this facile strategy, tetratopic [5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinato]zinc(II) (ZnTCPP) ligands were successfully installed into the cationic Zr-MOF to obtain ZnTCPP⊂(Br-)Etim-UiO-66. These MTV-MOFs, including TCPP⊂Im-UiO-66, TCPP⊂(Br-)Etim-UiO-66, and ZnTCPP⊂(Br-)Etim-UiO-66, were well characterized and used in CO2 capture and conversion into cyclic carbonate from allyl glycidyl ether and CO2 under cocatalyst-free and 1 bar CO2 pressure conditions. It was found that the structural features and CO2 affinity properties of these MTV-MOFs can be tuned by introducing imidazolium groups or doping zinc sites. Additionally, ZnTCPP⊂(Br-)Etim-UiO-66 exhibited enhanced catalytic activities compared to other MTV-MOFs herein for obtaining the 3-allyloxy-1,2-proplyene carbonate product, which was attributed to the cooperative effect of Zn2+ sites and Br- ions in this microporous ionic MTV-MOF. ZnTCPP⊂(Br-)Etim-UiO-66 can be recycled easily and used at least three times.

Multifunctional metal-organic framework catalysts: synergistic catalysis and tandem reactions.

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.

Soluble Metal-Nanoparticle-Decorated Porous Coordination Polymers for the Homogenization of Heterogeneous Catalysis.

Ultrasmall metal nanoparticles (MNPs) were decorated on soluble porous coordination polymers (PCPs) with high metal loadings. The solubility of the composite and the size of the MNPs can be controlled by varying the ratio of the precursors to the supports. The soluble PCPs can serve as a platform to homogenize heterogeneous MNPs catalysts, which exhibited excellent activity and recyclability in C-H activation and Suzuki reactions. This strategy combines the advantages of homogeneous and heterogeneous catalysis and may bring new inspiration to catalysis.