The conversion of the biomass into eco-friendly fuels and chemicals has been extensively recognized as the essential pathway to achieve the sustainable economy and carbon neutral society. Lignin, as a kind of promising biomass energy, has been certified to produce the high-valued chemicals and fuels. Numerous efforts have been made to develop various catalysts for lignin catalytic conversion. Both metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) belong to very important heterogeneous porous catalysts due to their regular porous structures, high specific surface area, and precisely tailored diversities. In the review, the first part focused on the catalytic conversion of lignin, lignin model compounds, and lignin derivatives using the pristine MOFs, functional MOF composites, and MOF-derived materials. The second part summarized the catalytic conversion of lignin model compounds using pristine COFs and functional COF composites. The review here mainly concentrated on the design of the materials, screening of catalytic conditions, and explorations of the corresponded mechanisms. Specifically, (1) we summarized the MOF- and COF-based materials for the effects on the catalytic transformation of lignin-related substances; (2) we emphasized the catalytic mechanism of C–C and C–O bonds cleavage together with the structure–activity relationships; (3) we in-depth realized the relationship between the chemical/electronic/structural properties of the MOF- and COF-based catalysts and their catalytic performance for lignin-related substances. Finally, the challenges and future perspectives were also discussed on the catalytic conversion of lignin-related substances by MOF- and COF-based catalysts.

The performance applications (e.g., photocatalysis) of zirconium (Zr) and hafnium (Hf) based complexes are greatly hindered by the limited development of their structures and the relatively inert metal reactivity. In this work, we constructed two ultrastable Zr/Hf-based clusters (Zr-9-TC4A and Hf-9-TC4A) using hydrophobic 4-tert-butylthiacalix[4]arene (H(4)TC4A) ligands, in which unsaturated coordinated sulfur (S) atoms on the TC4A(4-) ligand can generate strong metal-ligand synergy with nearby active metal Zr/Hf sites. As a result, these two functionalized H(4)TC4A ligands modified Zr/Hf-oxo clusters, as catalysts for the amine oxidation reaction, exhibited excellent catalytic activity, achieving very high substrate conversion (>99%) and product selectivity (>90%). Combining comparative experiments and theoretical calculations, we found that these Zr/Hf-based cluster catalysts accomplish efficient amine oxidation reactions through synergistic effect between metals and ligands: (i) The photocatalytic benzylamine (BA) oxidation reaction was achieved by the synergistic effect of the dual active sites, in which, the naked S sites on the TC4A(4-) ligand oxidize the BA by photogenerated hole and oxygen molecules are reduced by photogenerated electrons on the metal active sites; (ii) in the aniline oxidation reaction, aniline was adsorbed by the bare S sites on ligands to be closer to metal active sites and then oxidized by the oxygen-containing radicals activated by the metal sites, thus completing the catalytic reaction under the synergistic catalytic effect of the proximity metal-ligand. In this work, the Zr/Hf-based complexes applied in the oxidation of organic amines have been realized using active S atom-directed metal-ligand synergistic catalysis and have demonstrated very high reactivity. (c) 2023 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.

Well-defined crystalline coordination compound catalysts have showcased distinct advantages in the regulation of the species and selectivity of electrocatalytic CO2 reduction products. However, the systematic study of the crystal-facet effect of crystalline coordination compounds on the performance of electrocatalytic CO2 reduction has not yet been reported. Herein, a stable hexanuclear copper cluster (Cu6) catalyst model system is designed and synthesized. By effectively regulating the growth size (micro-nano size) and morphology of the Cu6 single crystal, Cu6(P) with the main (100) facet, Cu6(H) with the main (100) and (001) facets, and Cu6(S) with the main (001) facet are obtained. From Cu6(P) via Cu6(H) to Cu6(S), there is a shift from the predominantly exposed (100) facet (involving two non-adjacent active Cu sites) to the (001) facet (involving three adjacent active Cu sites), which directly affects the adsorption direction of the key *CO intermediate and the potential of C-C coupling, thus enabling effective regulation of the selectivity of C1 (CO and CH4) and C2 (C2H4) reduction products. This work provides an essential molecular model system and a novel design perspective for the systematic study of the crystal-facet effect of coordination compounds on the species and selectivity of CO2 reduction reaction products.

Designing and synthesizing well-defined crystalline catalysts for long-term electrocatalytic conversion of CO2 to specific products remain a great challenge. In this work, two very stable crystalline bismuth oxygen clusters functionalized by hydrophobic p-tert-butylthiacalix[4]arene ligand, Bi-3 and Bi-14, were constructed and treated as catalysts for efficient electrochemical CO2 reduction. Sandwich-type Bi-3 with synergistic bi-bismuth exhibits a remarkable performance for CO2-to-HCOOH conversion with a faradaic efficiency (FEHCOOH) of 96.47% at -1.3 V (vs reversible hydrogen electrode) and durability over 27.5 h, while rodlike Bi-14 with a monobismuth active site reached a maximum FEHCOOH of 92.76% at -1.2 V with durability over 23.9 h. Density functional theory calculation proves that adjacent double active bismuth atoms in Bi-3 are more beneficial to stabilize the *OCHO intermediate and then promote the electrocatalytic reduction of CO2 to HCOOH than Bi-14 with a single active site. This work represents the report of stable crystalline bismuth-oxo cluster catalysts for specific electrocatalytic CO2 reduction conversion.

Mimicking natural photosynthesis to convert CO 2 with H 2 O into value-added fuels achieving overall reaction is a promising way to reduce the atmospheric CO 2 level. Casting the catalyst of two or more catalytic sites with rapid electron transfer and interaction may be an effective strategy for coupling photocatalytic CO 2 reduction and H 2 O oxidation. Herein, based on the MOF ∪ COF collaboration, we have carefully designed and synthesized a crystalline hetero-metallic cluster catalyst denoted MCOF-Ti 6 Cu 3 with spatial separation and functional cooperation between oxidative and reductive clusters. It utilizes dynamic covalent bonds between clusters to promote photo-induced charge separation and transfer efficiency, to drive both the photocatalytic oxidative and reductive reactions. MCOF-Ti 6 Cu 3 exhibits fine activity in the conversion of CO 2 with water into HCOOH (169.8 μmol g −1 h −1 ). Remarkably, experiments and theoretical calculations reveal that photo-excited electrons are transferred from Ti to Cu, indicating that the Cu cluster is the catalytic reduction center.

Structural exploration and functional application of thorium clusters are still very rare on account of their difficult synthesis caused by the susceptible hydrolysis of thorium element. In this work, we elaborately designed and constructed four stable thorium clusters modified with different functionalized capping ligands, Th6-MA, Th6-BEN, Th6-C8A, and Th6-Fcc, which possessed nearly the same hexanuclear thorium-oxo core but different capabilities in light absorption and charge separation. Consequently, for the first time, these new thorium clusters were treated as model catalysts to systematically investigate the light-induced oxidative coupling reaction of benzylamine and thermodriven oxidation of aniline, achieving >90% product selectivity and approximately 100% conversion, respectively. Concurrently, we found that thorium clusters modified by switchable functional ligands can effectively modulate the selectivity and conversion of catalytic reaction products. Moreover, catalytic characterization and density functional theory calculations consistently indicated that these thorium clusters can activate O2/H2O2 to generate active intermediates O2·-/HOO· and then improved the conversion of amines efficiently. Significantly, this work represents the first report of stable thorium clusters applied to photo/thermotriggered catalytic reactions and puts forward a new design avenue for the construction of more efficient thorium cluster catalysts.

A series of metalloporphyrin based electrocatalysts with efficient CO2-to-CH4electroreduction properties have been facilely synthesized and relative direct-bonding interactions have been intensively studied.

Photo- or electroreduction of carbon dioxide into highly valued products offers a promising strategy to achieve carbon neutrality. Here, a series of polyoxometalate-based metal-organic frameworks (M-POMOFs) were constructed by metalloporphyrins [tetrakis(4-carboxyphenyl)-porphyrin-M (M-TCPPs)] and reductive POM for photo- and electrocatalytic carbon dioxide reductions (PCR and ECR, respectively), and the mysteries between the roles of single metal site and cluster in catalysis were disclosed. Iron-POMOF exhibited an excellent selectivity (97.2%) with high methane production of 922 micromoles per gram in PCR, together with superior Faradaic efficiency for carbon dioxide to carbon monoxide (92.1%) in ECR. The underlying mechanisms were further clarified. Photogenerated electrons transferred from iron-TCPP to the POM cluster for methane generation under irradiation, while the abundant electrons flowed to the center of iron-TCPP for carbon monoxide formation under the applied electric field. The specific multielectron products generated on iron-POMOF through switching driving forces to control electron flow direction between single metal site and cluster catalysis.

Hybrid CO 2 electroreduction (HCER) is recognized as an important strategy to improve the total value of redox products and energy conversion efficiency. In this work, a coordination catalyst model system (Ni 8 -TET with active oxidation sites, Ni-TPP with active reduction sites and PCN-601 with redox-active sites) for HCER was established for the first time. Especially, PCN-601 can complete both anodic methanol oxidation and cathodic CO 2 reduction with FE HCOOH and FE CO over 90 %. The performance can be further improved with light irradiation (FE nearly 100 %). DFT calculations reveal that the transfer of electrons from Ni II 8 clusters to metalloporphyrins under electric fields results in the raised oxidizability of Ni 8 clusters and the raised reducibility of metalloporphyrin, which then improves the electrocatalytic performance. This work serves as a well-defined model system and puts forward a new design idea for establishing efficient catalysts for hybrid CO 2 electroreduction.

In the electrochemical CO2 reduction reaction (CO2 RR), it is challenging to develop a stable, well-defined catalyst model system that is able to examine the influence of the synergistic effect between adjacent catalytic active sites on the selective generation of C1 or C2 products. We have designed and synthesized a stable crystalline single-chain catalyst model system for electrochemical CO2 RR, which involves four homomorphic one-dimensional chain-like compounds (Cu-PzH, Cu-PzCl, Cu-PzBr, and Cu-PzI). The main structural difference of these four chains is the substituents of halogen atoms with different electronegativity on the Pz ligands. Consequently, different synergistic effects between bi-copper centers lead to changes in the faradic efficiency (FE CH 4 :FE C 2 H 4 ). This work provides a simple and stable crystalline single-chain model system for systematically studying the influence of coordination microenvironment on catalytically active centers in the CO2 RR.

Metal–organic frameworks (MOFs), constructed from metal clusters/ions and organic ligands, are ideal materials for photo/electrocatalysis, mainly due to the advantages of large surface areas, high porosity, and easily tunable optical and electronic structures. Herein, the recent and important advances on MOF‐based photo/electrocatalysts including pristine MOFs, MOF composites, and MOF derivatives are summarized. The novel strategies to improve the photo/electrocatalytic performances are highlighted. Finally, the current challenges and future development of MOFs for photo/electrocatalysis are discussed ad outlined.

Two isostructural MOFs with coordination of different halogen ions (Cl- and Br-), namely NNU-17 and NNU-18, were utilized to reveal the influence of different electron-withdrawing halogen anions on ECR performance. The performance difference between them mainly originates from the different abilities of adsorption and activation of CO2 by halogen ions.