Biomass is increasingly used as a source of fuels and chemicals as a renewable alternative to fossil feedstocks. Cellulose, hemicellulose and lignin are converted into platform chemicals from which a ...large range of compounds are derived with different structures. These biomass transformation processes require the use of efficient and durable catalysts that should drive the selectivity of the process. This review focuses on the use of metal-organic frameworks (MOFs) and derivatives as catalysts for biomass conversion. After an introduction setting up the importance of the field and the MOF features that justify their prevalence as heterogeneous catalysts for liquid phase reactions, the two main parts of the review are the description of MOF synthesis and adaptation and coverage of the catalytic reactions involving biomass substrates organized according to the type of MOF. The last section summarizes the current state of the art and our outlook for the future development of the field.
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•Transition-metal based MOFs as electrocatalysts for OER are introduced.•Recent achievements of MOF-based materials for OER are discussed.•The perspectives for the future development ...of MOF-based materials for OER are shown.
Exploiting advanced electrocatalysts for oxygen evolution reaction (OER) is of vital importance for the development of metal-air batteries, fuel cells and water electrolyzers. Rational design and fabrication of electrocatalysts with high specific areas, abundant expose active sites, and porous structures is an effective approach to improve the electrocatalytic performances. Metal-organic frameworks (MOFs), an emerging class of porous crystalline materials, which possess large surface areas, high porosities, componential and structural diversity, has shown great potential as efficient OER electrocatalysts. This review focus on the recent progress of fabrication and utilization of transition metal (e.g., Fe, Co, and Ni) based MOF materials including pristine MOFs, MOF composites and their derivatives for OER. A variety of typical strategies, including synthetic designs, compositional, and structural modifications for activity improvement of the MOF-based materials in the OER are outlined and discussed. Based on the previous achievements, the current state of the art and the perspectives for the future development of the field are summarized.
Chirality is ubiquitous in nature and occurs at all length scales. The development of applications for chiral nanostructures is rising rapidly. With the recent achievements of atomically precise ...nanochemistry, total structures of ligand‐protected Au and other metal nanoclusters (NCs) are successfully obtained, and the origins of chirality are discovered to be associated with different parts of the cluster, including the surface ligands (e.g., swirl patterns), the organic–inorganic interface (e.g., helical stripes), and the kernel. Herein, a unified picture of metal–ligand surface bonding‐induced chirality for the nanoclusters is proposed. The different bonding modes of M–X (where M = metal and X = the binding atom of ligand) lead to different surface structures on nanoclusters, which in turn give rise to various characteristic features of chirality. A comparison of Au–thiolate NCs with Au–phosphine ones further reveals the important roles of surface bonding. Compared to the Au–thiolate NCs, the Ag/Cu/Cd–thiolate systems exhibit different coordination modes between the metal and the thiolate. Other than thiolate and phosphine ligands, alkynyls are also briefly discussed. Several methods of obtaining chiroptically active nanoclusters are introduced, such as enantioseparation by high‐performance liquid chromatography and enantioselective synthesis. Future perspectives on chiral NCs are also proposed.
Atomically precise, ligand‐protected metal nanoclusters provide an excellent opportunity to reveal that chirality is intrinsic and “outside‐in.” A unified picture of metal–ligand surface bonding‐induced chirality is provided; that is, the Aun(SR)n+1 staple motifs, Agn(SR)m mount motifs, and even the whole Ag‐SR cage are responsible for the chirality in Au‐SR and Ag‐SR nanoclusters.
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•A summary of synthetic strategies for the functionalization of MOFs.•Design of functional MOF catalysts to achieve fast diffusion rate, substrate accumulation/pre-activation, active ...site modification, cooperative multisite catalysis, and excellent stability/reusability.•The challenges and opportunities of functional MOFs for catalysis.
Metal–organic frameworks (MOFs), have received great attention for catalytic applications, which are regarded to combine the advantages of homogeneous and heterogeneous catalysis. The control of pore structure, adsorption properties, and the nature of active sites and co-active sites of MOF-based materials is of vital importance for the catalytic performance. In this review, we summarize recent progress achieved in the functionalization of MOFs through modification of inorganic nodes and organic linkers, encapsulation of active species in their pore/matrices, and coating with functional materials. We further focus on the design of functional MOFs for advanced catalysis to achieve fast substrate diffusion, substrate accumulation/pre-activation, active site modification, multifunctional sites for cooperative catalysis, and high stability/reusability. Finally, possible future development of functional MOF catalysts towards practical application is presented.
Gas adsorption experiments have been carried out on a zinc benzenetribenzoate metal−organic framework material, MOF-177. Hydrogen adsorption on MOF-177 at 298 K and 10 MPa gives an adsorption ...capacity of ∼0.62 wt %, which is among the highest hydrogen storage capacities reported in porous materials at ambient temperatures. The heats of adsorption for H2 on MOF-177 were −11.3 to −5.8 kJ/mol. By adding a H2 dissociating catalyst and using our bridge building technique to build carbon bridges for hydrogen spillover, the hydrogen adsorption capacity in MOF-177 was enhanced by a factor of ∼2.5, to 1.5 wt % at 298 K and 10 MPa, and the adsorption was reversible. N2 and O2 adsorption measurements showed that O2 was adsorbed more favorably than N2 on MOF-177 with a selectivity of ∼1.8 at 1 atm and 298 K, which makes MOF-177 a promising candidate for air separation. The isotherm was linear for O2 while being concave for N2. Water vapor adsorption studies indicated that MOF-177 adsorbed up to ∼10 wt % H2O at 298 K. The framework structure of MOF-177 was not stable upon H2O adsorption, which decomposed after exposure to ambient air in 3 days. All the results suggested that MOF-177 could be a potentially promising material for gas separation and storage applications at ambient temperature (under dry conditions or with predrying).
A novel MOF-derived metallic cobalt-based catalyst is developed for chemoselective hydrogenation of substituted nitroarenes. A broad range of substituted nitroarenes are converted to the ...corresponding anilines in 93–99% yields under industrially viable conditions with other reducible groups remaining intact.
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•Co/C–N was prepared by simple pyrolysis of MOFs.•Nitroarenes are converted to anilines with other reducing groups remaining intact.•Co-N centers present in the catalyst lead to the unique chemoselectivity.•The reaction showed a first-order dependence on H2 pressure.
The synthesis, characterization, and application of nitrogen-doped carbon supported Co catalysts in selective hydrogenation of nitroarenes are described. The cobalt-based catalysts are prepared by simple pyrolysis of ZIF-67, a typical MOF material, under inert atmosphere. Physicochemical properties of the Co/C–N catalysts have been investigated by X-ray diffraction, elemental analysis, atomic absorption spectroscopy, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The Co-based materials were found to be highly efficient in the chemoselective hydrogenation of nitroarenes. A broad range of substituted nitroarenes are converted to the corresponding anilines in excellent yields under industrially viable conditions with other reducing groups remaining intact. In situ ATR-IR and XPS characterizations reveal that the Co-N centers present in the catalyst favor the preferential adsorption of nitro groups, leading to this unique chemoselectivity. The kinetic parameters of 4-nitrostyrene hydrogenation over the Co/C–N catalyst were investigated.
Hollow yolk–shell nanoreactors are of great interest in heterogeneous catalysis owing to their improved mass transfer ability and stability. Here, we report a facile and straight route to synthesize ...a highly efficient and recyclable yolk–shell Co@C–N nanoreactor with controllable properties by the direct thermolysis of a hollow Zn/Co-ZIF precursor. Based on systematical optimization of the pyrolysis temperature and the shell-thickness of Zn/Co-ZIFs, we could completely anchor and stabilize uniform Co nanoparticles (NPs) in the hollow yolk, accommodated by the Co-ZIF derived N-doped carbon nanosheets. This nanosheet-assembled yolk was further confined by a permeable and robust N-doped carbon (C–N) shell to protect the Co NPs against leaching and also enabled the reaction to take place in the hollow void. Consequently, the optimal yolk–shell Co@C–N nanoreactor showed a significantly enhanced catalytic activity for the aqueous oxidation of alcohols, yielding >99% conversion under atmospheric air and base-free conditions, which was much higher than that of the solid counterparts derived from pure ZIF-67 and solid core–shell ZIF-67@ZIF-8 precursors (with 14% and 59% conversion under the same reaction condition, respectively). The enhanced catalytic activity should be attributed to the yolk–shell structure that could facilitate the transport of reactant/product and the strong interaction between the Co NPs and N-doped carbon nanosheet to afford positive synergistic effects. Moreover, this catalyst also showed good recyclability, magnetically reusability, and general applicability for a broad substrate scope, further highlighting the structure superiority of our yolk–shell nanoreactor. This strategy might open an avenue to synthesize various hollow yolk–shell nanoreactors with controllable structures and enhanced catalytic performances.
Conspectus Ultrasmall metal nanoparticles (often called nanoclusters) possess unique geometrical structures and novel functionalities that are not accessible in conventional nanoparticles. Recent ...progress in their synthesis and structural determination by X-ray crystallography has led to deep understanding of the structural evolution, structure–property correlation, and growth modes, such as the layer-by-layer growth in face-centered cubic (fcc)-type nanoclusters, linear assembly of vertex-shared icosahedral units, and other unique modes. The enriched knowledge on the correlation between the structure and the properties has rendered metal nanoclusters a new class of functional nanomaterials. Despite the significant achievements in structural determinations, mapping out the structure–property correlation is still very challenging because of the core–shell structures of nanoclusters (e.g., Au n (SR) m protected by thiolate ligands) with metal atoms partitioned between the core and the shell. In such structures, the core and the surface are entangled and cannot be separately studied because changing the core structure would inevitably change the surface (or vice versa). Thus, it is of great importance to develop the “tailoring” chemistry for structural modification of the core (or surface) while retaining the other parts, in order to achieve fundamental understanding of what part of the nanocluster structure plays what role in the functionalities. In this Account, we summarize some recent work on the strategies to control the atomic structures of metal nanoclusters for tuning their properties, such as stability, optical absorption, excited-state electron dynamics, and photoluminescence, as well as their catalytic reactivity. The development of a ligand-based strategy has permitted the synthesis of structural isomers of nanoclusters with the same size but different functionalities. Successful modification of the core (or surface) structure while maintaining the other components has led us to gain some fundamental understanding of the respective roles of the core and the surface in the nanocluster functionalities. Such “tailoring” chemistry on metal nanoclusters can provide a strong basis for functional nanomaterials consisting of nanocluster components with desired properties. Further development of the tailoring chemistry will guide materials chemists to new directions and tailor-made functional nanomaterials for specific applications.
A novel synthesis strategy is developed to encapsulate palladium precursors through ligand design prior to MOF assembly, achieving uniformly distributed palladium NPs inside the cavities of MOFs. ...This strategy can avoid the different diffusion resistance between external and internal surfaces, and thus allow metal precursors to be easily deposited into the pores and evenly distributed within MOF networks. The embedded Pd NPs exhibited excellent shape-selectivity in olefin hydrogenation, as well as high catalytic efficiencies in aerobic oxidation of alcohols and reduction of nitrobenzene, showing significantly enhanced catalytic activity and stability as compared to those synthesized using a traditional impregnation method. The superior catalytic activity and stability came from the synergetic effects of nano-confinement and electron-donation offered by the MOF framework.
The direct oxidation of alcohols to esters with molecular oxygen is an attractive and crucial process for the synthesis of fine chemicals. To date, the heterogeneous catalyst systems that have been ...identified are based on noble metals or have required the addition of base additives. Here, we show that Co nanoparticles embedded in nitrogen-doped graphite catalyze the aerobic oxidation of alcohols to esters at room temperature under base-free and atmospheric conditions. Our Co@C-N catalytic system features a broad substrate scope for aromatic and aliphatic alcohols as well as diols, giving their corresponding esters in good to excellent yields. This apparently environmentally benign process provides a new strategy with which to achieve selective oxidation of alcohols.
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