Bing An

Confinement of Ultrasmall Cu/ZnOx Nanoparticles in Metal–Organic Frameworks for Selective Methanol Synthesis from Catalytic Hydrogenation of CO2

The interfaces of Cu/ZnO and Cu/ZrO2 play vital roles in the hydrogenation of CO2 to methanol by these composite catalysts. Surface structural reorganization and particle growth during catalysis deleteriously reduce these active interfaces, diminishing both catalytic activities and MeOH selectivities. Here we report the use of preassembled bpy and Zr6(μ3-O)4(μ3-OH)4 sites in UiO-bpy metal-organic frameworks (MOFs) to anchor ultrasmall Cu/ZnOx nanoparticles, thus preventing the agglomeration of Cu NPs and phase separation between Cu and ZnOx in MOF-cavity-confined Cu/ZnOx nanoparticles. The resultant Cu/ZnOx@MOF catalysts show very high activity with a space-time yield of up to 2.59 gMeOH kgCu-1 h-1, 100% selectivity for CO2 hydrogenation to methanol, and high stability over 100 h. These new types of strong metal-support interactions between metallic nanoparticles and organic chelates/metal-oxo clusters offer new opportunities in fine-tuning catalytic activities and selectivities of metal nanoparticles@MOFs.

Networking Pyrolyzed Zeolitic Imidazolate Frameworks by Carbon Nanotubes Improves Conductivity and Enhances Oxygen‐Reduction Performance in Polymer‐Electrolyte‐Membrane Fuel Cells

A high-performance nonprecious-metal oxygen-reduction electrocatalyst is prepared via in situ growth of bimetallic zeolitic imidazolate frameworks on multiwalled carbon nanotubes (CNTs) followed by adsorption of furfuryl alcohol and pyrolysis. The networking boosts the conductivity and performance in a polymer electrolyte membrane fuel cell, yielding a maximal power density of 820 mW cm-2 .

Surface Modification of Two-Dimensional Metal-Organic Layers Creates Biomimetic Catalytic Microenvironments for Selective Oxidation

Microenvironments in enzymes play crucial roles in controlling the activities and selectivities of reaction centers. Herein we report the tuning of the catalytic microenvironments of metal-organic layers (MOLs), a two-dimensional version of metal-organic frameworks (MOFs) with thickness down to a monolayer, to control product selectivities. By modifying the secondary building units (SBUs) of MOLs with monocarboxylic acids, such as gluconic acid, we changed the hydrophobicity/hydrophilicity around the active sites and fine-tuned the selectivity in photocatalytic oxidation of tetrahydrofuran (THF) to exclusively afford butyrolactone (BTL), likely a result of prolonging the residence time of reaction intermediates in the hydrophilic microenvironment of catalytic centers. Our work highlights new opportunities in using functional MOLs as highly tunable and selective two-dimensional catalytic materials.

Sulfur-doping achieves efficient oxygen reduction in pyrolyzed zeolitic imidazolate frameworks

We report the first synthesis of sulfurated porous carbon materials with well-defined morphologies and uniform N/S distributions via pyrolysis of zeolitic imidazolate frameworks loaded with sulfur-containing molecules. The optimized sulfurated catalyst demonstrates excellent electrocatalytic activity for the oxygen reduction reaction (ORR) in both acid and alkaline media. The sulfurization process under optimized conditions can lower the ORR over-potential by ca. 170 mV at 3 mA cm−2, giving a non-precious metal catalyst with an onset ORR potential of 0.90 V (vs. RHE, similarly hereinafter)/half-wave potential of 0.78 V in 0.1 M HClO4 and an onset ORR potential of 0.98 V/half-wave potential of 0.88 V in 0.1 M KOH. Furthermore, the S-doped porous carbon materials perform better in the long-term durability test than the non-S-doped samples and standard commercially available Pt/C. We also discuss different sulfuration methods for the ZIF system, morphologies of pyrolyzed samples, and catalytically active sites.

Metal–Organic Frameworks Stabilize Mono(phosphine)–Metal Complexes for Broad-Scope Catalytic Reactions

Mono(phosphine)-M (M-PR3; M = Rh and Ir) complexes selectively prepared by postsynthetic metalation of a porous triarylphosphine-based metal-organic framework (MOF) exhibited excellent activity in the hydrosilylation of ketones and alkenes, the hydrogenation of alkenes, and the C-H borylation of arenes. The recyclable and reusable MOF catalysts significantly outperformed their homogeneous counterparts, presumably via stabilizing M-PR3 intermediates by preventing deleterious disproportionation reactions/ligand exchanges in the catalytic cycles.

Molecular Iridium Complexes in Metal–Organic Frameworks Catalyze CO2 Hydrogenation via Concerted Proton and Hydride Transfer

Molecular iridium catalysts immobilized in metal-organic frameworks (MOFs) were positioned in the condensing chamber of a Soxhlet extractor for efficient CO2 hydrogenation. Droplets of hot water seeped through the MOF catalyst to create dynamic gas/liquid interfaces which maximize the contact of CO2, H2, H2O, and the catalyst to achieve a high turnover frequency of 410 h-1 under atmospheric pressure and at 85 °C. H/D kinetic isotope effect measurements and density functional theory calculations revealed concerted proton-hydride transfer in the rate-determining step of CO2 hydrogenation, which was difficult to unravel in homogeneous reactions due to base-catalyzed H/D exchange.

Warm-White-Light-Emitting Diode Based on a Dye-Loaded Metal–Organic Framework for Fast White-Light Communication

A dye@metal-organic framework (MOF) hybrid was used as a fluorophore in a white-light-emitting diode (WLED) for fast visible-light communication (VLC). The white light was generated from a combination of blue emission of the 9,10-dibenzoate anthracene (DBA) linkers and yellow emission of the encapsulated Rhodamine B molecules. The MOF structure not only prevents dye molecules from aggregation-induced quenching but also efficiently transfers energy to the dye for dual emission. This light-emitting material shows emission lifetimes of 1.8 and 5.3 ns for the blue and yellow components, respectively, which are significantly shorter than the 200 ns lifetime of Y3Al5O12:Ce3+ in commercial WLEDs. The MOF-WLED device exhibited a modulating frequency of 3.6 MHz for VLC, six times that of commercial WLEDs.

Pyrolysis of metal–organic frameworks to hierarchical porous Cu/Zn-nanoparticle@carbon materials for efficient CO2 hydrogenation

Conversion of CO2 to CO via hydrogenation, also known as the reverse water-gas shift (RWGS) reaction, is an important chemical process to generate CO as a platform chemical for further conversions. Metallic Cu catalyses the RWGS reaction at a temperature of 500 °C with a high initial turnover frequency, but surface structural reorganization and particle growth at the reaction temperature deleteriously reduce its activity over time. In this work, we synthesized hierarchical structures of porous Cu@C and Cu/Zn@C materials via pyrolysis of Cu-BTC Metal–Organic Frameworks (MOFs) with or without Zn doping. Carbon encapsulation protects the Cu NPs from sintering, leading to stable catalytic activity at 500 °C under which RWGS is favored. Furthermore, the final catalyst pellet size can be controlled by tuning the crystal size of MOF precursors, eliminating the step of forming catalysts for fixed bed reactor applications.

A Dynamically Stabilized Single-Nickel Electrocatalyst for Selective Reduction of Oxygen to Hydrogen Peroxide

On-location electrochemical generation of H2 O2 is of great current interest. Herein, selective two-electron reduction of O2 to H2 O2 by a single [NiII (H2 O)6 ]2+ cation that is dynamically associated with a negatively charged metal-organic layer (MOL) by hydrogen bonding and coulombic interactions is reported. In contrast, NiII centers covalently immobilized on the MOL reduce O2 to H2 O in a four- electron process. Oxygen adsorption by [NiII (H2 O)6 ]2+ followed by two-electron reduction generates neutral [NiII (H2 O)4 (OH)(OOH)]0 , which momentarily disconnects from the negatively charged MOL to avoid the injection of additional electrons. Release of H2 O2 from [NiII (H2 O)4 (OH)(OOH)]0 regenerates [NiII (H2 O)6 ]2+ , which regains affinity to the MOL. Such dynamically associated NiII single-metal electrocatalysts ensure high selectivity and represent a new strategy for generating selective catalysts for electrochemical production of important chemicals.

Two-Dimensional Metal–Organic Layers on Carbon Nanotubes to Overcome Conductivity Constraint in Electrocatalysis

Application of metal-organic frameworks (MOFs) in electrocatalysis is of great interest, but is limited by low electrical conductivities of most MOFs. To overcome this limitation, we constructed a two-dimensional version of MOF-metal-organic layer (MOL) on conductive multiwalled carbon nanotubes (CNTs) via facile solvothermal synthesis. The redox-active MOLs supported on the CNT efficiently catalyze the electrochemical oxidation of alcohols to aldehydes and ketones. Interestingly, this CNT/MOL assembly also endowed the selectivity for primary versus secondary alcohols via well-designed interfacial interactions. This work opens doors toward a variety of designer electrocatalysts built from functional MOFs.