Liyu Chen

Metal−organic framework encapsulated Pd nanoparticles: towards advanced heterogeneous catalysts

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.

Controllable Encapsulation of “Clean” Metal Clusters within MOFs through Kinetic Modulation: Towards Advanced Heterogeneous Nanocatalysts

Abstract Surfactant‐free tiny Pt clusters were successfully encapsulated within MOFs with controllable size and spatial distribution by a novel kinetically modulated one‐step strategy. Our synthesis relies on the rational manipulation of the reduction rate of Pt ions and/or the growth rate of MOFs by using H2 as assistant reducing agent and/or acetic acid as MOF‐formation modulator. The as‐prepared Pt@MOF core–shell composites exhibited exceedingly high activity and excellent selectivity in the oxidation of alcohols as a result of the ultrafine “clean” Pt clusters, as well as interesting molecular‐sieving effects derived from the outer platinum‐free MOF shell.

In situ one-step synthesis of metal–organic framework encapsulated naked Pt nanoparticles without additional reductants

The encapsulation of metal nanoparticles (MNPs) into metal–organic frameworks has generated recent research because of the promising novel physical and chemical properties originating from synergetic interactions between MNPs and MOFs. However, the development of a facile one-step approach for the incorporation of tiny MNPs within MOFs without additional stabilizing agents and reductants remains a great challenge. Herein, we report a new and general synthesis strategy for MNPs@MOFs that allows preferential self-assembly of MOFs around the in situ formed MNP surface by directly mixing both the reactive metal (e.g., H2PtCl6) and MOF precursors in DMF. This in situ one-step assembly approach is applicable to various MOFs, affording well-defined Pt@MOF composites with highly dispersed naked Pt NPs in narrow diameter distribution. The resulting Pt@MOF nanocomposites exhibit excellent stability, significantly enhanced catalytic activity and selectivity as compared to the commercial Pt/C in liquid-phase aerobic oxidation of alcohols.

Encapsulation of Mono‐ or Bimetal Nanoparticles Inside Metal–Organic Frameworks via In situ Incorporation of Metal Precursors

A facile, in situ metal precursor incorporation strategy is established for good control over the location and composition of metal nanoparticles within metal-organic frameworks (MOFs). This one-step metal precursor incorporation route is successfully applied to the fabrication of ultrafine Pd, Ni, and PdNi alloys to be selectively encapsulated inside the pores of MOFs, achieving superior catalytic activity and stability in the hydrogenation of nitrobenzene.

One-step encapsulation of Pd nanoparticles in MOFs via a temperature control program

The control over the size and location of metal nanoparticles (MNPs) within metal–organic frameworks (MOFs) is achieved in one step through a cooperative in situ metal precursor incorporation and on-site moderate reduction process, which is operated by a temperature control program. The choice of operation temperatures is based on the MOF assembly temperature (T1), and an elevated temperature (T2) to elicit the reducibility of DMF solvent to fabricate MNPs. Such a rational design could effectively introduce metal precursors into the pores of MOFs and on-site moderately reduce the embedded metal ions to generate tiny MNPs by the penetrated DMF, which could not be achieved by a quick heating process. The proposed methodology has been successfully applied to the one-step fabrication of ultrafine Pd NPs selectively encapsulated inside the pores of UiO-67 without any external reducing agents. The obtained Pd-in-UiO-67 shows superior catalytic activity and selectivity in the hydrogenation of styrene even at room temperature and atmospheric pressure of H2.

Nanocomposites of Platinum/Metal-Organic Frameworks Coated with Metal-Organic Frameworks with Remarkably Enhanced Chemoselectivity for Cinnamaldehyde Hydrogenation

The encapsulation of metal nanoparticles (MNPs) within metal–organic frameworks (MOFs) to form core–shell structural nanocomposites is one of the most promising methods to enhance the durability and selectivity of MOF‐supported metal catalysts. However, it is still a challenge to fully encapsulate tiny MNPs inside MOFs. Herein, we report a facile and general strategy to coat MOFs on the surface of Pt/MOFs by direct homoepitaxial growth. The obtained Pt/MOFs@MOFs nanocomposites retained the intrinsic properties (e.g., crystalline structure, pore texture, and surface area) of Pt/MOFs. Strikingly, the MOF‐coated materials exhibited a significantly enhanced chemoselectivity compared to the uncoated materials, for example, in the hydrogenation of cinnamaldehyde, the selectivity to cinnamyl alcohol through C=O hydrogenation was improved from 55 to 96 % at complete conversions of cinnamaldehyde. Moreover, Pt/MOFs@MOFs can be recycled without any remarkable loss in both activity and selectivity. The enhanced catalytic selectivity and stability of MNPs/MOFs could be related to the synergetic effects of the electron donation and nanoconfinement offered by the surrounding MOF networks.