Synthesis of Pd/Carbon Hollow Spheres by the Microwave Discharge Method for Catalytic Debenzylation.

Pd/C catalysts have been widely applied in the debenzylation process due to their excellent ability of hydrogenolysis. However, they have been suffering from the problems of agglomeration and loss of active components, which lead to decreased and unstable activity. Thus, it is still a challenge to achieve Pd/C catalysts with high activity and stability. Herein, we propose a strategy for preparing Pd/C catalysts on porous carbon hollow spheres by a microwave discharge method. Due to the high-temperature property and reducibility of microwave discharge, Pd precursors can be rapidly reduced, resulting in well-dispersed Pd nanoparticles with a small size on the carbon carrier. Besides, the matched mesopores in the carbon hollow spheres can anchor Pd nanoparticles and effectively reduce the agglomeration and loss of Pd nanoparticles during the catalytic reaction. As a result, the as-prepared Pd/mesoporous carbon hollow spheres exhibit high and stable activity in the debenzylation reaction.

Water-assisted hydrogen spillover in Pt nanoparticle-based metal-organic framework composites.

Hydrogen spillover is the migration of activated hydrogen atoms from a metal particle onto the surface of catalyst support, which has made significant progress in heterogeneous catalysis. The phenomenon has been well researched on oxide supports, yet its occurrence, detection method and mechanism on non-oxide supports such as metal-organic frameworks (MOFs) remain controversial. Herein, we develop a facile strategy for efficiency enhancement of hydrogen spillover on various MOFs with the aid of water molecules. By encapsulating platinum (Pt) nanoparticles in MOF-801 for activating hydrogen and hydrogenation of C=C in the MOF ligand as activated hydrogen detector, a research platform is built with Pt@MOF-801 to measure the hydrogenation region for quantifying the efficiency and spatial extent of hydrogen spillover. A water-assisted hydrogen spillover path is found with lower migration energy barrier than the traditional spillover path via ligand. The synergy of the two paths explains a significant boost of hydrogen spillover in MOF-801 from imperceptible existence to spanning at least 100-nm-diameter region. Moreover, such strategy shows universality in different MOF and covalent organic framework materials for efficiency promotion of hydrogen spillover and improvement of catalytic activity and antitoxicity, opening up new horizons for catalyst design in porous crystalline materials.

New Function of Metal-Organic Framework: Structurally Ordered Metal Promoter.

The remarkable roles of metal promoters have been known for nearly a century, but it is still a challenge to find a suitable structure model to reveal the action mechanism behind metal promoters. Herein, a new function of metal-organic frameworks (MOFs) is developed as an ideal model to construct structurally ordered metal promoters by a targeted post-modification strategy. MOFs as model not only favor clearing the real action mechanism behind metal promoters, but also can anchor one or multiple kinds of metal promoters especially noble metal promoters. Typically, the as-prepared Pd/bpy-UiO-Cu catalysts show high selectivity (>99%) toward 4-nitrophenylethane in 4-nitrostyrene hydrogenation, mainly due to the enhanced interaction between Pd nanoparticles and MOF carriers induced by Cu promoters, thus inhibiting the hydrogenation of 4-nitrophenylethane. This strategy with flexibility and universality will open up a new route to synthesize efficient catalysts with structurally ordered metal promoters.

Anisotropic MOF-on-MOF Growth of Isostructural Multilayer Metal-Organic Framework Heterostructures.

Isostructural MOFs with similar crystallographic parameter are easily available for MOF-on-MOF growth and possible to form core-shell structure by isotropic growth. However, due to well-matched cell lattice, selective growth in isostructural MOF heterostructures remains a great challenge for engineering atypical MOF heterostructures. Herein, an anisotropic MOF-on-MOF growth strategy was developed to structure a range of multilayer sandwich-like ZIF-L heterostructures via stacking isostructural ZIF-L-Zn and ZIF-L-Co alternately with three-, five-, seven-, and more layer structures. Moreover, these heterostructures with highly designable feature were fantastic precursors for fabricating derivatives with tunable magnetic and catalytic properties. Such strategy explores a novel way of achieving anisotropic MOF-on-MOF growth between isostructural MOFs and opens up new horizons for regulating the properties by MOF modular assembly in versatile functional nanocomposites.

Construction of hierarchical-porous metal-organic frameworks through esterification reaction for efficient catalysis.

A solvent-assisted strategy was proposed by controlling the coordination equilibrium to fabricate hierarchical-porous metal-organic frameworks (HP-MOFs). The obtained HP-MOFs showed remarkable enhancement in catalytic efficiency in Lewis acid catalysis resulting from the joint efforts of the hierarchical pores and the exposed metal clusters.

Exploring the Fundamental Roles of Functionalized Ligands in Platinum@Metal-Organic Framework Catalysts.

The metal nodes, functionalized ligands, and uniform channels of metal-organic frameworks (MOFs) are typically utilized to regulate the catalytic properties of metal nanoparticles (MNPs). However, though the ligand functionalization could impact the properties of the metal nodes and channels, which might further regulate the catalytic activity and selectivity of MNPs, related research in the design of MNP/MOF catalysts was usually neglected. Herein, we synthesized a series of Pt@UiO-66 composites (Pt@UiO-66-NH2, Pt@UiO-66-SO3H, and Pt@UiO-66) with slightly different organic ligands, which enhanced steric hindrance and contributed to multipathway electron transfer in selective hydrogenation of linear citronellal. The selectivity toward citronellol was gradually improved along with the increased size of functional groups (hydrogen, amino groups, and sulfo groups) on organic ligands, which enhanced steric hindrance provided by channels. In addition, the X-ray photoelectron spectroscopy measurements also revealed that the electronic state of Pt NPs was regulated through multipathway electron transfer from Pt NPs to metal nodes, between organic ligands and Pt NPs/metal nodes. Our research proved that the ligand functionalization altered physiochemical properties of the channels and metal nodes, further together managing the catalytic performance of Pt NPs through enhanced steric hindrance and multi-pathway electron transfer.