Yi Luan

Nanoscaled copper metal-organic framework (MOF) based on carboxylate ligands as an efficient heterogeneous catalyst for aerobic epoxidation of olefins and oxidation of benzylic and allylic alcohols.

Aerobic epoxidation of olefins at a mild reaction temperature has been carried out by using nanomorphology of [Cu3(BTC)2] (BTC = 1,3,5-benzenetricarboxylate) as a high-performance catalyst through a simple synthetic strategy. An aromatic carboxylate ligand was employed to furnish a heterogeneous copper catalyst and also serves as the ligand for enhanced catalytic activities in the catalytic reaction. The utilization of a copper metal-organic framework catalyst was further extended to the aerobic oxidation of aromatic alcohols. The shape and size selectivity of the catalyst in olefin epoxidation and alcohol oxidation was investigated. Furthermore, the as-synthesized copper catalyst can be easily recovered and reused several times without leaching of active species or significant loss of activity.

A general post-synthetic modification approach of amino-tagged metal–organic frameworks to access efficient catalysts for the Knoevenagel condensation reaction

In this manuscript, four common transition-metal derived metal–organic frameworks have been extensively investigated as heterogeneous catalyst supports for Knoevenagel condensation reactions. A simple post-synthetic modification strategy was employed for the rapid and facile introduction of a primary alkyl amino group. The resulting novel MOF–RNH2 catalysts showed greatly enhanced Knoevenagel condensation reactivities towards a variety of aldehyde electrophiles. IRMOF-3 proved to be an unsuitable heterogeneous catalyst support due to its fragile nature upon treatment with bases. The novel zirconium based UiO-66–NH–RNH2 and chromium based Cr-MIL-101–NH–RNH2 materials showed excellent catalytic reactivities, while being highly convenient to synthesize. The basic catalytic activity was further extended to the Henry reaction, and excellent catalytic reactivity was achieved. The size-selectivity was also studied to show that the Knoevenagel condensation occurred inside of the porous structure of the MOF catalyst. The recycling properties of zirconium, aluminum and chromium derived MOFs were evaluated and zirconium based UiO-66 and chromium based Cr-MIL-101 showed excellent catalytic efficiency after five reaction cycles.

Synthesis of an amino-functionalized metal–organic framework at a nanoscale level for gold nanoparticle deposition and catalysis

In this study, highly dispersed Au nanoparticles have been immobilized on amino-functionalized metal–organic frameworks (MOFs) via a novel absorption/reduction method in solution. The amino functionality of the MOF rapidly coordinated with HAuCl4 and acted as the Au(0) precursor in the absence of protecting agents. The resulting Au@MOF catalyst was well dispersed in aqueous media taking advantage of its well-defined and uniform sizes and nanomorphologies. The as-synthesized Au@MOF catalyst exhibited high catalytic activities in a wide variety of reactions under ambient conditions, such as the base-free aerobic oxidation of alcohols and oxidation/imine formation/reduction reaction sequences. Furthermore, the Au@MOF catalyst can be easily recovered and reused several times without leaching of metals or significant loss of activity.

Merging metal–organic framework catalysis with organocatalysis: A thiourea functionalized heterogeneous catalyst at the nanoscale

A new thiourea-containing metal–organic framework (MOF) catalyst was synthesized. It overcomes recycling, self-aggregation and solvation issues that exist in homogeneous thiourea catalysts. Nanomorphology was introduced to increase the dispersion of the solid catalyst in solvent. Acetalization and Morita–Baylis–Hillman reactions were catalyzed using the new thiourea MOF catalyst.

Introduction of an organic acid phase changing material into metal–organic frameworks and the study of its thermal properties

The design and synthesis of a shape-stabilized composite phase change material (PCM) is the most practical approach for addressing the leakage issue of phase change materials. This manuscript describes a facile solution impregnation method to access a novel type of shape-stabilized PCM employing metal–organic frameworks as the matrix. A fatty acid@metal–organic framework (MOF) composite PCM for low temperature heat storage has been developed for the first time. The metal–organic framework serves as an ideal host material for achieving a composite PCM taking advantage of its highly porous structure and tunable host–guest interactions. PXRD, FTIR, SEM, TGA, BET and DSC characterization studies have been conducted to reveal the structural and thermal properties of the newly achieved PCM composites. The results showed that one-step synthesized MIL-101-NH2 provided the most optimal thermal properties and the highest stearic acid mass percentage was achieved at 70 wt%, which corresponds to the highest loading and highest enthalpy in the literature for organic acid derived shape-stabilized PCMs. Furthermore, the thermal performance of the fatty acid@MOF composite PCM was maintained after 50 cycles, which indicates its great thermal stability.

Synthesis of a flower-like Zr-based metal–organic framework and study of its catalytic performance in the Mannich reaction

The synthesis of metal–organic frameworks with Bronsted acid moieties is usually tedious and the study of metal–organic frameworks as a heterogeneous Bronsted acid catalyst is limited. In this manuscript, a facile one-step synthesis of UiO-66-(COOH)2 material with a flower-like morphology has been developed. The as-synthesized flower-like UiO-66-(COOH)2 can serve as an efficient Bronsted acid in nitro-Mannich and Mannich reactions taking advantage of its morphology assembled from nanoscaled plates. 72–99% yields of Mannich adducts were obtained for a variety of acyl imine substrates in the presence of 0.5 mol% MOF catalyst under extremely mild conditions. Furthermore, the as-synthesized flower-like UiO-66-(COOH)2 catalyst can be recycled several times without compromising the catalytic activity.

Hierarchical PS/PANI nanostructure supported Cu(II) complexes: facile synthesis and study of catalytic applications in aerobic oxidation

Hierarchical heterogeneous copper catalysts were prepared by immobilization of a homogeneous copper(II) complex on the surface of polystyrene/polyaniline (PS/PANI) microspheres with oriented PANI nanofibers. EDX element maps and XPS spectra indicated that Cu2+ ions strongly coordinated with PANI imine. PS/PANI@Cu(OSO2CF3)2 exhibited excellent catalytic activity for selective aerobic oxidation of alcohols and highly efficient aerobic epoxidation of alkenes under mild conditions. The supported copper(II) catalyst maintained high levels of conversion and selectivity in these reactions after six cycles and showed good stability.

Highly efficient sulfonated-polystyrene–Cu(II)@Cu3(BTC)2 core–shell microsphere catalysts for base-free aerobic oxidation of alcohols

A novel catalyst consisting of a functional sulfonated-polystyrene (SPS) core, a porous Cu3(BTC)2 shell and an active Cu(II) interface between the core and shell was developed via a facile step-by-step assembly method. The polystyrene core was sulfonated first to achieve functional –SO3H groups on its surface. The main function of the –SO3H groups was to graft Cu(II) ions to generate an active Cu(II) interface, and the excess –SO3H could provide acid conditions for the catalytic reaction. The Cu(II) interface along with the acid conditions and the co-catalyst 2,2,6,6-tetramethyl-piperidyl-1-oxy (TEMPO) enhanced the catalytic activity for the aerobic oxidation of alcohols to aldehydes by molecular oxygen under base-free conditions. A portion of Cu(II) ions on the SPS surface was then coordinated with H3BTC (1,3,5-benzenetricarboxylic acid) to form a porous Cu3(BTC)2 shell, which could protect the active metal from leaching as well as provide porous channels for mass transfer, resulting in high stability and recyclability in the catalysis procedure. The SPS–Cu(II)@Cu3(BTC)2 catalyst could be recycled ten times without a significant loss in its activity and selectivity. Furthermore, the SPS–Cu(II)@CuBDC (BDC = 1,4-benzenedicarboxylate) composite was also synthesized and showed high efficiency for catalyzing the aerobic oxidation of alcohols and aerobic homocoupling of arylboronic acids, suggesting that the unique nanostructure of SPS–Cu(II)@MOFs can be easily extended to design complex catalysts with high efficiency and good stability for different catalytic reactions.

A facile in situ self-assembly strategy for large-scale fabrication of CHS@MOF yolk/shell structure and its catalytic application in a flow system.

A hierarchical yolk/shell copper hydroxysulfates@MOF (CHS@MOF, where MOF = metal-organic frameworks) structure was fabricated from a homogeneous yolk/shell CHS template composed of an active shell and a stabilized core via a facile self-template strategy at room temperature. The active shell of the template served as the source of metal ion and was in situ transformed into a well-defined MOF crystal shell, and the relatively stabilized core retained its own nature during the formation of the MOF shell. The strategy of in situ transformation of CHS shell to MOF shell avoided the self-nucleation of MOF in the solution and complex multistep procedures. Furthermore, a flow reaction system using CHS@MOF as self-supported stationary-phase catalyst was developed, which demonstrated excellent catalytic performance for aldehyde acetalization with ethanol, and high yields and selectivities were achieved under mild conditions.

Synthesis of a Fe3O4–CuO@meso-SiO2 nanostructure as a magnetically recyclable and efficient catalyst for styrene epoxidation

A novel hybrid Fe3O4–CuO@meso-SiO2 catalyst was successfully fabricated by a multi-step assembly method. CuO nanoparticles were first deposited on the surface of Fe3O4 microspheres to form the Fe3O4–CuO hybrid microspheres through a solvothermal reaction. A mesoporous silica (meso-SiO2) shell, with perpendicularly aligned pore channels, was then coated on the hybrid microspheres using sol–gel technology. The Fe3O4 microspheres not only offered fast and effective recycling properties for the catalyst but also acted as electron donors to CuO, leading to a higher electron density on the CuO surface and a subsequently enhanced catalytic performance. The mesoporous silica shell provided strong protection against the aggregation and leaking of the active CuO nanoparticles and also offered appropriate channels for an efficient mass transfer of the catalytic reaction. The Fe3O4–CuO@meso-SiO2 catalyst exhibited excellent activity, convenient magnetic separability and good stability in the catalytic epoxidation of styrene.