Polyoxometalate-Based Metal-Organic Frameworks with Unique High-Nuclearity Water Clusters

Area of Science:

• Materials Chemistry
• Catalysis
• Supramolecular Chemistry

Background:

• Polyoxometalates (POMs) are crucial for enhancing catalytic performance.
• Incorporating POMs into metal-organic frameworks (MOFs) like HKUST-1 offers unique structural and catalytic properties.
• Maximizing POM exposure is key to improving catalytic efficiency.

Purpose of the Study:

• To synthesize novel POM-based MOFs by encapsulating phosphovanadomolybdates into HKUST-1.
• To investigate the structural characteristics, particularly the unique water clusters formed.
• To evaluate the catalytic performance of the synthesized materials in benzene hydroxylation and oxidative desulfurization.

Main Methods:

• Hydrothermal synthesis for encapsulating POMs into HKUST-1.
• Single-crystal X-ray diffraction for structural elucidation, including water cluster analysis.
• Heat treatment to remove water clusters and expose active sites.
• Catalytic testing for benzene hydroxylation and oxidative desulfurization.

Main Results:

• Two POM-MOFs, [Cu12(BTC)8(H2O)12][H4PMo11VO40]@(H2O)30 (1) and [Cu12(BTC)8(H2O)12][H5PMo10V2O40]@(H2O)49 (2), were successfully synthesized.
• Unique high-nuclearity water clusters, (H2O)30 and (H2O)49, were observed, substituting organic counter cations.
• Post-synthesis heat treatment fully exposed active sites, leading to significant catalytic activity.
• Compound 2 demonstrated bifunctional catalytic activity for both reactions.

Conclusions:

• The synthesized POM-MOFs exhibit novel structures with unusual water clusters.
• Removal of water clusters is an effective strategy to enhance catalytic site accessibility.
• Compound 2 shows promise as a bifunctional heterogeneous catalyst for benzene hydroxylation and oxidative desulfurization.