Node-Accessible Zirconium MOFs.

Area of Science:

• Materials Science
• Catalysis
• Nanotechnology

Background:

• Zirconium-based metal-organic frameworks (MOFs) are promising heterogeneous catalysts and supports.
• Ideal MOF activation involves terminal OH/H2O pairs for grafting catalytic clusters and exposing Lewis-acidic Zr(IV) sites.
• Conventional activation of Zr-MOFs like NU-1000 leads to formate ligand incorporation, hindering catalytic site accessibility.

Purpose of the Study:

• To develop an alternative activation protocol for Zr-MOFs that avoids formate incorporation.
• To install the full complement of terminal OH/H2O pairs for enhanced catalytic performance.
• To investigate the impact of formate removal on MOF properties and catalytic activity.

Main Methods:

• Single-crystal X-ray diffraction to characterize MOF intermediates and final structures.
• Development of an alternative activation protocol using specific solvent conditions.
• Assessment of catalytic activity for hydrolytic degradation of chemical warfare agent simulants.

Main Results:

• A novel activation protocol successfully removed modulators and formate, yielding an intermediate with eight aqua ligands and four chlorides.
• Complete replacement of formate with OH/OH2 pairs increased thermal lability of aqua ligands, enabling site exposure at lower temperatures.
• The modified NU-1000 exhibited approximately 10-fold higher activity in catalytic hydrolysis of a G-type chemical warfare agent simulant.

Conclusions:

• Eliminating formate during Zr-MOF activation is crucial for achieving optimal catalytic site accessibility and activity.
• The new protocol facilitates reversible pore size control and enhances thermal lability of catalytic sites.
• This work presents a significant advancement in designing highly active MOF-based catalysts for challenging chemical applications.