Framework stability and Brønsted acidity of isomorphously substituted interlayer-expanded zeolite COE-4: a density...

Area of Science:

• Materials Science
• Computational Chemistry
• Catalysis

Background:

• COE-4 zeolites exhibit a unique 2D ten-ring pore structure with Si(OH)2 hydroxyl groups.
• Previous work demonstrated interlayer-expansion for COE-4 zeolites.
• Isomorphous substitution of Si by trivalent heteroatoms can modify zeolite properties.

Purpose of the Study:

• Investigate framework stability and Brønsted acidity of T-COE-4 zeolites with heteroatom substitution.
• Determine the influence of substitution energy and geometry on stability.
• Analyze the relative acid strength of substituted T-COE-4 zeolites.

Main Methods:

• Density functional theory (DFT) calculations.
• Analysis of substitution energies and equilibrium geometry.
• Proton affinity, charge analysis, and NH3 adsorption studies.

Main Results:

• Framework stability is maintained by widening ⟨T-O-Si⟩ angles.
• Substitution energies increase: Al-COE-4 < Ga-COE-4 < Fe-COE-4 < B-COE-4.
• Relative Brønsted acid strength order: Al-COE-4 > Ga-COE-4 > Fe-COE-4 > B-COE-4.

Conclusions:

• Isomorphous substitution significantly impacts T-COE-4 zeolite stability and acidity.
• Al-substituted T-COE-4 exhibits the strongest Brønsted acidity.
• Findings aid in designing functional interlayer-expanded zeolites.