Acidity of two-dimensional zeolites.

Area of Science:

• Computational Chemistry
• Materials Science
• Zeolite Chemistry

Background:

• Zeolites are widely used catalysts and adsorbents.
• Understanding Brønsted acidity is crucial for catalytic applications.
• Aluminosilicates are key components in zeolite structures.

Purpose of the Study:

• To calculate absolute deprotonation energies for Brønsted sites in aluminosilicate bilayers.
• To compare deprotonation energies of 2D aluminosilicates with bulk zeolites.
• To investigate the influence of Al/Si ratio and dimensionality on deprotonation energetics.

Main Methods:

• Hybrid quantum mechanics:molecular mechanics (QM/MM) calculations.
• Periodic boundary conditions and the supercell method.
• Density functional theory (DFT) for electronic structure calculations.

Main Results:

• Significantly lower deprotonation energies were observed for aluminosilicate bilayers (1042-1091 kJ/mol) compared to bulk zeolites (1233 kJ/mol).
• Deprotonation energies varied with Al/Si ratios in the 2D systems.
• Effective dielectric constants for bilayers (1.6-1.9) were lower than for bulk zeolites (3.0).

Conclusions:

• Ultra-thin aluminosilicate bilayers exhibit enhanced Brønsted acidity due to lower deprotonation energies.
• The reduced effective dielectric constant of 2D systems stabilizes the negative charge formed upon deprotonation.
• These findings have implications for designing novel catalytic materials with tunable acidity.