Periodic, vdW-corrected density functional theory investigation of the effect of Al siting in H-ZSM-5 on chemisorption properties and site-specific acidity

• Physical and chemisorption properties of twelve distinct Brønsted acid sites
• High accuracy periodic DFT calculations including dispersion forces
• Chemical and structural properties suggest non-identical behavior of acid sites.
• Adsorption energies depend significantly on dispersion interactions.
• No common acidity scales were identified.

Twelve crystallographically distinct Al substitution sites of H-ZSM-5 are modeled by periodic density functional theory using the vdW-DF functional. While the stability of Al substitution and Brønsted acid OH bond length at different active site positions are similar, the OH stretch frequency, SiOAl bond angle, and adsorption energies of various probe molecules differ notably without observable correlations between these properties. Comparison of adsorption energy values with and without van der Waals corrections demonstrates the significance of the inclusion of dispersion interactions. Our data indicate that theoretical investigations of H-ZSM-5 require a careful selection of the location of the active site.

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