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Counting the Acid Sites in a Commercial ZSM-5 Zeolite Catalyst
Andrea Zachariou1,2, Alexander P Hawkins1,2, Russell F Howe3
1School of Chemistry, University of Glasgow, Joseph Black Building, GlasgowG12 8QQ, U.K.
ACS Physical Chemistry Au
|January 31, 2023
Summary
This study quantifies Brønsted acid protons in ZSM-5 zeolite using inelastic neutron scattering (INS). Results show about 50% of aluminum is extra-framework, impacting catalyst acidity.
Area of Science:
- Catalysis
- Materials Science
- Solid-state Chemistry
Background:
- Brønsted acid sites in ZSM-5 zeolites are crucial for catalytic activity.
- The concentration of Brønsted acid sites is linked to aluminum content, but not all aluminum contributes.
- Understanding aluminum speciation is key to optimizing zeolite catalysts.
Purpose of the Study:
- To directly quantify Brønsted acid protons in a commercial ZSM-5 zeolite.
- To determine the proportion of extra-framework aluminum species.
- To compare different analytical techniques for characterizing zeolite acid sites.
Main Methods:
- Inelastic neutron scattering spectroscopy (INS) for direct proton quantification.
- Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
- Ammonia temperature-programmed desorption (TPD).
- Neutron powder diffraction.
Main Results:
- INS directly measured Brønsted acid protons, silanol groups, and hydroxyl groups.
- Approximately 50% of the total aluminum content was identified as extra-framework.
- Results were corroborated by solid-state NMR and ammonia TPD.
- Neutron diffraction provided evidence for extra-framework aluminum oxide species.
Conclusions:
- Inelastic neutron scattering offers a novel method for direct proton counting in commercial zeolite catalysts.
- A significant portion of aluminum in this ZSM-5 catalyst exists as extra-framework species.
- Accurate characterization of aluminum speciation is vital for understanding and improving zeolite performance.
