(714g) Identification of Different Proton and Aluminum Species in H-ZSM5
AIChE Annual Meeting
Tuesday, November 17, 2020 - 9:30am to 9:45am
The chemical shift is valuable information for understanding the structure and properties of proton species in H-ZSM5 zeolite. Here, H1NMR and Al27NMR of protonic and aluminum species in H-ZSM5 zeolite have been calculated using Density Functional Theory (DFT) calculations, through with we show that computed data are in good agreement with experimental solid-state NMR spectra and provide insights for the location and configuration of the protons. Different protonic species consist of silanol group (Si-OH), isolated Bronsted acid site (BAS), extra-framework aluminum (EFAl), and acidic OH groups in the proximity of extra framework aluminum (BAS/EFAl). In particular, we find that protonic chemical shift of single BAS depends on its locations; a tighter confinement normally leads to a higher chemical shift value. The calculated chemical structure of BAS/EFAl synergies may also indicate enhanced catalytic activity. We further show that Al27NMR is dependent on the coordination number and the local environment and that the quadrupolar constant is greatly influenced by the geometrical symmetry. The combination of H1NMR and Al27NMR using DFT calculations thus helps characterize active sites in H-ZSM5 zeolite, as NMR spectra reveal fingerprint of the zeoliteâs structure.