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DFT insight into Brønsted acidity in MCM ‐22 zeolite by 31 P NMR of adsorbed trimethylphosphine oxide
Author(s) -
Thang Ho Viet,
Quang Duong Tuan,
Nam Pham Cam
Publication year - 2021
Publication title -
vietnam journal of chemistry
Language(s) - English
Resource type - Journals
eISSN - 2572-8288
pISSN - 0866-7144
DOI - 10.1002/vjch.202000132
Subject(s) - zeolite , trimethylphosphine , adsorption , chemistry , brønsted–lowry acid–base theory , oxide , inorganic chemistry , medicinal chemistry , catalysis , organic chemistry , molecule
The Brønsted acid (BA) strength plays an important role in the catalytic performance of protonic MCM‐22 zeolite. Although many studies including both theoretical calculations and experiments have been performed, it still remains somewhat unclear and needs to understand completely. By using density functional theory (DFT) calculation including dispersion contribution, DFT‐D3, the characteristics of bare protonic MCM‐22 zeolite and trimethylphosphine oxide (TMPO) adsorption complexes were optimized. The BA strength of H‐MCM‐22 zeolite was evaluated through chemical shift of 31 P NMR. The calculated 31 P NMR chemical shifts of adsorbed TMPO were in good agreement with those of experiment. The strength of BA sites in protonic MCM‐22 is mostly decided by the location of TMPO complexes with BA sites. The high chemical shifts (79‐85 ppm) corresponding to the high BA acid strength were observed for TMPO complexes located in 12‐membered ring supercage and the lower chemical shifts (73‐78 ppm) corresponding to lower BA strength, were due to TMPO interaction with BA sites inside supercage or in 10‐member ring crossing window or in 10‐member ring sinusoidal channels. Furthermore, the relationship between adsorption energies of TMPO with BA sites and 31 P NMR chemical shift of adsorbed TMPO was also evaluated.