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A computational exploration into isomorphously substituted effects on hydrogen electric field gradient and chemical shielding tensors in the H‐ZSM‐5 zeolite
Author(s) -
Soltanali Saeed,
Halladj Rouein,
Ektefa Fatemeh
Publication year - 2014
Publication title -
asia‐pacific journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.348
H-Index - 35
eISSN - 1932-2143
pISSN - 1932-2135
DOI - 10.1002/apj.1786
Subject(s) - zeolite , zsm 5 , brønsted–lowry acid–base theory , chemistry , chemical shift , quadrupole , electric field gradient , acid strength , hydrogen atom , molecular sieve , hydrogen , catalysis , organic chemistry , physics , adsorption , atomic physics , alkyl
Density functional theory calculations have been performed at the B3LYP/6‐31++G** level to investigate the effect of the isomorphously substituted ZSM‐5 zeolite with trivalent elements B, Al, and Ga on the hydrogen atom of the Brönsted acid site via nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) parameters. ZSM‐5 clusters were modeled as ((H) 3 SiO) 3 –Si–O(H)–M–(OSi(H) 3 ) 3 (M = B, Al, and Ga). Variations of isotropic chemical shifts, δ iso , of 1 H atom in the Brönsted acid site as well as quadrupole coupling constant, C Q , and asymmetry parameter, η Q , of 2 H atom in the Brönsted acid site are well correlated with the trend in acidic strength of isomorphously substituted H‐ZSM‐5, estimated from the experimental results: B‐ZSM‐5 < Ga‐ZSM‐5 < Al‐ZSM‐5. The C Q value of 2 H atom in the Brönsted acid site decreases in the order: B‐ZSM‐5, Ga‐ZSM‐5, Al‐ZSM‐5, respectively; eventually, their η Q values of 2 H atom in the Brönsted acid site increase concluding models with high C Q have a lower Brönsted acidity than those with low C Q . In addition, the calculated chemical shifts of the Brönsted proton increase in the sequence: B‐ZSM‐5 < Ga‐ZSM‐5 < Al‐ZSM‐5. All the results show a high consistency among NQR and NMR parameters and relative acidity of the isomorphously substituted ZSM‐5 zeolite. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.