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Acidity of the Brönsted acid sites of zeolites
Author(s) -
Soscún Humberto,
Castellano Olga,
Hernández Javier,
Hinchliffe Alan
Publication year - 2001
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/1097-461x(2001)82:3<143::aid-qua1014>3.0.co;2-o
Subject(s) - chemistry , basis set , ab initio , brønsted–lowry acid–base theory , ab initio quantum chemistry methods , charge density , computational chemistry , charge (physics) , density functional theory , molecule , catalysis , physics , organic chemistry , quantum mechanics
The acidity of Brönsted acid sites of the (H 3 SiO) n O q (X 3− n − q Si)(OH)Al p Y 3− m − q (OSiH 2 ) r (OSiH 3 ) m zeolitic clusters, with X=(H,OH), Y=(H,OH), ( n , m )=(0,1,3), r =(0,1,8), and ( p , q )=(0,1), is evaluated in terms of the intrinsic acidity þ of the OH groups. þ is defined as the ratio between the OH distance and the frequency of the OH vibration mode and has been calculated at ab initio Hartree–Fock (HF) and second‐order Møller–Plesset (MP2) levels and the standard 6‐31+G(d,p) basis set. The acidity þ is rationalized in terms of the topology of the charge density ρ( r ) calculated at the position of the critical point of the OH bond ρ( r c ) of the acid sites. It is shown that there exists a linear relationship between þ and the charge concentration ρ( r c ), with a correlation coefficient of r =−0.98 for HF results, and r =−0.96 for MP2 ones. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 143–150, 2001