Abstract
The properties of the OH groups in NaHZSM-5 zeolite absorbing at 3609 cm −1 were studied with respect to their hydrogen bonding to weak electron donor molecules ( n-hexane, fluorobenzene, chlorobenzene, benzene, toluene, p-xylene, ethene). The observed band splitting was attributed to the heterogeneity of the OH groups. A comparative study of systems with homogeneous OH groups did not show such a splitting. The Bellamy-Hallam-Williams (BHW) relation was obeyed for all kinds of OH groups, and the proton affinities (PA) were calculated from this relation. Two probable explanations of the heterogeneity of OH groups in NaHZSM-5 zeolite are considered. One assumes the presence of OH groups with various numbers of Al atoms in the immediate neighborhood, and the other (more plausible) assumes dependence of OH acid strength on SiO and AlO bond lengths and AlOHSi bond angles.
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