Quantum chemical study of the physical characteristics of the hydroxyl groups of zeolites. IV

Abstract

The CNDO/2 method was employed in the study of the electronic structure of the HX zeolite using cluster models Si 2Al 2O 4H(OH) − 8, Si 2Al 2O 4H 2-(OH) 8 and Si 2Al 2O 4H(OH) 8Na for various types of skeletal hydroxyl groups. It is shown that the hydroxyl groups of the O 1 and O 3 types are most likely to be formed among all studied groups even if formation of the remaining types of hydroxyl groups cannot be excluded. The calculations indicate that the hydroxyl groups of the HX zeolite are of a less acidic character than those of the HY zeolite and that the location of an Na + cation in the S 1 position excludes the formation of O—H groups of the O 3 type.