Changes in mordenite upon various treatments. Part 2.—Hydroxyl groups

Abstract

The hydroxyl groups of mordenite, whether dealuminated or not, and pretreated in various conditions (evacuation, dry or wet air, hydrogen stream) have been studied by means of infrared spectrometry. The usual acidic 3600 cm^–1 band is observed in all the samples not wet air treated. Two other bands may be formed by the replacement of removed aluminum atoms by four hydroxyl groups. A 3650 cm^–1 non-acidic band observed in some heat-treated or/and dealuminated mordenites is assigned to aluminium extraction from the less strongly bonded aluminum atoms located in sites “2”. A 3700–3740 cm^–1 acidic band would result from aluminum removal from “1” type locations. Further aluminum removal by wet air treatments eliminate the higher frequency band in forming new Si—O bonds while a broad 3600–3650 cm^–1 band remains which could also include hydroxyl vibrations of hydroxy-aluminum deposits in the channels.