Investigation of the ammonium form of mordenite by methods of differential thermal analysis and IR spectroscopy

Abstract

1. It was shown on the basis of a study of the decomposition of the ammonium form of mordenite in various atmospheres by the methods of differential thermal analysis (DTA) and IR spectroscopy that when NH4M is heated to 400° there is a dehydration (stage I) of mordenite; in the interval 400–600° (in air) there is a deamination (stage II), and above 600° there is a dehydroxylation (stage III). In an atmosphere of nitrogen, deamination (stage II) occurs in a higher temperature (500–800°) than in air; the exothermic effect on the DTA curve at 500° is due to a process of oxidation. 2. The decomposition of NH4M is accompanied chiefly by the formation of several types of hydroxyl groups, which differ both in thermal stability and in rate of exchange with D2. 3. A comparison with the literature data indicates an increase in the strength of the NH4+ bond with the zeolite with increasing ratio SiO2/Al2O3 as a result of an increase in the acidity.