Thermal analysis of synthetic (near-chabazite) zeolites with different Si/Al ratios

The thermal behaviour of synthetic K-G type zeolites (near-chabazites of Barrer) depends on their chemical composition. Samples with a Si/Si + Al fraction between 0.5 and 0.55 and consequently with a high potassium content, show a limited reversible dehydration between room temperature and 180°C. Above 180°C, after breakdown of the crystal structure, irreversible dehydration proceeds readily, with a sharp maximum near 270°C.Samples with a Si/Si + Al fraction greater than 0.57 and a lower potassium content dehydrate continuously over the whole range between room temperature and 450°C.