Zeolite metastability as a function of the composition of the surrounding solution: The case of faujasite and zeolite omega

The transient formation of faujasite has been observed during the synthesis of zeolite omega. The metastability between these zeolites has been studied by measuring their solubilities in alkaline solutions at temperature levels near to usual crystallization conditions. The use of silicate- and aluminate-enriched solutions has allowed to determine solubility curves at different alkalinity levels. The silicate concentration in solution controls the relative stability of the two structures. For Si/Al ratios in solution lower than 6–10 (80–115 °C), zeolite omega is more soluble than faujasite and can be dissolved to provide silicate and aluminate for the crystallization of aluminium-richer zeolite X. In the usual conditions for the synthesis of zeolite omega, with Si/Al in solution higher than 100, zeolite X is metastable and is dissolved to provide aluminate for the crystallization of silica-richer zeolite omega.

.Figure optionsDownload as PowerPoint slideHighlights
► The relative stability of zeolitic phases depends on the composition of the solution.
► Solubility diagrams of aluminosilicate zeolites from partial dissolution experiments.
► Excess silicate drives dissolution of faujasite in the synthesis of zeolite omega.