Dealumination of Y zeolites with ammonium hexafluorosilicate: Effect of washing on the hydrothermal stability

The number of washes with boiling water of a Y zeolite dealuminated with ammonium hexafluorosilicate strongly affects its stability under hydrothermal conditions. Traces of hexafluorosilicate, difficult to eliminate completely through washing, would be responsible for this effect. Hydrothermal treatments of mixtures of NH4NaY zeolite and of ammonium hexafluorosilicate (0.2-2 wt%) allow confirmation of this point.