Reversible modification of the Si environment in template-free SAPO-34 structure upon hydration-dehydration cycles below ca. 400 K

On hydration template-free SAPO-34 shows the opening of some Si–O–Al bonds as suggested by 29Si MAS NMR and XRD results, the effect being reversible upon dehydration; the hydrated distorted structure is stable for months with no further modifications and the ordered material can be regenerated by removal of water at 423 K.