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SAPO-34 (chabasite structure) is studied with regard to decomposition of the template [tetraethylammonium hydroxide (TEAOH) or morpholine] and subsequent hydration-dehydration cycles over a period of few hours up to 2 years. XRD, IR, 27Al and 29Si MAS NMR, and N2 adsorption are used to characterize the related structural changes. The template decomposition results into shifts in 27Al and 29Si MAS NhfR peaks reflecting its interaction with the framework. Hydration of the template-free materials leads at room temperature to a breaking of Si-OH-A1 bonds, giving a partial loss of crystallinity and the formation of Q', Q2, and Q3 Si species (Si(OT),(OH)+,). Dehydration of the materials after about 1 or 2 day hydration gives reversibly the initial crystallinity, the Si environment, and the porosity for the template-free materials. Long-term hydration, up to 2 years, shows that zeolites synthesized with morpholine as a template do not recover their full crystallinity and eventually none of their porosity. By contrast, TEAOH materials are more stable, keeping up to 80% of the starting crystallinity and 70% of their porosity. The influence of the template is correlated to the formation, during synthesis of Si islands with TEAOH, while morpholine gives a larger part of isolated Si. This restricts in the TEAOH sample the number of Si-OH-A1 bonds, Le., of points where water attacks the framework.

On hydration template-free SAPO-34 shows the opening of some Si-0-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.

The interaction of ammonia with the template-free SAPO-34 framework is studied by XRD, 29Si, 27AI and 31P magic angle spinning (MAS) NMR and IR spectroscopy and temperature-programmed desorption (TPD). A reversible loss of crystallinity upon NH, adsorption-desorption at room temperature is accompanied by the reversible formation of new 27AI and 31 P NMR spectroscopic peaks, and the displacement of the chemical shifts of 29Si, 27AI and 31P nuclei. Rupture of some AI-0-P bonds is proposed. Upon NH, desorption, the broken Al-0-P bonds are reformed. Lewis acidity, detected by IR spectroscopy, is assumed to proceed from the addition of ammonia on Al partly or fully connected to the framework. Such an interaction may affect acidity measurements made using ammonia adsorption.

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