REVERSIBLE INTERACTION OF NH3 WITH THE FRAMEWORK OF TEMPLATE-FREE ZEOLITE-TYPE SAPO-34

The interaction of ammonia with the template-free SAPO-34 framework is studied by XRD, Si-29, Al-27 and P-31 magic angle spinning (MAS) NMR and IR spectroscopy and temperature-programmed desorption (TPD). A rev ersible loss of crystallinity upon NH3 adsorption-desorption at room t emperature is accompanied by the reversible formation of new Al-27 and P-31 NMR spectroscopic peaks, and the displacement of the chemical sh ifts of Si-29, Al-27 and P-31 nuclei. Rupture of some Al-O-P bonds is proposed. Upon NH3 desorption, the broken Al-O-P bonds are reformed. L ewis acidity, detected by IR spectroscopy, is assumed to proceed from the addition of ammonia an Al partly or fully connected to the framewo rk. Such an interaction may affect acidity measurements made using amm onia adsorption.