Investigation of acidic properties of bridging hydroxy groups in SAPO-5 using isotope exchange and 1H NOE NMR spectroscopy

Abstract

The acidity and acid sites in SAPO-5 have been investigated using TPD, FTIR, MAS NMR and nuclear Overhauser effect (NOE) spectroscopy. Using [ ² H ₆ ]benzene as a probe molecule, variable-temperature FTIR and MAS NMR experiments have permitted the measurement of the relative strengths of different types (or different locations) of bridging hydroxy groups. The specificity of the distance between the adsorbate (benzene) and the two types of bridging hydroxy groups have been confirmed by ¹ H NOE techniques. Combination of measurements of through-space distance with the ¹ H NOE technique and of relative isotopic exchange rates between bridging hydroxy groups and the probe molecule provide a way for characterizing their locations and acidity in SAPO-5.