Multinuclear MAS NMR study on the microporous aluminophosphates AlPO4-41 and SAPO-41

Abstract

Medium pore aluminophosphate molecular sieves SAPO-41 and AlPO₄-41 and their manganese containing derivatives have been synthesized hydrothermally using di-n-propylamine as an organic template. ¹³C, ²⁷Al and ³¹P magic-angle spinning (MAS) NMRspectroscopy have been used to study the structural changes occurring upon isomorphous substitution of silicon into the alumino-phosphate framework. These changes are most pronounced in the ³¹P MAS NMR spectra. While SAPO-41 and MnAPSO-41 show only a single resonance at -30.5 ppm, AlPO₄-41 and MnAPO-41 exhibit multiple line ³¹P NMR spectra. After calcination of the latter samples only a single resonance at -31.5 ppm is observed. The different lines can be assigned to defect sites (e.g. P-OH) and the crystallographically inequivalent T-atoms present in the AFO structure on the basis of ¹H–³¹P cross-polarization experiments.