Further evidence of incorporation of chromium ions into the framework of silicoaluminophosphate molecular sieves

Three different molecular sieves were synthesised and characterized using P -31 and Al-27 magic angle spinning nuclear magnetic resonance (P-31 and Al- 27 MAS NMR) spectroscopy and acidity measurement techniques. The synthesize d solids were: a silicoaluminophosphate (SAPO-11) sample, a chromium-substi tuted silicoaluminophosphate (CrAPSO-11) sample and a chromium-supported SA PO-11 (Cr/SAPO-11) sample. Significant differences were observed between th e CrAPSO-11 MAS NMR spectra and the spectra for the other two solids. The d ifferences can be understood in terms of a different chemical environment f or the Al(III) and P(V) ions in the molecular sieve framework, as a result of a different type of interaction, probably with substituted chromium ions in the framework. The acidity measurements were in agreement with the MAS NMR spectroscopy results, providing further evidence for the incorporation of chromium ions into the molecular sieve framework.