Substitution of silicon and metal ions in small pore aluminophosphate molecular sieves with chabazite structure: synthesis and MASNMR study

Syntheses of MeAPO-34, MeAPO-44, MeSAPO-34 and MeSAPO-44 where Me = Mn or Mg with varying amounts of silicon and metal ions have been achieved. P-31, Al-27 and Si-29 MASNMR spectra of these compounds have been studied. The P-31 MASNMR of MnAPO-44 suggest the ordering of the Mn2+ ions give a P(Mn,3Al) environment. MASNMR of MgAPO-44 and MgAPO-34 showed a random distribution of Mg2+ ions. The P/Al ratios calculated from MASNMR are in good agreement with the chemical analyses. The substitution of silicon in the MeSAPOs are strongly influenced by the amount of Me present. Samples with small amount of Me essentially have Si(4Al) environments, but increase in the amount of the metal ions leads to the formation of silica-rich regions in the structure.