Synthesis and characterization of AlPO4-21 from aqueous and non-aqueous systems

Abstract

AlPO4-21 molecular sieve is synthesized in aqueous and non-aqueous media. It is characterized by XRD, SEM, C and N analysis, TG/DTA, FT-IR and 27Al and 31P MAS NMR techniques. Calcination of AlPO4-21 at 550oC gives AlPO4-25. XRD analysis shows that the sample synthesized from non-aqueous media is 2.0 to 2.7 times higher crystalline compared to aqueous media sample. SEM analysis shows the morphology is varied on changing the media. On silicon incorporation the particle size is increased. Carbon and nitrogen analysis shows that all AlPO4-21 samples are having four template molecules besides the aqueous media samples synthesized using aluminium isopropoxide is having three isopropnaol molecules in addition. Hexamethyleneimine is not incorporated. TG/DTA shows that AlPO4-21 synthesized using aluminium isopropoxide in aqueous media losses more weight compared to non-aqueous media samples due to incorporation of isopropanol molecules in its structure apart to equal amount of template to non-aqueous media samples. FT-IR bands are increased to higher values on changing the media to non-aqueous due to shrink in pore size (decrease in TO-T bond length). 27Al and 31P MAS NMR of AlPO4-21 indicate that the presence of three types of aluminium and phosphorous. The aluminium peaks further splits in to two on absorption of moiture due to reverse in co-ordination. The NMR pattern is similar to VPI-5 although the pore size differs is due to the similarity in secondary building units.