Effect of phosphorus and water contents on physico-chemical properties of SAPO-34 molecular sieve

SAPO-34 molecular sieves with different P and H2O contents were synthesized by adjusting P2O5/Al2O3 and H2O/Al2O3 molar ratios in starting gel. The crystal structure, crystal size, elemental composition, and acid site density of the synthesized samples were characterized with XRD, SEM, ICP, TPD, and FTIR. The morphology, crystallinity, and acidity of SAPO-34 materials varied with P2O5/Al2O3 and H2O/Al2O3 molar ratios in the starting gel and different Si substitution mechanisms were accompanied correspondingly. Samples with P2O5/Al2O3 and H2O/Al2O3 molar ratios of 1 and 60 had the best crystallinity with the largest crystals and maximum surface area. Increasing the concentration of strong acidic hydroxyl groups for samples SP-1 and SW-60 indicated the presence of a higher amount of Bronsted acid sites.