Synthesis of Small-Sized SAPO-34 Crystals with Varying Template Combinations for the Conversion of Methanol to Olefins

SAPO-34 molecular sieves were synthesized under hydrothermal conditions using different combinations of tetraethyl ammonium hydroxide (TEAOH)/morpholine (Mor)/triethylamine (TEA) as templates, with different silicon: aluminum ratios. The physicochemical properties of the synthesized SAPO-34 were characterized using XRD, SEM, N-2 adsorption-desorption, XRF, TG, NH3-TPD, FT-IR, and Si-29 MAS NMR analyses. According to the SEM and the N-2 adsorption-desorption of the catalysts produced by the ternary template exhibited a larger surface area and a smaller crystal size than those produced by the single or binary templates. The FT-IR analysis indicated the increased acidity of the catalyst prepared by the ternary template. A high activity and selectivity to olefins (C-2 = + C-3 =) and an optimal silicon to aluminum ratio of 0.4 were obtained from the catalyst synthesized with the ternary template. At the reaction temperature of 450 degrees C, the methanol conversion approached 100% and the ethylene-propylene selectivity and the lifetime of the catalyst reached maximums of 89.15% and 690 min, respectively.