Optimizing Crystal Size of SAPO-۳۴ via precursor Addition Strategy for Enhanced MTO Performance

SAPO-۳۴ zeolite, due to its chabazite-like framework, suitable acidity, microporous structure, and good thermal stability, exhibits outstanding performance in the methanol-to-olefins (MTO) reaction. However, rapid coke formation within its narrow channels can significantly reduce catalytic activity. Therefore, achieving an optimal crystal size distribution is essential to enhance reactant diffusion, improve active site accessibility, and extend catalyst lifetime. In this study, SAPO-۳۴ was synthesized hydrothermally at ۱۸۵°C for ۲۷ hours via four different methods by altering the sequence and manner of adding precursors (P₂O₅, Al₂O₃, SiO₂, and dual-template strategy). The results indicated that the method involving the gradual addition of SiO₂ into a preformed gel containing the template, while controlling the timing of other components, led to a significant reduction in crystal size (۱۳۴.۷ nm) and improved particle size distribution (۲ μm). FESEM images confirmed the formation of uniform cubic crystals with morphology consistent with the CHA structure and similar to that of natural chabazite. Moreover, the homogeneous distribution of particles suggested well-controlled nucleation and suppressed crystal overgrowth. The reduced crystal size enhanced surface area (۴۲۹ m²/g) and molecular diffusion, leading to improved catalytic performance in the MTO process. Specifically, light olefins selectivity of approximately ۸۵% and a catalyst lifetime of ۳۳۲ minutes were achieved. These findings highlight the critical role of synthesis procedure design, particularly the timing and order of precursor addition, in tuning the structural properties of SAPO-۳۴ and optimizing its catalytic behavior.

کلیدواژه ها:

SAPO-۳۴ ، Crystal size distribution ، MTO