Effects of micro and nano-sized SAPO-34 and SAPO-5 catalysts on the conversion of methanol to light olefins

In the present study, SAPO-34 and SAPO-5 catalysts with different crystallite size were synthesized under hydrothermal conditions and partially characterized by XRD, SEM, EDX, BET and NH3-TPD. Crystallite sizes in the range of 450 nm-8 mu m were obtained. To elucidate the effects of crystallite size on their catalytic performance, especially in terms of the conversion, life time and selectivity, the performance of the methanol-to-olefin reaction over these two SAPO catalysts was investigated. The SAPO-34 catalyst with small crystals showed a longer catalyst lifetime and higher conversion of methanol as well as more than 50 % selectivity toward light olefins. Synthesized catalysts with larger crystals showed significantly shorter life time and lower selectivity toward light olefins. The overall results of this study demonstrate that not only the phase (SAPO-34 or SAPO-5) but also the crystal size are critical factors governing the MTO conversion and selectivity.