Catalytic performances of Al-ITQ-13 zeolites with different SiO₂/Al₂O₃ ratios in the conversion of methanol to propene

Al-ITQ-13 zeolites with different SiO₂/Al₂O₃ molar ratios were synthesized by using seeds in the gel and characterized by XRD, SEM, N₂ physisorption, MAS NMR and NH₃-TPD. The effect of SiO₂/Al₂O₃ molar ratio on the catalytic performance of Al-ITQ-13 in the conversion of methanol to propene (MTP) was investigated in a fixed-bed micro-reactor. The results showed that the Al-ITQ-13 zeolites with different SiO₂/Al₂O₃ molar ratios are similar in their textural properties; however, the amount and strength of acid sites decrease with the increase of SiO₂/Al₂O₃ molar ratio. Moreover, the SiO₂/Al₂O₃ molar ratio has a significant influence on the catalytic behavior of Al-ITQ-13 in MTP. As the hydrogen transfer and aromatization reactions were suppressed over the Al-ITQ-13 zeolite with high SiO₂/Al₂O₃ molar ratio, with the increase of SiO₂/Al₂O₃ molar ratio, the selectivity to propene and butene is increased at the expense of the selectivity to propene; that is, with the increase of SiO₂/Al₂O₃ molar ratio from 137 to 309, the selectivity to propene is increased from 46.04% to 55.52% and meanwhile, the propene/ethene ratio is increased from 3.39 to 6.57.