不同硅铝比Al-ITQ-13分子筛的甲醇制丙烯反应催化性能

采用晶种法直接合成了硅铝比(SiO_2/Al_2O_3物质的量比)为137、224和309的三种Al-ITQ-13分子筛,并采用粉末X射线衍射(XRD)、扫描电镜(SEM)、N_2吸附-脱附、固体核磁共振(MAS NMR)和NH_3-程序升温脱附(NH_3-TPD)等分析方法对不同硅铝比分子筛进行了表征,并在固定床微型反应评价装置上,考察了硅铝比对甲醇转化制丙烯反应性能的影响。结果表明,不同硅铝比Al-ITQ-13分子筛呈现出相似的织构性质,酸量及酸强度随着硅铝比的升高逐渐下降。硅铝比对甲醇转化反应的产物分布存在较大的影响;随着硅铝比的升高,氢转移反应和芳构化反应活性降低,使得乙烯选择性下降,而丙烯和丁烯的选择性升高。硅铝比由137提高到309,丙烯的选择性(质量分数)由46.04%增加到55.52%,而丙烯/乙烯比由3.39提高到6.57。

Catalytic performances of Al-ITQ-13 zeolites with different SiO2/A12O3 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.