ZSM-5分子筛骨架铝落位对甲醇转化制芳烃催化性能影响

采用水热合成法,在合成过程中通过添加矿化剂、尿素和改变硅源,制备了不同骨架铝落位的ZSM-5分子筛。通过SEM、XRD、BET、XRF、MAS NMR、NH_3-TPD和Py-FTIR等表征手段对分子筛的形貌、织构、骨架铝落位和酸性进行了系统研究,同时考察了不同ZSM-5分子筛催化剂甲醇制芳烃的催化性能。研究结果表明,制备的ZSM-5分子筛均具有结晶度高和形貌均一等特点,但在骨架铝落位和酸性方面存在显著差异。椭球状ZSM-5分子筛的骨架铝主要分布于直通孔道或正弦孔道中,并表现出较多的酸性位。块状分子筛中骨架铝主要落位在孔道交叉处,且具有较低的强酸量。在甲醇制芳烃反应中,骨架铝主要位于直通或正弦孔道并表现出较多酸性位的椭球状ZSM-5分子筛催化剂具有较高的活性稳定性和芳烃选择性。

Effect of framework Al siting on catalytic performance in methanol to aromatics over ZSM-5 zeolites

ZSM-5 zeolites with different framework Al (AlF) siting were hydrothermally synthesized by adding mineralizer, urea, or by changing the silicon source. The morphology, textural properties, AlF siting, and acidity of different ZSM-5 zeolites were characterized using SEM, XRD, BET, XRF, MAS NMR, NH₃-TPD, and Py-IR. Furthermore, the conversion of methanol to aromatics (MTA) was used to investigate the catalytic performance of different catalysts.The results suggested that different ZSM-5 zeolites were highly crystalline with a uniform morphology, but there were large differences in AlF siting and acidity. The AlF in the ellipsoidal ZSM-5 sample was mainly distributed in straight or sinusoidal channels and displayed more acidic sites. AlF of bulk ZSM-5 was mainly located at the intersection of channels, and it showed the lowest amount of strong acid sites. The ellipsoidal ZSM-5 catalyst in which AlF was mainly located in straight or sinusoidal channels exhibited more acidic sites and higher stability and aromatic selectivity during the MTA reaction.