不同结构扩孔分子筛催化MTP反应行为及表面积炭物种表征

采用TEAOH溶液处理MFI结构ZSM-5分子筛、MWW结构MCM-22分子筛,NaOH溶液处理TON结构ZSM-22分子筛、CHA结构SSZ-13分子筛得到四种结构的扩孔分子筛。在反应温度480℃、反应压力0.1 MPa、甲醇与水质量比1∶1、甲醇质量空速1.5 h~(-1)的条件下,考察了四种扩孔分子筛的甲醇制丙烯(MTP)催化性能,并采用XRD、N_2吸附-脱附、NH_3-TPD、TG、UV-Raman和GC-M S等方法表征催化剂的物化性质及M TP反应2 h后的分子筛积炭性质。结果表明,四种分子筛扩孔改性后均出现介孔,其中,T-ZSM-5分子筛在MTP反应中寿命最长;T-MCM-22分子筛寿命次之且失活速率慢;而一维孔道结构N-ZSM-22分子筛和八元环尺寸较小的N-SSZ-13分子筛均失活迅速。受拓扑结构和孔道扩散的影响,MTP反应2 h后,分子筛积炭量增加的顺序为T-ZSM-5N-ZSM-22T-MCM-22N-SSZ-13且可溶焦分子质量随积炭量增加而增重,即从五甲基苯增重到菲、芘等多环芳烃。

Methanol to propylene reaction performance and trapped carbonaceous species over zeolites with different topologies

Mesoporous ZSM-5 (MFI), MCM-22 (MWW), ZSM-22 (TON) and SSZ-13 (CHA) zeolites were obtained by TEAOH and NaOH solution treatment. Under the following operating conditions:t=480℃, p=0.1 MPa, m(methanol):m(H₂O)=1:1 and WHSV (methanol)=1.5 h^-1, the catalytic properties of four mesoporous zeolites with different topologies were investigated in the methanol to propylene (MTP) reaction. The fresh and spent samples after 2 h were characterized with XRD, nitrogen adsorption experiments, NH₃-TPD, TG, UV-Rama and GC-MS techniques. It demonstrated that both zeolites exist mesopores after treated by alkali. The mesoporous T-ZSM-5 zeolite had the highest lifetime; the lifetime of T-MCM-22 zeolite with was secondary and deactivation rate was slow; The N-ZSM-22 with one-dimensional channel structure and N-SSZ-13 zeolite with 8-member ring channels both deactivated rapidly. Due to the difference of topology structure and diffusion performance, their coke contents after 2 h increased in the order:T-ZSM-5 < N-ZSM-22 < T-MCM-22 < N-SSZ-13. Moreover, the molecular weight of soluble coke increased with the increasing of coke contents, changed from pentamethylbenzene to polycyclic aromatic hydrocarbons, such as phenanthrene and pyrene.