碱酸联合处理法ZSM-22沸石介孔改性研究

通过水热合成及铵交换制备不同硅铝比的氢型沸石H-ZSM-22;用碱、酸介质对H-ZSM-22样品进行介孔改性。研究起始沸石硅铝比对改性沸石相对结晶度、介孔结构、晶貌和产率的影响。N2吸附-脱附和XRD分析表明,改性沸石兼有结晶性的微孔-介孔结构;随着起始沸石n(Si)∶n(Al)由31.7增至43.2,改性沸石介孔体积出现极大值而结晶度保留率和产率呈相反的变化趋势;典型样品n(Si)∶n(Al)=37.0]的介孔体积高达0.44cm3/g,结晶度保留率和相对产率分别为56.0%、44.4%。SEM观察显示,改性沸石的附加介孔结构主要源于H-ZSM-22骨架脱硅、脱铝产生的结构缺陷。

Investigation on mesoporous modification of zeolite ZSM-22 by sequential alkaline and acid treatments

Samples of H-ZSM-22 zeolites with different Si/A1 ratios were hydrothermally synthesized and ion-exchanged. The H-ZSM-22 samples obtained were treated by sequential alkaline and acid media for mesopore modification. The effects of framework Si/A1 ratios on relative crystallinity, mesopore structure, morphology as well as yield were investigated for the treated samples. The characterization of results associated with N2 adsorption-desorption and X-ray diffraction revealed the modified zeolites show crystalline micro-and mesoporous structures. In the range of initial framework Si/AI ratio from 31.7 to 43. 2 the modified zeolites are found having a highest mesopore volume along with the lowest values of crystallinity preservation and yield. The typical sample prepared from the intact H-ZSM-22 with a Si/A1 ratio around 37.0 exhibits significant mesopore properties,i, e. the mesoporous volume up to 0. 44 cm3/g, crystallinity preservation about 56.0% ,and yield of 44. 4 wt% relative to the initial ze- olite. Furthermore,it proved by SEM that additional mesopore structures of modified zeolites are de- rived essentially from the bulk structural defects formed by desilication and dealumination.