草酸脱铝改性的ZSM-50沸石的性质及其异构化性能

对ZSM-50沸石进行了草酸脱铝改性，利用X荧光光谱、X射线粉末衍射、NH₃吸附-程序升温脱附、吡啶吸附红外光谱等方法考察了草酸改性对ZSM-50沸石的化学组成、晶型及表面酸性的影响，并采用正庚烷作为模型化合物对其异构化性能进行评价。结果表明：对ZSM-50沸石进行草酸改性处理，在保持较高结晶度的同时，可以有效改变其骨架硅铝比；当脱铝程度达到约26%时，沸石分子筛的酸性中心数量增加20%以上、L/B酸的比例提高1倍以上，同时酸强度基本保持不变，沸石的异构化性能得到提高；当脱铝程度达到60%时，导致沸石骨架结构中铝空位过多，酸性中心数量降低30%，造成异构化反应选择性下降，副反应增强，不利于异构化反应。

Isomerization performance of ZSM-50 zeolite modified by oxalic acid

Dealumination of ZSM-50 zeolite using oxalic acid has been investigated in an attempt to improve its catalytic properties in the isomerization of straight-chain paraffins.The effects of oxalic acid treatment on the chemical composition,crystallinity and surface acidity of ZSM-50 zeolite were studied by XRF,XRD,NH3-TPD and pyridine IR.The isomerization performance was evaluated in a fixed-bed reactor using n-heptane as a model compound.The characterization results showed that oxalic acid treatment increased the framework SiO2/Al2O3 molar ratio in the ZSM-50 zeolite without significantly affecting the relative crystallinity.A dealumination degree of 26% increased the number of acid sites by 20% and raised the Lewis/Brnsted acid ratio by a factor of two,whilst retaining the acid intensity,resulting in an improvement in the isomerization performance of ZSM-50.A dealumination degree of 60% resulted in additional aluminum vacancies in the framework and decreased the number of acid sites by 30%,which favored the side reactions and lowered the selectivity of isomerization.