Pt-CeO_(2)/ZSM-22催化正庚烷异构化反应性能研究

Performance study of Pt-CeO_(2)/ZSM-22 catalyzed n-heptane isomerization reaction

结合浸渍法和物理混合法调控金属活性中心Pt的位点,使其单独落位到ZSM-22分子筛或氧化铈载体上,从而分别得到金属-酸双中心位点的间距达到原子级接触的Pt-ZSM-22/CeO_(2)催化剂和保持纳米级间距的Pt-CeO_(2)/ZSM-22催化剂。利用球差电镜、XRD、BET、H2-TPR和XPS等手段,表征了两种催化剂的物化性质,并对其正庚烷异构化反应性能进行了研究。另外,考察了不同还原温度下Pt-CeO_(2)/ZSM-22催化剂的物化性质和反应性能变化。结果显示,金属-酸中心保持纳米级间距Pt-CeO_(2)/ZSM-22催化剂具有更高的正庚烷异构化活性和异构烃收率,这是由于Pt在CeO_(2)载体上呈原子级分散的原因。在Pt-CeO_(2)/ZSM-22催化剂还原过程中,CeO_(2)载体释放更多的氧空位有助于延缓金属Pt的聚集且有利于庚烷分子的吸附。当还原预处理温度为300℃时,庚烷转化率和庚烷异构烃收率分别为79.2%和75.4%,异构化选择性达到95.2%。

A combination of impregnation and physical mixing methods was used to modulate the sites of the metal active center Pt,which were individually settled onto ZSM-22 molecular sieves or cerium oxide carriers,resulting in Pt-ZSM-22/CeO_(2)catalysts with atomic-level contacts at the spacing of the metal-acid bicenter sites and Pt�CeO_(2)/ZSM-22 catalysts that maintained nanoscale spacing,respectively.The physical and chemical properties of the two catalysts were characterized by means of spherical differential electron microscopy,XRD,BET,H2-TPR and XPS,and their n-heptane isomerization reaction performance was investigated.In addition,the changes of the physicochemical properties and reaction performance of Pt-CeO_(2)/ZSM-22 catalysts at different reduction temperatures were investigated.The results showed that the metal-acid center maintained nanoscale spacing Pt�CeO_(2)/ZSM-22 catalyst had higher n-heptane isomerization activity and isomeric hydrocarbon yield,which could be attributed to the atomic-level dispersion of Pt on the CeO_(2)carrier.During the reduction of Pt-CeO_(2)/ZSM-22 catalyst,the release of more oxygen vacancies from the CeO_(2)carrier helps to retard the aggregation of metal Pt and facilitates the adsorption of heptane molecules.When the reduction pretreatment temperature was 300℃,the heptane conversion and heptane isomerization hydrocarbon yield were 79.2%and 75.4%,respectively,and the isomerization selectivity reached 95.2%.