Performance study of Pt-CeO2/ZSM-22 catalyzed n-heptane isomerization reaction

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/CeO2 catalysts with atomic–level contacts at the spacing of the metal–acid bicenter sites and Pt-CeO2/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-CeO2/ZSM-22 catalysts at different reduction temperatures were investigated. The results showed that the metal–acid center maintained nanoscale spacing Pt-CeO2/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 CeO2 carrier. During the reduction of Pt-CeO2/ZSM-22 catalyst, the release of more oxygen vacancies from the CeO2 carrier helps to retard the aggregation of metal Pt and facilitates the adsorption of heptane molecules. When the reduction pretreatment temperature was 300 °C, the heptane conversion and heptane isomerization hydrocarbon yield were 79.2% and 75.4%, respectively, and the isomerization selectivity reached 95.2%.