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 ℃, the heptane conversion and heptane isomerization hydrocarbon yield were 79.2% and 75.4%, respectively, and the isomerization selectivity reached 95.2%.