Abstract:
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, H
2-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%.