Promotion effect of cerium in ZSM-22 zeolite on the hydroisomerization of n-hexadecane

The study fabricated ZSM-22 zeolites with Ce/Al molar ratios ranging from 0 to 1, which were subsequently loaded with Pt to perform n-hexadecane hydroisomerization. Various methods, such as XRD, 29Si NMR, FTIR, UV-Vis, XPS, and H2-TPR, confirmed the direct evidence of Ce incorporation into the zeolite framework, and the framework Ce content was of a volcanic nature. Furthermore, the study observed successful manipulation of textural and acidity properties of the samples through variation of the Ce content, as shown by N2-physisorption, NH3-TPD, and Py-IR. Increasing Ce content led to retardation of micropore diffusion due to lower micropore volume and surface area, as well as an increase in the distribution of weak Bronsted acid sites, which suppressed outside-of-pore cracking reactions. These changes rendered improved i-hexadecane selectivity and catalyst stability for Pt/ZSM-22. At a Ce/Al molar ratio of 0.5 with a WHSV of 12 h-1, the high selectivity to monobranched isomers resulted in a yield exceeding 75 wt%.