Study of High-Aluminum-Content Sulfated Zirconia: Influence of Aluminum Content and Washing

Abstract

A high-aluminum-content sulfated zirconia was prepared by the kneading method, and the washing process was considered as a key factor. Catalysts were characterized by XRD, BET analysis, SEM, TG, FT-IR spectroscopy, pyridine IR spectroscopy, NH3 TPD, H2 TPR, and 27Al NMR spectroscopy, and the reactivity was evaluated by n-hexane isomerization. The results showed that the high-aluminum-content sulfated zirconia has a high activity after being washed with water. Moreover, the aluminum content was found to strongly influence the crystal form, catalyst structure, and acidity, as well as the anchoring effect on the labile sulfates. Actually, the higher the aluminum content was, the more sulfates were left in the catalyst samples after washing. The O—H and S═O stretching vibrations were shifted in the presence of aluminum or water. With the support of the aluminum coordination state, a hydrolysis model was deduced for different aluminum contents in the catalysts, and it can explain the formation of more Brønsted acid sites and Al—O—S bonds.