FTIR Spectroscopic Studies of Silication of γ-Alumina with FCC Catalysts via Steaming

The framework structures, surface hydroxyls, and acidity of silicated γ-alumina with and without transition-metal oxides were studied using FTIR techniques. The silication was made via steaming γ-alumina with FCC catalysts. The results clearly show migration of silicon species from FCC catalysts to the surface of γ-alumina, forming Brönsted acid sites. The newly formed Brönsted acid sites are weaker in strength compared to those in zeolites. Reactions between mobile silicon species and surface sites of γ-alumina proceed selectively and occur only on stronger Lewis acid sites. Transition-metal oxides introduced by impregnation onto γ-alumina have no effect on the site-selective silication reactions.