Migration of Framework Aluminum and Tunable Acidity in Y Zeolite by Post-treatment

Abstract

Two industrial Y zeolites were treated sequentially by steaming and citric acid to investigate the Al migration and acidity of the modified Y zeolites. Even though the two parent Y zeolites displayed similar properties including crystallinity, Si/Al ratio, and textural structure, they showed different acidic and textural properties upon identical post-treatments by steaming and citric acid due to the different Al migration rules, resulting in their different activity and cracking ability in the methylcyclohexane transformation. Steaming treatment performed the prominent dealumination, leading to the increase of the framework Si/Al ratio from ca. 2.5 to ca. 5.0 and the formation of extra-framework Al species. During steaming treatment, the dealumination is related with the transformation from Al(IVb) to Al(V). The following citric acid leaching hardly removed the framework Al but removed the extra-framework Al species that existed in the form of Al(V) readily and some residual Na+ ions. The remaining framework-associated Al species are related to the generation of Lewis acid sites.