To elucidate the migration process of cerium-cations and the resulting chemical diversification in cerium-NaY (Ce-NaY) ion-exchange processes, three calcination atmospheres (N-2-atmosphere, O-2-oxidation, N-2-atmosphere followed by O-2-oxidation) were adopted to study the influence of variable valence (III to IV) on ion migration, thermal stability, and catalytic activity. The results indicated that under N-2-protection, significant amounts of Ce-(III) ions moved into the sodalite cage and increased the thermal stability of Ce-NaY. Under O-2-oxidation, most Ce-(III) were converted to Ce-(IV) and remained inside the supercage. Ce-(IV) promoted water polarization and exhibited a unique hydroxyl group at 3582 cm(-1) in the infrared spectra. Ce ion-exchanged ultrastable Y zeolite (CeUSYo2) exhibited the highest amount of Bronsted acid due to the location of the Ce ions. Compared to CeUSYN2, CeUSYo2 increased light oil selectivity in vacuum gas oil catalytic cracking due to its higher Bronsted acidity. (C) 2015 Elsevier Inc. All rights reserved.