Tuning of acidity in CeY catalytic cracking catalysts by controlling the migration of Ce in the ion exchange step through valence changes

Abstract

To elucidate the migration process of cerium-cations and the resulting chemical diversification in cerium-NaY (Ce-NaY) ion-exchange processes, three calcination atmospheres (N2-atmosphere, O2-oxidation, N2-atmosphere followed by O2-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 N2-protection, significant amounts of Ce-(III) ions moved into the sodalite cage and increased the thermal stability of Ce-NaY. Under O2-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 3582cm−1 in the infrared spectra. Ce ion-exchanged ultrastable Y zeolite (CeUSYO2) exhibited the highest amount of Brønsted 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 Brønsted acidity.