Synthesis, characterization and activity study of SO4 2−/CexZr1−xO2 solid superacid catalyst

Abstract

Sulfated CexZr1−xO2 catalyst was found to exhibit solid super-acidity and good catalytic activity for synthesis of -amino ketones by a threecomponent Mannich type reaction in the liquid phase under solvent free conditions at ambient temperature. To make the sulfated CexZr1−xO2 catalyst, Ce-Zr hydroxide gel was prepared by a coprecipitation method and SO4 2− ions were deposited by treating the gel with sulfuric acid and calcined at 923 K. Surface and bulk properties of the CexZr1−xO2 and SO4 2−/CexZr1−xO2 samples were investigated by means of X-ray powder diffraction, thermogravimetry, ammonia-TPD, Raman spectroscopy and BET surface area methods. Characterization results indicate that impregnated SO4 2− ions strongly influence the physicochemical characteristics of the CexZr1−xO2 solid solution. Powder XRD profiles reveal the presence of cubic Ce0.5Zr0.5O2 in the case of unpromoted sample and tetragonal Ce0.16Zr0.84O2 phase along with zirconium sulfate compounds in the case of SO4 2− promoted sample. In particular, the XRD and Raman results suggest a selective interaction of the sulfate ions with zirconia portion of the CexZr1−xO2 solid solution leading to the formation of zirconium sulfate compounds. The NH3-TPD profiles indicate significant changes in the distribution of acid sites on the CexZr1−xO2 upon sulfation. The SO4 2−/CexZr1−xO2 sample exhibits strong as well as super-acidic sites.