Infrared Spectroscopic Study of the Carbon Dioxide Adsorption on the Surface of Cerium-Gallium Mixed Oxides

Abstract

In order to modified the acid-base properties of pure cerium dioxide, a series of ceria-based oxides doped with gallium(III) cations (from 5 to 50% mol/mol of Ga) was prepared by co-precipitation in basic aqueous solution followed by calcination at 773 K. N 2 physisorption at 77 K showed that mesoporous materials with surface areas between 75 and 104 m 2/g were obtained. Ga(III) cations were incorporated into the ceria crystal structure up to a concentration close to 20-25% mol/mol of Ga, as revealed by powder X-ray diffraction analysis. Surface basicity was investigated using CO 2 chemisorption by mass spectrometry and in situ infrared spectroscopy. A progressive decrease in the surface basicity in the series of ceria-gallia materials was observed as the Ga content increases. Different carbonate and bicarbonate surface species were identified through their vibrational infrared modes. A remarkable decrease in the surface stability of carbonate species, particularly of the polydentate carbonate groups, was detected, which is correlated to the incorporation of gallium(III) into the ceria lattice.