Infrared spectroscopic study of carbon dioxide adsorption on the surface of cerium–gallium mixed oxides

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. N2 physisorption at 77 K showed that mesoporous materials with surface areas between 75 and 104 m2/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 CO2 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.

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► Mesoporous cerium dioxide doped with gallium(III) in a wide cationic molar range (Ce1−xGaxO2−x/2, with x: 0.05, 0.10, 0.20, 0.25 and 0.50) were synthesized.
► A non-linear decrease of the CO2 uptake was observed as the bulk or surface Ga molar content increased in the Ce–Ga mixed oxides.
► Different surface carbonate species were identified by means of in situ infrared spectroscopy.
► The thermal stability of the carbonaceous species was determined as follows: HCO3− < b-CO3 ∼ m-CO3 < p-CO3.
► All the carbonate groups were less stable on the surface of Ce–Ga mixed oxides.