Textural, structural, and morphological characterizations and catalytic activity of nanosized CeO 2–MO x (M = Mg 2+, Al 3+, Si 4+) mixed oxides for CO oxidation

Abstract

The present work focuses on the combination of ceria with another oxide of different ionic valences from period 3 (Mg 2+, Al 3+, and Si 4+) using coprecipitation method, followed by calcination at 450 and 750 °C, respectively. The textural, structural, morphological and redox properties of nanosized ceria–magnesia, ceria–alumina and ceria–silica mixed oxides have been investigated by means of N 2 physisorption, XRD, Raman, HRTEM, DRS, FT-IR, and H 2-TPR technologies. XRD results of these mixed oxides reveal that only nanocrystalline ceria ( ca. 3–6 nm for the 450 °C calcined samples) could be observed. The grain size of ceria increases with the increasing calcination temperature from 450 to 750 °C due to sintering effect. The highest specific surface area is obtained at CeO 2–Al 2O 3 mixed oxides when calcination temperature reaches 750 °C. Raman spectra display the cubic fluorite structure of ceria and the existence of oxygen vacancies, and displacement of oxygen ions from their normal lattice positions in the ceria-based mixed oxides. DRS measurements confirm that the smaller the grain size of the ceria, the higher indirect band gap energy. H 2-TPR results suggest that the reductions of surface and bulk oxygen of ceria were predominant at low and high calcination temperature, respectively. Finally, CO oxidation were performed over these ceria-based mixed oxides, and the combination of CeO 2–Al 2O 3 exhibited highest activity irrespective of calcination temperature, which may due to excellent textural/structural properties, good homogeneity, and redox abilities.