We combine first-principles calculations with EXAFS studies to investigate the origin of high oxygen storage capacity in ceriazirconia solid solution, prepared by solution combustion method. We find that nanocrystalline Ce 0.5 Zr 0.5 O 2 can be reduced to Ce 0.5 Zr 0.5 O 1.57 by H 2 upto 850°C with an OSC of 65 cc/gm which is extremely high. Calculated local atomic-scale structure reveals the presence of long and short bonds resulting in four-fold coordination of the cations, confirmed by the EXAFS studies. Bond valence analysis of the microscopic structure and energetics is used to evaluate the strength of binding of different oxide ions and vacancies. We find the presence of strongly and weakly bound oxygens, of which the latter are responsible for the higher oxygen storage capacity in the mixed oxides than in the pure CeO 2 .

We determine chemical origins of increase in the reducibility of CeO 2 upon Ti substitution using a combination of experiments and first-principles density functional theory calculations. Ce 1-x Ti x O 2 (x ) 0.0-0.4) prepared by a single step solution combustion method crystallizes in a cubic fluorite structure, confirmed by Rietveld profile analysis. Ce 1-x Ti x O 2 can be reduced by hydrogen to a larger extent compared to CeO 2 or TiO 2 . Temperature programmed reduction of CeO 2 , TiO 2 , Ce 0.75 Ti 0.25 O 2 and Ce 0.6 Ti 0.4 O 2 up to 700 °C in H 2 gave CeO 1.96 , TiO 1.92 , Ce 0.75 Ti 0.25 O 1.81 , and Ce 0.6 Ti 0.4 O 1.73 , respectively. An extended X-ray absorption fine structure (EXAFS) study of mixed oxides at the Ti K-egde showed that the local coordination of Ti is 4:4, with Ti-O distances of 1.9 and 2.5 Å, respectively, which are also confirmed by our first-principles calculations. Bond valence analysis of the microscopic structure and energetics determined from first principles is used to evaluate the strength of binding of different oxygen atoms and vacancies. We find the presence of strongly and weakly bound oxygens in Ce 1-x Ti x O 2 , of which the latter are responsible for the higher oxygen storage capacity in the mixed oxides than in pure CeO 2 .

Ce 1-x Sn x O 2 (x ) 0.1-0.5) solid solution and its Pd substituted analogue have been prepared by a single step solution combustion method using tin oxalate precursor. The compounds were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and H 2 /temperature programmed redution (TPR) studies. The cubic fluorite structure remained intact up to 50% of Sn substitution in CeO 2 , and the compounds were stable up to 700 °C. Oxygen storage capacity of Ce 1-x Sn x O 2 was found to be much higher than that of Ce 1-x Zr x O 2 due to accessible Ce 4+ /Ce 3+ and Sn 4+ /Sn 2+ redox couples at temperatures between 200 and 400 °C. Pd 2+ ions in Ce 0.78 Sn 0.2 Pd 0.02 O 2-δ are highly ionic, and the lattice oxygen of this catalyst is highly labile, leading to low temperature CO to CO 2 conversion. The rate of CO oxidation was 2 µmol g -1 s -1 at 50 °C. NO reduction by CO with 70% N 2 selectivity was observed at ∼200 °C and 100% N 2 selectivity below 260 °C with 1000-5000 ppm NO. Thus, Pd 2+ ion substituted Ce 1-x Sn x O 2 is a superior catalyst compared to Pd 2+ ions in CeO 2 , Ce 1-x Zr x O 2 , and Ce 1-x Ti x O 2 for low temperature exhaust applications due to the involvement of the Sn 2+ /Sn 4+ redox couple along with Pd 2+ /Pd 0 and Ce 4+ /Ce 3+ couples.