A. Martinez-arias et al., EPR study on oxygen handling properties of ceria, zirconia and Zr-Ce (1 : 1) mixed oxide samples, CATAL LETT, 65(4), 2000, pp. 197-204
The characteristics of ceria, zirconia and Zr-Ce (1 : 1 molar ratio) sample
s prepared by using inverse microemulsions have been studied to obtain info
rmation on the modifications produced in the oxygen handling properties of
the single oxides by the formation of the mixed oxide. The structural chara
cteristics of the samples are compared on the basis of XRD and Raman spectr
oscopy data, which show that the Zr-Ce sample forms a homogeneous mixed oxi
de structure corresponding to the (pseudocubic) tetragonal phase t'' while
CeO2 presents, as expected, a cubic fluorite structure and ZrO2 is formed m
ainly by a tetragonal phase with only traces of the thermodynamically most
stable monoclinic phase. Evaluation by EPR of the type and intensity of sup
eroxide radicals generated upon oxygen adsorption on the outgassed samples
reveals a higher surface reducibility in the mixed oxide sample, associated
vacancies defects being generated on it in higher amounts and at lower tem
peratures than on pure ceria. It is also shown that both Ce and Zr ions par
ticipate in the oxygen chemisorption process on the mixed oxide sample, act
ually giving rise to much larger amounts of O-2(-)-Zr4+ species than the pu
re ZrO2 sample; the latter species show a higher thermal stability than O-2
(-)-Ce4+ species.