Structural, morphological, and oxygen handling properties of nanosized cerium-terbium mixed oxides prepared by microemulsion

The structural/morphological and oxygen handling properties of two high-surface-area Ce-Tb mixed oxides prepared by a microemulsion method with Ce/Tb atomic ratios of ca. 4 and 1 have been analyzed in a multitechnique study (HREM, XEDS, XRD, Raman, XPS, O-2(-)-EPR, adsorbed methoxy IR, and (CO2)-O-18 isotopic exchange). Agglomerates of mixed-oxide nanoparticles (average size in the 5-7 nm range) with cubic fluorite structure are shown to be formed with varying lattice parameters as a function of the amount of Tb3+ and associated intrinsic oxygen vacancy defects present in each case. A trend toward stabilization of higher relative amounts of Tb4+ with increasing the Tb content of the mixed oxide is inferred from analysis of XRD and Raman results. Oxygen is shown to chemisorb as superoxide species on the outgassed samples. EPR analysis of these species shows that terbium promotes generation of clustered vacancies defects at the surface of the mixed-oxide nanoparticles, in agreement with adsorbed methoxy IR experiments. Employment of (CO2)-O-18 as a tracer molecule in isotopic exchange experiments suggests that oxygen bulk diffusion is moderately altered upon Tb doping of ceria, slightly decreasing with increasing the Tb content of the mixed-oxide nanoparticles.