Suspensions of cerium(IV) oxide (CeO2) particles in molten chloride salts were found to be active for molecular oxygen activation when doped with the larger Lanthanides, gadolinium (Gd), praseodymium, (Pr), and samarium, (Sm). The activity for O-2 oxidation of gas phase CO on suspended doped ceria in molten mixtures of LiCl-LiBr-KBr and NaCl-KCl is significantly higher than undoped ceria or the salt mixtures alone in the temperature ranges of 350-600 degrees C, and 700-800 degrees C, respectively. Surface tension measurements show that the solid doped ceria particles suspended in the melt are contacting the gas-liquid interface of the bubbles. The activity for O-2 oxidation of liquid phase MgCl2 in molten MgCl2-KCl to produce Cl-2 and solid MgO was also observed to be significantly increased on suspended CeO2 doped with 5 wt% or 10 wt% Gd. The rates of oxidation were observed to increase with catalyst loading. [GRAPHICS] .