Solid solutions of CeO2 with Yb2O3, Y2O3, Sm2O3, Gd2O3, La2O3, Nb2O5, Ta2O5, and Pr6O11 were prepared by sol-gel methods. All of the samples exhibited a single, cubic phase in x-ray diffraction and the lattice parameters were consistent with formation of the solid solutions. Surprisingly, all of the mixed oxides exhibited a much lower catalytic activity for n-butane oxidation than that of pure ...