In this paper, a series of nanostructured CeO 2 spheres with two different dopants, Co 2+ and Ni 2+ , were synthesized by a one-step hydrothermal synthesis free from the template-assisted calcination, and were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS) and nitrogen adsorption-desorption measurements. The formation process of the produced spheres involved Ostwald ripening, secondary nucleation and oriented attachment. Both the presence of Co 2+ , Ni 2+ and the interaction of Ce 4+ /Ce 3+ with dopants promoted the production of oxygen vacancies, which explained the result that the catalytic performance in CO oxidation of CeO 2 with both dopants was better than that with single dopant, and that with single dopant held much advantage towards pure CeO 2 .

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