A series of rare earth oxides were investigated as catalysts in the ketonization of acetic acid. High selectivity to acetone over 99% was obtained by reacting acetic acid over rare earth oxides such as La2O3, CeO2, Pr6O11, and Nd2O3. Especially, Pr6O11 showed the highest yield of 80% at 350 degrees C among the 14 rare earth oxides. The bulk structure of CeO2 was stable during the ketonization, while the surface acetate species were observed over CeO2 after ketonization. In contrast, the other active rare earth oxides such as La2O3, Pr6O11, and Nd2O3 were mainly basic oxides due to the formation of bulk oxyacetate such as MO(AcO), where M is La, Pr, and Nd and AcO indicates CH3COO group, in the initial period of the reaction. In any case, the catalytic ketonization proceeds over the surface of the oxyacetates and CeO2. Catalytic cycle of the ketonization is composed of two steps: the decomposition of surface M2O(AcO)(4) to produce MO(AcO), acetone, and carbon dioxide and the regeneration of surface M2O(AcO)(4) by reacting MO(AcO) and acetic acid to produce water. (C) 2011 Elsevier B.V. All rights reserved.