The existence of oxygen vacancies in heterogeneous catalysis plays an essential role in determining the catalytic reactivity of metal catalysts. In this work, Ru nanoparticles were immobilized onto the CeO2 nanocubes (NCs), nanorods (NRs), and nanopolyhedrons (NPs) with the dominantly exposed (100), (1 1 0), and {111 facet of CeO2 support, respectively. Their catalytic behavior toward CO2 methanation was studied in detail, and the highest catalytic rate per gram of catalyst was obtained over the Ru(3%)/CeO2-NCs catalyst (reaction rate: 4.85 x 10(-8) mol g(cat)(-1)s(-1); selectivity: 99%; 150 degrees C). The temperature-programmed reduction (TPR), Raman spectra, and oxygen storage capacity (OSC) test confirm that the Ru(3%)/CeO2-NCs catalyst possesses the highest concentration of oxygen vacancies owing to the Ru-promoted formation of oxygen vacancy on the CeO2-NCs. In addition, in situ infrared spectroscopy measurements demonstrate that the abundant oxygen vacancy in Ru(3%)/CeO2-NCs serves as the active site for CO2 activation, accounting for the significantly enhanced low-temperature reaction rate per gram of Ru/CeO2 catalyst. (C) 2015 Elsevier Inc. All rights reserved.