Selective methanation of CO was investigated in hydrogen-rich gas streams involving 20% CO2 over a Ru-modified Ni-Al mixed oxide catalyst. The Ni-Al mixed oxide was prepared by the solution-spray plasma technique, by which fine powders of homogeneous mixed oxides can be easily synthesized. By the addition of a small amount of Ru, the catalytic activity and selectivity of the Ni-Al mixed oxide catalyst for CO methanation was improved dramatically. The added Ru enhanced the formation of nano-sized Ni metal particles via reduction of the mixed oxide by spill-over-hydrogen during reduction treatment, even at low temperature. Kinetic measurements revealed that the methanation of CO took place predominantly over the Ni metal sites. Selectivity for the CO methanation was also improved significantly by the addition of Ru due to suppression of CO2 dissociation over the Ni metal sites. (C) 2010 Elsevier B.V. All rights reserved.