TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Catalyst: The catalyst comprises (wt.%) ruthenium component (0.01 - 10) in terms of elemental ruthenium and lanthanoid component (0.01 - 20) in terms of elemental lanthanoid. The ratio of lanthanoid component to ruthenium component is 20:1 - 1:20. Preferred Component: The lanthanoid component comprises lanthanum, cerium, praseodymium, neodymium, samarium and/or gadolinium. The metal oxide is alumina, silica, zirconia, titania, silica-alumina, zeolite or ceria (preferably alumina or silica). EXAMPLE - Ruthenium chloride (1.27 g) was dissolved in pure water (100 ml), KHA-24 (RTM: alphalumina pellet) (100 g) was added, and the resulting mixture was evaporated to dryness, to yield a pellet-like mixture. The pellet-like mixture was put in an aqueous hydrazine solution, which had been prepared by dissolving hydrazine monohydrate (2.5 g) in pure water (200 ml) and soaked to reduce the ruthenium. The pellet-like mixture after reduction treatment was washed with pure water, and dried at 110degreesC in air for 12 hours to give a ruthenium-supporting alumina carrier (comparative). To portion of the ruthenium-supporting alumina carrier (100 g) was added an aqueous solution (50 ml) containing lanthanum nitrate hexahydrate (9.4 g). After drying at 110degreesC, the resulting mixture was calcined at 500degreesC in the stream of a mixed gas composed of hydrogen (10 vol.%) and nitrogen (90 vol.%) under a reducing atmosphere to give catalyst (test) which carried ruthenium (49 wt.%) and lanthanum (3 wt.%). The test and comparative catalyst were introduced onto the reaction tube to provide catalyst layer. In to the reaction tube was introduced simulated reformed gas comprising (vol.%) carbon monoxide (0.5), carbon dioxide (16), steam (20) and hydrogen (balance) as a test gas and oxygen in a quantity 1.5 times the volume of the carbon monoxide at a space velocity (SV) (per hour) of 10000 and 7500 for comparative and test catalyst respectively. The temperature of the test gas at the inlet of the reaction tube was maintained at 174degreesC and the carbon monoxide and methane concentration of the treated gas at the outlet of the reaction tube and presence or absence of generation of carbon dioxide methanation were observed. The test/comparative catalyst showed concentration (ppm) of carbon monoxide and methane of 0/not detected due to generation of carbon dioxide methanation and 1010/not detected respectively.