TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Device: The substrate is a honeycomb substrate having several parallel, axially enclosed cells. The substrate is an open-celled foam substrate. The first layer has a length of at least 80 (preferably at least 60)% of the wall element's length. The second layer has a length of at least 30% of the wall element's length. The optional promoter in the CO oxidation catalyst is iron component. The platinum metal-based catalyst consists of platinum in an amount of 1 - 5 (preferably 5) wt.%, a support and iron 0.1 - 0.5 (preferably 0.3) wt.%; and the palladium metal-based catalyst consists of palladium in an amount of 1 - 5 (preferably 5) wt.%, a support and iron 0.1 - 0.5 wt.%. The methanation catalyst consists of ruthenium in an amount of 1 - 10 wt.%, and an alumina support.Preferred Method: The hydrogen stream is at a temperature of 80 - 180degreesC. EXAMPLE - An aqueous ruthenium nitrosyl nitrate solution (52.8 g) was diluted with deionized water to provide a solution (73 ml). This solution was used to impregnate 100 g of gamma alumina powder using incipient wetness impregnation technique. After mixing well, the powder was dried at 120degreesC for 2 hours, and then calcined at 250degreesC for 2 hours. The powder was slurried with water to form the (Ru/alumina) washcoat. A commercially available, monolithic catalyst coated along the entire axial length of a substrate with a washcoat having platinum ( approximately 5 wt.%) and iron (0.3 wt.%) on alumina support was used as the starting workpiece. The ceramic monolith substrate contained 400 cells per square inch (cpsi). The monolith substrate was dipped into the 5% Ru/alumina washcoat to a depth of 50% of the substrate's axial length to form the second (top layer). The washcoat loading of the second layer was 2 g/inch3, based on the coated volume. The excess slurry was removed by blowing air through the channels of the monolith. The catalyst was then dried at 120degreesC and calcined at 250degreesC in air to form an article (A). The ruthenium layer in the article was activated after the calcination by exposure to the process stream at 200degreesC. The performance of the article (A) was evaluated as a second stage in a two stage system for treatment of hydrogen stream containing 0.75% CO. The first stage of the system contained a preferential oxidation catalyst article composed of a single layer containing 5 wt.% Pt and about 0.3 wt.% iron on an alumina support that was coated on 400 cpsi cordierite substrate. Article (A) was used in the second stage. Each of the stages was placed in separate reactors that were fluidly connected. The two-stage system was exposed to a test gas having a dry gas composition of CO (0.75%), CO2 (15%), H2 (50%) and the balance was N2 (30%). Steam was added as a diluent. Air was added as a source of oxygen, and the volume of air was split between the two carbon monoxide treatment stages so that 85% of the air was injected in the first stage (Prox stage) and 15% of the total was injected into the second stage (containing article A). The operating parameters and performance results were as follows. The inlet hydrogen stream temperature was 140degreesC and space velocity of the stream was 42 k/hour at prox stage, and 35 k/hour at second stage. The inlet CO in the hydrogen stream was 0.75%, inlet O2 was at 0.68% at first stage and 0.1% at second stage. The results obtained after the first stage and second stage were as follows: outlet CO quantity was (ppm): 700 and 7 respectively; CO conversion (% of total): 91 and 99.9 respectively; and outlet methane (CH4) quantity: less than 200 ppm after second stage (having methanation catalyst). The results showed that outlet CO threshold of less than 10 ppm at temperature of less than or equal to 140degreesC was achieved using the article (A). This threshold was achieved with less than 200 ppm of methane produced in the outlet gas stream.