Development of a novel Ru-based catalyst system for the selective oxidation of CO in hydrogen rich gas mixtures Original Research Article

The hydrogen feedstock for fuel cell applications can be supplied by reforming reactions followed by a water-gas-shift stage, where most of the CO is removed. Still the hydrogen rich gas mixture has to be purified further to prevent the anode’s catalyst from severe degradation. At DLR, a novel, technically applicable Ru-based catalyst system was developed for the removal of CO from these gas mixtures by selective oxidation. Reticulated ceramic foams were used as matrix structure. These were coated with a γ-Al2O3 washcoat. Ru was applied as the active metal catalyst by the method of incipient wetness impregnation. Three different precursor materials were investigated. As Ru-nitrosylnitrate turned out to be the most favorable one, the oxidation temperature and the metal loading were varied using this precursor. Both parameters turned out to have a strong influence on catalyst activity and selectivity. The best foam-based catalyst was able to reduce the CO content in a simulated shift exit gas stream containing H2, CO2, H2O and CO below 30 ppm applying an oxygen excess of λ=3 in a temperature range between 100 and 160 °C, while charging the catalyst with space velocities up to 5000 h−1.