TiO2 and ZrO2 supported Ru catalysts for CO mitigation following the water-gas shift reaction

CO oxidation and methanation over Ru-TiO₂ and Ru-ZrO₂ catalysts were investigated for CO removal for applications in proton exchange membrane fuel cells. The catalysts were synthesised by the deposition precipitation method at a pH of 7–7.5 for better interactions between the support and the active Ru metal. Various characterization experiments such as TPR, XPS, FTIR-CO, CO chemisorption and HRTEM were conducted to better understand the physio-chemical properties of Ru on the supports. Both catalysts showed excellent activity for the total oxidation of CO, however, with the addition of H₂, the catalysts activity to CO oxidation decreased significantly. Higher temperatures for the preferential oxidation reaction indicated that the Ru catalysts not only oxidize CO, but hydrogenate it as well. Furthermore, H₂ oxidation was favoured over the catalysts. Hydrogenation of CO over these catalysts gave high CO conversion and selectivity towards CH₄. Both the catalysts showed similar activity across the temperature range screened and gave maximum CO conversions of 99.9% from 240 °C onwards, with 99.9% selectivity towards CH₄. The catalysts also showed good stability in the reaction and the similarities in the catalytic activity of these were attributed to the well-dispersed Ru metal over the supports. The Ru catalysts effectively reduced CO concentrations in the reformate gas to less than 10 ppm, as is required for practical applications.