Studies On CO Selective Oxidation In H₂ Over Silver And Platinum Based Catalysts On Carbon Materials

Proton exchange membrane fuel cells (PEMFC), operating at relatively low temperatures (e.g. 60-80oC) with pure hydrogen or reformed gas as fuels, have attracted much attention as a potential power source of electric vehicles. However, the Pt anode catalysts can be seriously poisoned by traces of CO in the reformed gas, which has motivated the search of high efficient catalysts for the CO preferential oxidation in excess H2 at low temperature.The present work was focused on the catalytic properties of carbon materials supported Ag, PtAg, PtFeNi catalysts for CO selective oxidation in H2 feed gas and three parts were included: (1) The effects of textural properties, surface chemistry of activated carbon supports and the roles of hydrogen activation on the activities of Ag/AC catalysts were investigated. The following conclusions can be drawn (a) large amounts of mesopore tend to increase the dispersions of Ag particles, thus, giving higher maximum CO conversion at low temperature; (b) there is maybe negative effect of microporous structure on the dispersions of Ag particles and catalytic performance; (c) rich surface functional groups on one hand make size distribution of Ag particles bimodal, but on the other hand promote the formation of very fine Ag particles, leading to low maximum CO conversion at low temperature; (d) after pretreatment with H2, AC can form superoxide species, O2-; the existence of Ag promotes the formation of superoxide species. With silver, superoxide species can react with CO, the higher pre-treatment temperaturesenhance the formation ability of superoxide species over AC support, leading to better catalytic performance. (2) The catalytic properties and catalyst structure of carbon black supported PtAg bimetal catalysts were investigated. It is found that no obvious PtAg alloy has been observed; however, there maybe exists some interaction between Pt and Ag, leading to evidently synergistic effects for PtAg bimetal catalysts. (3) The Fe and/or Ni promotion and catalytic properties of different carbon materials supported PtFeNi catalysts have been studied in details. It is found that the multiwall carbon nanotubes with Fe and Ni catalyst residues supported Pt catalyst is able to remove all CO at room temperature, with high activity, high selectivity and high stability. The promotion effects of Fe and/or Ni were observed, and the good electron-conductivity of carbon supports played an important role for the good catalytic properties.