Abstract
Oxide-supported noble metal catalysts were tested in the preferential oxidation of carbon monoxide (PROX) reaction in the temperature range between 50 and 300°C. Both the influence of the noble metal nature (Pt, Ir, Pd), the support physical and chemical properties (redox, acidity, basicity) and the reaction conditions (oxygen stoichiometry) on the catalyst activity and selectivity was evaluated. Platinum and iridium were shown to be the most active and selective catalysts in the whole temperature range compared with palladium. Furthermore, noble metals supported over ceria-based oxides were shown to be active and selective, especially at low temperature. Additionally, it was observed that the higher the molar fraction in ceria in the oxide, the higher the activity and the selectivity in the PROX reaction. Ceria, with the highest oxygen mobility at the oxide surface, was shown to be the best support. Accordingly, on simple oxides (CeO2, SiO2–Al2O3, Al2O3, SiO2, La2O3 and MgO), the induced mobility of the oxygen atoms at the surface of the support determined elsewhere, well correlated with the basicity of the support, was shown to be one key parameter for the performances of the catalysts in the PROX reaction. Finally, the formation of water (hydrogen oxidation) at high temperature and high oxygen excess was shown to be responsible for the increasing activity of the catalysts in the conversion of CO to CO2 via the water gas shift reaction (WGSR).
Highlights
Proton exchange membrane fuel cells (PEMFC) have been extensively studied in the past decades
Complete oxygen conversion was reached at ca. 100 ◦C in the case of platinum and ca. 130 ◦C in the case of iridium
Ceria–zirconia supports are well-known reducible oxides, highly active for the oxygen storage [22,23]. This specific property of these oxides could explain the high activity and selectivity of these samples, especially at much lower temperatures compared to alumina-supported noble metal catalysts [2,7,8,9]
Summary
Proton exchange membrane fuel cells (PEMFC) have been extensively studied in the past decades. Applications in mobile energy sources have been paid an increasing attention. Pure hydrogen is the ideal fuel for such systems. Mature technologies for a safe and efficient storage of hydrogen on-board of the vehicle are still not commercially available. Hydrogen could likely be generated on-board using a reformer. Gasoline or alcohols (methanol, ethanol) are the potential hydrogen sources [1]
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