Influence of the partner oxide on the catalytic properties of Au/CexZr1-x highly loaded gold catalysts

National @ ING+FMO:JROInternational audienceSince the pioneering work of Haruta et al [1] gold catalysts have been shown to be more active at low temperature than platinum-b ased catalysts for the oxidation of pure carbon monoxide [2] Gold nanoparticles deposited on suitable oxide supports are even extremely active for several other oxidation reactions. Among these, the water gas shift reaction [3], the epoxidation of propylene [4] the direct synthesis of H2O2 from H2 and O2 [5], CO oxidation, preferential oxidation (PrOx) of CO in the presence of hydrogen [6-12] and the oxidation of H2 [13] are all known to be catalyzed by gold. Consequently, the possibility of using gold catalysts as efficient catalysts for low-temperature preferential oxidation of CO in the presence of hydrogen gave rise to a great interest for the purification of the gas feed in proton exchange membrane fuel cells (PEM-FC). (near the operating temperature of the PEM-FC:80–120°C without oxidizing the hydrogen fuel). The study of support with different redox properties should help to find catalysts having better activity but above all selectivity for CO oxidation in the presence of H2 in a wide temperature range. In addition, low-temperature CO oxidation and PrOx have been used as test-reactions to investigate the mechanisms of oxygen activation and/or H2 adsorption and dissociation that proceed in a more complex way on gold than over platinum group metals. Indeed several active sites have been suggested for oxygen activation: interfacial metal-oxide sites [14-17] cationic gold sites [18,19] or low-coordination gold atoms [20]. Other molecules and their interactions with gold surfaces have been investigated although to a lesser extent than CO or O2. Among them, hydrogen adsorption and activation, which is a key step in many reactions like hydrogenations, the reverse water gas shift reaction and other processes as CO preferential oxidation (PrOx) [21-27]. Despite these studies, the mechanisms responsible for the catalytic activity are still under debate especially in what way and on which site O2 is activated. According to literature [15, 28-33] the support should play a role in this activation process. Since the ability to provide lattice oxygen should be an important factor dictating the catalytic activity of supported gold catalysts, we synthezised, simply by oxidation of the primary AuCe, AuZr, AuCeZr alloys, intimate mixtures of nanostructured Au with CeO2, ZrO2 or Ce-Zr mixed oxides which have unique redox properties and high mobility of lattice oxygen. The present work is following a study on the catalytic properties of Au/ZrO2 material, obtained by the same method which leads to the formation of an intimate mixture of nanostructured gold and zirconia [34] The obtained materials were tested in three catalytic reactions, the oxidation of CO, the selective oxidation of CO in the presence of H2, and the oxidation of H