title: Synergy and Anti-Synergy between Palladium and Gold in Nanoparticles Dispersed on a Reducible Support.
abstract: Highly active and stable bimetallic Au-Pd catalysts have been extensively studied for several liquid-phase oxidation reactions in recent years, but there are far fewer reports on the use of these catalysts for low-temperature gas-phase reactions. Here we initially established the presence of a synergistic effect in a range of bimetallic Au-Pd/CeZrO4catalysts, by measuring their activity for selective oxidation of benzyl alcohol. The catalysts were then evaluated for low-temperature WGS, CO oxidation, and formic acid decomposition, all of which are believed to be mechanistically related. A stronganti-synergybetween Au and Pd was observed for these reactions, whereby the introduction of Pd to a monometallic Au catalyst resulted in a significant decrease in catalytic activity. Furthermore, monometallic Pd was more active than Pd-rich bimetallic catalysts. The nature of the anti-synergy was probed by several ex situ techniques, which all indicated a growth in metal nanoparticle size with Pd addition. However, the most definitive information was provided by in situ CO-DRIFTS, in which CO adsorption associated with interfacial sites was found to vary with the molar ratio of the metals and could be correlated with the catalytic activity of each reaction. As a similar correlation was observed between activity and the presence of Au0* (as detected by XPS), it is proposed that peripheral Au0* species form part of the active centers in the most active catalysts for the three gas-phase reactions. In contrast, the active sites for the selective oxidation of benzyl alcohol are generally thought to be electronically modified gold atoms at the surface of the nanoparticles.
authors.affiliation: Cardiff Catalysis Institute, School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff CF10 3AT, U.K.
authors.forename: James H
authors.initials: JH
authors.lastname: Carter
authors.affiliation: Department of Materials Science and Engineering, Lehigh University , 5 East Packer Avenue, Bethlehem, Pennsylvania 18015-3195, United States.
authors.forename: Sultan
authors.initials: S
authors.lastname: Althahban
authors.affiliation: Cardiff Catalysis Institute, School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff CF10 3AT, U.K.
authors.forename: Ewa
authors.initials: E
authors.lastname: Nowicka
authors.affiliation: Cardiff Catalysis Institute, School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff CF10 3AT, U.K.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Freakley
authors.affiliation: Cardiff Catalysis Institute, School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff CF10 3AT, U.K.
authors.forename: David J
authors.initials: DJ
authors.lastname: Morgan
authors.affiliation: Cardiff Catalysis Institute, School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff CF10 3AT, U.K.
authors.forename: Parag M
authors.initials: PM
authors.lastname: Shah
authors.affiliation: Cardiff Catalysis Institute, School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff CF10 3AT, U.K.
authors.forename: Stanislaw
authors.initials: S
authors.lastname: Golunski
authors.affiliation: Department of Materials Science and Engineering, Lehigh University , 5 East Packer Avenue, Bethlehem, Pennsylvania 18015-3195, United States.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Kiely
authors.affiliation: Cardiff Catalysis Institute, School of Chemistry, Cardiff University , Main Building, Park Place, Cardiff CF10 3AT, U.K.
authors.forename: Graham J
authors.initials: GJ
authors.lastname: Hutchings
keywords: CO oxidation; ceria−zirconia; formic acid; gold; gold−palladium alloy; palladium; water-gas shift