Catalysis on nanoporous gold–silver systems: Synergistic effects toward oxidation reactions and influence of the surface composition

• Published in: Journal of catalysis Vol. 311; pp. 221 - 229
• Main Authors: Déronzier, Thierry, Morfin, Franck, Lomello, Marc, Rousset, Jean-Luc
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.03.2014; Elsevier; Elsevier BV
• Subjects: Catalysis; Catalysts; Chemical Sciences; Chemistry; CO oxidation; Colloidal state and disperse state; Environment and Society; Environmental Sciences; Exact sciences and technology; General and physical chemistry; Gold; H2 oxidation; LEIS; Nanoporous alloys; Oxidation; Porous materials; PrOx; Silver; Surface chemistry; Surface segregation; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; LEIS; Gold; Silver; H2 oxidation; CO oxidation; Surface segregation; Nanoporous alloys; Catalysis; PrOx; Composition; Catalytic reaction; Alloys; H; Transition metal; Porous material; Heterogeneous catalysis; Oxidation; Nanoporosity
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2013.12.001

[Display omitted] •Au–Ag nanoporous systems with controlled composition were successfully synthesized.•A strong synergistic effect between Au and Ag in oxidation reactions is observed.•Au–Ag exhibited high activity toward CO and/or H2 oxidation and very high selectivity.•We establish a correlation between very surface Ag concentration and reactivity.•A catalytic process implying multiple Ag atom sites is proposed. Au–Ag nanoporous systems were prepared by a recently developed method. Contrary to the electrochemical dealloying, the methodology applied in this work proved that it allowed to prepare bimetallic AuAg NP systems with controlled chemical compositions. Compared with monometallic Au or Ag catalysts, the alloy catalysts exhibited high activity toward CO and/or H2 oxidation and exceptionally high selectivity at low temperature for CO oxidation in the presence of H2 showing a synergistic effect between Au and Ag. Among the different characterizations, Low-Energy Ion-Scattering Experiments provided composition data about the topmost atomic layer, i.e., where catalytic reactions occur and allowed us to establish a clear correlation between top layer surface concentration and reactivity. A pronounced dependence of the reaction rate on the silver concentration has been observed only for H2 oxidation. This strong dependence has been correlated with the number of surface sites constituted of adjacent Ag atoms required for dissociative oxygen adsorption. The high selectivity of the Au–Ag alloys with respect to pure gold has been ascribed to a large segregation of silver, especially on low coordination sites, inhibiting the H2 adsorption.