INVESTIGADORES
ALVAREZ mariana
congresos y reuniones científicas
Título:
XAS study on the gold particle size of Au catalysts
Autor/es:
MARIANA ALVAREZ; BETIANA C. CAMPO; MARÍA A. VOLPE
Lugar:
Camerino
Reunión:
Conferencia; 14th International Conference on X-ray Absorption Fine Structure; 2009
Institución organizadora:
International X-ray Absorption Society
Resumen:
Supported gold catalysts are very active in catalyzing many types of reactions. Gold particles smaller than 5 nm, in addition to low chlorine residue, are considered essential for the high activity[1]. The support is also reported to play an important role in hydorgenation reactions[2] although this role might be dependent on the reagent, being for some reactions practically negligible. This role can be the one providing a source of hydrogen to the metal sites, or interacting with gold to produce more selective electron-rich gold particles. This work proposes the XAFS study of gold catalysts prepared using g-Al2O3 as a support. Iron acethyl acetonate, Fe(C5H7O2)3, was used to surface-functionalize the support in a direct method. The solid was calcinated in order to eliminate the remanent ligands and to form superficial species that we named FexOy, probably formed by hematite supported on the g-Al2O3. Gold particles were fixed following the direct anionic exchange(DAE) method[3] from HAuCl4 aqueous solutions at pH 5. XANES spectra of the modified support and the corresponding gold catalyst were analyzed. At the Fe K-edge, the first prominent signal of both samples appears at 7133.4 eV, and the energy position coincides with that of the Fe+3 reference (Fe2O3), confirming that Fe is present in its trivalent state. At the Au LIII-edge, the catalyst signal appears at 11923 eV, coincident with the Au0 profile. Two resonante features, at +21 and +45 eV, above the white line can also be observed, probably associated with isolated and polymeric Au+3(OH)3 species. EXAFS data about Au and Fe atomic distances are also presented and discussed.2O3 as a support. Iron acethyl acetonate, Fe(C5H7O2)3, was used to surface-functionalize the support in a direct method. The solid was calcinated in order to eliminate the remanent ligands and to form superficial species that we named FexOy, probably formed by hematite supported on the -Al2O3. Gold particles were fixed following the direct anionic exchange(DAE) method[3] from HAuCl4 aqueous solutions at pH 5. XANES spectra of the modified support and the corresponding gold catalyst were analyzed. At the Fe K-edge, the first prominent signal of both samples appears at 7133.4 eV, and the energy position coincides with that of the Fe+3 reference (Fe2O3), confirming that Fe is present in its trivalent state. At the Au LIII-edge, the catalyst signal appears at 11923 eV, coincident with the Au0 profile. Two resonante features, at +21 and +45 eV, above the white line can also be observed, probably associated with isolated and polymeric Au+3(OH)3 species. EXAFS data about Au and Fe atomic distances are also presented and discussed.