Zr and Ag L-edge XANES studies of Ag nanoparticles in nanoporous Zr-Si-O thin films

ANDRINI, L.; ANGELOME, P; WOLOSIUK, A; SOLER-ILLIA, GJAA; REQUEJO, FG

Campinas, SP - Brasil

Jornada; 19a Reunión Anual de Usuarios del LNLS; 2009

Mesoporous zirconia-silica (MZS) have been extensively investigated, for their high potential in catalysis, in particular for creating controlled nanometric cavities with regular spatial separation [1]. The well-known activity of silver for selective oxidation of hydrocarbons [2] becomes the Ag-MZS system as a promissory model catalyst because the introduction of silver in the pores of MZS oxides gives highly ordered active catalytic sites.    We studied the modifications in the MZS oxide after introduction of silver into their pores. According to the crystal-field information obtained from the Zr L2,3 and Ag L2,3-XANES spectra we obtained direct evidence of charge transference between Ag nanoparticles and Zr ions in the surface of MSZ.    The Zr and Ag L2,3 XANES measurements were carried out at D04A-SXS beamline at LNLS (Campinas, Brazil). The preparation of oxides and the films were already reported elsewhere [3]. The Ag nanoparticles were introduced into the pores of the MZS by immersion in a AgNO3-EtOH solution followed with a slow chemical reduction with HCHO [4]. The MZS thin films supported on FTO have a molar ratio Zr/(Zr+Si) = 10, 90, and were studied before and after the Ag incorporation.    We have quantitatively obtained the nature of changes at the Δh3/2;5/2 holes in Ag nanoparticles in MZS. There is an increment in the number of holes with respect to the pure Ag. After introducing Ag in the pores of the MZS film, there is a decrement of the splitting due to crystal field interactions, consistently with the electronic transfer from Ag to Zr.