XAFS STUDY ON CHEMISTRY IN PREPARATION OF AU TIO2 AND AU/AL2O3/

Active Au/TiO2 and lesser-active Au/TiO2 and Au/Al2O2 catalysts, which have different morphology of ultra fine gold particles with a few to 20 Nn in diameter on the surface of TiO2 and Al2O3 fine particles, wer e obtained from precursors precipitated in solution with different pH values by firing in air. AuL3 XAFS analysis was made for the catalysts to investigate dependence of valence state and local structure of gol d on the pH value. In Au/TiO2 system the height of absorption at edge, which corresponds to transition from 2p to 5d, decreased with increas ing pH even below that of metallic one. The ratio of heights of Au-M(M = Au, Ti or Al) peaks at 1.8-2.2 Angstrom, which were found more clea rly in radial distribution function for Au/TiO2 than for Au/Al2O3, ove r that of Au-Au peak increased with increasing pH value.