Characterizations of alumina-supported gold with temperature-programmed reduction Original Research Article

Supported Au/Al2O3 samples of different gold loadings were prepared by the deposition-precipitation of AuCl3 onto alumina. Prepared samples were physically characterized by techniques of atomic emission (ICP), X-ray diffraction (XRD), transmission electron microscope (TEM) and temperature-programmed reduction (TPR). According to TEM and XRD observations, the size of gold crystallites dispersed on samples freshly prepared at 300 K was ca. 8 nm. TPR characterizations of oxidized samples distinguished three kinds of reductive peaks at temperatures ca. 180, 300 and 1000 K. These peaks are attributed to reductions of gold oxides (AusOx) and gold chloride (AusCly) on the surface of supported gold crystallites, and of gold ions (Aui) incorporated into the subsurface of alumina support, respectively. The stoichiometry x of AusOx increased with the temperature of oxidation treatment (T0) and attained a peak value of 2.0 ca. T0=600 K. Using this adsorption stoichiometry, variations in the dispersions of gold crystallites on alumina were determined. Through dispersion measurements, supported nano-crystallites of gold were found to sinter at T>673 K in both oxidative and reductive environments.