The activation of supported Au catalysts prepared by impregnation

In this study, Au/TiO2, Au/γ-Al2O3, and Au/C catalysts were prepared by an incipient-wetness impregnation method. The CO oxidation activity after different pretreatment was analyzed. Two pretreatments are found possible to activate these catalysts for CO oxidation: (i) high-temperature hydrogen reduction and (ii) aqueous base treatment using NH3(aq). The high-temperature hydrogen reduction is effective for Au/TiO2 and Au/C, but not Au/Al2O3. The base treatment is effective for Au/Al2O3 and Au/TiO2, but not Au/C. Small Au particles of ca. 2 nm size were observed in activated Au catalysts from both pretreatments; however, the high-temperature H2 reduction procedure also resulted in large Au particles of ca. 25 nm size which makes it a less efficient pretreatment than the base treatment. The activated Au/TiO2 catalysts show comparable turnover frequency as the Au/TiO2 catalyst prepared by a deposition precipitation method. The effective pretreatments were found to be accompanied by a reduced acidity, which is measured by the pH of aqueous catalyst suspension. Reasons for such activation are discussed.