Effect of oxygen mobility in the lattice of Au/TiO2 on formaldehyde oxidation

Two Au catalysts supported on TiO2 were prepared by impregnation method followed by sodium borohydride reduction or calcination in air (Au/TiO2-R and Au/TiO2-C, respectively). The 1 wt % Au/TiO2-R sample was found to be highly efficient for the oxidation of low concentrated formaldehyde at room temperature. A HCHO conversion of 98.5% was achieved with this catalyst, whereas the Au/TiO2-C sample showed almost no activity under the same conditions. Highly dispersed metallic Au nanoparticles with small size (similar to 3.5 nm) were identified in the 1 wt % Au/TiO2-R catalyst. A significant negative shift of Au4f peak in XPS spectra with respect to bulk metallic Au was observed for the 1 wt % Au/TiO2-R but no similar phenomena was found for the heat-treated catalyst. More Au nanoparticles and higher content of surface active oxygen were identified on the surface of the Au/TiO2-R in comparison with the Au/TiO2-C, suggesting that the Au/TiO2-R catalyst can enhance the amount of active sites and species involved in for HCHO oxidation. The reduction treatment by sodium borohydride promotes the formation of dispersed metallic Au nanoparticles with small size because it facilitates the electron transfer and increases the content of surface Au nanoparticles and activated oxygen. All these factors are responsible for a high activity of this catalyst in the oxidation of HCHO.