Au/TiO2 nanostructured catalyst: pressure and temperature effects on the FTIR spectra of CO adsorbed at 90 K

The effects of the equilibrium pressure and of the temperature on the FTIR spectra of CO adsorbed on a nanostructured Au/TiO2 catalyst are discussed. At 90 K, at full coverage, in addition to strong bands assigned to CO adsorbed on Ti4+ cations at usual frequencies, a band related to CO adsorbed on gold sites, significantly red shifted in respect to the usual position, is detected. By reducing the CO pressure, a large fraction of CO adsorbed on titania is desorbed and the band ascribed to CO adsorbed on gold sites blue shifts up to the usual frequency. The possibility that ligand effects of CO coverage on the support play a role is proposed. Starting from an incomplete monolayer, an intensity transfer from the band assigned to CO adsorbed on Ti4+ to that of CO adsorbed on the gold sites is observed. A blue shift is also detected. It appears that the CO molecules weakly adsorbed on the support cations act as precursors for CO chemisorbed on gold sites.