Chemisorption of CO on Au/TiOx/Pt(111) Model Catalysts with Different Stoichiometry and Defectivity

Au/TiOx/Pt(111) model catalysts were prepared starting from well characterized TiOx/Pt(111) ultrathin films, according to an established procedure consisting in a reactive evaporation of Ti, subsequent thermal treatment in O2 or in UHV, and final deposition of submonolayer quantities of Au. Temperature Programmed Desorption measurements were performed to compare the interaction of CO in the case of two reduced TiOx/Pt(111) substrates (indicated as w-TiOx and w′-TiOx, being the former characterized by an ordered array of defects that can act as template for the deposition of a stable array of Au nanoparticles), with the case of a stoichiometric rect′-TiO2/Pt(111) substrate. It was found that in all cases CO is molecularly adsorbed and two different desorption peaks are detected: one at ≈140 K corresponding to CO desorption from less active adsorption sites (terraces) of the Au nanoparticles and one at ≈200 K corresponding to CO desorption from Au nanoparticles step sites. After annealing at 770 K, the high temperature CO desorption peak is still present in the case of the defective reduced w-TiOx phase, supporting the good templating and stabilizing effect of such phase. On the rect′-TiO2 stoichiometric phase, the CO uptake decreases after annealing but only to a minor extent.