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

Au/TiO _x /Pt(111) model catalysts were prepared starting from well characterized TiO _x /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 TiO _x /Pt(111) substrates (indicated as w-TiO _x and w′-TiO _x , 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-TiO _x 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.