Active TiO 2 -Nanostructured Surfaces for CO Oxidation on Rh Model Catalysts at Low-Temperature

We investigated the CO oxidation at low temperature over Rh (1 wt%) supported on TiO2-nanotubes and nanoparticles. We found that tri-titanic acid phase of the nanotubes promotes the interaction between Ti4+ and Rh3+ to reduce Rh3+ to Rh1+ and Rh+1 to Rh0, compared to the anatase phase. In fact, as the Rh0/Ti4+ ratio increases, CO and OH adsorption increases and CO oxidation light-off shifts to lower temperature, from 120 to 60 °C. We found that there is a redox equilibrium between Rh0 + Ti4+ and Rhδ+ + Ti3+ (δ < 3). However, the Rh0/Ti4+ ratio, hence redox equilibrium, seems to be limited by the valence band energy of the catalysts. We concluded that there is a strong electronic metal-support interaction between nanotubes of TiO2 and Rh-nanoparticles that promotes the catalytic performance. Therefore, the valence band is a major factor determining the catalytic activity.