EFFECT of TRANSITION METALS (Y, La, Zr, Nb) MODIFIED TiO2 on Pt DISPERSION and CO OXIDATION ACTIVITY of Pt/TiO2 CATALYST

Abstract

Transition Metal (Y, La, Zr, Nb) modified TiO2 supported Pt catalysts were prepared by successive impregnation with different M/Ti mole ratios in the range of 0.001-0.1, where M is the transition metal. The Pt/Y-TiO2 with Y/Ti 0.001-0.05 showed higher active sites as measured by CO chemisorption than the unmodified Pt/TO2. The highest Pt active sites were found at Y/Ti = 0.001 and declined as the Y/Ti ratio was further increased. The Pt/0.001Y-TiO2 exhibited the lowest light-off temperature at 85°C for CO oxidation. The declined activity at higher Y/Ti mole ratio than 0.001 was probably due to Pt deposited on yttria. Thus, the CO adsorbed on Pt could not react with the oxygen in TiO2 lattice. The ESR results showed the highest Ti3+ on Pt/0.001Y-TiO2 and decreased when increasing dopant ratio. The presence of which Ti3+ promoted metal distribution and activity. The number of active sites and activity of the other transition metals (La, Zr, Nb) doped TiO2 supported Pt catalysts were also increased with the Pt/0.005M-TiO2 exhibited the highest values. Further increase of M/Ti ratios resulted in lower activity which was similar to the Pt/Y-TiO2. For a dopant 0.005M-TiO2 exhibited Ti3+ higher than TiO2. The increasing of Ti3+ probably corresponded to atomic radius or electronegativity of dopant. In conclusion, doping the transition metals (Y, La, Zr, Nb) on the TiO2 support in the range 0.001-0.005 mole ratio is an effective method to increase Pt dispersion on TiO2 and CO oxidation activity of Pt/TiO2.