Tunable catalytic activities and selectivities of metal ion doped TiO2 nanoparticles--oxidation of organic compounds.

A series of metal ion doped TiO2 nanoparticles (M-TiO2, M = Cr(3+), Mn(2+), Fe(3+), V(5+), Zn(2+), Ni(2+), Ag(+), Cu(2+) and Co(2+)) were prepared by a facile co-precipitation approach and characterized by means of ICP-AES, N2 adsorption-desorption isotherms, XRD, TEM and HRTEM. Their catalytic performance was investigated via the oxidation of organic compounds. The variation of metal ion species and doping contents allowed tuning the catalytic properties of the M-TiO2. Among them, the catalyst Cu-10 displayed excellent activity (97.5%) in the oxidation of styrene and the selectivity of benzaldehyde was as high as 99.4%. Surprisingly, the product distribution of styrene oxidation experienced a reverse trend over the Co-TiO2 catalysts with different doping amounts of cobalt ions: Co-10 was in favor of forming benzaldehyde (80.2% selectivity), in contrast with Co-15, which produced styrene oxide as the dominant product (84.7% selectivity). The M-TiO2 catalysts also showed catalytic activities for the oxidation of benzyl alcohol and toluene to generate chlorine-free benzaldehyde in excellent selectivities (>99%).