Titania supported Pd-Cu bimetallic catalyst for the reduction of nitrate in drinking water

Titania supported palladium-copper bimetallic catalysts (Pd-Cu/TiO2) are prepared by the liquid phase chemical reduction method and then applied in the liquid phase catalytic reduction of nitrate ions (NO3−). Compared with the conventional impregnation method that needs the post-thermal reduction to prepare the supported metallic catalysts, the liquid phase chemical reduction at room temperature can inhibit the aggregation of metal active components and have been proved to exhibit high catalytic activity in this work. The conversions of NO3− are 29.18% and 54.12% over the catalysts treated at 873 and 298 K, respectively. The conversion of NO3− and selectivity to N2 influenced by the effect of the support, the loading of Pd+Cu, the molar ratio of Pd to Cu, the H2 flow rate, the addition of CO2 and the pH value of solution are also discussed in detail with the surface characterizations by X-ray photoelectron spectrum (XPS), X-ray diffraction (XRD), in situ FT-IR and transmission electron microscopy (TEM). A mechanism has been proposed that Cu2O component involved the reaction course and acted as the active center for nitrate-to-nitrite conversion. The spilt-over hydrogen on Pd is suggested to reduce the adjacent Cu2O into metal Cu, and on the latter the conversion of NO3− to NO2− occurs. However, in strongly acidic solution, copper is dissolved from the Pd-Cu/TiO2 catalyst and released into the solution in the form of copper(II) ions, so the reduction of Cu2O to Cu is inhibited and the nitrate reduction cannot be accomplished.