Hydrocatalytic Reduction of Nitrate in Aqueous Solution over Titania Supported Pd-Au Catalysts

Some Pd and/or Au containing catalysts supported on TiO2 were prepared by impregnation (I) and incipient witness (IW) methods. These catalysts that include Au3%/TiO2-I, Au1.5%/TiO2-I, Au1.5%Pd1.5%/TiO2-I, Pd1.5%/TiO2-I, Pd3%/TiO2-I and Au6.0%Pd0.2%/TiO2/IW were characterized by means of XRD. The supported metal was thereby determined to have a particle size around 50 nm. All catalysts were tested in the reduction of nitrate ions in aqueous solution and in the presence of hydrogen gas. All tested catalysts were found to be of relatively high activity and with high dinitrogen selectivity in this respect. Pd-Au/TiO2 catalysts were found to have high selectivity but slightly lower activity than Pd-catalysts. Incorporation of Au into Pd catalysts has improved their selectivity. Au1.5%Pd1.5%/TiO2-I produces less nitrite than Pd3%/TiO2- I, indicating that alloying has positive effects on the reduction of nitrate. The alloying effects were much more pronounced in the case of Au6%Pd0.2%/TiO2/IW where more than 87% nitrate conversion was achieved with ~100% dinitrogen selectivity in 30 min. of reaction and without any detectable nitrogen fixation.