Pd- and/or Au-loaded Nb- and V-doped macro-mesoporous TiO2 supports as catalysts for the total oxidation of VOCs

Two sets of hierarchically structured titania (TiO 2) supports were doped with group V metal oxides, one with Nb 2O 5 and the other with V 2O 5. It was noted that before thermal treatment the prepared materials were amorphous, whereas after calcination at 400 °C the XRD patterns showed well-defined peaks that indicated that the materials were a crystalline anatase phase. Treating these supports at high temperatures was followed by a decrease in their Brunauer-Emmett-Teller (BET) specific surface area values. The catalytic performance of these materials and their corresponding noble metal (Pd and Au) loaded catalysts was investigated in the total oxidation of toluene. It was clear that after noble-metal loading, the activity was much higher than that of the unloaded supports, with Pd5VTi and PdAu3NbTi offering the best performances in the oxidation reaction. XRD patterns of the noble-metal-loaded catalysts showed peaks associated with the presence of metallic gold particles and palladium species on the supports; diffuse-reflectance UV/Vis spectra also showed the presence of these noble metals, as well as a reduction in the intensities of the bands relative to those in the spectra of the unloaded doped titania supports, which is due to the metal-support interactions. Spectra obtained with this characterization technique also showed a shift of the Au bands to higher wavelengths, which should be correlated to changes in the size of the gold particles.