Effects of chlorinated Pd precursors and preparation methods on properties and activity of Pd/TiO 2 catalysts.

We investigated the effects of Pd precursors and preparation methods on the physicochemical properties and performance of Pd/TiO 2 catalysts in the photocatalytic degradation of methyl violet. To confirm the influence of the precursors, Pd/TiO 2 catalysts were prepared via chemical reduction (CR) using four different Pd precursors. Additionally, to determine the effects of preparation methods, Pd/TiO 2 catalysts were fabricated using K 2 PdCl 4 precursor via three different methods: CR, deposition-precipitation (DP), and impregnation. The CO chemisorption results showed that the catalyst prepared via DP using the K 2 PdCl 4 precursor, i.e. , Pd/TiO 2 _K_ DP , displayed the highest Pd dispersion of 12.42% owing to the stable formation of Pd(OH) 2 , which strongly interacted with the -OH groups on the TiO 2 support. Although the catalyst prepared via CR using the Pd(NH 3 ) 4 Cl 2 ·H 2 O (PA) precursor, i.e. , Pd/TiO 2 _PA_ CR , had the lowest Pd dispersion of 0.7%, it exhibited the highest absorption of 26% after 30 min in the dark. It was found that high Pd 2+ /Pd 0 ratio in dark conditions adversely affected the absorption of MV owing to electrostatic repulsion between the cationic dyes and metal nanoparticles. However, the Pd dispersion and the specific surface area played a key role in the photocatalytic activity under UV irradiation. Pd/TiO 2 _K_ CR with higher Pd dispersion showed the highest photocatalytic activity and reaction rate of 0.0212 min -1 .