Catalytic SO3 Decomposition Activity and Stability of Pt Supported on Anatase TiO2 for Solar Thermochemical Water-Splitting Cycles

Pt-loaded anatase TiO 2 (Pt/TiO 2 -A) was found to be a highly active and stable catalyst for SO 3 decomposition at moderate temperatures (∼600 °C), which will prove to be the key for solar thermochemical water-splitting processes used to produce H 2 . The catalytic activity of Pt/TiO 2 -A was found to be markedly superior to that of a Pt catalyst supported on rutile TiO 2 (Pt/TiO 2 -R), which has been extensively studied at a higher reaction temperature range (≥800 °C); this superior activity was found despite the two being tested with similar surface areas and metal dispersions after the catalytic reactions. The higher activity of Pt on anatase is in accordance with the abundance of metallic Pt (Pt 0 ) found for this catalyst, which favors the dissociative adsorption of SO 3 and the fast removal of the products (SO 2 and O 2 ) from the surface. Conversely, Pt was easily oxidized to the much less active PtO 2 (Pt 4+ ), with the strong interactions between the oxide and rutile TiO 2 forming a fully coherent interface that limited the active sites. A long-term stability test of Pt/TiO 2 -A conducted for 1000 h at 600 °C demonstrated that there was no indication of noticeable deactivation (activity loss ≤ 4%) over the time period; this was because the phase transformation from anatase to rutile was completely prevented. The small amount of deactivation that occurred was due to the sintering of Pt and TiO 2 and the loss of Pt under the harsh reaction atmosphere.