Catalytic SO3 Decomposition Activity and Stability of Pt Supportedon Anatase TiO2 for Solar Thermochemical Water-SplittingCycles

摘要

Pt-loaded anatase TiO2 (Pt/TiO2-A) was found to be a highly active and stable catalyst for SO3 decomposition at moderate temperatures (∼600 °C), which will prove to be the key for solar thermochemical water-splitting processes used to produce H2. The catalytic activity of Pt/TiO2-A was found to be markedly superior to that of a Pt catalyst supported on rutile TiO2 (Pt/TiO2-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 (Pt⁰) found for this catalyst, which favors the dissociative adsorption of SO3 and the fast removal of the products (SO2 and O2) from the surface. Conversely, Pt was easily oxidized to the much less active PtO2 (Pt⁴⁺), with the strong interactions between the oxide and rutile TiO2 forming a fully coherent interface that limited the active sites. A long-term stability test of Pt/TiO2-A conducted for 1000 h at 600 °C demonstrated that therewas no indication of noticeable deactivation (activity loss ≤4%) over the time period; this was because the phase transformationfrom anatase to rutile was completely prevented. The small amountof deactivation that occurred was due to the sintering of Pt and TiO2 and the loss of Pt under the harsh reaction atmosphere.