Photoassisted water-gas shift reaction over Pt TiO₂(100)

Sustained production of hydrogen was observed over platinized TiO₂(100) in the presence of water vapor and carbon monoxide with or without uv illumination. The thermal reaction proceeds with an activation energy of 26.3 ± 0.5 kcal/mole and is dominant at temperatures above 400 °K. The photoreaction, which dominates at temperatures below 400 °K with an activation energy of 7 ±2 kcal/mole, was extensively studied in this work. In the photoreaction, the hydrogen production rate was found to be independent of water and CO partial pressure in the range of 0.5 to 18 Torr and 0.1 to 10 Torr, respectively. The reaction rate increases monotonically with increasing uv intensity. Platinum coverage study suggested that the periphery of deposited Pt islands is involved in the photogeneration of H₂. A reaction mechanism assuming CO photoreduction of TiO₂ at Pt-TiO₂ periphery sites to be the rate-limiting step is proposed that appears to account for all experimental observations.