Effect of reaction temperature and sacrificial agent on the photocatalytic H2-production of Pt-TiO2

Abstract

TiO2 nano-particles based photocatalysts were modified with different Pt percentages photodeposited on the surface, optimizing the method in order to obtain the best performance for the production of hydrogen. For testing hydrogen production, a novel reaction setup equipped with an elliptical cylindrical reflector to focus the radiation on the reactor has been used, being possible to control the reaction temperature. The hydrogen production has been measured in continuous by means of mass spectrometry. The effects of the reaction temperature and of the sacrificial reagent (methanol, ethanol or isopropanol) on the photocatalytic activity of Pt-TiO2 were studied. The best results at 25 °C were achieved for 2 wt% Pt-TiO2 (2Pt-TiO2) using methanol as sacrificial reagent, with a large maximum production over 16.0 mmol g−1h−1, which decreases to the half of this value after a long period of 72 h. These H2 production rates are larger, by a factor close to 30, than the ones obtained for the commercial P25 TiO2 in the same experimental conditions. The effect of the reaction temperature was analyzed on 2Pt-TiO2/water and 2Pt-TiO2/water/MeOH systems in the temperature range 5–60 °C. The apparent activation energy was determined for both photocatalysts, obtaining values of 17.5 and 23.3 kJ mol−1, respectively. The hydrogen production increases continuously with temperature in this range, achieving at 60 °C a H2 production of 0.83 and 38.0 mmol g−1h−1 for the photocatalyst in water and water/MeOH, respectively, after 2 h of reaction time.