Photoreduction of carbon dioxide with water over K2Ti6O13 photocatalyst combined with Cu/ZnO catalyst under concentrated sunlight Original Research Article

Photoreduction of CO2 with water into valuable organic compounds under concentrated sunlight as well as Xe- or Hg-lamp irradiation was investigated using a Pt-loaded potassium hexatitanate (K2Ti6O13) photocatalyst or a composite catalyst in which the Pt-K2Ti6O13 photocatalyst was combined with a CO2 hydrogenation catalyst of Cu/ZnO. When the Pt-K2Ti6O13 photocatalyst was used under Xe- or Hg-lamp irradiation, H2, CH4, HCHO and HCOOH were formed. On the other hand, when the composite catalyst was used under concentrated sunlight, CH3OH was successfully formed in addition to the above products. For the composite catalyst, H2 resulting from the water decomposition over the photocatalyst serves as the reducing agent for the CO2 hydrogenation over the Cu/ZnO catalyst. The reaction temperature in this study exceeded 580 K due to concentrating the sunlight. Such a high reaction temperature is sufficient for the Cu/ZnO catalyst to reduce CO2 with H2 into CH3OH. It should also be noted that product yields for the photocatalysts were much improved under concentrated sunlight. This study revealed that a simultaneous supply of photons and thermal energy could improve the activity of photocatalysts.