Photocatalytic hydrogenation of carbon dioxide (CO2) is a promising technology to mimic photosynthesis
by the conversion of solar energy into methanol (CH3OH) for the development of sustainable energy. This
technology not only can potentially cut down the atmospheric CO2, but also reduce the world’s dependence
on fossil fuel. Using a novel twin reactor, the hydrogen, which is directly generated from the water
splitting, could be utilized to hydrogenate CO2 into a desirable fuel and simultaneously reduce greenhouse
gas. Remarkable result has been observed by using a gaseous mixture of CO/CO2 to yield CH3OH
under artificial sunlight, compared with the one using solely CO or CO2. Although direct hydrogenation
of CO to form CH3OH on either Pt/CuAlGaO4 or Pt/SrTiO3:Rh photocatalysts is not likely to occur, CO still
plays an important role on the generation of either H2 via water–gas shift reaction or methyl formate
(HCOOCH3), the intermediate product of CH3OH. Nevertheless, adding too much CO as the co-feed will
adversely decrease the yield of CH3OH. A possible mechanism of CO/CO2 photo-hydrogenation over Pt/
CuAlGaO4 and Pt/SrTiO3:Rh photocatalysts is proposed to explain the key experimental trends observed
as well as the species involved during the reaction.