Anthropogenic activities are causing an increase in greenhouse gases in the atmosphere, with carbon dioxide (CO2) being the key cause of global warming. The conversion of CO2 into valuable hydrocarbons serves as a promising route for mitigating the effects of global warming and meeting future energy demands. Herein, we show the comparison between the photocatalytic reduction of CO2 for metal coated TiO2 nanoparticles in a slurry batch annular reactor system and metal coated TiO2 monoliths in an internally illuminated photoreactor system using the 1 wt% Pd/0.01 wt% Rh-TiO2 catalyst. Carbon based fuels, such as methane, methanol or acetaldehyde were produced in the gas phase from the CO2 reduction with water by titania nanoparticles modified by Pd and Rh for improved reactivity. The modified photocatalysts synthesized by the improved sol-gel method were tested under UV light irradiation. The quantum efficiency of the internally illuminated monolith reactor was near one order of magnitude higher than the slurry batch annular reactor. This efficiency was due to the reactor's flexible configuration; which allows maximum exploitation of the combined advantages of the high surface area of the monolith and the elimination of uneven light distribution via the optical fibres. (C) 2012 Elsevier B.V. All rights reserved.