A Cr-doped film was prepared by sol-gel and dip-coating method and used as the photocatalyst for reforming under the visible light. The ratio of amount of Cr added to amount of Ti in sol solution (R) varied from 0 to 100？wt%. The total layer number of Cr-doped film (N) coated was up to 7. The reforming performance with the Cr-doped film was evaluated by illuminating under a Xe lamp with or without ultraviolet (UV) light. The concentration of CO which was a product from reforming was maximized for ？wt% when N equals to 1. The visible light responsibility was also maximized for ？wt%. The amount of Cr within film coated on copper disc was increased with the increase in R up to 70？wt% and started to decrease when R is over 70？wt%. The reforming performance of film with one layer Cr-doped was found better than that of film with multi Cr-doped layers under illuminating of UV light. Under the visible light, the performance was maximized at ？wt% and with one layer Cr-doped. 1. Introduction Due to mass consumption of fossil fuels, global warming and fossil fuels depletion have become a serious global environmental problem in the world. After the industrial revolution, the averaged concentration of CO2 in the world has been increased from 280？ppmV to 385？ppmV by 2008. Therefore, it is necessary to develop a new energy production technology with less or no CO2 emission. It is reported that CO2 can be reformed into fuels, for example, CO, CH4, CH3OH, and H2, by TiO2 photocatalyst under ultraviolet (UV) light illumination [1–6]. If this technique could be applied practically, a carbon circulation system would be able to be established with the use of solar energy. Many works on this technology have been carried out, but mainly for the experimental systems that TiO2 particle loaded with Cu, Pd, Pt reacts with CO2 dissolved in solution [2–4, 7–11]. Recently, nanoscale TiO2 [12, 13], porous shape TiO2 [14], and TiO2 film combined with metal [15] are developed for this process. However, the fuel concentration in the products is still low ranging from 10？ppmV to 1000？ppmV [2–8, 10–13]. Therefore, a further way is necessary to investigate the ways to promote the CO2 reforming performance of TiO2 further. In the applications such as water-splitting and purification of pollutant, the photoresponse extension of TiO2 to the visible spectrum has been investigated well [16–20]. TiO2 by itself can only work under UV light due to its wide bandgap of 3.0–3.2？eV, which means only about 4% of the incoming solar energy on the surface can be utilized [21]. On the other hand, the
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