Transition metal doping is an appropriate way to increase the photocatalytic activity of TiO2 as it offers the chance to also utilize visible light to generate charge carriers. Here, we investigated the photocatalytic activity of commercially available Evonik Aeroxide (R) TiO2 P25 and its iron-doped analog Evonik Aeroxide (R) TiO2 PF2. For this study, we used as model reaction the photocatalytic oxidation of methanol (CH3OH) to formaldehyde (HCHO) employing artificial solar illumination with and without UV-light. Apparently, the iron content in PF2 is too high and therefore has a negative effect on its photocatalytic activity. Furthermore, by the comparison of photonic efficiencies (xi) and quantum efficiencies (Phi) we could show the importance of not just calculating photonic efficiencies but also shed some light on the mechanism how the charge carriers in P25 are generated.