The photo-oxidation of glycerol in aqueous suspensions containing commercial and home-prepared TiO2 samples in the anatase, rutile or anatase-rutile polymorphic phases was investigated by using two different batch photoreactors, an annular photoreactor and a cylindrical photoreactor. The glycerol oxidation products detected in the aqueous phase were: 1,3-dihydroxyacetone, glyceraldehyde, formic acid and carbon dioxide. Two unknown compounds were also detected by electrospray ionization mass spectrometry as peaks at m/z 268 and m/z 176. A plausible mechanism for their formation was suggested based on ESI-MS and MSn experiments. The results indicate that in both systems the commercial samples showed the best performances both for reaction rate and selectivity toward 1,3-dihydroxyacetone, glyceraldehyde, formic acid and CO2. (C) 2010 Elsevier B.V. All rights reserved.