A heterogeneous Fenton-like reaction occurring on the thermally modified surface of a synthetic iron oxide previously treated with a H₂ stream was investigated. The quinoline decomposition, used as an organic substrate model, was monitored with electrospray ionization mass spectrometry. Quinoline was found to be oxidized through a successive hydroxylation mechanism. These results strongly suggest that highly reactive hydroxyl radicals, generated during the reaction involving H₂O₂ on the catalysts surface, respond for this oxidation, and confirm that the material is an efficient heterogeneous Fenton-like catalyst. Theoretical quantum mechanics calculations, by the density functional theory (DFT), were carried out in order to understand the basic molecular degradation steps for quinoline decomposition mechanism on this H₂-treated goethite (αFeOOH) surface.