Mechanisms of isopropanol (IPA) conversion on ?-Al2O3 by dielectric barrier discharge plasma are elucidated by the means of operando Fourier transformed infrared spectroscopy. In that case, it is shown that the IPA conversion proceeds by successive steps. Firstly, via the oxidation of IPA into acetone by atomic oxygen and ozone produced in the plasma composed of dry air. Secondly, after aldolization of acetone into mesityl oxide at the surface of the ?-Al2O3 catalyst. Thirdly, after fragmentation of mesityl oxide into acetaldehyde and isobutene. Such cascade reactions are only possible when a catalyst is placed in the discharge zone (in-plasma catalysis). It initially supports the IPA molecules and then allows products condensation before their fragmentation.