An experimental study on the removal of NOx in a simulated vehicle exhaust gas has been carried out using point to plane and multipoint to plane DBD corona reactors. Hydrocarbon (C3H6) and NOx by-products were systematically investigated with a Gas Chromatography coupled to a Mass Spectrometry (GC/MS). NOx (NO and NO2) and CO output were also monitored with a gas analyzer in order to complete the mass balance. O-18 tracer technique analyzes is applied to investigate the mechanism of propylene decomposition. From the plasma chemical reaction pathway proposed, it is apparent that the oxygen activation is one of the important steps for initiating the oxidation processes and the R-NOx formation. We present data for the reaction of the (N-2/O-2/C3H6/CO2NO/H2O system in the corona discharge reactors mentioned above. This system has been shown to generate a significant amount of aldehyde. CH3NO2 and CH3ONO2 are the main R-NOx compounds produced. Reactant composition and discharge energy densities (controlled by a numerical oscilloscope) were the operating parameters under study in wet and dry air mixture. Water vapors played an important role in NOx removal (especially in NO2 removal) via the reaction forming HNO3. Therefore, in wet-gas mixture supplied reactors the highest removal rates of NOx were as high as 30%, while in dry-gas only 15%. Different dielectric materials such as Al2O3/SiO2 and TiO2 on Al2O3/SiO2 support have been used.