Diesel engines are widely used in agricultural machinery, vehicles, and ships because of their high thermal efficiency. The sulfur contained in the diesel fuel is oxidized to sulfur dioxide by combustion. This sulfur dioxide not only harms human health but also causes deactivation of the catalysts used to treat NO x in the exhaust stream.

This problem can be overcome by using sulfur-free fuels based on biomass or clean coal technology or by installing a desulfurizing filter to remove sulfur oxides upstream of the NO x catalyst. Researchers at Kanazawa university have developed a plasma-assisted MnO 2 filter that produces exhaust free of NO x and SO x . This technology augments the desulfurization properties of MnO 2 with the activity of ozone from an atmospheric-pressure non-equilibrium plasma. Activated chemical species (O 3 , OH radicals, etc.) present in the plasma promote desulfurization and denitration reactions.

MnO 2 reacts with sulfur and nitrogen oxides to produce sulfates and nitrates, respectively. The interaction between SO 2 and NO 2 degrades the performance of MnO 2 catalysts in eliminating both species. Prof Huang of the Guangzhou Institute of Energy Conversion analyzed the MnO2 catalyst material after exposure to simulated exhaust gas containing both SO 2 and NO 2 and found that both manganese nitrate and manganese sulfate were produced.

We evaluated the impact of ozone on the performance of the catalyst for SO 2 and NO 2 removal. An atmospheric-pressure non-equilibrium plasma was generated by the dielectric barrier discharge method. The performance of the catalyst in eliminating both SO 2 and NO 2 was improved by the introduction of ozone at a low concentration of about 50 ppm. The enhancement in NO 2 elimination was particularly notable. The introduction of ozone seems to give a reaction to reduce nitrogen oxides to nitrogen. At the initial stage of the reaction, over 99% of SO 2 and NO 2 were removed from the exhaust stream. The Kanazawa University researchers, led by Yugo Osaka, demonstrated for the first time that zero emissions of NO x can be achieved even in the presence of sulfur oxides by using a plasma-assisted MnO 2 filter. The plasma-assisted filter seems to augment the elimination of SO 2 because of SO 3 generation and also reduce nitrogen oxides to nitrogen.