Japan, China researchers develop plasma-assisted MnO2 filter that produces zero-NO2, -SO2 diesel exhaust
A team led by researchers from Kanazawa University in Japan, with colleagues from Guangzhou Institute of Energy Conversion in China, have used ozone from an atmospheric-pressure non-equilibrium plasma together with the desulfurization catalyst MnO2 to almost completely eliminate NO2 and SO2 from diesel exhaust gas at a low temperature of 473 K (200 ˚C).
This research, published in the journal Separation and Purification Technology, shows that ozone can be used to remove not only SOx but also NOx from fossil fuel combustion exhaust streams.
Conceptual scheme of plasma-assisted MnO2 filter. Activated chemical species (O3, OH radicals etc.) are generated by inducing an atmospheric pressure non-equilibrium plasma. These species promote desulfurization and denitration reactions with MnO2. Osaka et al.
In our previous study, we found that MnO2 can absorb not only SO2 but also NO2 simultaneously. In this study, to improve absorption performance of SO2 and NO2, we added ozone in exhaust gas. Therefore, we investigated the effect of ozone on the desulfurization and denitration performances experimentally. Results showed that maintaining the absorption rate of 90% or more in SO2 and NO2 absorption was possible by adding ozone. The amount of NO2 absorption significantly increased by adding ozone. However, the utilization rate of MnO2 exceeded the theoretical absorption amount. This result suggested that SO2/NO2 purification may have not only a simple absorption reaction but also a purification reaction similar to reduction denitration.—Osaka et al.
MnO2 reacts with sulfur and nitrogen oxides to produce sulfates and nitrates, respectively. The interaction between SO2 and NO2 degrades the performance of MnO2 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 SO2 and NO2 and found that both manganese nitrate and manganese sulfate were produced.
The researchers then evaluated the impact of ozone on the performance of the catalyst for SO2 and NO2 removal. An atmospheric-pressure non-equilibrium plasma was generated by the dielectric barrier discharge method.
The performance of the catalyst in eliminating both SO2 and NO2 was improved by the introduction of ozone at a low concentration of about 50 ppm. The enhancement in NO2 elimination was particularly notable, the researchers said.
The effect of ozone induction on SO2 and NO2 elimination. Ozone generated in an atmospheric-pressure non-equilibrium plasma was passed through the MnO2 filter together with simulated exhaust gas. The simulated exhaust gas consisted of 500 ppm SO2, 500 ppm NO2,10 wt% O2, 6 wt% CO2, an N2 base, and 50 ppm O3 (when plasma is induced). The MnO2 was supported on an alumina honeycomb filter and the flow conditions (space velocity of 104 h−1) mimicked typical vehicle exhaust streams and filter dimensions. Osaka et al.
The introduction of ozone appears to give a reaction to reduce nitrogen oxides to nitrogen. At the initial stage of the reaction, more than 99% of SO2 and NO2 were removed from the exhaust stream.
The researchers expect the findings to be widely applicable in the purification of exhaust from diesel engines using sulfur-containing fuels.
Yugo Osaka, Kentaro Iwai, Takuya Tsujiguchi, Akio Kodama, Xing Li, Hongyu Huang, (2019) “Basic study on exhaust gas purification by utilizing plasma assisted MnO2 filter for zero-emission diesel,” Separation and Purification Technology, Volume 215, Pages 108-114 doi: 10.1016/j.seppur.2018.12.077