Simultaneous Reduction of Diesel Particulate and NOx Using a Catalysis-Combined Nonthermal Plasma Reactor

Particulate matter (PM) and NOx emitted from diesel engines is simultaneously reduced by a barrier-type catalyst-packed nonthermal plasma (NTP) application, driven by a pulse high-voltage power supply under oxygen-lean conditions. Catalyst particles of gamma Al2O3 and Ag/gamma Al2O3 with a diameter of 2-4 mm are used as packed pellets and carbon PM is loaded among the pellets. The reduction results are compared with those in a previous study using a noncatalytic BaTiO2 pellet packed bed reactor. NOx is reduced by N radicals, and PM is incinerated by oxygen radicals induced either by NOx or ozone (O-3) reduction at elevated local temperatures among the pellets. Since CO and CO2 are generated, the carbon PM is actually combusted under oxygen-lean conditions, resulting in the simultaneous removal of PM and NOx with NTP-assisted catalysts. It is found that in the presence of the catalysts, PM removal calculated from CO and CO2 generation increases with an increase in the oxygen concentration. The maximum PM removal energy efficiency of 0.92 g(C) /kWh is observed for O-2 = 2%. Furthermore, NOx removal decreases with an increase in the oxygen concentration. The maximum NOx removal energy efficiency of 14.2 g(NO2) /kWh is observed for O-2 = 0%. Compared with the experimental results obtained without the catalyst pellets, the NOx removal energy efficiency increases by a maximum of 47% for O-2 = 2%. When comparing the present results with those in the previous study using BaTiO3 pellets, NOx removal energy efficiency is larger, but the PM removal is lower in the case of catalyst packed-bed reactor.