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

Particulate matter (PM) and NO
_x
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 γAl
₂
O
₃
and Ag/γAl
₂
O
₃
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 BaTiO
₂
pellet packed bed reactor. NO
_x
is reduced by N radicals, and PM is incinerated by oxygen radicals induced either by NO
_x
or ozone (O
₃
) reduction at elevated local temperatures among the pellets. Since CO and CO
₂
are generated, the carbon PM is actually combusted under oxygen-lean conditions, resulting in the simultaneous removal of PM and NO
_x
with NTP-assisted catalysts. It is found that in the presence of the catalysts, PM removal calculated from CO and CO
₂
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, NO
_x
removal decreases with an increase in the oxygen concentration. The maximum NO
_x
removal energy efficiency of 14.2 g(NO
₂
) /kWh is observed for O
₂
= 0%. Compared with the experimental results obtained without the catalyst pellets, the NO
_x
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 BaTiO
₃
pellets, NO
_x
removal energy efficiency is larger, but the PM removal is lower in the case of catalyst packed-bed reactor.