Low-temperature NOx reduction processes using combined systems of pursed corona discharge and catalysts

In this paper, we will report NOx removal via reduction processes using two types of combined system of pulse corona discharge and catalysts: the sing le-stage plasma-driven catalyst (PDC) system, and the two-stage plasma-enha nced selective catalytic reduction (PE-SCR) system. Several catalysts, such as gamma -alumina catalysts, mechanically mixed catalysts of gamma -alumin a with BaTiO3 or TiO2, and Co-ZSM-5 were tested. In the PDC system, which i s directly activated by the discharge plasma, it was found that the use of additives was necessary to achieve NOx removal by reduction. Removal rates of NO and NOx were linearly increased as the molar ratio of additive to NOx increased. The dependence of NO and NOx removal on the gas hourly space ve locity (GHSV) at a fixed specific input energy (SIE) indicates that plasma- induced surface reaction on the catalyst plays an important role in the PDC system. It was found that the optimal GHSV of the PDC system with the gamm a -alumina catalyst was smaller than 6000 h(-1). Mechanical mixing of gamma -alumina with BaTiO3 or TiO2 did not enhance NO and NOx removal and gamma -alumina alone was found to be the most suitable catalyst. The dielectric c onstant of the catalyst only influenced the plasma intensity, not the NOx r emoval. In the PE-SCR system, plasma-treated NOx (mostly NO2) was reduced e ffectively with NH3 over the Co-ZSM-5 catalyst at a relatively low temperat ure of 150 degreesC. Under optimal conditions the energy cost and energy yi eld were 25 eV/molecule and 21 g-N (kWh)(-1), respectively.