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

In this paper, we will report NO(x) removal via reduction processes using two types of combined system of pulse corona discharge and catalysts: the single-stage plasma-driven catalyst (PDC) system, and the two-stage plasma-enhanced selective catalytic reduction (PE-SCR) system. Several catalysts, such as gamma -alumina catalysts, mechanically mixed catalysts of gamma -alumina with BaTiO(3) or TiO(2), and Co-ZSM-5 were tested. In the PDC system, which is directly activated by the discharge plasma, it was found that the use of additives was necessary to achieve NO(x) removal by reduction. Removal rates of NO and NO(x) were linearly increased as the molar ratio of additive to NO(x) increased. The dependence of NO and NO(x) removal on the gas hourly space velocity (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 gamma -alumina catalyst was smaller than 6000 h(-1). Mechanical mixing of gamma -alumina with BaTiO(3) or TiO(2) did not enhance NO and NO(x) removal and gamma -alumina alone was found to be the most suitable catalyst. The dielectric constant of the catalyst only influenced the plasma intensity, not the NO(x) removal. In the PE-SCR system, plasma-treated NO(x) (mostly NO(2)) was reduced effectively with NH(3) over the Co-ZSM-5 catalyst at a relatively low temperature of 150 degreesC. Under optimal conditions the energy cost and energy yield were 25 eV/molecule and 21 g-N (kWh)(-1), respectively.