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

Abstract

In this paper, we will report NOx removal via reduction processesusing two types of combined system of pulse corona discharge and catalysts:the single-stage plasma-driven catalyst (PDC) system, and the two-stageplasma-enhanced selective catalytic reduction (PE-SCR) system. Severalcatalysts, such as γ-alumina catalysts, mechanically mixed catalysts ofγ-alumina with BaTiO3 or TiO2, and Co-ZSM-5 were tested. In thePDC system, which is directly activated by the discharge plasma, it was foundthat the use of additives was necessary to achieve NOx removal byreduction. Removal rates of NO and NOx were linearly increased as the molarratio of additive to NOx increased. The dependence of NO and NOx removalon the gas hourly space velocity (GHSV) at a fixed specific input energy (SIE)indicates that plasma-induced surface reaction on the catalyst plays animportant role in the PDC system. It was found that the optimal GHSV of thePDC system with the γ-alumina catalyst was smaller than 6000 h-1.Mechanical mixing of γ-alumina with BaTiO3 or TiO2 did notenhance NO and NOx removal and γ-alumina alone was found to be themost suitable catalyst. The dielectric constant of the catalyst onlyinfluenced the plasma intensity, not the NOx removal. In the PE-SCR system,plasma-treated NOx (mostly NO2) was reduced effectively with NH3 overthe Co-ZSM-5 catalyst at a relatively low temperature of 150 °C. Underoptimal conditions the energy cost and energy yield were 25 eV/molecule and21 g-N (kWh)-1, respectively.