NOx Abatement in Diesel Exhaust With Plasma-Activated Solid Wastes/Commercial Catalysts: A Comparative Study

In this work, abatement of oxides of nitrogen (NOx) was carried out in diesel exhaust utilizing solid wastes, such as iron tailings and oyster shells, activated under electrical discharge plasma. The plasma catalysis with these wastes was carried out at room temperature. The results were then compared with commercial NOx catalysts, namely Fe2O3-Cr2O3 and CuO-ZnO-Al2O3, heated at their operating temperature of 350 °C (thermal catalysis mode). The purpose of this study is to discuss relative merit of plasma catalysis approach over thermal catalysis, be it industrial wastes or commercial catalysts. The solid wastes used in the work are rich in oxides of calcium, iron, aluminum, etc., which in turn enabled plasma catalytic activity leading to removal/decrease of oxides of nitrogen. The electrical discharge plasma was realized through dielectric barrier discharge reactor energized with high voltage repetitive pulses. The performance analysis indicated that the solid wastes exhibited significant catalytic activity in the presence of plasma yielding reduction of NOx close to 75%–95% at about 140 J/L of specific energy. On the other hand, at the same energy the commercial catalysts, when blended with plasma, exhibited close to 90% NOx reduction efficiency which is far better than the conventional thermal catalysis where it was about 60%–67% efficiency at 350 °C.