Essential Features of Gliding Arc Plasma for High-Performance Hydrocarbon Selective Catalytic Reduction of NOxat Low Temperatures

Abstract

The high removal efficiency of NOx from diesel engine exhaust gas at low temperatures remains challenging due to the poor activity of catalysts under this condition. This work investigated the effectiveness of gliding arc plasma in the NOx removal over the Ag/γ-Al2O3 catalyst with n-heptane as a reducing agent source for NOx reduction. The plasma conjugated with the catalyst was performed like an injection method, i.e., a small part flow (1/26) that consisted of n-heptane was reformed to H2 and oxygenated hydrocarbons (OHCs) by gliding arc plasma before mixing it with the gas containing NOx. Then, the overall gas was passed through the catalyst stage at various temperatures from 127 to 253 °C. The experimental data revealed that NOx removal efficiency significantly increased with plasma treatment. The enhancement by plasma treatment increased with temperature from 127 to 226 °C, but the enhancement reduced at a temperature of 253 °C. The result came from formation of H2 and OHCs in the treated plasma gas, which reactivated NOx removal over the catalyst at low temperatures. Moreover, the enhanced NOx removal efficiency in a wide low-temperature range is obtained due to considerable hydrogen formation by the gliding arc plasma. To sum up, the highest NOx removal efficiency was 68.5% under a temperature of 226 °C and specific energy input of 34.6 J/L, while it was 20.3% for the catalyst alone; in other words, the removal efficiency increased by 48.1% with using plasma under these conditions. Owing to its low energy consumption, high-throughput gas treatment, and effectiveness at low temperatures, the technology is promising in practical applications for refining diesel exhaust gases.