Removal of NOx with Selective Catalytic Reduction Based on Nonthermal Plasma Preoxidation

Abstract

An extensive series of experiments have been conducted using a nonthermal plasma generated by dielectric barrier discharge (DBD) process combined with vanadium pentoxide catalyst to reduce the nitrogen oxides (NOx) from diesel engine exhaust over a broad reaction temperature (100−500 °C). In this system, the effects of input voltage, propylene (C3H6) concentration, and sulfur content, etc. on the plasma facilitated (PF) selective catalytic reduction of NOx with NH3 were examined. In the presence of C3H6 as an additive, the oxidation of NO to NO2 is largely enhanced even with lower input voltages. The PF NH3−SCR system enhanced the overall reaction and showed a remarkable improvement in NOx removal efficiency at temperatures of 100−250 °C. The removal of NOx was found to be largely increased by the input voltage and the addition of propylene. Besides the small amount of nitrous oxide and the significant amount of carbon monoxide, aldehydes-type unregulated byproduct such as formaldehyde and acetaldehyde were also observed at the outlet of the DBD reactor, while formaldehyde and acetaldehyde could be almost completely removed in the NH3−SCR reactor. The NOx conversion decreases at lower temperatures but increases at higher temperatures with SO2 concentration increases. The PF NH3−SCR hybrid system can be used stably with several hundreds of ppm of SO2 in durability tests. Moreover, the presence of SO2 inhibits N2O formation at all employed reaction temperatures.