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

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 (NO x ) from diesel engine exhaust over a broad reaction temperature (100−500 °C). In this system, the effects of input voltage, propylene (C 3 H 6 ) concentration, and sulfur content, etc. on the plasma facilitated (PF) selective catalytic reduction of NO x with NH 3 were examined. In the presence of C 3 H 6 as an additive, the oxidation of NO to NO 2 is largely enhanced even with lower input voltages. The PF NH 3 −SCR system enhanced the overall reaction and showed a remarkable improvement in NO x removal efficiency at temperatures of 100−250 °C. The removal of NO x 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 NH 3 −SCR reactor. The NO x conversion decreases at lower temperatures but increases at higher temperatures with SO 2 concentration increases. The PF NH 3 −SCR hybrid system can be used stably with several hundreds of ppm of SO 2 in durability tests. Moreover, the presence of SO 2 inhibits N 2 O formation at all employed reaction temperatures.