Multi-Step Discharge/Catalyst Processing of NOx in Synthetic Diesel Exhaust

In the discharge-catalyst treatment of diesel exhaust the discharge chemistry is known to oxidize NO to NO₂ as well as to produce partially oxidized hydrocarbons for the heterogeneous reduction step. We find NO₂ to be much more easily reduced to N₂ on our catalysts, as long as there is a sufficient supply of reductant present. Unfortunately we typically find that a fraction of the NO₂ is only partially reduced back to NO. Since much of the original hydrocarbon survives both the plasma and our catalyst, a subsequent stage of plasma will oxidize NO back to NO₂ while at the same time replenishing the supply of partially oxidized hydrocarbon for another stage of heterogeneous catalysis. We present experimental evidence illustrating the advantages of multi-step discharge-catalyst treatment of NOx in simulated diesel exhaust.