Selective Reduction of NOx in Oxygen Rich Environments with Plasma-Assisted Catalysis: The Role of Plasma and Reactive Intermediates

The catalytic activity of selected materials (BaY and NaY zeolites, and γ-alumina) for selective NO_x reduction in combination with a non-thermal plasma was investigated. Our studies suggest that aldehydes, formed during the plasma treatment of simulated diesel exhaust, are the important species for the reduction of NO_x to N₂. Indeed, all materials that are active in plasma-assisted catalysis were found to be very effective for the thermal reduction of NO_x in the presence of aldehydes. For example, the thermal catalytic activity of a BaY zeolite with aldehydes gives 80-90% NO_x removal at 250°C with 200ppm NO_x at the inlet and a VHSV=12,000 h^-1.

The hydrocarbon reductants, n-octane and 1-propyl alcohol, have also shown high thermal catalytic activity for NO_x removal over BaY, NaY and γ-alumina. We believe that this activity is due to the fact that in an oxygen rich environment these compounds can be thermally oxidized over the catalysts to form the important aldehyde reaction intermediates.