Nitrous Oxide (N₂O) is a greenhouse gas with a Global Warming Potential (GWP) of 298-310 [1,2] (298-310 times more potent than carbon dioxide (CO₂)). As a result, any aftertreatment system that generates N₂O must be well understood to be used effectively. Under low temperature conditions, N₂O can be produced by Selective Catalytic Reduction (SCR) catalysts. The chemistry is reasonably well understood with N₂O formed by the thermal decomposition of ammonium nitrate [3]. Ammonium nitrate and N₂O form in oxides of nitrogen (NO_x) gas mixtures that are high in nitrogen dioxide (NO₂)[4]. This mechanism occurs at a relatively low temperature of about 200°C, and can be controlled by maintaining the nitric oxide (NO)/NO₂ ratio above 1. However, N₂O has also been observed at relatively high temperatures, in the region of 500°C. The ammonium nitrate mechanism is unsatisfactory because ammonium nitrate is not stable above about 210°C, and yet N₂O formation can begin close to 480°C and increase above 500°C for some formulations.

The objective of this brief study was to collect data showing under what conditions high temperature N₂O is formed, and to provide evidence towards understanding the mechanism that leads to high temperature N₂O production.

Presenter
Gordon J. Bartley, Southwest Research Institute