Nitrous Oxide (N₂O) is a greenhouse gas with a Global Warming
Potential (GWP) of 298-310 (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. Ammonium nitrate and N₂O form in oxides of
nitrogen (NOx) gas mixtures that are high in nitrogen
dioxide (NO₂). 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.