SAE International Brief Investigation of SCR High Temperature N 2 O Production 2012-01-1082

Nitrous Oxide (N\u2082O) is a greenhouse gas with a Global Warming Potential (GWP) of 298-310 (298-310 times more potent than carbon dioxide (CO\u2082)). As a result, any aftertreatment system that generates N\u2082O must be well understood to be used effectively. Under low temperature conditions, N\u2082O can be produced by Selective Catalytic Reduction (SCR) catalysts. The chemistry is reasonably well understood with N\u2082O formed by the thermal decomposition of ammonium nitrate. Ammonium nitrate and N\u2082O form in oxides of nitrogen (NO x ) gas mixtures that are high in nitrogen dioxide (NO\u2082). This mechanism occurs at a relatively low temperature of about 200°C, and can be controlled by maintaining the nitric oxide (NO)/NO\u2082 ratio above 1. However, N\u2082O 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 N\u2082O 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 N\u2082O is formed, and to provide evidence towards understanding the mechanism that leads to high temperature N\u2082O production.