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Brief Investigation of SCR High Temperature N2O Production

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 (NOx) gas mixtures that are high in nitrogen dioxide (NO2)[4]. This mechanism occurs at a relatively low temperature of about 200C, 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 500C. The ammonium nitrate mechanism is unsatisfactory because ammonium nitrate is not stable above about 210C, and yet N2O formation can begin close to 480C and increase above 500C 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

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