Ammonium Nitrate Formation and Decomposition on an Extruded Vanadium-Based SCR Catalyst

In this study, the formation and decomposition of ammonium nitrate (AN) on a state-of-the-art extruded vanadium-based SCR catalyst (V-SCR) under simulated exhaust conditions has been evaluated. Results show that AN readily forms and accumulates at temperatures below 200°C when exposed to NH₃ and NO₂. The rate of AN accumulation increases with decreasing temperature. A new low temperature NH₃ release peak (not present following NH₃ storage conditions with NH₃ only) becomes apparent after AN accumulation at 100 and 125°C. This new NH₃ release, with a peak release temperature of approximately 180°C, is evaluated in detail to better determine its origin. BET surface area, and thermal gravimetric analysis/differential scanning calorimetry (TGA/DSC), and reactor-based experiments are all used to characterize AN formed on the V-SCR catalyst in comparison to pure AN. Experiments on pure AN crystals reveal that the new low temperature NH₃ peak is attributable to the release of NH₃ from AN that is not related to AN volatilization, since this does not occur until above T > 200°C.This study expands the present understanding of AN formation over an extruded V-SCR catalyst.