Formation and Decomposition of Ammonium Nitrate on an Extruded Vanadium-based SCR Catalyst 2020-01-1320
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 storage site (not present following NH3 storage conditions with NH3 only) becomes apparent after AN accumulation at 100 and 125°C for an extended duration (e.g., t > 30 min). This new NH3 storage site, with a peak release temperature of approximately 185°C, is then evaluated in detail to better determine its origin. BET surface area, diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), thermal gravimetric analysis (TGA), and reactor-based experiments are all used to characterize AN formed on the V-SCR catalyst in comparison to pure AN powder. Experiments on AN powder reveal that the new low temperature NH3 peak can be attributed to the release of NH3 bound to the accumulated AN, even though the thermal decomposition of AN does not occur until above T > 200°C. Furthermore, reactor-based experiments show that pure AN powder reacts with NO to form NO2, indicating that NO titration can be used to quantify and remove bulk AN formed on the V-SCR catalyst. This study expands the present understanding of AN formation over an extruded V-SCR catalyst.
Nathan Ottinger, Yuanzhou Xi, Christopher Keturakis, Z. Gerald Liu