Alternative Ammonia Storage Materials for SCR

Abhi  Karkamkar, PNNL

Ammonia is an active molecule for the selective catalytic reduction of NO_x in the exhaust. Use of liquid ammonia on-board in a pressure vessel has been excluded due to safety issues. Current technology employs the use of urea dissolved in water or Diesel Exhaust Fluid (DEF) as ammonia source. However, this system has its own limitations such as freezing at low temperature (-12ºC), solid deposit formation in the exhaust line, and difficulties in dosing ammonia at exhaust temperatures below 200ºC. A number of alternative materials such as ammonium carbamate and metal ammine salts have been proposed for direct injection of ammonia gas. Metal ammines are very attractive functional materials due to their remarkable reversible ammonia storage property and a high volumetric ammonia density of up to 93% of that of liquid ammonia. Herein, we present recent developments in the area of alternative ammonia storage materials for SCR.