(364f) Alternative Ammonia Storage Materials for SCR of NOx

Increase in the stringent diesel emission standards world-wide has led to a clear need for improved emission control system for NO_x. It is well known that 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. Another major drawback of AdBlue urea solution is its limited ammonia capacity, due to which there has to be an additional automotive fluid distribution system at every gas station. These critical challenges must be overcome for efficient vehicle integration when indirect ammonia storage is applied.

Considering this, a number of alternative materials such as ammonium carbamate and metal amine salts have been proposed for direct injection of ammonia gas. Metal amines 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 have examined a number of ammonium salts and metal amine chlorides as ammonia storage materials. The TGA profiles of several metal ammine chlorides are shown in the figure below. Important properties such as volumetric capacity, gravimetric capacity (moles of ammonia/g) and ammonia release temperature were evaluated. Furthermore, we have synthesized a range of stable mixed metal chloride solid solutions for the ammonia storage. Studying these different materials will help us in developing a technology that enables direct ammonia dosing for NO_x abatement using simple, high-density storage and delivery system.