The problem of the purification of exhaust gases produced by ammonia-fueled engines is presented. The possible catalytic systems for conversion of NO_x (NH₃-SCR) as well as selective catalytic oxidation of residual ammonia to nitrogen and water vapor (NH₃-SCO) are discussed and compared. Small and medium pore zeolites modified with copper and iron belong to the most promising NH₃-SCR catalysts.

Abstract

Ammonia is a potential fuel for use in engines. Burning of ammonia does not result in the CO_x formation, and therefore, ammonia could be classified as a sustainable fuel. On the other hand, in this case, exhaust gases may contain significant amounts of unburned ammonia and nitrogen oxides (including N₂O) as pollutants. The problem of the possible catalytic systems for exhaust gases purification is analyzed and discussed, mainly with respect to the application of catalytic processes for NO_x, N₂O, and ammonia conversions. The various types of catalysts operating under condtions of exhaust gases (e.g., temperature and composition) were compared and the most promissing catalytic systems were proposed. Attention was mainly focused on the use of pure ammonia as a fuel, although some issues relating to the combustion of mixed fuels, such as ammonia - hydrocarbon fuels as well as ammonia - hydrogen (H₂ obtained by catalytic decomposition of ammonia) were also presented and discussed.