Selective catalytic reduction (SCR) is a means of converting nitrogen oxides (NoX) with the aid of a catalyst into diatomic nitrogen and water. A reductant, typically anhydrous ammonia, aqueous ammonia, or a urea solution, is added to a stream of exhaust gas and is reacted onto a catalyst. As the reaction drives toward completion, nitrogen and carbon dioxide, in the case of urea use, are produced. SCR systems are the method for meeting EURO 6 diesel emissions standards for heavy trucks, light commercials & cars. As a result, emissions of NOx, particulates, and hydrocarbons have been reduced by as much as 95% when compared with pre-emissions engines.
