CleanUp Technologies: Selective Catalytic Reduction

This type of catalyst uses ammonia as the agent to reduce nitrogen oxide emissions. The technology was initially developed for large plant and marine applications. Trials on heavy duty vehicles have shown over 70% NOx reduction with a potential of up to 90%. It is expected that SCR will rival EGR as a Euro 4 technology on new vehicles. SCR is likely to provide a larger NOx reduction in a well developed system but does require replenishment of the agent whereas EGR is "fit-and-forget".

As an SCR catalyst only converts the NOx exhaust component and, typically, an oxidation catalyst is added to give the expected normal reductions in carbon monoxide and hydrocarbons of 90% and, specifically, to minimise the risk of ammonia emissions to the atmosphere.

The ammonia may be directly injected or be held in the form of solid urea, urea solution or in crystalline form. Other than pure ammonia, a certain temperature must be reached to release ammonia. Storage of the agent requires space on the vehicle. The catalyst itself is rather large due to the requirement for a low space velocity to allow the exhaust gas sufficient residence time for the reaction to take place.

CleanUp are supporting a light duty (retrofit) application for SCR, and are negotiating heavy duty applications.