An ammonia slip catalyst (ASC) is used to remove excess ammonia (NH₃) from exhaust gas streams. In selective catalytic reduction (SCR) systems, aqueous urea solution (CH₄N₂O) is injected to reduce NOₓ emissions.
However, under real operating conditions, excess NH₃ often occurs due to uneven NH₃ distribution on the catalyst and NH₃ oxidation at higher temperatures, which leads to an increased demand for reagents. The resulting NH₃ slip refers to the proportion of ammonia that remains unconsumed in the exhaust gas.
Since even low NH₃ concentrations are undesirable for toxicological and odor reasons, an ASC is used downstream of the SCR reactor.
In the ASC, excess NH₃ is preferentially converted to nitrogen and water via platinum-containing catalysts. ASC systems are used, among other things, in power plants, waste incineration plants and chemical industry plants to ensure compliance with the relevant emission limits according to TA-Luft.
