Nitrogen oxides (NOx) are some of the primary pollutants emitted during a combustion process. Along with sulfur oxides (SOx) and particulate matters (PM), NOx emissions contribute to acid rain and ozone formation, visibility degradation, and human health concerns.

SCR technology is currently the most effective method of post-combustion NOx reduction. In the SCR System process, a catalyst facilitates a chemical reaction between NOx and a reagent (usually ammonia) to produce harmless nitrogen and water vapor inside a sealed reactor.