with harmful ozone production. SCR removes NOx in flue gas by reacting oxides of nitrogen with ammonia to form nitrogen and water. SCR was first commercialized in Japan and is now being used extensively there. It has also been commercialized in Germany. The catalyst is the heart of SCR technology, and it must afford both high activity and high selectivity (toward nitrogen formation). Major improvements in SCR catalyst performance can be achieved through strategic design of the catalyst pore structure.