Cu-Zeolite Selective Catalytic Reduction Catalysts for NOx Conversion

Abstract

Cu-exchanged zeolites are commercially being used in the ammonia selective catalytic reduction (NH3-SCR) of NOx, especially in the use for mobile sources. In particular Cu exchanged zeolites having the CHA structure (Cu-SSZ-13 and Cu-SAPO-34) show an excellent performance in the NH3-SCR of NOx. The materials have been characterized extensively in current literature, using the latest analysis techniques. Due to the large amount of research performed on this topic, it has resulted in some deviations in the conclusions about the active site, which could partly be explained by variations in the used catalyst systems, such as different Si/Al ratios, different Cu/Al ratios and different synthesis procedures to get an active Cu zeolite catalyst. This chapter will start with an introduction about into the emission control system in road transport vehicles, followed by shortly explaining the different catalysts which able to perform the NH3-SCR of NOx. The following sub chapters will focus on the Cu containing zeolites, and in particular the small pore exchanged Cu zeolites having the CHA structure. This is followed by an overview of the used Cu exchange and synthesis methods and their differences, and the location of the Cu inside the CHA framework. Lastly, deactivation mechanisms for Cu exchanged zeolites are being discussed.