Deactivation of Cu-Exchanged Automotive-Emission NH 3 -SCR Catalysts Elucidated with Nanoscale Resolution Using Scanning Transmission X-ray Microscopy

• Published in: Angewandte Chemie (International ed.) 2020-09, Vol.59 (36), p.15610-15617
• Main Authors: Ye, Xinwei, Schmidt, Joel E, Wang, Ru-Pan, van Ravenhorst, Ilse K, Oord, Ramon, Chen, Tiehong, de Groot, Frank, Meirer, Florian, Weckhuysen, Bert M
• Format: Article
• Language: English
• Subjects: automotive catalysis; catalyst deactivation; copper; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; X-ray microscopy; zeolites
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201916554

To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NO with an ammonia reductant, we employed scanning transmission X-ray microscopy (STXM) to study Cu-exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000-mile aging. X-ray absorption near-edge structure (XANES) measurements were performed at the Al K- and Cu L-edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi-factor-induced catalytic deactivation. In Cu-exchanged MFI, a transformation of Cu to Cu and Cu O was observed. We also found a spatial correlation between extra-framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of Cu and tri-coordinated Al. By inspecting both Al and Cu in fresh and aged Cu-exchanged zeolites, we conclude that the importance of the preservation of isolated Cu sites trumps that of Brønsted acid sites for NH -SCR activity.