Combining Kinetics and Spectroscopy to Interrogate the Mechanism and Active Site Requirements of NO Selective Catalytic Reduction with NH on Cu-Zeolites.

NO selective catalytic reduction (SCR) with NH on Cu-zeolites is a commercial emissions control technology for diesel and lean-burn engines. Mitigating low-temperature emissions remains an outstanding challenge, motivating an improved understanding of the reaction mechanism, active site requirements, and rate-determining processes at low temperatures (<523 K). In this Perspective, we discuss how spectroscopy provides crucial information about how the structures, coordination environments, and oxidation states of Cu active sites depend on reaction conditions and sample composition; when combined with kinetic measurements, such data provide insights into the Cu site and spatial density requirements for reduction and oxidation steps relevant to the Cu(II)/Cu(I) SCR redox cycle. Isolated Cu ions coordinated to zeolite oxygen atoms become coordinated to NH and dynamically interconvert between mononuclear and binuclear NH-solvated Cu complexes to catalyze SCR turnovers. We conclude with future research directions that can benefit from combining quantitative kinetic measurements with spectroscopy.