Enhancing the application and activity of Cu-SSZ-13 through inclusion of a secondary mixed metal oxide
Kenneth Rappe, Pacific Northwest National Laboratory
Enhancing the application and activity of Cu-SSZ-13 through inclusion of a secondary mixed metal oxide
Bo Peng, Yanran Cui, Kenneth G. Rappé
Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA 99352
Cu-SSZ-13 is currently considered as state-of-the-art for eliminating NOx emissions from transportation sources via NH3-SCR (selective catalytic reduction using NH3 as a reducing agent), owing to superior activity and durability versus its predecessors (e.g., MFI- and BEA-based SCR catalysts). [1] However, criteria emission (i.e., NOx) legislation combined with the pursuit of improved combustion efficiency dictate that low temperature activity for NOx reduction must be improved while high temperature selectivity must remain high in durable fashion. In the presence of NH3, the transformation of surface adsorbed NO species forming a reactive NO2-like intermediate was demonstrated as the rate determining step for the reduction of NO at low temperature. [2] One approach to improve performance is through the inclusion of a secondary oxidative promoter that, when coupled with the parent SCR catalyst, can facilitate this rate limiting step. Such an approach has additional associated benefits, including low-temperature reduction of NOx by the secondary oxide promoter directly, and shifting to an oxidative realm at higher temperature to reduce fast SCR dependence on incoming NO2.
In this presentation, a series of ZrO2-based transition metal oxide materials were prepared and used as the oxidative promoter of Cu-SSZ-13 SCR catalyst. Proper integration of the secondary oxide with Cu-SSZ-13 facilitates improved low-temperature activity while retaining superior high-temperature selectivity. XRD and EPR were used for characterization of the active species, and to shed light on the pathway of secondary oxide impact on the parent Cu-SSZ-13, which will be discussed in detail. Secondary oxide phase chemistry and the pathway of integration with Cu-SSZ-13 will also be discussed as it relates to key parameters of the system.
[1] C. H. F. Peden et al., J. Catal. 275, 187, 2010
[2] S. Bordiga, S. Mossin, P. Beato et al., ACS Catal. 5, 2832, 2015
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