Revisiting effects of alkali metal and alkaline earth co-cation additives to Cu/SSZ-13 selective catalytic reduction catalysts
Cu,M/SSZ-13 (M = Na+, K+ and Ca2+) SCR catalysts with Si/Al = 6 and M/Cu ratios varying from 0.1 to 1.0 are prepared by solution ion-exchange, and followed by slurry drying and hydrothermal aging at 800 ?C. The catalysts are characterized with XRD and N2 adsorption isotherms to probe their textural properties, 27Al and 29Si NMR and NH3-TPD to probe their acidity properties and levels of dealumination, and EPR and H2-TPR to quantitatively explore the nature of Cu moieties in the catalysts. These studies are followed by DFT calculations to elucidate Cu and co-cation interactions at an atomic level, and SCR reaction tests to reveal correlations between the chemical and physical properties of the catalysts and their SCR performance. Through such comprehensive investigations, it is discovered that alkali co-cation addition can be used in practice for the synthesis of highly stable, and highly active and selective Cu/SSZ-13 catalysts with relatively high Al content. In catalysts with optimal alkali incorporation, dealumination of the SSZ-13 substrate is largely inhibited, allowing high concentrations of SCR active isolated Cu-ions. At the same time, repulsive interactions between Cu-ions and alkali co-cations preclude excessively high isolated Cu-ion loadings. Interplay between and optimization of these two factors is considered as the underlying origin for this successful catalyst synthesis strategy. On the other hand, the alkaline earth co-cation Ca2+ fails to demonstrate any beneficial effects since it destabilizes isolated Cu-ions via a site competition mechanism. The authors gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed in the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle. The authors gratefully appreciate fruitful discussions with CRADA collaborators Craig Dimaggio, Kiran Premchand, Vencon Easterling and Mike Zammit from Fiat Chrysler Automobiles (FCA).
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1608545
- Report Number(s):
- PNNL-SA-141699
- Journal Information:
- Journal of Catalysis, Vol. 378
- Country of Publication:
- United States
- Language:
- English
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