Time-resolved copper speciation during selective catalytic reduction of NO on Cu-SSZ-13

Abstract

Practical catalysts often operate under dynamic conditions of temperature variations and sudden changes of feed composition that call for understanding of operation and catalyst structure under analogous experimental conditions. For instance, the copper-exchanged small-pore SSZ-13 catalyst used currently in the selective catalytic reduction of harmful nitrogen oxides from the exhaust gas of diesel-fuelled vehicles operates under recurrent ammonia dosage. Here, we report the design of unsteady state experiments that mimic such a dynamic environment to obtain key mechanistic information on this reaction. Through the combination of time-resolved X-ray absorption spectroscopy and transient experimentation, we were able to capture an ammonia inhibition effect on the rate-limiting copper re-oxidation at low temperature. The practical relevance of this observation was demonstrated by optimization of the ammonia dosage on a catalyst washcoat on cordierite honeycomb, resulting in lower ammonia consumption and an increase in nitrogen oxide conversion at low temperature.

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Fig. 1: Cu K-edge X-ray absorption near-edge structure spectra of Cu-SSZ-13 during transient experiments.
Fig. 2: Switching off the SCR reaction by NH3 removal.
Fig. 3: Initiation of the SCR reaction by NO addition.
Fig. 4: Temperature-dependent evolution of Cu species.
Fig. 5: Optimization of NH3 dosage in monolithic catalytic converters.

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Acknowledgements

The authors acknowledge financial support from the Swiss National Science Foundation and Competence Center for Materials Science and Technology.

Author information

A.M. and A.W.P. designed the experiments, analysed the data, performed the LCF of the XAS data and prepared the catalysts. P.S. performed the catalytic tests and analysed the data. D.F., M.N. and O.K. led the project. D.F. and M.N. designed the experiments and analysed the data. All authors discussed the results and contributed to writing the manuscript.

Correspondence to Maarten Nachtegaal or Davide Ferri.

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Supplementary Information

Supplementary Figures 1–10; Supplementary Discussion; Supplementary Tables 1–2; Supplementary Methods; Supplementary References

Supplementary Video 1

Time-resolved XPS.

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Marberger, A., Petrov, A.W., Steiger, P. et al. Time-resolved copper speciation during selective catalytic reduction of NO on Cu-SSZ-13. Nat Catal 1, 221–227 (2018). https://doi.org/10.1038/s41929-018-0032-6

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