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A comprehensive experimental and theoretical study of the CO + NO reaction catalyzed by Au/Ni nanoparticles

Kyriakou, Georgios; Márquez, Antonio M.; Holgado, Juan P.; Taylor, Martin Joe; Wheatley, Andrew E. H.; Mehta, Joshua P.; Fernández Sanz, Javier; Beaumont, Simon K.; Lambert, Richard M.

Authors

Georgios Kyriakou

Antonio M. Márquez

Juan P. Holgado

Andrew E. H. Wheatley

Joshua P. Mehta

Javier Fernández Sanz

Simon K. Beaumont

Richard M. Lambert



Abstract

The catalytic and structural properties of five different nanoparticle catalysts with varying Au/Ni composition were studied by six different methods, including in situ XAS and DFT calculations. The asprepared materials contained substantial amounts of residual capping agent arising from the commonly used synthetic procedure. Thorough removal of this material by oxidation was essential for the acquisition of valid catalytic data. All catalysts were highly selective towards N2 formation, with 50-50 Au:Ni material best of all. In situ XANES showed that although Au acted to moderate the oxidation state of Ni, there was no clear correlation between catalytic activity and nickel oxidation state. However, in situ EXAFS showed a good correlation between Au-Ni coordination number—highest for Ni50Au50— and catalytic activity. Importantly, these measurements also demonstrated substantial and reversible Au/Ni intermixing as a function of temperature between 550 °C (reaction temperature) and 150 °C, underlining the importance of in situ methods to the correct interpretation of reaction data. DFT calculations on smooth, stepped, monometallic and bimetallic surfaces showed that N+N recombination rather than NO dissociation was always rate-determining and that the activation barrier to recombination reaction decreased with increased Au content, thus accounting for the experimental observations. Across the entire composition range the oxidation state of Ni did not correlate with activity, in disagreement with earlier work, and theory showed that NiO itself should be catalytically inert. Au-Ni interactions were of paramount importance in promoting N+N recombination, the rate-limiting step.

Journal Article Type Article
Publication Date Jun 7, 2019
Journal ACS Catalysis
Electronic ISSN 2155-5435
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 9
Issue 6
Pages 4919-4929
APA6 Citation Kyriakou, G., Márquez, A. M., Holgado, J. P., Taylor, M. J., Wheatley, A. E. H., Mehta, J. P., …Lambert, R. M. (2019). A comprehensive experimental and theoretical study of the CO + NO reaction catalyzed by Au/Ni nanoparticles. ACS Catalysis, 9(6), 4919-4929. https://doi.org/10.1021/acscatal.8b05154
DOI https://doi.org/10.1021/acscatal.8b05154
Keywords Bimetallic catalysts; In situ measurements; DFT; Active species; Effect of Au; Reaction mechanism
Publisher URL https://pubs.acs.org/doi/10.1021/acscatal.8b05154

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Copyright Statement
This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.



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