10.1021/acscatal.8b05154.s002 Georgios Kyriakou Georgios Kyriakou Antonio M. Márquez Antonio M. Márquez Juan Pedro Holgado Juan Pedro Holgado Martin J. Taylor Martin J. Taylor Andrew E. H. Wheatley Andrew E. H. Wheatley Joshua P. Mehta Joshua P. Mehta Javier Fernández Sanz Javier Fernández Sanz Simon K. Beaumont Simon K. Beaumont Richard M. Lambert Richard M. Lambert Comprehensive Experimental and Theoretical Study of the CO + NO Reaction Catalyzed by Au/Ni Nanoparticles American Chemical Society 2019 nickel oxidation state material method Ni DFT catalyst N recombination importance calculation X-ray absorption spectroscopy CO N 2 formation edge structure spectroscopy X-ray absorption data oxidation state correlation 2019-04-19 00:00:00 Dataset https://acs.figshare.com/articles/dataset/Comprehensive_Experimental_and_Theoretical_Study_of_the_CO_NO_Reaction_Catalyzed_by_Au_Ni_Nanoparticles/8059922 The catalytic and structural properties of five different nanoparticle catalysts with varying Au/Ni composition were studied by six different methods, including in situ X-ray absorption spectroscopy and density functional theory (DFT) calculations. The as-prepared 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 toward N<sub>2</sub> formation, with 50–50 Au:Ni material being best of all. In situ X-ray absorption near edge structure spectroscopy 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 extended X-ray absorption fine structure spectroscopy showed a good correlation between Au–Ni coordination number (highest for Ni<sub>50</sub>Au<sub>50</sub>) and catalytic activity. Importantly, these measurements also demonstrated substantial and <i>reversible</i> 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.