The selective catalytic oxidation of NH3 to N2 presents a promising solution for the abatement of unused NH3-based reductants from diesel exhaust after treatment. Supported Pd nanoparticle catalysts show selectivity to N2 rather than NOx, which is investigated in this work. The link between Pd nanoparticle structure and surface reactivity was found using operando X-ray absorption fine structure spectroscopy, diffuse reflectance infrared Fourier-transformed spectroscopy and on-line mass spectrometry. Nitrogen insertion into the metallic Pd nanoparticle structure at low temperatures (<200 °C) was found to be responsible for high N2 selectivity, whereas the unfavourable formation of NO is linked to adsorbed nitrates, which form at the surface of bulk PdO nanoparticles at high temperatures (>280 °C). Our work demonstrates the ability of combined operando spectroscopy and density functional theory calculations to characterize a previously unidentified PdNx species, and clarify the selectivity-directing structure of supported Pd catalysts for the selective catalytic oxidation of NH3 to N2.
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The data that support the findings of this study are available from the University of Southampton repository with the identifier https://doi.org/10.5258/SOTON/D0709, or from the authors upon reasonable request.
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We acknowledge UCL and the EPSRC for the iCASE studentship of E.K.D; the beamline scientists at the Swiss Light Source and staff at the Paul Scherrer Institut for the provision of beamtime (proposal 20160396); and the beamline scientists at XMaS, European Synchrotron Radiation Facility, for the provision of beamtime (experiment 28-01-1213). XMaS is a UK national facility supported by EPSRC. We recognize staff at the University of Warwick and University of Liverpool for support in facilitating the beamtime. We also acknowledge the RCaH for the use of facilities, and Johnson Matthey for providing catalyst precursor materials and testing facilities. We thank the UK Catalysis Hub for resources and support provided via our membership of the UK Catalysis Hub Consortium (portfolio grants EP/K014706/1, EP/K014668/1, EP/K014854/1, EP/K014714/1 and EP/I019693/1). Via our membership of the UK’s HEC Materials Chemistry Consortium, which is funded by the EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing service (http://www.archer.ac.uk). We acknowledge the use of Athena at HPC Midlands+, which was funded by the EPSRC (grant EP/P020232/1), in this research, via the EPSRC RAP call of spring 2018. We also thank HPC Wales for the computing time.
The authors declare no competing interests.
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Dann, E.K., Gibson, E.K., Blackmore, R.H. et al. Structural selectivity of supported Pd nanoparticles for catalytic NH3 oxidation resolved using combined operando spectroscopy. Nat Catal 2, 157–163 (2019) doi:10.1038/s41929-018-0213-3
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