Structural selectivity of supported Pd nanoparticles for catalytic NH₃ oxidation resolved using combined operando spectroscopy

Abstract

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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Identifiers

ORCID for Peter P. Wells: orcid.org/0000-0002-0859-9172

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