Catalytic NH3 oxidation affected by the nanometric roughness of the platinum overlayer

Abstract

Pulsed cathodic arc–plasma deposition was employed to create a few nanometre-thick Pt overlayer on a 50 μm-thick Fe–Cr–Al metal (SUS) foil, resulting in an effective NH₃ oxidation catalyst fabrication. This catalyst exhibited a turnover frequency (TOF) exceeding 100 times that of Pt nanoparticles. In this study, Pt overlayer catalysts with varying degrees of surface roughness were fabricated using different metal foil substrates: mirror-polished (Pt/p-SUS), unpolished (Pt/SUS) and roughened by the formation of a surface oxide layer (Pt/Al₂O₃/SUS). The nanoscale roughness was comprehensively analysed using electron microscopy, laser scanning confocal microscopy and chemisorption techniques. NH₃ oxidation activity, measured at 200 °C, followed an increasing trend in the order of Pt/Al₂O₃/SUS < Pt/SUS < Pt/p-SUS, despite a decrease in the apparent Pt surface area in the same order. Consequently, the calculated TOF was markedly higher for Pt/p-SUS (267 min⁻¹) compared to Pt/SUS (107 min⁻¹) and Pt/Al₂O₃/SUS (≤22 min⁻¹). The smooth Pt overlayer surface also favoured N₂ yield over N₂O at this temperature. This discovery enhances our fundamental understanding of high-TOF NH₃ oxidation over Pt overlayer catalysts, which holds significance for the advancement and industrial implementation of selective NH₃ oxidation processes.