Nanometric Platinum Overlayer to Catalyze NH3 Oxidation with High Turnover Frequency
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Abstract
A pulsed cathodic arc-plasma deposition of a few-nanometer-thick Pt(111) overlayer on a 50 μm-thick Fe–Cr–Al metal foil produced a thin-film catalyst; this catalyst exhibited high activity for low-temperature NH3 oxidation and was superior to that of a conventional powder catalyst (Pt/Al2O3). A metal honeycomb that was fabricated using a metal foil catalyst successfully demonstrated a light-off performance at a practical gas hourly space velocity of 1.2 × 105 h–1. Despite its nonporosity and small surface area, the Pt overlayer is a promising alternative to Pt/Al2O3 for more efficient ammonia-slip catalysts that use less Pt loading; this is because the turnover frequency for the NH3 oxidation at 200 °C is more than 180-fold greater than that achieved with Pt/Al2O3 consisting of Pt nanoparticles. Although the nanometric Pt overlayer structure was thermally unstable at reaction temperatures of ≥600 °C, inserting a 250 nm-thick Zr buffer layer between the Pt overlayer and the metal foil substrate significantly mitigated the thermal deterioration. The undesired byproducts of NH3 oxidation, NO and NO2, can be efficiently converted to N2 by a selective catalytic reduction over a V2O5–WO3/TiO2 catalyst in a tandem reactor system.
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