Nanometric Platinum Overlayer to Catalyze NH3 Oxidation with High Turnover Frequency

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 NH 3 oxidation and was superior to that of a conventional powder catalyst (Pt/Al 2 O 3 ). 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 × 10 5 h –1 . Despite its nonporosity and small surface area, the Pt overlayer is a promising alternative to Pt/Al 2 O 3 for more efficient ammonia-slip catalysts that use less Pt loading; this is because the turnover frequency for the NH 3 oxidation at 200 °C is more than 180-fold greater than that achieved with Pt/Al 2 O 3 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 NH 3 oxidation, NO and NO 2, can be efficiently converted to N 2 by a selective catalytic reduction over a V 2 O 5 –WO 3 /TiO 2 catalyst in a tandem reactor system.