Restructuring Transition Metal Oxide Nanorods for 100% Selectivity in Reduction of Nitric Oxide with Carbon Monoxide

Transition metal oxide is one of the main categories of heterogeneous catalysts. They exhibit multiple phases and oxidation states. Typically, they are prepared and/or synthesized in solution or by vapor deposition. Here we report that a controlled reaction, in a gaseous environment, after synthesis can restructure the as-synthesized transition metal oxide nanorods into a new catalytic phase. Co₃O₄ nanorods with a preferentially exposed (110) surface can be restructured into nonstoichiometric CoO_1–x nanorods. Structure and surface chemistry during the process were tracked with ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and environmental transmission electron microscopy (E-TEM). The restructured nanorods are highly active in reducing NO with CO, with 100% selectivity for the formation of N₂ in temperatures of 250–520 °C. AP-XPS and E-TEM studies revealed the nonstoichiometric CoO_1–x nanorods with a rock-salt structure as the active phase responsible for the 100% selectivity. This study suggests a route to generate new oxide catalysts.