Nanophase-separated Ni3Nb as an automobile exhaust catalyst

Abstract

Catalytic remediation of automobile exhaust has relied on precious metals (PMs) including platinum (Pt). Herein, we report that an intermetallic phase of Ni and niobium (Nb) (i.e., Ni₃Nb) exhibits a significantly higher activity than that of Pt for the remediation of the most toxic gas in exhaust (i.e., nitrogen monoxide (NO)) in the presence of carbon monoxide (CO). When subjected to the exhaust-remediation atmosphere, Ni₃Nb spontaneously evolves into a catalytically active nanophase-separated structure consisting of filamentous Ni networks (thickness < 10 nm) that are incorporated in a niobium oxide matrix (i.e., NbO_x (x < 5/2)). The exposure of the filamentous Ni promotes NO dissociation, CO oxidation and N₂ generation, and the NbO_x matrix absorbs excessive nitrogen adatoms to retain the active Ni⁰ sites at the metal/oxide interface. Furthermore, the NbO_x matrix immobilizes the filamentous Ni at elevated temperatures to produce long-term and stable catalytic performance over hundreds of hours.