Ni in CNFs: Highly Active for Nitrite Hydrogenation

Nickel hairy foam, consisting of carbon nanofibers (CNFs) grown on the surface of nickel foam, were synthesized and tested for nitrite hydrogenation. The results showed that nickel "hairy" foam is catalytically active in the absence of any noble metal, which is attributed to the formation of nickel particles with high carbon content during CNF growth. These C-doped nickel particles showed catalytic properties similar to those of noble metals, but were easily deactivated as a result of oxidation treatments. This deactivation is partially attributed to nickel passivation, which is reversible by reducing with H₂ at room temperature in the gas or liquid phase. In addition, oxidation treatment also caused partial removal of the carbon dissolved in the nickel particles, causing irreversible deactivation. Increasing severity of the oxidation treatment induced slower reactivation via reduction, as well as lower steady-state activities after reactivation. This irreversible deactivation is attributed to the decreased concentration of dissolved carbon. Therefore, nickel "hairy" foam is a promising hydrogenation catalyst, provided it is protected against oxygen.