Molten salt synthesis of CrMnFeNi alloy nanopowder passivated by TiOx–ZrOy shell used as a superior catalyst support in liquid-phase hydrogenation

Abstract

A molten salt method was used to prepare CrMnFeNi alloy nanopowder passivated by TiO_x–ZrO_y surface shell with a high specific surface area (23 m² g⁻¹) from the oxide precursors. Analyses by scanning electron microscopy/transmission electron microscopy with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed the formation of an alloyed Cr–Mn–Fe–Ni-rich core surrounded by an oxide surface shell with a Ti/Zr-rich composition, confirming the formation of TiO_x–ZrO_y/CrMnFeNi nanopowder. It was speculated that the CrMnFeNi alloy nanoparticles were preferentially formed from the constituent metals by a faster reduction of any oxides of Cr, Mn, Fe, and Ni and a subsequent alloying with Ti and Zr could hardly occur due to the high thermodynamic stability of CrMnFeNi alloy. A Ni-loaded TiO_x–ZrO_y/CrMnFeNi catalyst exhibited superior catalytic performance to common Ni-loaded TiO₂ and ZrO₂ in the liquid-phase hydrogenation of p-nitrophenol at room temperature. The enhancement could have originated from an excellent electrical property of CrMnFeNi alloy, promoting the formation of active metallic nickel on the surface during the reaction. Leaching amounts of the constituent elements of Ti–Zr–Cr–Mn–Fe–Ni and loaded Ni was very little in the reaction solution after the reaction; the results confirmed that the prepared CrMnFeNi alloy nanopowder was very stable due to the protection of the Ti/Zr-rich oxide shell. Thus, the potential application of the alloyed powder used as catalyst support was demonstrated.