General synthesis of nanostructured phase-pure bimetallic carbides of molybdenum and tungsten

Abstract

Nanostructured transition metal carbides are considered to be promising catalytic materials. Their electronic properties, which are related to the modification effect on the metal d-band upon carbide formation, can be further tuned by the addition of a transition metal into their lattices to form bimetallic carbides. In this study, we report a general route for the synthesis of nanostructured phase-pure bimetallic carbides of molybdenum and tungsten with nickel, cobalt, and iron (Ni₆Mo₆C, Co₃Mo₃C, Fe₃Mo₃C, Ni₆W₆C, Co₆W₆C, and Fe₃W₃C with a η-carbide structure), that is, by the carbothermal hydrogen reduction of hydrothermally treated bimetallic oxides. The phase separation of bimetallic carbides is effectively avoided by the hydrothermal treatment of the bimetallic oxide, and the formation temperatures of bimetallic carbides are lowered to 600 °C–750 °C by the reduction effect of hydrogen. Good dispersion of phase-pure bimetallic carbide particles with nanometer dimensions (10–33 nm) is achieved using an activated carbon material with a high surface area as a carbon source and support. As an example, η-Ni₆Mo₆C exhibits good performance in the hydrogenation of naphthalene, which can be attributed to its porous nanostructure, clean surface and special electronic properties.