Fabrication of La₂O₃ Uniformly Doped Mo Nanopowders by Solution Combustion Synthesis Followed by Reduction under Hydrogen.

This work reports the preparation of La₂O₃ uniformly doped Mo nanopowders with the particle sizes of 40⁻70 nm by solution combustion synthesis and subsequent hydrogen reduction (SCSHR). To reach this aim, the foam-like MoO₂ precursors (20⁻40 nm in size) with different amounts of La₂O₃ were first synthesized by a solution combustion synthesis method. Next, these precursors were used to prepare La₂O₃ doped Mo nanopowders through hydrogen reduction. Thus, the content of La₂O₃ used for doping can be accurately controlled via the SCSHR route to obtain the desired loading degree. The successful doping of La₂O₃ into Mo nanopowders with uniform distribution were proved by X-ray photon spectroscopy and transmission electron microscopy. The preservation of the original morphology and size of the MoO₂ precursor by the La₂O₃ doped Mo nanopowders was attributed to the pseudomorphic transport mechanism occurring at 600 °C. As shown by X-ray diffraction, the formation of Mo₂C impurity, which usually occurs in the direct H₂ reduction process, can be avoided by using the Ar calcination-H₂ reduction process, when residual carbon is removed by the carbothermal reaction during Ar calcination at 500 °C.