A mechanistic study on the production of nanosized Mo in microwave assisted combustive reduction of MoO3 by Zn

• Molybdenum nanoparticles are synthesized with combustion reduction of MoO3 by Zn.
• Elemental Mo is synthesized during a two-step reduction process.
• Zn2Mo3O8 phase appears as an undesired phase formed among the products.
• Decreasing the adiabatic temperature of the process can prevent Zn2Mo3O8 to be synthesized.
• Zn2Mo3O8 reduces to Mo by further heating after the combustion moment.

The combustion synthesis of elemental Mo nanoparticles by zincothermic reduction of MoO3 was investigated in this research. It was determined that MoO3 reduces to Mo by means of two sub-reactions. The results showed that MoO3 reduces initially to MoO2 and subsequently dioxide phase reduces to elemental Mo. Due to the formation of MoO2 during the combustion moment, a considerable amount of unwanted Zn2Mo3O8 (2ZnO·3MoO2) phase was synthesized. Since the presence of this phase would prevent the reduction to be completed, hence this article was devoted to introduce some ways by which the zincothermic reduction of MoO3 can be completed. In one approach, the results indicated that by increasing the microwave heating duration after combustion moment, the unwanted Zn2Mo3O8 compound reduced successfully to Mo. In the other approach, the use of over-stoichiometric amounts of Zn led to prevent the formation of the undesired phase. In this research, X-ray diffraction technique (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to characterize the products of the reactions.