Steering the reaction kinetics of the MgO-V2O5 system toward selective synthesis of magnesium vanadates

Abstract

Magnesium vanadates (MgV2O6, Mg2V2O7 and Mg3V2O8) are common redox catalysts for organic reactions and excellent energy storage materials. However, due to the diversity of magnesium vanadates and their interconvertibility, it is difficult to accurately synthesize a species of magnesium vanadate or control its stability during functioning. Herein, the reaction kinetics of MgO-V2O5 system was studied for controllable synthesis of magnesium vanadates. The MgO-V2O5 diffusion couples were prepared to explore the interface reaction characteristics of the MgO-V2O5 system at different reaction time. During reaction, the thickness of the diffusion layer and diffusion coefficient gradually increased and reached a maximal value of 29.55 μm and 6.06 × 10−11 cm2 s−1 at 10 h, which diffusion is faster than that of CaO-V2O5 system. Additionally, the interconvertible mechanisms of different magnesium vanadates were investigated using XRD and SEM/EDS techniques. MgV2O6 was produced during the synthesis of Mg2V2O7 in the initial 4 h, which converted into Mg2V2O7 at a longer synthesis time. Mg2V2O7 was found during the generation process of Mg3V2O8; with abundant MgO, Mg2V2O7 converted into Mg3V2O8. These findings provide important insights into the accurate control of magnesium vanadate synthesis and even the vanadium extraction process.