Mechanism and kinetic study of hydrogen reduction of ultra-fine spherical MoO3 to MoO2

The mechanism and kinetics of hydrogen reduction of ultra-fine spherical MoO3 to MoO2 have been investigated in the present work. The results show that the reduction of MoO3 to MoO2 obeys the two-step reduction mechanism with the generation of intermediate product Mo4O11. The final product MoO2 always keeps the same morphology as Mo4O11. The experimental data can be well described by using the dual interface reaction model. It was found that the rate controlling steps for the first (from MoO3 to Mo4O11) and second reactions (from Mo4O11 to MoO2) were interface chemical reaction and diffusion, respectively, with the activation energies extracted to be 122 kJ/mol and 114 kJ/mol. When the reaction extent (defined as the ratio of weight loss of MoO3 at time t to the theoretical maximum weight loss from MoO3 to MoO2 due to the removal of oxygen during the reduction process) is in the range of 0 to 0.7, both the reduction of MoO3 to Mo4O11 and Mo4O11 to MoO2 occurred simultaneously; when the reaction extent is in the range of 0.7 to 1, only the reduction of Mo4O11 to MoO2 occurred in the reduction process.