Mechanism and Kinetic Study of Reducing MoO3 to MoO2 with CO-15 vol % CO2 Mixed Gases

In the present paper, the reduction reaction of high-purity MoO3 with CO-15 vol % CO2 mixed gases in the temperature range of 901-948 K is investigated via the thermogravimetric analysis technology. The results show that reduction of MoO3 to MoO2 follows a three-step reaction process, viz., MoO3 is first reduced into Mo9O26, followed by Mo4O11, and finally to MoO2. The reaction sequences of MoO3 -> Mo9O26 -> Mo4O11 -> MoO2 are proposed, which are quite different from those observed on reduction of MoO3 by pure H-2 or CO gases. Pure Mo9O26 and Mo4O11 could be synthesized once suitable time was controlled. Rate-controlling steps for the reduction from MoO3 to Mo9O26 and Mo9O26 to MoO2 (include both Mo9O26 to Mo4O11 and Mo4O11 to MoO2) are interfacial chemical reactions, with the activation energies of 318.326 and 112.047 kJ/mol, respectively. This study also discovers that the as-synthesized MoO2 keeps the same platelet-shaped and smooth morphology as the MoO3 raw material; however, its particles size gradually increased as the reaction proceeds due to the formation of low-melting-point eutectic and the sticking of different particles.