Thermal kinetics study on the conversion of β-MoO3 to α-MoO3; A molybdenite concentrate derivative as a catalyst
2022
Vosough, Mahtab | Khayati, Gholam Reza | Sharafi, Shahriar
Herein, thermal decomposition kinetics of molybdic acid (MA) obtained from the leaching of molybdenite concentrate are extensively studied as a precursor for the preparation of molybdenum trioxide (MoO₃). The thermal kinetics equation of the reaction suggests that the precursor (MA, H₂MoO₄.H₂O) is converted to β-MoO₃ and then to α-MoO₃ due to the heating process, giving rise to a transformation temperature of 260-320°C, the average activation energy of about 26.53 ± 0.02 kJ/mol, and a pre-exponential factor of 10⁷ 1/min for the transformation of β-MoO₃ to α-MoO₃. Moreover, differential scanning calorimetry reveals that the volume diffusion mechanism controls the crystallization reaction, leading to the decomposition of MA. Our results indicate that Johnson-Mehl-Avrami (JMA) kinetics with nucleation and three-dimensional growth mechanism can model the experimental data with acceptable accuracy. The catalytic attributes of the stable β-MoO₃/α-MoO₃ compound provided an efficiency of over 89 % for the oxidation process of methanol to formaldehyde.
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