Kinetic Studies on Hydrogen Reduction of MoO3 and Morphological Analysis of Reduced Mo Powder

Abstract

The studies on hydrogen reduction of MoO 3 indicated two main stages, namely, MoO 3 to MoO 2 and MoO 2 to Mo. In both stages, temperature and time of reduction progressively increased on diluting hydrogen from 100 to 10 pct. Detailed kinetic analysis of the MoO 2 to Mo stage was conducted by carrying out isothermal reduction between 625°C and 900°C by pure hydrogen.The kinetic equation was found to be g a ð Þ ¼ À ln 1 À a ð Þ ½1=n ¼ kt, with n ranging from 1.49 to 2.13. The rate constant k obeyed the Arrhenius temperature dependence with the associated activation energy of 136 kJ mol -1 . The X-ray diffraction (XRD) analysis of the product confirmed the phases predicted by thermal analysis. The scanning electron microscope (SEM) analysis of molybdenum powder revealed the presence of a greater number of pores and cracks in the individual particles produced at lower reduction temperatures and the tendency of acquiring spherical morphology with increasing reduction temperature. Based on the studies conducted, the optimum conditions for MoO 3 to Mo reduction were predicted.

Study on reduction reaction of MoO2 powder with NH3

“…While at the higher temperatures (from 1078 to 1273 K), the stable phase is metal Mo with a little solution of N. The significant increase in the density from MoO 2 (6.47 g/cm 3 ) to Mo (10.22 g/cm 3 ) would result in the presence of lots of pores as shown in Figures and . At the higher temperatures, the reaction sequence may also have two parallel reactions as described in Figure .…”

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

“…Molybdenum metal powders with suitable morphology, size and purity are of immense importance for alloy preparation by powder metallurgy (PW) [1,2]. The industrial production of metallic molybdenum powders is a stepwise process that begins with the reduction of MoO 3 to MoO 2 by hydrogen [3][4][5].…”

Effective hydrodeoxygenation of biomass-derived oxygenates into unsaturated hydrocarbons by MoO3 using low H2 pressures

“…S5 †). 11 A temperature programed reduction (TPR) analysis suggests that the reduction of MoO 3 to MoO 2 is less likely to occur at temperatures below 873-1073 K. 12 Even though the partial surface reduction of MoO 3 to form oxygen vacancies was undetectable by PXRD and XPS techniques, their formation is thermodynamically favourable. DFT calculations show a Gibbs free energy of oxygen vacancy generation of 60.6 kJ mol À1 at 673 K, which translates to $5% of surface oxygen that can be removed to generate vacancies sites.…”