Reduction of Molybdenum Trioxide by Using Hydrogen

Abstract

Metallic molybdenum was synthesized through reduction of molybdenum trioxide (MoO3) by using hydrogen as a reducing agent. The reduction behavior of MoO3 were investigated by using temperature programmed reduction (TPR). The reduced phases were characterized by X-ray diffraction spectroscopy (XRD). The XRD results indicate that the reduction of MoO3 proceed in two steps reduction (MoO3 → MoO2 → Mo) with formation of intermediate phases of Mo4O11 during first step of reduction. However, the TPR results showed only one broad peak that correspond to all reduction step that was merge into one peak. It seem that, increasing the temperature cause the rapid reduction that correlated with thermodynamic consideration data that show the formation of metallic molybdenum is become feasible by increasing the temperature.

Strong Interface Enhanced Hydrogen Evolution over Molybdenum-Based Catalysts

“…It is known that the reduction of pure Mo oxides is very slow at temperatures below 450 °C because of the poor ability of the oxides for hydrogen splitting. 47,48 In the temperature range from 100 to 400 °C, Figure 4b shows that the hydrogen consumption of the MoO 3 -700 catalyst (with the Mo/MoO 2 interface) is much higher than that of the MoO 3 -600 sample (without the Mo/MoO 2 interface). For example, the hydrogen consumption per surface area of the MoO 3 -700 catalyst is about three times higher than that of MoO 3 -600 at 300 °C.…”

“…To test the hydrogen spillover hypothesis, hydrogen temperature-programmed reduction analysis (H 2 -TPR) is performed to study the various interactions between the surface site and hydrogen on two catalysts with and without the metal–oxide interface (MoO 3 -700 and MoO 3 -600). It is known that the reduction of pure Mo oxides is very slow at temperatures below 450 °C because of the poor ability of the oxides for hydrogen splitting. , In the temperature range from 100 to 400 °C, Figure b shows that the hydrogen consumption of the MoO 3 -700 catalyst (with the Mo/MoO 2 interface) is much higher than that of the MoO 3 -600 sample (without the Mo/MoO 2 interface). For example, the hydrogen consumption per surface area of the MoO 3 -700 catalyst is about three times higher than that of MoO 3 -600 at 300 °C.…”

In situ studies on the industrial production process for molybdenum dioxide, MoO2

“…[15] Furthermore, the content of Mo 4 O 11 formed during the reduction was recently shown to influence the particle morphology of the molybdenum dioxide product phase. [17] The endothermic reduction of molybdenum dioxide to molybdenum powder [18] is industrially performed at temperatures about 1373 K, but may already be observed at temperatures above 773 K given hydrogen concentrations above 10 vol-%. [16] In previous contributions we use the concept of in situ characterization techniques to investigate the occurrence of intermediates in the reduction of molybdenum oxide and to explain different reaction pathways depending on heating rate and hydrogen gas flow.…”

In Situ X-ray Diffraction Studies on the Production Process of Molybdenum

“…5 The resulting Mo 4 O 11 and MoO 2 show different size distributions and grain shapes depending on the local partial pressure of H 2 O during the reduction. 4 At temperatures above 773 K, the formation of molybdenum metal can be observed given H 2 concentrations above 10 vol % 5 following the endothermic reduction of molybdenum dioxide to molybdenum powder 6 that is industrially applied typically at temperatures about 1373 K. Depending on the local dew point, molybdenum is either formed by pseudomorphic transformation or chemical vapor transport following the shrinking core model. 4 Molybdenum's high melting point, resistance toward creep, wear, and corrosion as well as thermal and electrical conductivity open up a wide range of applications in lighting, such as cold cathode fluorescent lamps (CCFL) and high brightness light-emitting diodes (HBLED), glassmaking, hightemperature furnaces, X-ray tubes, electronics, and coatings.…”

“…The resulting Mo 4 O 11 and MoO 2 show different size distributions and grain shapes depending on the local partial pressure of H 2 O during the reduction . At temperatures above 773 K, the formation of molybdenum metal can be observed given H 2 concentrations above 10 vol % following the endothermic reduction of molybdenum dioxide to molybdenum powder that is industrially applied typically at temperatures about 1373 K. Depending on the local dew point, molybdenum is either formed by pseudomorphic transformation or chemical vapor transport following the shrinking core model …”