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

Dorsch

Kohlmann

2023

Chemistry A European J

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The reduction of metal oxides with hydrogen is widely used for the production of fine chemicals and metals both on the laboratory and industry scale. In situ methods can help to elucidate reaction pathways and to gain control over such synthesis reactions. In this study, the reduction of WO3 and V2O5 with hydrogen was investigated by in situ X‐ray powder diffraction with regard to intermediates and the influence of heating rates and hydrogen flow rates. Mixtures of V4O9, V6O13 and VO2 in two modifications were identified as intermediates on the way to phase‐pure V2O3. None of the intermediates occurs in a single phase and therefore cannot be prepared this way. In contrast, the intermediates of the WO3 reduction, H0.23WO3 and W10O29, appear consecutively and can be isolated. For both reactions, the heating and flow rates have little influence on the formation of intermediates.

Section: Introductionmentioning

confidence: 71%

In Situ X‐ray Diffraction Studies on the Reduction of V₂O₅ and WO₃ by Using Hydrogen

Dorsch

Kohlmann

2023

Chemistry A European J

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“…[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. [19] Such rational approaches to solidstate synthesis planning like the investigation of reaction pathways by in situ methods [20] are rarely applied to industrial processes, but can yield very valuable information on the effect of process parameters on the products. Furthermore, they may help controlling product properties, avoiding unwanted byproducts and optimizing reaction conditions and energy consumption.…”

Section: Introductionmentioning

confidence: 99%

“…It was shown that an orthorhombic molybdenum bronze H x MoO 3 occurs as an intermediate of the reduction of MoO 3 at low heating rates while Mo 4 O 11 can only be observed at higher rates. [19] High hydrogen flow rates favor the formation of molybdenum at lower temperatures. Furthermore, the content of potassium as an additive in MoO 3 in the industrial process influences the amount of Mo 4 O 11 formed during the reduction as well as the time it takes to form Mo 4 O 11 and MoO 2 .…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, the content of potassium as an additive in MoO 3 in the industrial process influences the amount of Mo 4 O 11 formed during the reduction as well as the time it takes to form Mo 4 O 11 and MoO 2 . [19] In this contribution, additional experiments were conducted to further improve the understanding of the formation of Magnéli phases during the reduction, the influence of potassium on the reduction and the formation of molybdenum at temperatures below 1200 K. To perform measurements under conditions comparable to the industrial process, the time-temperature program as well as the flow rate used were accommodated to match operating parameters. Further, products were validated by comparing the resulting particle sizes to those of industrial products.…”

Section: Introductionmentioning

confidence: 99%

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

Zeitschrift anorg allge chemie

Uhlenhut

Gabke

et al. 2023

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In the industrial production of molybdenum the reduction of molybdenum trioxide with hydrogen is a two‐step process. In order to get a deeper understanding of the chemistry involved, in situ studies were performed on the thermal behavior of molybdenum trioxide and the first reduction step to molybdenum dioxide. MoO3 shows a very strong anisotropy for thermal expansion (linear expansion coefficients α in 10−4 K−1: 1.32(4) for a, 5.5(1) for b, −0.246(5) for c). Upon heating in air, preferred orientation in XRPD patterns decreases and the color changes from grey to yellow, probably caused by decreasing oxygen vacancy concentration. The reduction of MoO3 by hydrogen was investigated via in situ X‐ray powder diffraction for varying heating rate, hydrogen flow and potassium content. The formation of the intermediate γ‐Mo4O11 shows a higher rate for increasing potassium content; it does not play a role whether potassium is present in the starting material MoO3 or in MoO2 formed in the reaction. The high‐temperature modification of K2MoO4 was found to crystallize in the α‐K2SO4 type (P63/mmc, a=6.3463(2) Å, c= 8.1331(2) Å). Heating up MoO3 in vacuum (1 Pa) with the same T,t protocol as above yields MoO2 even without the presence of hydrogen.

“…[11,12] Time-resolved analytical techniques can be used to follow chemical reactions of solids and can uncover reaction pathways as well as provide information on the dynamics, making them a welcome extension of the otherwise often static picture of solids in industrial processes. [13,14] The production process of rhenium has not been thoroughly studied by means of in situ X-ray diffraction yet, but similar studies that have been performed on other refractory metals produced via reduction with hydrogen, like molybdenum, [15][16][17][18] delivered promising results by revealing intermediates, explaining their formation in the context of ambient conditions and clarifying the influence of additives on the reaction. Therefore, in this contribution, we use this concept to investigate the reduction of ammonium perrhenate with regards to intermediates and influences of the gas atmosphere.…”

Section: Introductionmentioning

confidence: 99%

In situ X‐ray diffraction studies on the production process of rhenium

Zeitschrift anorg allge chemie

Kohlmann

Uhlenhut³

et al. 2022

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Rhenium powder is industrially produced in a two‐step reaction by reducing NH4ReO4 with hydrogen at 623 and 1173 K. In this study, both steps of the production process have been investigated via in situ X‐ray powder diffraction. Up to 550 K no reaction with hydrogen can be observed. Between 550 K and 623 K poorly crystalline rhenium is formed. Crystallinity is increased during the second step at 1173 K. Annealing under hydrogen or nitrogen provides a comparable product in respect to the examined crystal and real structure parameters independent of the gas atmosphere.