In situ X‐ray analysis of MoO₃ reduction

Abstract

The reduction of MoO 3 to MoO 2 under hydrogen/argon atmosphere (5 vol. % H 2 /95 vol. % Ar) in the temperature range 323 K…623 K was studied in situ by means of wide-angle X-ray scattering. It has been found that the starting material, MoO 3 , consists of two different orthorhombic MoO 3 phases A and B with nearly the same structure parameters. The phase A (fraction of 37.1 wt%) describes the larger crystallites whereas the phase B (fraction of 62.9 wt.%) describes the smaller crystallites. Under the reduction to monoclinic MoO 2 phase during the heating , the thermal evolution of the phase fractions is different. A conclusion is drawn that MoO 2 is formed preferably in big crystallites. About 10 wt. % of MoO 2 has been found to form at 623 K resulting in about 69 wt. % after cooling to room temperature followed by holding in Ar/H 2 atmosphere about 24 h. Additionally, about 4.4 wt. % of the Mo 4 O 11 oxide probably formed in large crystallites was detected in the reduced powder after the cooling.

An XAS study of molybdenum speciation in hydrothermal chloride solutions from 25–385°C and 600bar

“…6). The local structure around Mo is tetrahedral for Na 2 MoO 4 Á2H 2 O (s) (Matsumoto et al, 1975;Capitelli et al, 2006) and octahedral for MoO 3(s) (Andersson and Magnéli, 1950;Leisegang et al, 2005), MoO 2 Cl 2(s) (Barraclough and Stals, 1966) and MoO 2(s) (Brandt and Skapski, 1967;Bolzan et al, 1995) (Table 2; Fig. 2b).…”

“…Takenaka et al (1998) also used intensity and integrated area of this pre-edge feature to estimate the asymmetry of the species. The tetrahedral moiety [MoO 4 ] 2À in Na 2 MoO 4(s) displays a more intense pre-edge than MoO 3(s) , which has a distorted octahedral [MoO 6 ] structure (Takenaka et al, 1998;Leisegang et al, 2005; Table 2). Such a distorted octahedral structure is typical of Mo(VI) compounds containing Mo in octahedral coordination; usually, Mo is bonded to 2 oxygen atoms at short distance ($1.60 Å ), 2 at intermediate distance, and 2 at a long distance ($2.3-2.4 Å ; Table 2).…”

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid—structure, function and dynamics of the V–Mo–W mixed oxides

“…The stabilisation effect of W and of the smaller particles compared to the crystallised samples inhibit a faster deactivation which is supported by the literature. 9,43 For spray-dried samples with W contents y 4 2 the phase composition seems to be stable against phase transformation under the investigated conditions. ACR with a concentration of 5 vol% in the reaction gas seems to have only negligible effects on the phase transformations.…”

The Formation of Icositetrahedron Molybdenum Powder and the Characteristics of Sintering Performance

“…[4] The experiments of MoO 3 fed with a different particle size indicated that MoO 3-X appeared only when certain large MoO 3 were reduced. [5] Intermediate molybdenum oxides functioning as one kind of important catalyst affected the microstructure of MoO 2 for the formation of crystallographic shear. [6] Then, how can the reduction conditions be controlled to obtain polyhedral Mo powder?…”