Solid-solid phase equilibria in the binary system cobalt molybdate (CoMoO4)-iron molybdate (FeMoO4) and effect of iron on the phase equilibria

Comparative study of polymorphic phase transition by differential thermal analysis, high temperature x-ray diffraction and temperature programmed electrical conductivity measurements: case study of mixed iron and cobalt molybdate

“…In a recent work, we have studied the phase diagram of the binary system CoMo04-FeMo04 and the effect on Fe3+ on the phase equilibria of this system. 10 We have been able to show that this system exhibited two solid solutions « and ß with a linear variation of the a/ß phase transition temperature with the molar fraction x in Co1_xFeIMo04, from CoMo04 to FeMo04, since the latter phase presents the same two polymorphic types. This system had never been investigated before, and, by contrast to CoMo04, little information is available on the phase transformation of «-FeMo04 to /3-FeMo04.9 This is presumably due on one hand to the low thermicity of the reaction and on the other hand to the high oxidizability of the ferrous compound, when the temperature is raised.…”

“…A Feo.12Cou^Mo04 mixed cobalt-iron molybdate was prepared by coprecipitation from cobalt nitrate Co(N03)2-6H20, ferrous chloride FeCl2*4H20 and ammonium heptamolybdate (NH4)6Mo7024*4H20 mixture, under controlled atmosphere, as previously described. 10 The initial pH was equal to 7 and decreased progressively to 5 by the end of the reaction. The precursor obtained was calcined at 450 °C for 10 h and at 900 eC for 2 h under pure nitrogen flow.…”

“…The prepared solid contained some Fe3+ cations (Fe3+/(Co + Fe) = 0.026) and a small excess of molybdenum compared to the other cations ((Fe + Co)/Mo = 0.91) according to the chemical analysis. 10 The excess of molybdenum may be due to the presence of MoG3 which is lost when the solid is calcinated at 900 °C.10 (b) Differential Thermal Analysis. The differential thermal analysis (DTA) was performed using a Setaram MTD 85 analyzer equipped with platinum/rhodium thermocouples (30/6).…”

Continuous supercritical synthesis of unsupported and high specific surface area catalyst precursors for deep-hydrodesulfurization

“…The β-isomorph is clearly the majority phase. Nothing surprising since it has already been proved that, unlike β-NiMoO4, which is unstable below 180 °C, β-CoMoO4 can be easily stabilized at room temperature 52 . As the XRD patterns also shown ( Figure 4.b), the α-phase almost disappears after thermal treatment at 400 °C for 3 h.…”

Chemical Imaging of Mixed Metal Oxide Catalysts for Propylene Oxidation: From Model Binary Systems to Complex Multicomponent Systems

“…In particular, the potential interaction or cooperative function of specific phases often cannot be accurately determined based on studies of model or binary systems alone. For example, catalytic performance may be influenced also by pure metal oxide phases ( e. g ., MoO 3 or CoO) as well as mixed or intermediate phases ( e. g ., Fe x Co 1‐x MoO 4 or Bi 3 FeMo 2 O 12 ) that may act as selective, promotor, inert or unselective phases [12–13] . Consequently this complicates the collection of meaningful data describing the presence and interaction of individual phases in industrially‐relevant systems, such as quaternary MMOs.…”