Deactivation behavior of an iron-molybdate catalyst during selective oxidation of methanol to formaldehyde

Raun, Kristian Viegaard; Lundegaard, L. F.; Chevallier, J.; Beato, Pablo; Appel, C.C.; Agersted, Karsten; Thorhauge, Max; Jensen, Anker Degn; Høj, Martin

doi:10.1039/c8cy01109e

Cited by 36 publications

(59 citation statements)

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“…However, the intensity of feature B is higher than for Fe 2 (MoO 4 ) 3 , showing that Mo is present in both tetrahedral (as in Fe 2 (MoO 4 ) 3 ) as well as octahedral geometry (MoO 3 and surface MoO x ). Since the fresh catalyst contained 17 wt.% α-MoO 3 and 83 wt.% Fe 2 (MoO 4 ) 3 according to XRD, [19] which corresponds to 22 mol.% of the Mo is bound as MoO 3 and 78 mol.% as Fe 2 (MoO 4 ) 3 , this is in reasonable agreement. Since the fresh catalyst contained 17 wt.% α-MoO 3 and 83 wt.% Fe 2 (MoO 4 ) 3 according to XRD, [19] which corresponds to 22 mol.% of the Mo is bound as MoO 3 and 78 mol.% as Fe 2 (MoO 4 ) 3 , this is in reasonable agreement.…”

Section: Initial Catalyst Characterization By X-ray Absorption Spectrsupporting

confidence: 58%

“…EXAFS fitting results are given in Table 1 3 in the initial state of the catalyst, as also found by ex situ XRD and reported previously. [19] Additionally, this was also confirmed by XRD measured at the beginning of the operando experiments (see Section 3.2.3).…”

Section: Initial Catalyst Characterization By X-ray Absorption Spectrsupporting

confidence: 55%

“…[19] For the operando XAS/XRD studies, the catalyst was calcined at 535°C in air, subsequently crushed and ground with silica (Sigma-Aldrich) in a 1/5 catalyst/silica weight ratio. [19] For the operando XAS/XRD studies, the catalyst was calcined at 535°C in air, subsequently crushed and ground with silica (Sigma-Aldrich) in a 1/5 catalyst/silica weight ratio.…”

Section: Experimental Catalyst Preparationmentioning

confidence: 99%

“…[19] The Mo K-edge XANES spectrum of the initial state of the catalyst at 100°C in 10 % O 2 /He along with the XANES spectra of Fe 2 (MoO 4 ) 3 and MoO 3 references are shown in Figure 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 20006 eV is attributed to the dipole-forbidden/quadrupoleallowed 1 s-4 d transition associated primarily with tetrahedral geometry, but is also present with weak intensity in distorted octahedral geometry. [19] The Mo K-edge XANES spectrum of the initial state of the catalyst at 100°C in 10 % O 2 /He along with the XANES spectra of Fe 2 (MoO 4 ) 3 and MoO 3 references are shown in Figure 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42...…”

Section: Initial Catalyst Characterization By X-ray Absorption Spectrmentioning

confidence: 99%

“…[15] Additional redox cycle experiments with iron molybdate (without excess of MoO 3 ) showed that Fe 2 (MoO 4 ) 3 is reduced to FeMoO 4 and MoO 2 through formation of two intermediate phases: an oxygen defective intermediate pseudo-molybdate and a MoC phase. [19] Operating at high space velocity, with significant MeOH concentration also at the outlet, the catalyst bed was uniformly deactivated. [16] The above studies indicate that there is a need for not only understanding the structure of the active site and the structural dynamics during redox cycling, but also the deactivation by molybdenum volatilization observed in industrial reactors near the inlet, where the MeOH concentration is high.…”

Section: Introductionmentioning

confidence: 99%

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Operando XAS/XRD and Raman Spectroscopic Study of Structural Changes of the Iron Molybdate Catalyst during Selective Oxidation of Methanol

et al. 2019

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The structural changes of an iron molybdate/molybdenum oxide (Mo/Fe = 2.0) catalyst for the selective oxidation of methanol to formaldehyde were studied using combined operando X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) as well as operando Raman spectroscopy. Under operating conditions, the Mo K-edge XANES spectra showed a transition from a mixture of α-MoO 3 and Fe 2 (MoO 4 ) 3 towards only Fe 2 (MoO 4 ) 3 . XRD and Raman spectroscopy also showed disappearance of the α-MoO 3 phase with time on stream. The results evidenced that the α-MoO 3 component evaporated completely, while the Fe 2 (MoO 4 ) 3 component remained stable. This was linked to a decrease in catalytic activity. Further studies unraveled that the rate of α-MoO 3 evaporation increased with increasing MeOH concentration, decreasing O 2 concentration and increasing temperature. The simultaneous measurements of catalytic activity and spectroscopy allowed to derive a structure-activity relationship showing that α-MoO 3 evaporation needs to be prevented to optimize MoO 3 -based catalysts for selective oxidation of methanol.

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Section: Initial Catalyst Characterization By X-ray Absorption Spectrsupporting

confidence: 58%

Section: Initial Catalyst Characterization By X-ray Absorption Spectrsupporting

confidence: 55%

Section: Experimental Catalyst Preparationmentioning

confidence: 99%

Section: Initial Catalyst Characterization By X-ray Absorption Spectrmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Operando XAS/XRD and Raman Spectroscopic Study of Structural Changes of the Iron Molybdate Catalyst during Selective Oxidation of Methanol

et al. 2019

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

et al. 2021

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Industrially-applied mixed metal oxide catalysts often possess an ensemble of structural components with complementary functions. Characterisation of these hierarchical systems is challenging, particularly moving from binary to quaternary systems. Here a quaternary BiÀ MoÀ CoÀ Fe oxide catalyst showing significantly greater activity than binary BiÀ Mo oxides for selective propylene oxidation to acrolein was studied with chemical imaging techniques from the microscale to nanoscale. Conventional techniques like XRD and Raman spectroscopy could only distinguish a small number of components. Spatially-resolved characterisation provided a clearer picture of metal oxide phase composition, starting from elemental distribution by SEM-EDX and spatially-resolved mapping of metal oxide components by 2D Raman spectroscopy. This was extended to 3D using multiscale hard X-ray tomography with fluorescence, phase, and diffraction contrast. The identification and co-localisation of phases in 2D and 3D can assist in rationalising catalytic performance during propylene oxidation, based on studies of model, binary, or ternary catalyst systems in literature. This approach is generally applicable and attractive for characterisation of complex mixed metal oxide systems.

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Highly Stable Apatite Supported Molybdenum Oxide Catalysts for Selective Oxidation of Methanol to Formaldehyde: Structure, Activity and Stability

et al. 2021

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Molybdenum oxide (5 to 20 wt.%) supported on calcium or strontium hydroxyapatite were investigated as catalysts for selective oxidation of methanol to formaldehyde. These catalysts were both active and selective, with a maximum yield achieved at 95 % conversion and 96 % selectivity. The main byproducts were CO (3.2 %) and dimethyl ether (DME, 0.7 %). The catalytic performance of the catalysts was measured for up to 600 h at 350 °C. Compared to an industrial iron molybdate catalyst, the hydroxyapatite based catalysts deactivated slower.The active species were found to be a surface layer of MoO x on the hydroxyapatite support, while excess molybdenum formed crystalline (Ca/Sr)MoO 4 , acting as a reservoir replenishing surface MoO x lost by volatilization with methanol. The excess molybdenum in the form of (Ca/Sr)MoO 4 was found to volatilize significantly slower than the excess MoO 3 in iron molybdate catalysts. The combination of high activity and selectivity with low rate of Mo volatilization makes this class of catalysts interesting for industrial production of formaldehyde.

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Deactivation behavior of an iron-molybdate catalyst during selective oxidation of methanol to formaldehyde

Abstract: Molybdenum loss, phase transformations and catalytic performance of an iron molybdate catalyst.

Cited by 36 publications

References 36 publications

Operando XAS/XRD and Raman Spectroscopic Study of Structural Changes of the Iron Molybdate Catalyst during Selective Oxidation of Methanol

Operando XAS/XRD and Raman Spectroscopic Study of Structural Changes of the Iron Molybdate Catalyst during Selective Oxidation of Methanol

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

Highly Stable Apatite Supported Molybdenum Oxide Catalysts for Selective Oxidation of Methanol to Formaldehyde: Structure, Activity and Stability

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