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Oxidation of methanol to formaldehyde over a series of Fe(1-x)Al(x)-V-oxide catalysts

Häggblad, Robert LU ; Wagner, Jakob LU ; Hansen, Staffan LU and Andersson, Arne LU (2008) In Journal of Catalysis 258(2). p.345-355
Abstract
A series of triclinic Fe1−xAlxVO4 phases with 0 <= x <= 1 were prepared and used in the oxidation of methanol to formaldehyde. The activity measurements revealed that both the activity and especially the selectivity to formaldehyde increased with time of operation for at least 16 h, indicating restructuring of the catalysts. Characterisation of the catalysts with XRD, XANES, and electron microscopy after use in methanol oxidation showed that the stability of the bulk phases improved when Al was substituted for Fe in the structure. XRD and XANES of the used FeVO4 showed that it partly transformed into a cation-vacant spinel-type Fe1.5V1.5O4 phase, whereas the AlVO4 phase showed no change in the bulk structure. HRTEM imaging of used... (More)
A series of triclinic Fe1−xAlxVO4 phases with 0 <= x <= 1 were prepared and used in the oxidation of methanol to formaldehyde. The activity measurements revealed that both the activity and especially the selectivity to formaldehyde increased with time of operation for at least 16 h, indicating restructuring of the catalysts. Characterisation of the catalysts with XRD, XANES, and electron microscopy after use in methanol oxidation showed that the stability of the bulk phases improved when Al was substituted for Fe in the structure. XRD and XANES of the used FeVO4 showed that it partly transformed into a cation-vacant spinel-type Fe1.5V1.5O4 phase, whereas the AlVO4 phase showed no change in the bulk structure. HRTEM imaging of used catalysts confirmed that structural changes,including in the surface, occurred during catalysis. Quantitative surface analysis by XPS of the catalysts before and after use in methanol oxidation revealed no significant change in the metal composition, in good agreement with the corresponding bulk values, except for a lower Fe value. Steady-state activity data showed a modest increase in specific activity with the Al content, whereas the selectivity to formaldehyde was about 90% for all samples at high methanol conversion. The similar catalytic behaviour of the vanadates irrespective of the differences in the bulk structure indicates that the surface structure differed from the bulk structure. Compared with pure vanadia, the vanadates had lower activity per V atom and slightly greater selectivity to formaldehyde. Consequently, for methanol oxidation, the role of Al and Fe on the catalyst surface can be described as that of a spacer, decreasing the surface concentration of active V sites and the number of less selective V–O–V ensembles. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
SEM¨, XPS, Formaldehyde, Methanol, Fe1−xAlxVO4 catalysts Fe–V–O spinel-type phases, Selective oxidation, XRD, XANES, HRTEM
in
Journal of Catalysis
volume
258
issue
2
pages
345 - 355
publisher
Elsevier
external identifiers
  • wos:000259409800007
  • scopus:48849098874
ISSN
1090-2694
DOI
10.1016/j.jcat.2008.06.029
language
English
LU publication?
yes
id
c7057742-dc92-4d11-a63d-a4a8c6b4ec32 (old id 1274287)
date added to LUP
2008-12-18 10:34:16
date last changed
2017-01-01 05:10:18
@article{c7057742-dc92-4d11-a63d-a4a8c6b4ec32,
  abstract     = {A series of triclinic Fe1−xAlxVO4 phases with 0 &lt;= x &lt;= 1 were prepared and used in the oxidation of methanol to formaldehyde. The activity measurements revealed that both the activity and especially the selectivity to formaldehyde increased with time of operation for at least 16 h, indicating restructuring of the catalysts. Characterisation of the catalysts with XRD, XANES, and electron microscopy after use in methanol oxidation showed that the stability of the bulk phases improved when Al was substituted for Fe in the structure. XRD and XANES of the used FeVO4 showed that it partly transformed into a cation-vacant spinel-type Fe1.5V1.5O4 phase, whereas the AlVO4 phase showed no change in the bulk structure. HRTEM imaging of used catalysts confirmed that structural changes,including in the surface, occurred during catalysis. Quantitative surface analysis by XPS of the catalysts before and after use in methanol oxidation revealed no significant change in the metal composition, in good agreement with the corresponding bulk values, except for a lower Fe value. Steady-state activity data showed a modest increase in specific activity with the Al content, whereas the selectivity to formaldehyde was about 90% for all samples at high methanol conversion. The similar catalytic behaviour of the vanadates irrespective of the differences in the bulk structure indicates that the surface structure differed from the bulk structure. Compared with pure vanadia, the vanadates had lower activity per V atom and slightly greater selectivity to formaldehyde. Consequently, for methanol oxidation, the role of Al and Fe on the catalyst surface can be described as that of a spacer, decreasing the surface concentration of active V sites and the number of less selective V–O–V ensembles.},
  author       = {Häggblad, Robert and Wagner, Jakob and Hansen, Staffan and Andersson, Arne},
  issn         = {1090-2694},
  keyword      = {SEM¨,XPS,Formaldehyde,Methanol,Fe1−xAlxVO4 catalysts
Fe–V–O spinel-type phases,Selective oxidation,XRD,XANES,HRTEM},
  language     = {eng},
  number       = {2},
  pages        = {345--355},
  publisher    = {Elsevier},
  series       = {Journal of Catalysis},
  title        = {Oxidation of methanol to formaldehyde over a series of Fe(1-x)Al(x)-V-oxide catalysts},
  url          = {http://dx.doi.org/10.1016/j.jcat.2008.06.029},
  volume       = {258},
  year         = {2008},
}