A density functional theory study of the oxidation of methanol to formaldehyde over vanadia supported on silica, titania, and zirconia

Journal Article · Thu Sep 05 04:00:00 EDT 2002 · Journal of Physical Chemistry B

DOI:https://doi.org/10.1021/jp014695h· OSTI ID:836790

Khaliullin, Rustam Z ^[1]; Bell, Alexis T

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1. LBNL Library

Density functional theory was used to investigate the mechanism and kinetics of methanol oxidation to formaldehyde over vanadia supported on silica, titania, and zirconia. The catalytically active site was modeled as an isolated VO{sub 4} unit attached to the support. The calculated geometry and vibrational frequencies of the active site are in good agreement with experimental measurements both for model compounds and oxide-supported vanadia. Methanol adsorption is found to occur preferentially with the rupture of a V-O-M bond (M = Si, Ti, Zr) and with preferential attachment of a methoxy group to V. The vibrational frequencies of the methoxy group are in good agreement with those observed experimentally as are the calculated isobars. The formation of formaldehyde is assumed to occur via the transfer of an H atom of a methoxy group to the O atom of the V=O group. The activation energy for this process is found to be in the range of 199-214 kJ/mol and apparent activation energies for the overall oxidation of methanol to formaldehyde are predicted to lie in the range of 112-123 kJ/mol, which is significantly higher than that found experimentally. Moreover, the predicted turnover frequency (TOF) for methanol oxidation is found to be essentially independent of support composition, whereas experiments show that the TOF is 10{sup 3} greater for titania- and zirconia-supported vanadia than for silica-supported vanadia. Based on these findings, it is proposed that the formation of formaldehyde from methoxy groups may require pairs of adjacent VO{sub 4} groups or V{sub 2}O{sub 7} dimer structures.

• Research Organization: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director. Office of Science. Office of Basic Energy Sciences. Chemical Sciences Division; Civilian Research and Development Foundation RC1-2204 (US)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 836790
• Report Number(s): LBNL--49412
• Journal Information: Journal of Physical Chemistry B, Journal Name: Journal of Physical Chemistry B Journal Issue: 32 Vol. 106
• Country of Publication: United States
• Language: English

Related Subjects

''OXIDATION OF METHANOL'' FORMALDEHYDE VANADIA SILICA TITANIA ZIRCONIA
10 SYNTHETIC FUELS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ACTIVATION ENERGY
ADSORPTION
ATOMS
DIMERS
FORMALDEHYDE
FUNCTIONALS
GEOMETRY
KINETICS
METHANOL
OXIDATION
RUPTURES
SILICA