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Research
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Interfacial charge transport in
oxidation catalysts for the selective oxidation of ethane, propane
and n-butane
Anna Maria Wernbacher
Selective oxidation catalysis will be playing
a crucial role in the ambitious goal of replacing the crude-oil
based raw materials of today`s petro-chemical industry by more sustainable,
ideally renewable resources. One of the key challenges is the efficient
and direct functionalization of alkanes from natural gas or future
regenerative carbon-based feedstocks. However, a major breakthrough
in this field is still impeded by the lack of suitable catalysts
and the absence of a detailed mechanistic understanding of the few
efficient alkane oxidation reactions.

(to see full size, click on the image)
The so far only industrially applied selective alkane oxidation
reaction is the oxidation of n-butane (C4) to maleic anhydride (MA)
on vanadyl pyrophosphate (VPP) catalysts, though the achieved MA
yield of about 60% still shows potential for improvement. The direct
oxidation of propane to acrylic acid (AA) on the M1 phase of the
polynary transiton metal oxide MoVTeNbO x is with optimized
AA yields of 50% still awaiting its commercial breakthrough. Though
the oxidative dehydrogenation (ODH) of ethane over the same catalyst
exhibits ethylene yields in the range of 70%, this process is still
economically unfavourable in comparison to steam-cracking, not to
mention the either very low yields or very harsh conditions needed
for the selective oxidation of methane to valuable products. Due
to the rather high amount of charge carriers formally transferred
in a catalytic redox cycle (e.g. 14 electrons from C4 to MA), it
is still controversially debated if such oxidation reactions can
be explained just on the basis of the single site concept with an
isolated active center large enough to “store” reversibly
the high charge carrier number, or if (and how) subsurface layers
with appropriate charge transfer properties have to be taken into
account. |
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References
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M. Eichelbaum, et al.,
Phys. Chem. Chem. Phys 2012, 14,
1302-1312.
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M. Eichelbaum, et al.,
Angewandte Chemie, International Edition 2012,
51, 6246–6250.
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C. Heine, et al.,
Applied Physics A 2013, 112,
289-296.
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M. Eichelbaum, et al.,
ChemCatChem 2013, 5, 2318–2329.
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