Catalytic hydrocarbon reactions over supported metals Page: 4 of 6
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had a Cr (2p3/2) binding energy (BE) of 578.3 eV that is associated with Cr6+. Photoreduction
was not wavelength dependent between 400-200 nm and produced a Cr (2p3/2) XPS BE at 577.8
eV that is assigned to Cr2+. The shape of the Cr (2p3/2) XPS band for photoreduced chromium
oxide suggests the presence of some Cr4+. The C (Is) BE was also observed at 284.9 eV. The
spectra for 12C160 produced three bands, a weak band at 2201 cm-1 that is associated with Cr4+-
monocarbonyl, a band at 2183 cm-1 that is associated with Cr2+-monocarbonyl, and a band at 2098
cm-1 that is a monocarbonyl and may be associated with reduced Cr modified by carbon.
R. D. Roark and J. G. Ekerdt, Reductive Acetaldehyde Coupling to 2-Butenes over Silica-
Supported Molybdenum(IV) and Tungsten(IV), Manuscript in preparation.
Acetaldehyde was found to couple over silica-supported W(IV) at 150 and 350 *C and over
silica-supported Mo(IV) at 350 *C, producing 2-butenes. Mo2(CO)4Cp2 and W2(CO)4Cp2 (Cp =
cyclopentadienyl) were used to attach the metals to the support at 7.5 wt % for Mo and 5.5 wt %
for W. Oxygen titration experiments reveal the metals to be in the 4+ oxidation state following
exchange of the Cp ligands with silica hydroxyl groups and heating to 375 *C to remove the
carbonyl ligands. Infrared spectra of the adsorbed complexes contain bridging carbonyl modes
suggesting cation dimers form that contain metal-metal bonds. The reductive coupling reaction is
proposed to proceed through a p-ethylidene intermediate.
We are also continuing to work on several problems associated with photoreduction and
carbonyl coupling over silica-supported Mo and W. Experiments are planned with various carbon
and oxygen isotopes to determine the structure of the W-carbonyls formed during photoreduction.
XPS experiments will be performed in parallel with the IR studies and with oxygen titration
experiments to better characterize the oxidation state of the photoreduced W and Mo cations. It
may also be possible to deposit the complexes onto silica wafers in an antechamber on the XP
spectrometer and study the oxidation state using XPS. Extensive infrared experiments are planned
to follow the evolution of the M2(CO)4Cp2 carbonyl ligands and to determine if ethylidene forms
as a reaction intermediate. We will also investigate the coupling of aldehydes and ketones to
determine if cross coupling is possible in a two step process during which the aldehyde is used to
generate the p-alkylidene at a low temperature and the ketone is reacted at a higher temperature to
form the olefin coupling product; such a process would further support the presence of a metal
dimer with a M-M bond.
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Ekerdt, J.G. Catalytic hydrocarbon reactions over supported metals, report, March 29, 1993; United States. (https://digital.library.unt.edu/ark:/67531/metadc1207843/m1/4/: accessed March 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.