Catalytic hydrocarbon reactions over supported metals Page: 2 of 6
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This research program is directed toward developing a fundamental understanding of how
catalyst composition, redox ability, and structure control the catalytic properties of metal oxides.
Molybdenum and tungsten oxide systems that permit examination of the role of metal oxide cations
separately and in pairwise combinations are being developed. The research involves
characterization of the organometallic deposition process used to prepare the catalysts,
characterization of the resulting oxides using spectroscopic techniques, studies of the catalytic
properties of the fully oxidized cations in oxidation reactions, studies of the photoreduction of the
oxides to lower oxidation states, and studies of the catalytic properties of coordinatively
unsaturated sites resulting either from photoreduction or precursor decomposition in olefin
metathesis and reductive aldehyde coupling reactions.
During the past year we have completed our characterization of the factors that control the
structure of fully oxidized W and Mo on silica and have established that support hydroxyl groups
play a central role in dispersing and attaching cations to the support oxide. Our work with the
M2(CO)4Cp2 (M2=MoMo, WW, MoW) system has been very encouraging and continues to
support the notion that it may be possible to control the structure of adsorbed catalysts (in this case
generate metal dimers) by use of organometallic precursors. Finally, we are developing the
techniques necessary to employ XPS as a means to characterize the attachment process and the
oxidation state of the cations after various thermal and photolytic reduction steps.
SUMMARY THE EFFORT
The abstracts are listed below for the papers that appeared in print or are in press.
R. D. Roark, S. D. Kohler, and J. G. Ekerdt, Role of Silanol Groups in Dispersing Mo(VI) on
Silica, Catal. Lett. 16 (1992) 71.
Infrared spectroscopy was used to follow the intensity of the isolated silanol stretching
mode during the reversible transformation of supported molybdenum between the hydrated,
polymolybdate structure and the dehydrated, isolated Mo6+ structure. The isolated silanol
absorbance intensity was attenuated upon dehydration and spreading of Mo6+. The Si-OH (or Si-
OD) silanol band was regenerated by rehydration with H20 (or D20). A model for spreading is
proposed in which the surface silanol groups are the sites for attachment of the isolated Mo6+
R. D. Roark, S. D. Kohler, J. G. Ekerdt, D. S. Kim, and I. E. Wachs, Monolayer Dispersion of
Molybdenum on Silica, Catal. Lett. 16 (1992) 77.
Laser Raman spectroscopy was used to characterize the hydrated and dehydrated states of
surface-supported Mo6+ on Davison 952 silica gel. Silica-supported Mo samples were prepared
form Mo2(li3-C3H5)4 and (r15-C5H5)2Mo2(CO)4. Metal loadings of 5.1-7.8 wt % Mo were
studied. Crystallites of MoO3 were not observed at these high loadings. An upper limit for
dispersing dehydrated, isolated Mo6+ was found at about 1 Mo atom/nm2, which corresponds to
the isolated silanol density of silica.
S. D. Kohler, J. G. Ekerdt, D. S. Kim, and I. E. Wachs, Relationship Structure and Point of Zero
Surface Charge for Molybdenum and Tungsten Oxides Supported on Alumina, Catal. Lett. 16
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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/m1/2/: accessed March 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.