Grants and Contracts Details
Description
I. INTRODUCTION
Transition metal oxides are widely used as both catalysts and catalytic supports in petroleum
refining and other industrial processes. However, catalyst development is still carried out by try and
error, and the rational design of new catalysts with predictable properties is a long-term goal
requiring both basic and applied research. To help understand chemistry occurring at the surface of
heterogeneous catalysts, an approach termed molecular surface science' has gained considerable
attention in surface science2 and gas-phase cluster chemistry. ~ This approach recognizes that many
industrial catalysts involve highly dispersed metals, and surface defects are often the active sites for
chemistry. Although they will not account for the precise thermodynamics and kinetics operating in
applied catalysis, gas-phase measurements provide an efficient means to investigate reactivity
patterns, reaction mechanisms, bonding and structures, and structure-reactivity relationships of
crucial intermediates. These outcomes of the gas-phase research on a wide range of cluster sizes are
valuable to model surface chemistry, surface defects, and surface-reactivity relationships of catalytic
materials.
The growing interests in the transition metal oxides have motivated numerous research
groups to study the size-dependent physical and chemical properties of their clusters in the gas phase,
where complications of solvents and counterions are removed. Extensive studies have been
reported on reactivity5 and photodissociation,6~8 photoelectron,9" and photoionization
spectroscopy.4'8"2 In addition, matrix-isolation infrared spectroscopy has been used to study a
number of small neutral clusters.'3
In spite of the extensive studies, the current knowledge about the electronic states and
molecular structures of the transition metal oxide clusters is largely from theoretical predictions.
However, the reliable prediction of the electronic and geometric structures is complicated by many
low-energy structural isomers and high-dense, low-lying electronic states of each isomer.
Inconsistent theoretical results have been reported on the ground electronic states and the minimum
energy structures of both neutral and ionic clusters.14 Therefore, a reliable identification of the
cluster structure generally requires the confirmation by spectroscopic measurements. Previous
spectroscopic measurements have yielded valuable structural information for a variety of transition
metal oxides. However, some of these measurements have limitations. For example, the
multiphoton infrared ionization or dissociation spectroscopy requires a high-power infrared laser
with wavelength tunable to far-infrared region, which is still not widely available. Therefore, most
of these multiphoton infrared measurements have been carried out with intense free electron lasers.
Moreover, the nonlinear nature of the multiphoton process may yield an infrared spectrum that is not
necessarily the same as a regular linear absorption spectrum, complicating the interpretation of the
measured spectra.7'14'15 On the other hand, the anion photoelectron spectra generally show
unresolved vibrational structures for transition metal clusters, except for a few special cases.9"
Pulsed-field ionization-zero electron kinetic energy (ZEKE) photoelectron spectroscopy
provides exceptional spectral resolution, and we have successftilly applied this tecbnique to study
metal-organic complexes.
Status | Finished |
---|---|
Effective start/end date | 7/1/09 → 6/30/10 |
Funding
- KY Science and Technology Co Inc: $50,000.00
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