Electronic Structures and Activity of
Oxide-Supported Metal Nano-Clusters
Our research focus here
is to gain fundamental understanding
on how point defects, particularly, surface oxygen vacancies on metal
oxide
surfaces affect adsorption properties of small molecules and metal
clusters and
how they modulate the reactivity of adsorbed transition metal clusters
by using
first-principles quantum chemistry methods. Results
from such a research would have broad
impacts in environmental chemistry and electrochemistry, in rational
design of
supported metal nano-cluster catalysts, electronic devices, chemical
sensors,
and biocompatible materials. Surface
vacancies are known to be active centers for chemisorption of small
molecules
and to be nucleation centers for metal clusters. Furthermore, the
degree of
charge transfer from the vacancies can alter the reactivity of the
adsorbed
metal cluster. Thus, information gain
from this proposed study would be useful for rational design of
supported
transition metal nano-cluser catalysts.
MgO(100) and TiO2(110) are well-characterized
surfaces and
are being used as supports in many experiments for dispersed metal
nano-cluster
catalysts, and thus will be used here as models of oxide surfaces. To
achieve
our objectives, the first step is to have a firm understanding on the
electronic structure of vacancies and its reactivity toward adsorption
of small
gas-phase molecules such as H2, O2, CO, and H2O. In another front, studies on the adsorption
of different small transition metal clusters on vacancies of MgO(100)
and TiO2(110)
and the reactivity of these adsorbed clusters are also be carried out. The differences between MgO and TiO2
surfaces in the electronic structures and in the nature of the
interactions
with transition metal clusters allow us to provide insight into the
origin of
the not well-understood Strong Metal-Support Interaction (SMSI)
phenomenon
observed on the TiO2, but not on the MgO surface. Our
interests are
to validate different models that were previously proposed to explain
the SMSI
phenomenon, to determine the effects of the electron transfer between
the oxide
surface and the adsorbed metal atom on the catalytic activity of the
system and
how such activity depends on the degree of d-shell filling of the
adsorbed
metal atom, the band gap of the support, and the nature of the
vacancies. State-of-the-art embedded
cluster and
periodic electronic structure methods are being employed for this
research.
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