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           COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER
                              College of Science
                       (CDS Department CSI 898-Sec 001)
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       Dynamics and Chemistry of Molecular Oxygen on Rutile TiO2(110)

                          Devina Pillay

            Center for Computational Materials Science, 
           Naval Research Laboratory,Washington DC 20375

The rutile TiO2(110) surface has been widely used as a catalyst for 
photochemical reactions and a support for transition metal catalysts.  
Molecular O2 adsorption plays an important role in determining the 
activity of TiO2 and supported metal catalysts.  Surface bound oxygen 
species may directly influence chemical and photochemical processes 
occurring on TiO2.  In addition, O2 exposure leads to significant 
structural changes of supported metal particles, which may in turn 
affect their catalytic activity.  It has been found that molecular 
O2 adsorbs on TiO2(110) only when O-vacancies are present. Despite 
its importance, however the chemistry and dynamics of adsorbed oxygen 
molecules on a reduced TiO2(110) surface are still unclear. 

Using density functional theory calculations, we have investigated 
the adsorption and diffusion of oxygen species on the reduced 
TiO2 (110) surface.  We have found that molecular O2 strongly binds 
not only to O-vacancies, but also to Ti(5c) neighbors, due to 
delocalization of unpaired electrons arising from the removal of 
neutral bridging oxygen atoms.  Our results show that molecular O2 
can jump across an oxygen vacancy and diffuse along a Ti(5c) row 
with moderate barriers.  On the other hand, atomic O diffusion along 
a Ti(5c) row is unlikely at low temperatures (< 300K), because of 
the relatively higher probability of O-O formation by interaction 
with an adjacent bridging O(2c) atom.  Based on our calculation 
results, we will discuss the diffusion and healing of O vacancies 
associated with O2 adsorption.  We will also present the structure 
and energetics of higher coverage O2 adsorption and the chemistry 
of O2 on a reduced TiO2(110) surface.   

                        Monday, February 18, 2008
                                  4:30 pm
                     Room 301, Research I, Fairfax Campus

Refreshments will be served at 4:15 PM.
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Find the schedule at www.cmasc.gmu.edu/seminar/schedule.html
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