Mardi 13 juillet 2010 à 11h salle O. Kahn
Dr M. NOLAN, Université de Cork, Irelande
"Simulation of reactions at metal oxide surfaces"
Reactions at metal oxide surfaces are everywhere, e.g. in catalysis,gas sensing, film growth, etc. In this talk we present results of simulations of how atoms and molecules react with metal oxide surfaces. We focus on the following aspects:
(i) Adsorption and reaction of CO at undoped and doped cerium dioxide surfaces, which is the key reaction in the oxidation of CO to CO2.
(ii) Reaction of NO2 and NO at undoped and doped ceria (110) surface. We show that as long as reduced Ce3+ ions are present, NOx will react with the surface and dissociate, facilitating formation of N2.
(iii) Deposition of metal atoms at the rutile TiO2 (110) surface. Ti and Cr atoms have been deposited at 1/16th coverage both experimentally and in DFT calculations. XPS and UPS results show the presence of reduced Ti in both cases a new state is found between the top of the valence band and the Fermi level in UPS. We used DFT corrected for on-site Coulomb interactions, DFT+U to model reduced Ti and found that U > 3 eV gives a consistent description of reduced Ti; in fact there are two different contributions one from adsorbed Ti, which is in a Ti2+ oxidation state and a surface Ti, reduced to Ti3+.
(iv) With Cr adsorption, adsorbed Cr is in a 2+ oxidation state and a surface Ti is reduced to Ti3+. Reaction of oxygen with Cr depletes the surface of Ti3+ and oxidises Cr to Cr3+