14 research outputs found
Composition, structure and stability of RuO_2(110) as a function of oxygen pressure
Using density-functional theory (DFT) we calculate the Gibbs free energy to
determine the lowest-energy structure of a RuO_2(110) surface in thermodynamic
equilibrium with an oxygen-rich environment. The traditionally assumed
stoichiometric termination is only found to be favorable at low oxygen chemical
potentials, i.e. low pressures and/or high temperatures. At realistic O
pressure, the surface is predicted to contain additional terminal O atoms.
Although this O excess defines a so-called polar surface, we show that the
prevalent ionic model, that dismisses such terminations on electrostatic
grounds, is of little validity for RuO_2(110). Together with analogous results
obtained previously at the (0001) surface of corundum-structured oxides, these
findings on (110) rutile indicate that the stability of non-stoichiometric
terminations is a more general phenomenon on transition metal oxide surfaces.Comment: 12 pages including 5 figures. Submitted to Phys. Rev. B. Related
publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm
Composition and structure of the RuO2(110) surface in an O2 and CO environment: implications for the catalytic formation of CO2
The phase diagram of surface structures for the model catalyst RuO2(110) in
contact with a gas environment of O2 and CO is calculated by density-functional
theory and atomistic thermodynamics. Adsorption of the reactants is found to
depend crucially on temperature and partial pressures in the gas phase.
Assuming that a catalyst surface under steady-state operation conditions is
close to a constrained thermodynamic equilibrium, we are able to rationalize a
number of experimental findings on the CO oxidation over RuO2(110). We also
calculated reaction pathways and energy barriers. Based on the various results
the importance of phase coexistence conditions is emphasized as these will lead
to an enhanced dynamics at the catalyst surface. Such conditions may actuate an
additional, kinetically controlled reaction mechanism on RuO2(110).Comment: 12 pages including 8 figure files. Submitted to Phys. Rev. B. Related
publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm