Coverage Dependence of Oxygen Decomposition and Surface Diffusion on Rhodium (111): A DFT Study

A systematic study of oxygen adsorption, decomposition and diffusion on Rh~111! and its
dependence on coadsorbed oxygen molecules has been performed using density functional theory
calculations. First, the bonding strength between metal surface and adsorbed oxygen molecules has
been studied as a function of initial oxygen coverage. The bonding strength decreases with
increasing oxygen coverage, which points towards a self-inhibition of the adsorption process. The
potential energy hypersurface ~PES! for the dissociation of oxygen molecules adsorbed on a
threefold fcc position perpendicular to the surface was calculated using a combined linear/quadratic
synchronous transit method with conjugate gradient refinements. The results indicate that a minor
amount of oxygen on the surface enhances the decomposition of further oxygen molecules, while
this process is inhibited at higher coverage. Moreover, PES calculations of a single site jump of
atomic oxygen on rhodium ~111! indicate that the activation energy increases as well with increasing
oxygen coverage. All results are discussed with respect to a rhodium based catalytic NOx reduction/
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decomposition system proposed by Nakatsuji, which decomposes nitrogen oxides in oxygen excess.
© 2005 American Institute of Physics.