Theoretical analysis of hydrogen chemisorption on Pd(111), Re(0001), and Pd_ML/Re(0001), Re_ML/Pd(111) pseudomorphic overlayers.

Pd(111) pseudomorphic overlayers.¶

by V. Pallassana, M. Neurock, L. B. Hansen, B. Hammer, and J. K. Norskov.

Abstract¶

Gradient-corrected density functional theory (DFT-GGA) periodic slab calculations have been used to analyze the binding of atomic hydrogen on monometallic Pd(111), Re(0001) and bimetallic PdML/Re(0001) [pseudomorphic monolayer of Pd(111) on Re(0001)] and ReML/Pd(111) surfaces. The computed binding energy of atomic hydrogen adsorbed in the fcc hollow site, at 100% surface coverage, on the Pd(111), Re(0001), PdML/Re(0001) and ReML/Pd(111) surfaces are -2.66 eV, -2.82 eV, -2.25 eV and -2.78 eV, respectively. Formal chemisorption theory was used to correlate the predicted binding energy with the location of the d-band center of the bare metal surfaces, using a model developed by Hammer and Norskov. The DFT-computed adsorption energies were also analyzed on the basis of the density of states (DOS) at the Fermi level for the clean metal surfaces. The results indicate a clear correlation between the d-band center of the surface metal atoms and the hydrogen chemisorption energy. The further the d-band center is from the Fermi-level, the weaker is the chemisorption bond of atomic hydrogen on the surface. Although the DOS at the Fermi level may be related to the location of the d-band, it does not appear to provide an independent parameter for assessing surface reactivity. The weak chemisorption of hydrogen on the PdML/Re(0001) surface relates to substantial lowering of the d-band center of Pd, when it is pseudomorphically deposited as a monolayer on a Re substrate.