First principles analysis of hydrogen chemisorption on Pd-Re alloyed overlayers and alloyed surfaces

Gradient corrected periodic density functional theory (DFT-GGA) slab calcul ations were used to examine the chemisorption of atomic hydrogen on various Pd-Re alloyed overlayers and uniformly alloyed surfaces. Adsorption was ex amined at 33% surface coverage, where atomic hydrogen preferred the three-f old fcc sites. The binding energy of atomic hydrogen is observed to vary by as much as 0.7 eV due to Pd-Re interactions. The computed adsorption energ ies were found to be between -2.35 eV [for monolayer Pd-on-Re, i.e., Pd-ML/ Re(0001)] and -3.05 eV [for Pd-33 Re-66/Pd(111)]. A d-band weighting scheme was developed to extend the Hammer-Norskov surface reactivity model [Surf. Sci. 343, 211 (1995)] to the analysis of bimetallic Pd-Re alloyed systems. The hydrogen chemisorption energies are correlated linearly to the surface d-band center, which is weighted appropriately by the d-band coupling matr ix elements for Pd and Re. The farther the weighted d-band center is shifte d below the Fermi energy, the weaker is the interaction of atomic hydrogen with the alloyed Pd-Re surface. (C) 2000 American Institute of Physics. [S0 021-9606(00)70809-9].