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

Gradient corrected periodic density functional theory (DFT–GGA) slab calculations were used to examine the chemisorption of atomic hydrogen on various Pd–Re alloyed overlayers and uniformly alloyed surfaces. Adsorption was examined at 33% surface coverage, where atomic hydrogen preferred the three-fold 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 energies were found to be between −2.35 eV for monolayer Pd-on-Re, i.e., PdML/Re(0001) and −3.05 eV for Pd33 Re66/Pd(111). A d-band weighting scheme was developed to extend the Hammer–Nørskov 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 matrix elements for Pd and Re. The farther the weighted d-band center is shifted below the Fermi energy, the weaker is the interaction of atomic hydrogen with the alloyed Pd–Re surface.