Ab initiostudies of stepped Pd surfaces with and without S

Abstract

We have performed a comprehensive first-principles study of the electronic and geometric structure of a set of clean and S covered vicinal Pd surfaces of ͑111͒ and ͑110͒, namely Pd͑211͒, Pd͑331͒, Pd͑320͒, and Pd͑551͒, each having three-atom wide terraces. The trends in the multilayer relaxation patterns can generally be explained on the basis of charge smoothening which makes the vicinals of Pd͑110͒ prone to larger and deeper relaxations in comparison to the Pd͑111͒ counterparts. A range of adsorption energies for preferred adsorption sites for S is found on all four surfaces, with Pd͑320͒ being the most receptive. We show that the adsorbate can have considerable effect on multilayer relaxations and registry of the substrate atoms. We discuss the nature of the S-Pd bonding and how this bonding is affected by the surface geometry and coordination. We relate the poisoning effect of S to the changes in the electronic structure of the substrate atoms.

Site selectivity in chemisorption of C on Pd(211)

“…2 we have also included the results for S adsorption from Ref. 22. The adsorption energy is found to be much higher for C than that for S for the sites studied.…”

“…The changes in the multilayer relaxation for clean Pd(211) and in the presence of S in the site 1 from Ref. 22 are also displayed in Table II. The most noticeable change is the outward relaxation of the step atom for C adsorption near it.…”

“…10) also showed a reduction of the density of states at the Fermi level resulting from a strong hybridization of the p states of S with the d states of Pd. More recent studies of Makkonen et al 22 for S adsorption on a set of stepped Pd surfaces, which are vicinal to Pd(111) and Pd(110), also show a depletion of the density of states of neighboring Pd atoms on S adsorption, but for these vicinal surfaces the effect is site selectivity and dependent on the surface geometry and local coordination. The effect of S adsorption on multilayer relaxation and surface registry of the Pd surfaces was also found to be remarkable and led to site specific modification in the surface electronic structure.…”

“…The calculations were performed for the 7 ϫ 3 ϫ 1 k-point mesh in the Brillouin zone. Earlier calculations of S on Pd(211) 22 were performed using only the plane wave basis (as in VASP). Since our intention in this paper is to compare the effects of C adsorption with those of S, we have extended the FLAPW calculations to S / Pd͑211͒ system.…”

Kinetics of the sulfur oxidation on palladium: A combined in situ x-ray photoelectron spectroscopy and density-functional study

“…The adsorption of these sulfur traces on the catalyst surface can lead to a substantial decrease of its reactivity. 10,11,[13][14][15][16][17][18][19][20][21] First endeavors to understand the effects of sulfur on the electronic structure, the adsorption capacity, and reactivity of palladium have been undertaken, 22 a) K. Gotterbarm and N. Luckas contributed equally to this work. b) Authors to whom correspondence should be addressed.…”