Ja. Rodriguez et al., Interaction of sulfur with Pt(111) and Sn/Pt(111): Effects of coverage andmetal-metal bonding on reactivity toward sulfur, J CHEM PHYS, 113(24), 2000, pp. 11284-11292
In the chemical and petrochemical industries, Pt-based catalysts are very s
ensitive to sulfur poisoning. Synchrotron-based high-resolution photoemissi
on, thermal desorption mass spectroscopy (TDS), and first-principles densit
y-functional slab calculations were used to study the adsorption of sulfur
on Pt(111) and a p(2x2)-Sn/Pt(111) surface alloy. Our results show importan
t variations in the nature of the bonding of sulfur to Pt(111) depending on
the coverage of the adsorbate. For small coverages, theta (S)<0.3 ML, atom
ic sulfur is the most stable species. The adsorbate is bonded to hollow sit
es, has a large adsorption energy (> 75 kcal/mol), and desorbs as S. The Pt
-S bonds are mainly covalent but sulfur induces a significant decrease in t
he density of Pt 5d states near the Fermi level. When the sulfur coverage i
ncreases on the surface, theta (S)>0.4 ML, there is a substantial weakening
in the Pt <---->S interactions with a change in the adsorption site and a
tendency to form S-S bonds. Desorption of S-2 is now observed in TDS and th
e S2p core levels shift to higher binding energy. At coverages near a full
monolayer, S-2 is the most stable species on the surface and its adsorption
energy is similar to 45 kcal/mol. Similar trends are observed for the adso
rption of sulfur on a p(2x2)-Sn/Pt(111) surface alloy, but the adsorbate <-
---> substrate interactions are weaker than on Pt(111). The formation of Pt
-Sn bonds reduces the reactivity of Pt toward sulfur. Electronic effects as
sociated with bimetallic bonding can be useful for controlling or preventin
g sulfur poisoning. (C) 2000 American Institute of Physics. [S0021-9606(00)
70348-5].