Influence of Sulfur Poisoning on CO Adsorption on Pd(100)

Investigations of CO adsorption on sulfur covered Pd(100) surface were conducted in order to obtain insight into the deleterious effects of sulfur on this system. First-principles density functional theory calculations indicate that CO is markedly destabilized when it shares surface atoms with neighboring sulfur. Based on the analysis of the electronic properties, the decrease in binding is attributed to localized S-Pd bonding plus the interaction between CO and S. The internal C-O stretching frequency was blue shifted relative to that on the clean surface as a result of the weakening of the C-Pd bonds. The poisoning effect is predicted to diminish for distant sites. Kinetic Monte Carlo simulations (with adsorbate lateral interactions included) revealed that the introduction of S creates competition for adsorption sites. At a finite temperature, CO adsorption is essentially nullified when the surface is covered by a quarter of monolayer of sulfur in agreement with experiments. Aside from reduction of possible adsorption sites, sulfur severely inhibits the mobility of CO as well.