The chemistry of sulfoxy species on clean, oxygenated, and caesiated Ag{100}: A study of surface reactivity by fast XPS and TPR

SANTRA, A K; BIRD, D P C; SYKES, E C H; WILLIAMS, F J; GOLDONI, A; BARALDI, A; LAMBERT, R M

JOURNAL OF PHYSICAL CHEMISTRY B - (Print)

AMER CHEMICAL SOC

Año: 2001 vol. 105 p. 10062 - 10068

1520-6106

High-resolution XPS, including time- and temperature-dependent measurements, and temperature-programmed reactions, including 18O isotope mixing studies, have been used to study the sulfoxy species formed on Ag- {100} in the absence and presence of Cs. On the alkali-free preoxygenated surface, SO2 adsorbs to form a surface sulfite which decomposes at ∼460 K releasing gaseous SO2 and dissolved oxygen. Cs induces the formation of a more strongly bound alkali sulfite which reacts further to form alkali sulfate. The alkali sulfite and sulfate decompose at ∼525 and ∼575 K, respectively, releasing gaseous SO2, dissolved oxygen, and a small amount of adsorbed sulfur. Isotope mixing data indicate that the sulfoxy species formed in the presence of alkali have a higher bond order with the Ag surface than the sulfite formed on the alkali-free surface. All these species are labile with respect to oxygen release in the temperature regime relevant to oxyanion-promoted ethene epoxidation, and a reaction scheme is proposed that accounts for their formation, interconversion, and decomposition.