The Chemistry of Sulfoxy Species on Clean, Oxygenated, and Caesiated Ag{100}:  A Study of Surface Reactivity by Fast XPS and TPR

• Published in: The journal of physical chemistry. B 2001-10, Vol.105 (41), p.10062-10068
• Main Authors: Santra, Ashok K, Bird, Daniel P. C, Sykes, E. Charles H, Williams, Federico J, Goldoni, Andrea, Baraldi, Alessandro, Lambert, Richard M
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp011883z

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.