Sulfur dioxide adsorption and reaction with atomic oxygen on the Ag(110) surface

Abstract

The adsorption of SO 2 on Ag(110) and the reaction of SO 2 with oxygen adatoms have been studied under ultrahigh vacuum conditions using low energy electron diffraction, temperature programmed reaction spectroscopy and photoelectron spectroscopy. Below 300 K, SO 2 adsorbs molecularly giving p(1×2) and c(4×2) LEED patterns at coverages of one half and three quarter monolayers. respectively. At intermediate coverages, streaked diffraction patterns, similar to those reported for noble gas and alkali metal adsorption on the (110) face of face-centered cubic metals were observed, indicating adsorption out of registry with the surface. A feature at low binding energy in the ultraviolet photoemission spectrum appeared which was assigned to a weak chemisorption bond to the surface via the sulfur, analogous to bonding observed in SO 2-amine charge transfer complexes and in transition metal complexes. SO 2 exhibited three binding states on Ag(110) with binding energies of 41, 53 and 64 kJ mol −1; no decomposition on clean Ag(110) was observed. On oxygen pretreated Ag(110), SO 2 reacted with oxygen adatoms to form SO 3(a), as determined by X-ray photoelectron spectroscopy. Reacting preadsorbed atomic oxygen in a p(2 × 1) structure with SO 2 resulted in a c(6 × 2) pattern for SO 3(a). The adsorbed SO 3(a) decomposed and disproportionated upon heating to 500 K to yield SO 2( g) , SO 4(a) and subsurface oxygen.