Reaction of sulfur dioxide with Ag(1 1 0)–p(2×1)-O: a LEED, TPRS, and STM investigation

STM has been combined with LEED, TPRS, XPS, and EELS to further the understanding of the chemical and structural changes accompanying the reaction of SO2(g) with oxygen adsorbed on Ag(1 1 0). At 300 K sulfur dioxide reacts with the p(2×1) oxygen overlayer to yield a surface covered by sulfite in a c(6×2) arrangement with six sulfite species per unit cell; i.e., SO2(g)+O(a)→SO3(a). This reaction appears to involve rearrangement of the “added” silver in the original p(2×1)-O structure to precipitate new islands of sulfite-covered surface on top of the original surface. Overall, sulfite disproportionates according to 6SO3(a)→2SO2(g)+4SO3(a)+2O(subsurface) upon heating to 500 K. This heating yields a surface with a p(1×1) LEED pattern, which is shown to consist of irregular, narrow rows of c(3×2) unit cells aligned 22° from the [0 0 1] direction, separated by domain boundaries. Continued heating to 600 K results in the further loss of SO3(a), yielding a surface covered with sulfate in a p(3×2) structure, with one sulfate moiety per unit cell. The results of these experiments suggest the following surface reaction for the conversion of sulfite to sulfate: 6SO3(a)→4SO2(g)+2SO4(a)+2O(subsurface). A detailed two-dimensional depiction of the surface with substrate registry is proposed.