Reaction of sulfur dioxide with Ag(110)-p(2 * 1)-O. A LEED, TPRS, and STM investigation.
STM was combined with LEED, TPRS, XPS, and EELS to further the understanding of the chem. and structural changes accompanying the reaction of SO2(g) with O adsorbed on Ag(110). At 300 K SO2 reacts with the p(2 * 1) O 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\" Ag in the original p(2 * 1)-O structure to ppt. new islands of sulfite-covered surface on top of the original surface. Overall, sulfite disproportionates according to 6SO3(a) -> 2 SO2(g) + 4 SO3(a) + 2 O(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 Deg from the  direction, sepd. 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 expts. suggest the following surface reaction for the conversion of sulfite to sulfate: 6 SO3(a) -> 4 SO2(g) + 2SO4(a) + 2O(subsurface). A detailed 2D depiction of the surface with substrate registry is proposed.
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