FORMATION OF ADSORBED SULFATE FROM THE OXIDATION OF SULFUR-DIOXIDE ON PD(100)

Sulfur dioxide was adsorbed near 120 K on Pd(100); decomposition occurred above 240 K to yield adsorbed SO which dissociated to form adsorbed sulfur and oxygen atoms at higher temperatures. For high SO//2 coverages on clean Pd(100) or for SO//2 adsorbed on the surface with a low oxygen precoverage, an eta **2-SO//4 species was formed above 300 K which decomposed at 450 K to yield SO//2//(//g//). In the presence of //p(2 multiplied by 2)O islands (local theta //o equals 0. 25)SO//2 reacted to form eta **3-SO//4. The eta **3 species also decomposed to yield SO//2//(//g//); it was approximately 30 kJ mol** minus **1 more stable than the eta **2 species. Several sparsely populated desorption states were also observed; they are attributed to destabilization of adsorbed SO//4 by atomic adsorbates and by SO//4-SO//4 lateral interactions.