Adsorption, Desorption, Dissociation and Recombination of SO2 on a Palladium (111) Surface The adsorption, desorption as well as decomposition- and recombination-reactions of SO2 on Pd(1 1 1) were studied for temperatures T = 160-1200 K using LEED, AES, thermal desorption-mass-spectrometry and molecular beam techniques. At 160 K SO2 adsorption with an initial sticking coefficient s0 = 1 is molecular and non-ordered; it is characterized by a precursor state and leads to a saturation coverage Θ ≈ 0,3. Heating up the adlayer SO2 is the only desorption product, namely directly from (SO2)ad in the α-peak (Tmax = 240 K) and as the product of recombination of (SO)ad and Oad in the β-peak (Tmax = 330-370 K). A great part of the oxygen originating from SO2-dissociation is incorporated into the subsurface region, resulting in an atomic S-adlayer with ΘS = 1/7 which exhibits a (documentclass{article}pagestyle{empty}begin{document}$ sqrt 7 {rm x}sqrt 7 $end{document}) R ± 19,1°-superstructure. This structure is also observed, if a 320 K-SO2-exposure induced (2 × 2)-SO saturation layer with ΘSO = 0,5 is heated up or if SO, is exposed at T > 500 K, where it corresponds to ΘS, values of 3/7 and 2/7, respectively. Furthermore the poisoning effect of adsorbed sulfur on the dissociative O2,-adsorption and the oxidation of sulfur by heating up an O? S-coadsorption layer were studied. As a result the following kinetic parameters (activation energies and frequency factors) were determined: .
≈ 0,3. Heating up the adlayer SO2 is the only desorption product, namely directly from (SO2)ad in the α-peak (Tmax = 240 K) and as the product of recombination of (SO)ad and Oad in the β-peak (Tmax = 330-370 K). A great part of the oxygen originating from SO2-dissociation is incorporated into the subsurface region, resulting in an atomic S-adlayer with ΘS = 1/7 which exhibits a (documentclass{article}pagestyle{empty}begin{document}$ sqrt 7 {rm x}sqrt 7 $end{document}
) R ± 19,1°-superstructure. This structure is also observed, if a 320 K-SO2-exposure induced (2 × 2)-SO saturation layer with ΘSO = 0,5 is heated up or if SO, is exposed at T > 500 K, where it corresponds to ΘS, values of 3/7 and 2/7, respectively. Furthermore the poisoning effect of adsorbed sulfur on the dissociative O2,-adsorption and the oxidation of sulfur by heating up an O? S-coadsorption layer were studied. As a result the following kinetic parameters (activation energies and frequency factors) were determined: 