SO2 ADSORPTION ON PT(111) - HREELS, XPS AND UPS STUDY

The chemistry of SO2 on Pt(111) has been studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). At 100 K, SO2 adsorbs molecularly through the S and one O atom. Photoemission results indicate that significant charge transfer occurs between the Pt d-band and the lowest unoccupied molecular orbital of SO2. Molecular orbital analysis reveals that atop and two-fold sites are energetically feasible for SO2 adsorption, but two-fold sites are more favorable. Upon heating to 300 K, SO2 molecules undergo desorption and dissociation. The latter leads to adsorbed S, SO and SO4. An SO2 lattice vibration mode was observed by HREELS when an SO2 multilayer was dosed at 100 K; and it was enhanced when SO2 was dosed at 110 K. There is a resonance in this feature as the incident electron energy is varied, which implies that a nondipolar scattering process contributes. Multilayer SO2, formed upon adsorption at 100 K, is metastable.