Interaction of SO3 with c-ZrO2(111) films on Pt(111)

Abstract

Single-crystalline sulfated c-ZrO₂(111) films of the cubic (c) type have been prepared by reactive deposition of Zr onto Pt(111) in an O₂ atmosphere and subsequent exposition to a SO₃ atmosphere. The morphology, atomic structure, and composition have been examined by scanning tunneling microscopy, low-energy electron diffraction (LEED), Auger electron spectroscopy, and density functional theory (DFT) calculations. The clean c-ZrO₂(111) films display a (2 × 2) surface structure. During SO₃ exposure at room temperature, a clear (√3 × √3)R30° structure develops. At about 700 K, the SO₃-induced (√3 × √3)R30° structure disappears and the bright (2 × 2) LEED pattern of the clean ZrO₂ films reappears. The energies of plausible c-ZrO₂(111)/SO₃ structures have been examined by DFT. The (√3 × √3)R30° structure found in the experiments turned out to be the most stable one for temperatures below 700 K. At temperatures around 700 K, a disordered low coverage structure may exist, which can not be observed by conventional LEED. A comparison of cubic zirconia surfaces with the alternative tetragonal system yields similar results for the SO₃ adsorption in the DFT calculations and shows that c-ZrO₂ surfaces are good models for the industrial used tetragonal ZrO₂ supports.