Adsorption and reaction of acetaldehyde on Pt(1 1 1) and Sn/Pt(1 1 1) surface alloys

Haibo Zhao, Jooho Kim, Bruce E. Koel

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80 Scopus citations

Abstract

Adsorption and reaction of acetaldehyde (CH3CHO) on Pt(1 1 1) and two ordered Pt-Sn alloys has been studied primarily by using temperature-programmed desorption (TPD) mass spectrometry and high-resolution electron-energy loss spectroscopy (HREELS). The two alloys investigated were the (2×2) and (√3 × √3)R30 °Sn/Pt(1 1 1) surface alloys with θSn = 0.25 and θSn = 0.33, respectively, as-prepared by vapor deposition of Sn on a Pt(1 1 1) single-crystal substrate. The desorption products in TPD experiments following CH3CHO exposures on the Pt(1 1 1) surface were CH3CHO, CO, H2, and CH4. Auger electron spectroscopy (AES) detected some carbon (θC ∼ 0.1 ML) left on the surface following TPD experiments. At small coverages, CH3CHO adsorption on Pt(1 1 1) is completely irreversible and all CH3CHO decomposes during heating in TPD. At near monolayer coverages, CH3CHO is partially reversibly adsorbed, with desorption competing effectively with decomposition so that 52% of the adsorbed monolayer of acetaldehyde decomposed during heating in TPD. CH3CHO bonds molecularly, mainly in a η1(O) configuration on Pt(1 1 1) at 90 K. On both of the (2×2)Sn/Pt(1 1 1) and (√3 × √3)R30°Sn/Pt(1 1 1) alloys, no CH3CHO decomposition took place during TPD and the adsorption-desorption behavior was entirely reversible. HREELS revealed that only η1(O)-CH3CHO was present on the two Sn/Pt(1 1 1) alloys. CH3CHO is adsorbed more weakly and the chemical reactivity of CH3CHO on these Sn/Pt alloys is decreased from that on the Pt(1 1 1) surface. Thus, the presence of Sn in the surface layer of these Pt-Sn alloys does not thermally activate acetaldehyde for reaction in UHV due to the thermodynamic driving force provided by the Sn-O interaction. We attribute this to be primarily because of kinetic barriers that arise from Pt-Sn bonding interactions in the alloy and acknowledge the important implications of this observation for the synthesis of organic molecules by selective oxidation over PtSn catalysts.

Original languageEnglish (US)
Pages (from-to)147-159
Number of pages13
JournalSurface Science
Volume538
Issue number3
DOIs
StatePublished - Jul 20 2003

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

Keywords

  • Alloys
  • Chemisorption
  • Electron energy loss spectroscopy (EELS)
  • Metallic surfaces
  • Platinum
  • Thermal desorption

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