Adsorption selectivity of Lewis acids and bases on an oxidized Mo(100) surface studied by LEED, Auger, and XPS

R. M. Henry, B. W. Walker, P. C. Stair

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


The adsorption of a wide range of Lewis acids (CO, CO2, B(OCH3)3, B(CH3)3, and BF3) and Lewis bases (NH3, N(CH3)3, NH(CH3)2, NH2CH3, pyridine, 2,6-dimethylpyridine, pyrrole, water, methanol, ethanol, furan, ethylene, propylene, butene, toluene and benzene) on an oxidized Mo(100) single crystal surface has been studied by LEED, Auger and XPS. The oxidized molybdenum surface was prepared by exposing clean Mo(100) at 1023 K to molecular oxygen in ultrahigh vacuum (UHV) in order to produce an ordered P(2 × 1) surface structure having an atomic oxygen concentration of 1.3-1.5 monolayers. Only the strong Lewis acids B(CH3)3 and BF3 adsorbed and remain on the surface under UHV conditions suggesting that the surface oxygen anions are only weakly basic. Only bases containing nitrogen adsorb strongly on the oxidized surface. No trace of benzene or ethylene could be detected on the surface even after exposures at atmospheric pressure. XPS measurements of the carbon and nitrogen (1s) core levels for gas phase and adsorbed phase NH2CH3, pyridine, and 2,6-dimethylpyridine indicate that bonding to the surface is through the nitrogen lone pair electrons consistent with an acid-base interaction. The preference of the oxidized surface for adsorption of lone pair electron donors in comparison to w-electron donors can be understood by considering the geometry of the electron donor orbitals. The results indicate that the overlap of the unperturbed donor and acceptor orbitals is a primary factor in determining adsorption selectivity.

Original languageEnglish (US)
Pages (from-to)732-750
Number of pages19
JournalSurface Science
Issue number2-3
StatePublished - Jun 2 1985

ASJC Scopus subject areas

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


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