Surface structure of MgF2-supported vanadium oxide monolayer catalysts

✍ Scribed by J. Haber; J. Stoch; M. Wojciechowska

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 624 KB
• Volume: 15
• Category: Article
• ISSN: 0142-2421
• DOI: 10.1002/sia.740151202

✦ Synopsis

Abstract

Vanadium oxides supported on MgF~2~ with rutile structure, obtained by impregnation and precipitation–deposition, were investigated. XPS, ESR, IR and XRD studies revealed that the surface of MgF~2~ is partially covered by non‐acidic OH groups, which persist after loading with vanadium oxides. In impregnated samples, the surface fraction of vanadium is linearly dependent on loading. In precipitated–deposited samples, the surface fraction of vanadium remains constant because of the increase of surface area due to peptization of MgF~2~ aggregates. At a low concentration of vanadate solution, (VO)F~5~‐type surface complexes are formed. At higher concentrations, isolated VO~4~ tetrahedra appear at the surface, which undergo polymerization to form chains of tetrahedra or trigonal bipyramids. These may condense further into islands of the monolayer of polyvanadate species, with the σπ‐bonded terminal oxygen sticking out perpendicular to the surface.