Preparation, characterization, and catalytic properties of tungsten trioxide cyclic trimers on FeO(111)/Pt(111)

The structure and catalytic activity of tungsten oxide clusters formed via sublimation of monodispersed cyclic (WO ₃) ₃ onto FeO(111)/Pt(111) has been studied by a combination of scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRAS), temperature-programmed desorption (TPD), and density functional theory (DFT). After (WO ₃) ₃ deposition, STM images reveal new features composed of three bright maxima arranged in a equilateral triangular configuration with an edge length of ∼10 Å. This length is significantly larger than the size of (WO ₃) ₃, indicating that the clusters dissociated. This conclusion is corroborated by DFT calculations showing that cluster dissociation into surface-bound WO ₃ monomers is exothermic and kinetically feasible at 300 K. The dissociation is accompanied by significant FeO(111) rearrangements with the Fe ions being pulled on top of the surface and bonded to the WO ₃ fragments. Both surface spectroscopies (XPS and IRAS) and calculations indicate that the W ions in the WO ₃ monomers remain in their original oxidation state (6+) and possess a single terminal W=O group. TPD studies show that this system does not efficiently catalyze alcohol dehydration. This inactivity is explained on the basis of the reaction mechanism calculated by DFT.