PNNL

Abstract

The structure and catalytic activity of tungsten oxide clusters formed via sublimation of monodispersed cyclic (WO3)3 onto FeO(111)/Pt(111) surface 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 function theory (DFT). After the (WO3)3 sublimation, STM images reveal new features composed of three bright maxima arranged in triangular configurations with the distances of ~10 Å. These distances are significantly larger compared to the size of (WO3)3 indicating that the clusters dissociated. This conclusion is corroborated by DFT calculations showing that the cluster dissociation into the surface-bound WO3 monomers is endothermic 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 WO3 fragments. Both surface spectroscopies (XPS and IRAS) and calculations indicate that the W ions in the WO3 monomers remain in (6+) oxidation state and possess terminal W=O groups. Our TPD studies show that this system do not efficiently catalyze alcohol dehydration. This inactivity is explained based on the reaction mechanism calculated by DFT.