3 Search Results

Hydrogen adsorption on TiO₂ is of importance in chemical and photochemical reduction processes. Using several surface science methods, we clearly distinguish two kinds of H species on the surface of rutile TiO₂(110)-1 × 1. In contrast with the well-studied bridge-bonded OH species (α-H) originating from H₂O dissociation on the surface oxygen vacancy site on TiO₂(110), atomic H adsorption on the TiO₂(110) (denoted as β-H) exhibits special high sensitivity to the electronic excitation of the TiO₂(110) by either electrons or UV photons. The formation of molecular H₂ gas by photoexcitation of β-H/TiO₂(110) surfaces has been observed, which may shed light onmore » the basic understanding of the processes of photocatalytic H₂ production by splitting water.« less

Here, we report experimental as well as theoretical evidence that suggests Au CO complex formation upon the exposure of CO to active sites (step edges and threading dislocations) on a Au(111) surface. Room-temperature scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, transmission infrared spectroscopy, and density functional theory calculations point to Au CO complex formation and migration. Room-temperature STM of the Au(111) surface at CO pressures in the range from 10^ 8 to 10^ 4 Torr (dosage up to 10^6 langmuir) indicates Au atom extraction from dislocation sites of the herringbone reconstruction, mobile Au CO complex formation and diffusion, and Aumore » adatom cluster formation on both elbows and step edges on the Au surface. The formation and mobility of the Au CO complex result from the reduced Au Au bonding at elbows and step edges leading to stronger Au CO bonding and to the formation of a more positively charged CO (CO +) on Au. These studies indicate that the mobile Au CO complex is involved in the Au nanoparticle formation and reactivity, and that the positive charge on CO increases due to the stronger adsorption of CO at Au sites with lower coordination numbers.« less

Here, the partial oxidation of model C₂–C₄ (acetic, propionic, and butyric) carboxylic acids on Au/TiO₂ catalysts consisting of Au particles ~3 nm in size was investigated using transmission infrared spectroscopy and density functional theory. All three acids readily undergo oxidative dehydrogenation on Au/TiO₂. Propionic and butyric acid dehydrogenate at the C2–C3 positions, whereas acetic acid dehydrogenates at the C1–C2 position. The resulting acrylate and crotonate intermediates are subsequently oxidized to form β-keto acids that decarboxylate. All three acids form a gold ketenylidene intermediate, Au₂C=C=O, along the way to their full oxidation to form CO₂. Infrared measurements of Au₂C=C=O formation asmore » a function of time provides a surface spectroscopic probe of the kinetics for the activation and oxidative dehydrogenation of the alkyl groups in the carboxylate intermediates that form.« less