No abstract

No abstract

Direct evidence for C-O bond cleavage in the partial oxidation of 2-butanol on oxygen precovered Au(111) is provided using temperature programmed desorption (TPD) and molecular beam reactive scattering (MBRS) under ultrahigh vacuum (UHV) conditions. The oxygen precovered Au(111) surface can promote the partial oxidation of 2-butanol into 2-butanone with near 100% selectivity at low oxygen coverages, while 2-butanol adsorbs and desorbs molecularly on the clean Au(111) surface. Both C(2)H(5)C(16)OCH(3) and C(2)H(5)C(18)OCH(3) are observed in TPD after 2-butanol (C(2)H(5)CH(16)OHCH(3)) was dosed onto Au(111) precovered with (18)O(a). This oxygen exchange phenomenon serves as strong evidence for the C-O bond cleavage in 2-butanol partial oxidation to 2-butanone. Two surface intermediates are proposed for the selective oxidation of 2-butanol: 2-butoxide and eta(2)-aldehyde. As oxygen coverage increases, full oxidation is activated in addition to selective partial oxidation.

Partial oxidation of alcohols is a topic of great interest in the field of gold catalysis. In this work, we provide evidence that the partial oxidation of allyl alcohol to its corresponding aldehyde, acrolein, over oxygen-precovered gold surfaces occurs via multiple reaction pathways. Utilizing temperature-programmed desorption (TPD) with isotopically labeled water and oxygen species, reactive molecular beam scattering, and density functional theory (DFT) calculations, we demonstrate that the reaction mechanism for allyl alcohol oxidation is influenced by the relative proportions of atomic oxygen and hydroxyl species on the gold surface. Both atomic oxygen and hydroxyl species are shown to be active for allyl alcohol oxidation, but each displays a different pathway of oxidation, as indicated by TPD measurements and DFT calculations. The hydroxyl hydrogen of allyl alcohol is readily abstracted by either oxygen adatoms or adsorbed hydroxyl species on the gold surface to generate a surface-bound allyloxide intermediate, which then undergoes α-dehydrogenation via interaction with an oxygen adatom or surface hydroxyl species to generate acrolein. Mediation of a second allyloxide with the hydroxyl species lowers the activation barrier for the α-dehydrogenation process. A third pathway exists in which two hydroxyl species recombine to generate water and an oxygen adatom, which subsequently dehydrogenates allyloxide. This work may aid in the understanding of oxidative catalysis over gold and the effect of water therein.

Osteoblast behavior playing an important role in the biointegration of the Ti implant with host bone in vivo can be regulated by surface properties and magnetic field. In order to endow the Ti surface with good osteogenesis activity, Si monosubstituted and Fe and Si cosubstituted hydroxyapatite (HAp) nanorods were fabricated on microporous TiO2 by microarc oxidation (MAO) followed with hydrothermal treatment (HT). The surface properties including microstructure, microroughness, hydrophilicity, ion release, magnetic property, cytocompatibility, and biointegration of substituted HAp nanorods were observed and evaluated, together with pure HAp nanorods and microarc oxidated (MAOed) TiO2 as controls. After being doped with Fe, MAOed TiO2 has no changes in phase composition and microroughness, whereas it displays weakly ferromagnetic behavior and can enhance osteoblast differentiation in vitro and formation of new bone in vivo, compared with the undoped one. The substituted HAp nanorods adhere firmly to TiO2 and have almost the same wettability and microroughness but additional Si, Fe, and/or Ca released into the medium, compared with pure HAp nanorods. Moreover, the cosubstituted HAp has a small ferromagnetic signal, while its saturation magnetization value is less than that of the MAOed doped with Fe. Compared to pure HA nanorods, the substituted HAp nanorods not only improve cell proliferation and differentiation in vitro, but also enhance the ability of bone integration in vivo, especially for the cosubstituted one, which should be ascribed to the combined effect of microstructure, magnetic property, and released ions.

Oxidative dehydrogenation of amines using heterogeneous gold catalysts has unanticipated potential; chemisorbed atomic oxygen is used to activate propylamine, producing propionitrile and/or propionaldehyde on a single-crystal Au(111) surface.

No abstract

No abstract