Increasing the number of oxygen vacancies on TiO2 by doping with iron increases the activity of supported gold for CO oxidation

The addition of iron to high-area TiO2 (Degussa P25, a mixture of anatase and rutile) increases the number of oxygen defect sites that react with O2 to form peroxide and superoxide species. In the presence of gold nanoclusters on the TiO2 surface, the superoxide species become highly reactive, and the activity of the supported gold catalyst for CO oxidation is approximately twice that of the most active comparable catalysts described in the literature. Images of the catalyst obtained by scanning transmission electron microscopy combined with spectra of the catalyst measured in the working state (Raman, extended X-ray absorption fine structure, and X-ray absorption near-edge structure) indicate strong interactions of gold with the support and the presence of iron near the interfaces between the gold clusters and the TiO2 support. The high activity of the catalysts is attributed to the presence of defects in these sites that activate oxygen.     

Selective modification of the acid-base properties of ceria by supported Au

Au supported on CeO(2) prepared by deposition-precipitation with urea leads to a basic catalyst. Au acts in two ways as surface modifier. First, Au selectively interacts with Ce(4+) cations by either blocking access to or reducing Ce(4+) to Ce(3+). Second, the resulting Au atoms (presumably as Au(+) ions) act as soft, weak Lewis acid sites stabilizing carbanion intermediates and enhancing hydride abstraction in the dehydrogenation of alcohols. In consequence, the thus-synthesized basic catalyst catalyzes the dehydrogenation of propan-2-ol to acetone with high efficiency and without notable deactivation. Additionally, the dehydration pathway of propan-2-ol is eliminated, as Au also quantitatively blocks access to strongly acidic Ce(4+) ions or reduces them to Ce(3+).     

Cover picture: transition-metal-catalyzed unzipping of single-walled carbon nanotubes into narrow graphene nanoribbons at low temperature (angew. Chem. Int. Ed. 35/2011)

Narrow, smooth-edged graphene nanoribbons are needed for graphene electronics to replace the current silicon technology. In their Communication on page?8041?ff., J. Wang, F. Ding, et?al. report a smart strategy for cutting single-walled carbon nanotubes (gray) into narrow graphene nanoribbons in H(2) gas (green) with a single transition-metal atom (Cu, red) as the chemical scissors.     

Ab initio study of ice catalyzation of HOCl + HCl reaction

Experiments proved that the reaction of HOCl + HCl was very slow in the gas phase, but on ice surface it was rapid. In this work the ice catalysis of HOCl + HCl reaction was investigated by using ab initio molecular orbital theory. We applied the Hartree–Fock self‐consistent field and the second‐order Møller–Plesset perturbation theory with the basis sets of 6‐31G* to the model system. The complexes and transition state were obtained along the reaction with and without the presence of ice surface. By comparing the results, a possible catalyzation mechanism of ice on the reaction is proposed. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 281–284, 2000     

Initial Subsurface Incorporation of Oxygen into Ru(0001): A Density Functional Theory Study

The adsorption and diffusion of oxygen on Ru(0001) surfaces as a function of coverage are systematically investigated by using density functional theory. A high incorporation barrier of low‐coverage adsorbed oxygen into the subsurface is discovered. Calculations show that the adsorption of additional on‐surface oxygen can lower the penetration barrier dramatically. The minimum penetration barrier obtained is 1.81 eV for a path starting with oxygen in mixed on‐surface hcp and fcc sites at an oxygen coverage of 0.75 ML, which should be regarded as close to 1 ML. Energy diagrams show that oxygen‐diffusion barriers on the surface and in the subsurface are much lower than the penetration barrier. Oxygen diffusion on the surface is an indispensable step for its initial incorporation into the subsurface.     

CO Oxidation Catalytic Effects of Intrinsic Surface Defects in Rhombohedral LaMnO3

There is an ongoing effort to replace rare and expensive noble-element catalysts with more abundant and less expensive transition metal oxides. With this goal in mind, the intrinsic defects of a rhombohedral perovskite-like structure of LaMnO₃ and their implications on CO catalytic properties were studied. Surface thermodynamic stability as a function of pressure (P) and temperature (T) were calculated to find the most stable surface under reaction conditions (P=0.2 atm, T=323 K to 673 K). Crystallographic planes (100), (111), (110), and (211) were evaluated and it was found that (110) with MnO₂ termination was the most stable under reaction conditions. Adsorption energies of O₂ and CO on (110) as well as the effect of intrinsic defects such as Mn and O vacancies were also calculated. It was found that O vacancies favor the interaction of CO on the surface, whereas Mn vacancies can favor the formation of carbonate species.     

Transition-metal-catalyzed unzipping of single-walled carbon nanotubes into narrow graphene nanoribbons at low temperature

Open, sesame! Graphene nanoribbons (GNRs) with smooth edges and controllable widths are crucial for graphene electronic and spintronic applications. High-quality narrow GNRs can be synthesized from single-walled carbon nanotubes at 200-300?°C using a Cu-atom catalyst, which dramatically reduces the energy barrier of unzipping from 3.11 to 1.16?eV.     

Organometallic Iridium(III) Complex Sensitized Ternary Hybrid Photocatalyst for CO2 to CO Conversion

A series of heteroleptic iridium(III) complexes functionalized with two phosphonic acid (−PO₃H₂) groups ( ^dfppy IrP , ^ppy IrP , ^btp IrP , and ^piq IrP ) were prepared and anchored onto rhenium(I) catalyst (ReP)-loaded TiO₂ particles (TiO₂/ReP) to build up a new IrP -sensitized TiO₂ photocatalyst system ( IrP /TiO₂/ReP). The photosensitizing behavior of the IrP series was examined within the IrP /TiO₂/ReP platform for the photocatalytic conversion of CO₂ into CO. The four IrP -based ternary hybrids showed increased conversion activity and durability than that of the corresponding homo- ( IrP +ReP) and heterogeneous ( IrP +TiO₂/ReP) mixed systems. Among the four IrP /TiO₂/ReP photocatalysts, the low-energy-light (>500 nm) activated ^piq IrP immobilized ternary system ( ^piq IrP /TiO₂/ReP) exhibited the most durable conversion activity, giving a turnover number of ≥730 for 170 h. A similar kinetic feature observed through time-resolved photoluminescence measurements of both ^btp IrP /TiO₂ and TiO₂-free ^btp IrP films suggests that the net electron flow in the ternary hybrid proceeds dominantly through a reductive quenching mechanism, unlike the oxidative quenching route of typical dye/TiO₂-based photolysis.