Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation.

The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviours after heat treatment of Au/FeO materials prepared via co-precipitation and deposition precipitation methods.

Palladium-tin catalysts for the direct synthesis of H₂O₂ with high selectivity.

The direct synthesis of hydrogen peroxide (H2O2) from H2 and O2 represents a potentially atom-efficient alternative to the current industrial indirect process. We show that the addition of tin to palladium catalysts coupled with an appropriate heat treatment cycle switches off the sequential hydrogenation and decomposition reactions, enabling selectivities of >95% toward H2O2. This effect arises from a tin oxide surface layer that encapsulates small Pd-rich particles while leaving larger Pd-Sn alloy particles exposed.

The direct synthesis of hydrogen peroxide using platinum-promoted gold-palladium catalysts.

The direct synthesis of hydrogen peroxide offers a potentially green route to the production of this important commodity chemical. Early studies showed that Pd is a suitable catalyst, but recent work indicated that the addition of Au enhances the activity and selectivity significantly. The addition of a third metal using impregnation as a facile preparation method was thus investigated.

Strategies for designing supported gold-palladium bimetallic catalysts for the direct synthesis of hydrogen peroxide.

Hydrogen peroxide is a widely used chemical but is not very efficient to make in smaller than industrial scale. It is an important commodity chemical used for bleaching, disinfection, and chemical manufacture. At present, manufacturers use an indirect process in which anthraquinones are sequentially hydrogenated and oxidized in a manner that hydrogen and oxygen are never mixed.

Fabrication of complex model oxide catalysts: Mo oxide supported on Fe3o4(111).

Industrial catalysts for the oxidation of methanol to formaldehyde consist of iron molybdate [Fe2(MoO4)3]. Using a variety of techniques we have previously shown that the surface of these catalysts is segregated in MoO3, and in order to understand the relationship between surface structure and reactivity for these systems we have begun a surface science study of this system using model, single crystal oxides. Model catalysts of molybdenum oxide nanoparticles and films on an Fe3O4(111) single crystal were fabricated by the hot-filament metal oxide deposition technique (HFMOD), where molybdenum oxides were produced using a molybdenum filament heated in an oxygen atmosphere.

Enhancing surface reactivity with a noble metal.

Gold, the archetypal noble metal, is usually associated with an inhibition of surface reactivity by site blocking. In this paper however, we show that on Cu(100) surfaces a gold adlayer can actually increase the extent of reaction with the substrate.

Osteogenic potential of bone marrow stromal cells on smooth, roughened, and tricalcium phosphate-modified titanium alloy surfaces.

Purpose: This study investigated the influence of smooth, roughened, and tricalcium phosphate (TCP)-coated roughened titanium-aluminum-vanadium (Ti-6Al-4V) surfaces on the osteogenic potential of rat bone marrow stromal cells (BMSCs).

Methods: Machined smooth (MS), grit-blasted roughened (MT), and roughened surfaces coated with TCP were prepared from Ti-6Al-4V. Plastic surfaces were used as a control.

Synthesis of stable ligand-free gold-palladium nanoparticles using a simple excess anion method.

We report a convenient excess anion modification and post-reduction step to the impregnation method which permits the reproducible preparation of supported bimetallic AuPd nanoparticles having a tight particle size distribution comparable to that found for sol-immobilization materials but without the complication of ligands adsorbed on the particle surface. The advantageous features of the modified impregnation materials compared to those made by conventional impregnation include a smaller average particle size, an optimized random alloy composition, and improved compositional uniformity from particle-to-particle resulting in higher activity and stability compared to the catalysts prepared using both conventional impregnation and sol immobilization methods. Detailed STEM combined with EDX analyses of individual particles have revealed that an increase in anion concentration increases the gold content of individual particles in the resultant catalyst, thus providing a method to control/tune the composition of the nanoalloy particles.

Non-lattice surface oxygen species implicated in the catalytic partial oxidation of decane to oxygenated aromatics.

The one-step transformation of C(7)-C(12) linear alkanes into more valuable oxygenates provides heterogeneous catalysis with a major challenge. In evaluating the potential of a classic mixed-metal-oxide catalyst, we demonstrate new insights into the reactivity of adsorbed oxygen species. During the aerobic gas-phase conversion of n-decane over iron molybdate, the product distribution correlates with the condition of the catalyst.

Niobium phosphates as new highly selective catalysts for the oxidative dehydrogenation of ethane.

Several niobium phosphate phases have been prepared, fully characterized and tested as catalysts for the selective oxidation of ethane to ethylene. Three distinct niobium phosphate catalysts were prepared, and each was comprised predominantly of a different bulk phase, namely Nb(2)P(4)O(15), NbOPO(4) and Nb(1.91)P(2.

Facile removal of stabilizer-ligands from supported gold nanoparticles.

Metal nanoparticles that comprise a few hundred to several thousand atoms have many applications in areas such as photonics, sensing, medicine and catalysis. Colloidal methods have proven particularly suitable for producing small nanoparticles with controlled morphologies and excellent catalytic properties. Ligands are necessary to stabilize nanoparticles during synthesis, but once the particles have been deposited on a substrate the presence of the ligands is detrimental for catalytic activity.

Synthesis of glycerol carbonate from glycerol and urea with gold-based catalysts.

The reaction of glycerol with urea to form glycerol carbonate is mostly reported in the patent literature and to date there have been very few fundamental studies of the reaction mechanism. Furthermore, most previous studies have involved homogeneous catalysts whereas the identification of heterogeneous catalysts for this reaction would be highly beneficial. This is a very attractive reaction that utilises two inexpensive and readily available raw materials in a chemical cycle that overall, results in the chemical fixation of CO(2).

CO bond cleavage on supported nano-gold during low temperature oxidation.

The oxidation of CO by Au/Fe(2)O(3) and Au/ZnO catalysts is compared in the very early stages of the reaction using a temporal analysis of products (TAP) reactor. For Au/Fe(2)O(3) pre-dosing the catalyst with (18)O labelled water gives an unexpected evolution order for the labelled CO(2) product with the C(18)O(2) emerging first, whereas no temporal differentiation is found for Au/ZnO. High pressure XPS experiments are then used to show that CO bond cleavage does occur for model catalysts consisting of Au particles deposited on iron oxide films but not when deposited on ZnO films.

Direct synthesis of hydrogen peroxide and benzyl alcohol oxidation using Au-Pd catalysts prepared by sol immobilization.

We report the preparation of Au-Pd nanocrystalline catalysts supported on activated carbon prepared via a sol-immobilization technique and explore their use for the direct synthesis of hydrogen peroxide and the oxidation of benzyl alcohol. In particular, we examine the synthesis of a systematic set of Au-Pd colloidal nanoparticles having a range of Au/Pd ratios. The catalysts have been structurally characterized using a combination of UV-visible spectroscopy, transmission electron microscopy, STEM HAADF/XEDS, and X-ray photoelectron spectroscopy.

Effect of the reaction conditions on the performance of Au-Pd/TiO(2) catalyst for the direct synthesis of hydrogen peroxide.

The direct synthesis of hydrogen peroxide from H(2) and O(2) has been studied using a high activity AuPd/TiO(2) catalyst. In particular, the effect of variation in the reaction conditions on the productivity of hydrogen peroxide formation is investigated in detail. The effect of H(2)/O(2) molar ratio, temperature, total pressure and solvent composition has been studied and optimised conditions identified.

Transient oxygen states in catalysis: ammonia oxidation at Ag(111).

Although the reactive sticking probability of oxygen at Ag(111) is of the order of 10(-6) at 295 K, ammonia oxidation is a facile process at low temperatures. A combination of quantitative analysis of photoelectron spectra together with high resolution electron energy loss spectroscopy provides kinetic and spectroscopic evidence for an ammonia-dioxygen complex, stable at 100 K, as the key intermediate. The reactive oxygen O(2)(s) is a transient dioxygen precursor of the unreactive peroxo state O(2)(δ-)(a).

Effects of the nanostructuring of gold films upon their thermal stability.

We report results relating to the thermal stability of nanoparticles and show a remarkable effect of nanostructuring of the metal. Au films are nanostructured by focused ion beam sputtering (FIB) to produce isolated areas of metal, which are imaged by atomic force microscopy (AFM). Images of the surface show that, if the islands are made small enough, the metal in the islands is lost by evaporation, whereas the nonfabricated areas outside are relatively stable and the nanoparticles remain present there.

A low energy pathway to CuCl2 at Cu(110) surfaces.

The reaction of hydrogen chloride gas with partially oxidised Cu(110) surfaces follows a different structural pathway than its reaction with a clean surface. In the latter case a c(2 x 2)Cl structure develops which is compressed in the [110] direction for chlorine atom concentrations greater than 5.5 x 10(14) cm(-2).

Oxidation of glycerol to glycolate by using supported gold and palladium nanoparticles.

Glycolic acid is an important chemical that has uses as a cleaning agent as well as a chemical intermediate. At present glycolic acid is manufactured from either chloroacetic acid or from formaldehyde hydrocyanation, both routes being nongreen and using nonsustainable resources. We investigate the possibility of producing glycolate from the oxidation of glycerol, a sustainable raw material.

Solvent-free oxidation of benzyl alcohol using Au-Pd catalysts prepared by sol immobilisation.

We report the preparation of Au-Pd nanocrystalline catalysts supported on TiO(2) and carbon prepared via a sol-immobilisation technique using three different preparation strategies; namely, simultaneous formation of the sols for both metals or initial formation of a seed sol of one of the metals followed by a separate step in which a coating sol of the second metal is added. The catalysts have been structurally characterised using a combination of transmission electron microscopy and X-ray photoelectron spectroscopy. The catalysts have been evaluated for the oxidation of benzyl alcohol under solvent-free conditions.

Oxidation of glycerol using gold-palladium alloy-supported nanocrystals.

The use of bio-renewable resources for the generation of materials and chemicals continues to attract significant research attention. Glycerol, a by-product from biodiesel manufacture, is a highly functionalised renewable raw material, and in this paper the oxidation of glycerol in the presence of base using supported gold, palladium and gold-palladium alloys is described and discussed. Two supports, TiO(2) and carbon, and two preparation methods, wet impregnation and sol-immobilisation, are compared and contrasted.