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/FeOx materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed to reveal the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. Correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeOx catalyst

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

Hydrogen peroxide is synthesized industrially without direct contact of hydrogen and oxygen in order to achieve high concentrations. For many applications, only dilute aqueous solutions are needed. Freakley et al. report an improvement in the direct synthesis of hydrogen peroxide over using palladium-tin alloys. This catalyst still achieves selectivities of >95%, like palladium-gold alloys, but is cheaper and can suppress reactions that decompose the product

Interpersonal and intrapersonal functions of NSSI

Color poster with text, charts, and graphs.Non-suicidal Self-injury (NSSI) is the deliberate harm to bodily tissues without the intent to die. NSSI is problematic in college age students as they attempt to juggle classes, jobs, social relationships, and extracurricular activities. There are many reasons people engage in NSSI, and many are divided into inter-and intra-personal functions. These consist of intrapersonal functions such as self-punishment and self-care, and interpersonal functions such as peer-bonding and interpersonal boundaries. Previous literature indicates that interpersonal functions are fulfilled by engaging in NSSI. Additional research suggests interpersonal functions are associated with a higher frequency of NSSI.University of Wisconsin--Eau Claire Office of Research and Sponsored Program

Direct synthesis of hydrogen peroxide from H2 and O2 using Au–Pd/Fe2O3catalysts

The direct synthesis of hydrogen peroxide from H2 and O2 using a range of Au, Pd and Au–Pd metal nanoparticles supported on iron oxide is described and discussed, and in particular the microstructure of the catalysts are investigated using a detailed electron microscopy study. Iron oxide was selected as a support because Au/Fe2O3 catalysts are known to be very active for low temperature CO oxidation. Hydrogen peroxide synthesis was investigated at low temperatures (2 °C) and short reaction (residence) time, and the addition of Pd to the Au catalyst was found to increase the rate of hydrogen peroxide synthesis as well as the concentration of hydrogen peroxide formed. Indeed the rates of hydrogen peroxide synthesis are higher for the Au–Pd alloy catalysts as compared to the Au or Pd only catalysts. These catalyst materials were also investigated for CO oxidation at 25 °C and all were found to be almost inactive. In contrast, Au-based catalysts that are very effective for low temperature CO oxidation were found to be totally inactive for H2 oxidation to H2O2. This suggests an inverse correlation between catalysts that are active for either CO or H2 activation. The microstructure of the Au–Pd/Fe2O3 catalysts was studied using scanning transmission electron microscopy and the metal alloy nanoparticles were found to have a core–shell morphology with Pd concentrated on the catalyst surface

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. The addition of a small amount of Pt to a CeO2-supported AuPd (weight ratio of 1:1) catalyst significantly enhanced the activity in the direct synthesis of H2O2 and decreased the non-desired over-hydrogenation and decomposition reactions. The addition of Pt to the AuPd nanoparticles influenced the surface composition, thus leading to the marked effects that were observed on the catalytic formation of hydrogen peroxide. In addition, an experimental approach that can help to identify the optimal nominal ternary alloy compositions for this reaction is demonstrated

Reactivity studies of Au-Pd supported nanoparticles for catalytic applications

The utilisation of gold-palladium nanoparticles either in the form of colloids or supported nanoparticles has received enormous attention in recent years. These materials are very effective for the transformation of organic compounds to highly useful chemical products. The catalytic materials are usually prepared using deposition-precipitation and impregnation techniques, but recently significant attention has been focused on the use of colloidal methods. Here we compare and contrast the preparation and catalytic reactivity of Au-Pd supported nanoparticles synthesised by deposition-precipitation and colloidal methods. The catalyst materials have been evaluated for three different reactions, namely, the oxidation of benzyl alcohol, the direct synthesis of hydrogen peroxide and the oxidation of carbon monoxide. In addition, we have focused our attention on the pre-treatment temperature and the improvement of the deposition-precipitation method by using urea and sodium borohydride for the preparation of highly active Au-Pd supported nanoparticles. \ua9 2010 Elsevier B.V. All rights reserved

Au-Pd supported nanocrystals prepared by a sol immobilisation technique as catalysts for selective chemical synthesis

Catalysis by gold and gold-palladium nanoparticles has attracted significant research attention in recent years. These nanocrystalline materials have been found to be highly effective for selective and total oxidation, but in most cases the catalysts are prepared using precipitation or impregnation. We report the preparation of Au-Pd nanocrystalline catalysts supported on carbon prepared via a sol-immobilisation technique and these have been compared with Au-Pd catalysts prepared via impregnation. The catalysts have been evaluated for two selective chemical syntheses, namely, oxidation of benzyl alcohol and the direct synthesis of hydrogen peroxide. The catalysts have been structurally characterised using a combination of scanning transmission electron microscopy and X-ray photoelectron spectroscopy. The catalysts prepared using the sol immobilisation technique show higher activity when compared with catalysts prepared by impregnation as they are more active for both hydrogen peroxide synthesis and hydrogenation, and also for benzyl alcohol oxidation. The method facilitates the use of much lower metal concentrations which is a key feature in catalyst design, particularly for the synthesis of hydrogen peroxide. \ua9 the Owner Societies