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

Influence of the support in aqueous phase oxidation of ethanol on gold/metal oxide catalysts studied by ATR-IR spectroscopy under working conditions

Effects of supports (Co3O4, CeO2, NiO) in the gold-catalyzed aqueous phase oxidation of ethanol (EtOH) to acetic acid (AcOH) were examined. ATR-IR spectroscopy under working conditions of the catalysts uncovered on gold particles bidentate ethoxy, and on supports monodentate ethoxy species, multi-layered ethanol, and acetate. Preferential formation of bidentate ethoxy species and adsorbed EtOH were identified as key factors for high activity and selectivity to AcOH. These requirements were best matched with Au/Co3O4. On NiO, monodentate ethoxy species on the support deteriorated the catalytic performance due to consecutive esterification of AcOH and/or acetate species with EtOH producing undesirable ethyl acetate

エキタイフッカ スイソチュウデノデンカイハンノウニカンスルケンキュウ

京都大学0048新制・課程博士工学博士甲第1754号工博第467号新制||工||344(附属図書館)4845UT51-51-K27京都大学大学院工学研究科工業化学専攻(主査)教授 渡辺 信淳, 教授 吉沢 四郎, 教授 安藤 貞一学位規則第5条第1項該当Kyoto UniversityDA

Creation of Novel Catalytic Functions by Nanoparticulation of Gold

Gold was regarded as an inactive element for longer than a century. However, it exhibited unique catalytic properties when deposited on base metal oxides as nanoparticles with mean diameters smaller than 10 nm. Especially, gold nanoparticles catalysts with 2 to 6 nm diameters are active for many reactions, such as CO oxidation at a temperature as low as - 70 degrees C. Some typical reactions in liquid and gas phases are listed. A new area is clusters that are smaller than 2 nm and less than 200 atoms. Unique catalytic performances of gold clusters have recently been found. This paper summarizes the characteristic features of gold nanopardcles and clusters catalysts as well as their applications

Size- and Structure-specificity in Catalysis by Gold Clusters

Although gold in bulk is poorly active as a catalyst, it exhibits surprisingly high catalytic activity when deposited as nanoparticles (NPs) on base metal oxides. The catalytic performance of supported gold NPs can be created by choosing the kind of support materials, by controlling the size of gold, and by building up strong contact of gold with the supports. Since perimeter interfaces around gold NPs act, in principle, as the active sites for oxidation and hydrogenation, gold should be smaller than 10 nm in diameter. A new area of research is clusters, which are smaller than 2 nm in diameter and less than 200 atoms. Gold clusters possess electronic structures different from those of bulk gold and at the same time provide increased fractions of edges and corners which are highly unsaturatedly coordinated sites. Accordingly, gold clusters will be blessed by unique catalytic performance, and many examples have recently been emerging. This article summarizes such examples in terms of "size- and structure-specificity," covering gas-phase free clusters, polymer- or organic-ligand-stabilized clusters in liquid phase, and clusters supported on base metal oxides, carbon materials, and organic polymers for gas-phase and liquid-phase reactions

Aerobic oxidation of benzyl alcohol in water catalyzed by gold nanoparticles supported on imidazole containing crosslinked polymer

A series of imidazole containing crosslinked copolymer poly(divinylbenzene-co-N- vinylimidazole) (PDVB-VI-n) supported Au catalysts were prepared by using AuCI3 as the precursor. The resulting Au/PDVB-VI-n catalysts were employed to catalyze the aerobic oxidation of benzyl alcohol with molecular oxygen as the sole oxidant and water as the solvent. By optimizing the sizes of Au NPs and the composition of PDVB-VI-n, Au/PDVB-VI-n exhibited the excellent activities even only using a small amount of basic K2CO3. Interestingly, the conversion of benzyl alcohol increased monotonously with the increase of Au sizes in the range of 2-5 nm, but the selectivity to benzoic acid increased first and then decreased gradually. The highest selectivity to benzoic acid of similar to 80%was achieved over similar to 3.2 nm Au NPs. (C) 2017 Elsevier B.V. All rights reserved

Electron Microscopy Study of Gold Nanoparticles Deposited on Transition Metal Oxides

Many researchers have investigated the catalytic performance ofgold nanoparticles (GNPs) supported on metal oxides for various catalytic reactions of industrial importance. These studies have consistently shown that the catalytic activity and selectivity depend on the size of GNPs, the kind of metal oxide supports, and the gold/metal oxide interface structure. Although researchers have proposed several structural models for the catalytically active sites and have identified the specific electronic structures of GNPs induced by the quantum effect, recent experimental and theoretical studies indicate that the perimeter around GNPs in contact with the metal oxide supports acts as an active site in many reactions. Thus, it is of immense importance to investigate the detailed structures of the perimeters and the contact interfaces of gold/metal oxide systems by using electron microscopy at an atomic scale.This Account describes our investigation, at the atomic scale using electron microscopy, of GNPs deposited on metal oxides. In particular, high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) are valuable tools to observe local atomic structures, as has been successfully demonstrated for various nanoparticles, surfaces, and material interfaces. TEM can be applied to real powder catalysts as received without making special specimens, in contrast to what is typically necessary to observe bulk materials. For precise structure analyses at an atomic scale, model catalysts prepared by using well-defined single-crystalline substrates are also adopted for TEM observations. Moreover, aberration-corrected TEM, which has high spatial resolution under 0.1 nm, is a promising tool to observe the interface structure between GNPs and metal oxide supports including oxygen atoms at the interfaces. The oxygen atoms in particular play an important role in the behavior of gold/metal oxide interfaces, because they may participate in catalytic reaction steps. Detailed information about the interfacial structures between GNPs and metal oxides provides valuable structure models for theoretical calculations which can elucidate the local electronic structure effective for activating a reactant molecule. Based on our observations with HRTEM and HAADF-STEM, we report the detailed structure of gold/metal oxide interfaces