Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Surface functionalized magnetic iron oxide nanoparticles (NPs) are a kind of novel functional materials, which have been widely used in the biotechnology and catalysis. This review focuses on the recent development and various strategies in preparation, structure, and magnetic properties of naked and surface functionalized iron oxide NPs and their corresponding application briefly. In order to implement the practical application, the particles must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of iron oxide NPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The problems and major challenges, along with the directions for the synthesis and surface functionalization of iron oxide NPs, are considered. Finally, some future trends and prospective in these research areas are also discussed.

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Magnetic Iron Oxide Nanoparticles: Synthesis and Surface Functionalization Strategies

Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Tubular and fibrous nanostructures of titanates have recently been
synthesized and characterized. Three general approaches (template assisted, anodic oxidation, and alkaline hydrothermal) for the preparation of nanostructured titanate and TiO2 are reviewed. The crystal structures, morphologies, and mechanism of formation
of nanostructured titanates produced by the alkaline hydrothermal method are critically discussed. The physicochemical properties of nanostructured titanates are highlighted and the links between properties and applications are emphasized. Examples of early applications of nanostructured titanates in catalysis, photocatalysis, electrocatalysis, lithium batteries, hydrogen storage, and solar-cell technologies are reviewed. The stability of titanate nanotubes at elevated temperatures and in acid media is considered.

Protonated Titanates and TiO2 Nanostructured Materials: Synthesis, Properties, and Applications

Gold catalysts have recently been attracting rapidly growing interests due to their potential applicabilities to many reactions of both industrial and environmental importance. This article reviews the latest advances in the catalysis research on Au. For low-temperature CO oxidation mechanistic arguments are summarized, focusing on Au/TiO 2 together with the effect of preparation conditions and pretreatments. The quantum size effect is also discussed in the adsorption and reaction of CO over Au clusters smaller than 2 nm in diameter. In addition, recent developments are introduced in the epoxidation of propylene, water-gas-shift reaction, hydrogenation of unsaturated hydrocarbons, and liquid-phase selective oxidation. The role of perimeter interface between Au particles and the support is emphasized as a unique reaction site for the reactants adsorbed separately, one on Au and another on the support surfaces.

Advances in the catalysis of Au nanoparticles

Low-temperature water-gas shift reaction over Au/CeO2 catalysts

Low-temperature water-gas shift reaction over Au/α-Fe2O3

Titanium oxide nanotubes (TNTs) have been synthesized via the reaction of TiO 2 crystalline powders of either anatase or rutile phase and NaOH aqueous solution. Their application as an active supports of gold particles prepared by deposition–precipitation (DP) method is investigated. The TNT supports and the gold catalysts were characterized by a range of methods including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), N 2 adsorption analysis and temperature programmed reduction (TPR). The catalytic activity of gold-supported titania nanotubes (Au/TNTs) was evaluated for the first time in water-gas shift reaction (WGSR) at wide temperature range (140–300 °C) and has been compared with Au/surfactant-templated-mesoporous-titania and Au/Al 2 O 3 catalysts under the same operating conditions. We try to establish a correlation between the catalytic performance of Au/TNTs and the nature of the support.

Titanium oxide nanotubes as supports of nano-sized gold catalysts for low temperature water-gas shift reaction

The water-gas shift reaction (WGSR) has been studied on Auα-Fe2O3 catalyst. The structure of the samples has been investigated by chemical and physical methods—TEM, X-ray, DTA, FTIR. A high dispersion degree of the gold particles and an increased concentration of the hydroxyl groups on Auα-Fe2O3 has been established in comparison to the pure α-Fe2O3. The results obtained can be explained on the basis of the associative mechanism of the WGSR. The essential aspects are the dissociative adsorption of water on ultrafine gold particles, followed by spillover of active hydroxyl groups onto adjacent sites of the ferric oxide. The formation and decomposition of intermediate species is accompanied by redox transfer Fe3+ Fe2+ in Fe3O4.

Low-temperature water-gas shift reaction on Auα-Fe2O3 catalyst

It has been established that the gold catalysts on well crystallized supports, Au/Fe2O3 and Au/ZrO2, display higher catalytic activity in the water gas shift (WGS) reaction in comparison with the samples on amorphous and not well crystallized supports — Au/ZnO, Au/ZrO2, Au/Fe2O3–ZnO and Au/Fe2O3–ZrO2. It could be concluded that the catalytic activity of the gold/metal oxide catalysts depends strongly not only on the dispersion of the gold particles but also on the state and the structure of the supports.

Influence of the microscopic properties of the support on the catalytic activity of Au/ZnO, Au/ZrO2, Au/Fe2O3, Au/Fe2O3–ZnO, Au/Fe2O3–ZrO2 catalysts for the WGS reaction

Vasko Idakiev

Papers

Low-temperature water-gas shift reaction over Au/CeO2 catalysts

Low-temperature water-gas shift reaction over Au/α-Fe2O3

Titanium oxide nanotubes as supports of nano-sized gold catalysts for low temperature water-gas shift reaction

Low-temperature water-gas shift reaction on Auα-Fe2O3 catalyst

Influence of the microscopic properties of the support on the catalytic activity of Au/ZnO, Au/ZrO2, Au/Fe2O3, Au/Fe2O3–ZnO, Au/Fe2O3–ZrO2 catalysts for the WGS reaction