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.

3.2.3. Hydroformylation 2467 3.2.4. Dimerization 2468 3.2.5. Oxidative Cleavage and Ozonolysis 2469 3.2.6. Metathesis 2470 4. Terpenes 2472 4.1. Pinene 2472 4.1.1. Isomerization: R-Pinene 2472 4.1.2. Epoxidation of R-Pinene 2475 4.1.3. Isomerization of R-Pinene Oxide 2477 4.1.4. Hydration of R-Pinene: R-Terpineol 2478 4.1.5. Dehydroisomerization 2479 4.2. Limonene 2480 4.2.1. Isomerization 2480 4.2.2. Epoxidation: Limonene Oxide 2480 4.2.3. Isomerization of Limonene Oxide 2481 4.2.4. Dehydroisomerization of Limonene and Terpenes To Produce Cymene 2481

Chemical Routes for the Transformation of Biomass into Chemicals

Size- and support-dependency in the catalysis of gold

Interest in catalysis by metal nanoparticles (NPs) is increasing dramatically, as reflected by the large number of publications in the last five years. This field, "semi-heterogeneous catalysis", is at the frontier between homogeneous and heterogeneous catalysis, and progress has been made in the efficiency and selectivity of reactions and recovery and recyclability of the catalytic materials. Usually NP catalysts are prepared from a metal salt, a reducing agent, and a stabilizer and are supported on an oxide, charcoal, or a zeolite. Besides the polymers and oxides that used to be employed as standard, innovative stabilizers, media, and supports have appeared, such as dendrimers, specific ligands, ionic liquids, surfactants, membranes, carbon nanotubes, and a variety of oxides. Ligand-free procedures have provided remarkable results with extremely low metal loading. The Review presents the recent developments and the use of NP catalysis in organic synthesis, for example, in hydrogenation and C--C coupling reactions, and the heterogeneous oxidation of CO on gold NPs.

Nanoparticles as Recyclable Catalysts: The Frontier between Homogeneous and Heterogeneous Catalysis

Mesoporous organic-inorganic hybrid materials, a new class of materials characterized by large specific surface areas and pore sizes between 2 and 15 nm, have been obtained through the coupling of inorganic and organic components by template synthesis. The incorporation of functionalities can be achieved in three ways: by subsequent attachment of organic components onto a pure silica matrix (grafting), by simultaneous reaction of condensable inorganic silica species and silylated organic compounds (co-condensation, one-pot synthesis), and by the use of bissilylated organic precursors that lead to periodic mesoporous organosilicas (PMOs). This Review gives an overview of the preparation, properties, and potential applications of these materials in the areas of catalysis, sorption, chromatography, and the construction of systems for controlled release of active compounds, as well as molecular switches, with the main focus being on PMOs.

Silica-based mesoporous organic-inorganic hybrid materials.

Bifunctional Catalysis of Mo/HZSM-5 in the Dehydroaromatization of Methane to Benzene and Naphthalene XAFS/TG/DTA/MASS/FTIR Characterization and Supporting Effects

Following P.H. Emmett's pioneering work, much research was focused on the mechanisms of Fischer-Tropsch catalysis, and it has been discovered that certain base metal ions promote the activity and selectivity of Rh metal to catalyze the conversions of CO + H/sub 2/ to aldehydes and alcohols. Recent IR, Moessbauer, and EXAFS evidence in conjunction with catalytic tests suggests that the highly oxophilic ions Mn, Ti, Zr, and Nb, when located at the Rh surface, enhance CO dissociation, possibly through direct interaction with the oxygen atom of tilted adsorbed CO. A different mechanism emerges for Fe and Zn ions. These seem to block sites, thus inhibiting the formation of bridging CO and its dissociation to C + O. These steps are characterized by large ensemble requirements. Remarkably, the rate of CO insertion on Rh appears enhanced but the rate of hydrogenation is markedly suppressed by Zn. Consequently, the hydroformylation of olefins and the synthesis of methanol are efficiently catalyzed. This result suggests that the latter reactions require only very small Rh ensembles; possibly they are catalyzed by single Rh atoms.

Catalytic site requirements for elementary steps in syngas conversion to oxygenates over promoted rhodium

Novel templating synthesis of necklace-shaped mono- and bimetallic nanowires in hybrid organic-inorganic mesoporous material.

Highly efficient evolution of hydrogen is achieved in the dehydrogenation of cycloalkanes such as cyclohexane, methylcyclohexane, and decalin over Pt catalyst supported on active carbon (AC) under “wet–dry multiphase conditions”. Formation rate of hydrogen is largely dependent on reaction conditions such as reactant/catalyst ratio, temperature, and support. The highest initial rate of formation of hydrogen, k =8.0×10 −3  mol min −1 , was obtained in the dehydrogenation of cyclohexane over Pt/AC at 623 K and the reactant/catalyst ratio=3.3 ml g −1 . The addition of second metals such as Mo, W, Re, Rh, Ir, and Pd on the carbon-supported Pt catalysts enhances the dehydrogenation rate due to the promotion of CH bond cleavage and/or desorption of aromatic products. A physical mixture of Pt/AC and Pd/AC catalysts exhibits higher activities than the monometallic Pt/AC catalyst owing to the synergistic effects of spillover, migration, and recombination of hydrogen over Pt and Pd catalysts.

Efficient evolution of hydrogen from liquid cycloalkanes over Pt-containing catalysts supported on active carbons under “wet–dry multiphase conditions”

Highly efficient production of hydrogen without CO 2 emission is achieved in the dehydrogenation of cyclic hydrocarbons under a non-steady spray pulse operation over supported Pt and Pt-M (M=Re, Rh, Pd) catalysts. Cyclohexane, methylcyclohexane, tetralin and decalin were efficiently dehydrogenated by the Pt-containing catalysts supported on thin active carbon cloth (CFF-1500S) sheets and alumite (anodized aluminum) plates. Production rate of hydrogen under the spray pulse mode is higher than the conventional batch-type liquid phase reaction and the steady state gas phase reaction in the flow system. The highest rate, 3800 mmol g Pt −1  min −1 , was obtained in the dehydrogenation of cyclohexane over Pt/alumite heated at 375 °C and cyclohexane feed of 190 mmol min −1 with 3.5 mmol pulse at 1.0 s interval. Bimetallic Pt-Rh/CFF-1500S catalyst showed a higher activity than monometallic Pt/CFF-1500S. Production rate of hydrogen is greatly dependent on the rate of reactant feed, the reaction temperature, and the support. Retardation by products adsorbed on the catalysts was negligible under the spray-pulse operation.

Masaru Ichikawa

Papers

Bifunctional Catalysis of Mo/HZSM-5 in the Dehydroaromatization of Methane to Benzene and Naphthalene XAFS/TG/DTA/MASS/FTIR Characterization and Supporting Effects

Catalytic site requirements for elementary steps in syngas conversion to oxygenates over promoted rhodium

Novel templating synthesis of necklace-shaped mono- and bimetallic nanowires in hybrid organic-inorganic mesoporous material.

Efficient evolution of hydrogen from liquid cycloalkanes over Pt-containing catalysts supported on active carbons under “wet–dry multiphase conditions”

Efficient hydrogen production using cyclohexane and decalin by pulse-spray mode reactor with Pt catalysts