Search

Biomass constitutes a renewable source for new chemical platforms. Among other processes the catalytic ones represent a green alternative when active and selective catalysts can be developed. In this paper, applications of gold and gold‐based catalysts have been reviewed in the field of the selective oxidations. Indeed, from the discovery of the peculiarity of gold as catalytic material, the liquid phase oxidations have been differently viewed. Three important biomass‐derived molecules, namely glucose, hydroxymethyl furfural (HMF) and glycerol have been considered as precursors for products of industrial interest where gold catalysts have played an important role. This review starts from the research on monometallic gold catalysts which have been explored initially and then look at gold as modifier of other metal catalyst. This latter field is still in evolution and probably needs to be look at in the future. Golden path: Applications of gold and gold‐based catalysts for selective liquid‐phase oxidation of biomass‐derived products have been reviewed. Three important molecules, namely glucose, hydroxymethyl furfural (HMF) and glycerol have been considered as precursors for products of industrial interest. [ABSTRACT FROM AUTHOR]

The influence of the size and oxidation state of Au nanoparticles (AuNPs) as electrocatalysts for the electro-oxidation of cellulose was studied. Carbon paper electrodes modified with AuNPs were used as the electrocatalysts for the electro-oxidation of cellulose dissolved in 1.3 m NaOH. The size and oxidation state of the AuNPs were determined by using SEM, TEM, and X-ray photoelectron spectroscopy. Both the size and the oxidation state of the AuNPs were found to influence the electrocatalytic properties of the electrode, as studied by using cyclic voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy. The carbon paper electrodes decorated with AuNPs (less than 25 nm) that consist of metallic Au gave rise to a significantly higher electrocatalytic activity than a bare polycrystalline Au electrode. [ABSTRACT FROM AUTHOR]

Adipic acid (AA) is one of the highest volume chemicals in world use with a wide range of commercial applications. This paper demonstrates the possibility of producing significant proportions of AA by the selective oxidation of cyclohexane (CH) in one step using various supported gold-nanoparticle (AuNP) catalysts. The catalysts were characterized by ICP, BET, XRD, X-ray photoelectron microscopy, and TEM. The catalytic activity tests were carried out in the liquid phase using autoclaves in the temperature range of 100-170 °C at 10 bar. A CH conversion of over 25 %, with 26% selectivity of AA and 70% selectivity of KA oil (cyclohexanone+cyclohexanol), was achieved over a nano-gold/TiO2 (anatase) catalyst. The superior performance of this catalyst is attributed to the smaller size of AuNPs, which has an average particle size of 2 nm. Good correlation between activity and Au particle size could be achieved. Overall, the particle size of the AuNPs showed a strong influence on catalytic performance. [ABSTRACT FROM AUTHOR]

The cover picture shows puffball‐shaped, flavin‐functionalized, monolayer‐protected gold nanoparticles that efficiently catalyze aerobic transformations. In their Full Paper, Y. Imada, T. Naota and co‐workers describe the synthesis of PPh3‐protected gold clusters functionalized with cationic and neutral flavins, and their catalytic activities for the aerobic oxidation of sulfides and reduction of alkenes. Both the oxidation and reduction reactions proceed with high efficiency under atmospheric pressure in O2 or air and mild conditions. The advantages of the nanoparticle catalysts over conventional methods are discussed from synthetic and mechanistic viewpoints. The article highlighted by this cover can be found on p. 99 ff. of Issue 1, 2015. [ABSTRACT FROM AUTHOR]

The Cover shows an industrial landscape, where Au nanoparticles are used as catalysts for oxidation reactions.In their Full Paper, L. M. D. R. de Sousa Martins et al. demonstrate an efficient single‐pot oxidative functionalization of cyclohexane and benzyl and methylbenzyl alcohols under mild conditions with high selectivity, catalyzed by reusable Au nanoparticles on Al2O3, Fe2O3, ZnO, and TiO2. Au nanoparticles on Fe2O3 led to an unusual almost exclusive formation of cyclohexanol by control of reaction time, but Au nanoparticles on TiO2 had a remarkable catalytic effect on acetophenone yield. [ABSTRACT FROM AUTHOR]

Brown and gold The cover picture illustrates the concept of using gold nanoparticle‐decorated carbon nanotubes to directly electrochemically oxidize alginate—the principle, difficult‐to‐degrade component of brown macroalgae (as shown in the background of the cover picture). In their Full Paper on p. 135 ff., L. Q. Hoa, E. Tamiya et al. present analyses that suggest a reaction pathway similar to the chemical oxidation process by strong oxidants that results in oxidized alginate usable for cell and tissue engineering. This straightforward approach, in contrast to currently employed alginate‐metabolizing microbial approaches, can enhance the energy extraction efficiency of the whole biomass‐to‐energy conversion process through a fuel cell system without requiring any external energy, while simultaneously producing high‐value chemicals, paving the way for the future production of energy and feedstock materials from inedible biomass. [ABSTRACT FROM AUTHOR]

The cover picture shows the TEM pictures of new gold nanoparticles confined in the ORMOSIL matrix of SiliaCat Au catalyst as background, with superimposed reaction scheme for the model oxidation of 1‐phenylethanol with hydrogen peroxide. In their Full Paper, L. M. Ilharco, M. Pagliaro and co‐workers explain why and how this new catalyst series is ideally suited for the practical utilization of sol‐gel encapsulated gold nanoparticles in a number of different reactions. The catalyst has a huge surface area and has been extensively characterized. The article highlighted by this cover can be found on p. 254 ff. of Issue 2, 2015. [ABSTRACT FROM AUTHOR]

Selective oxidation The inside cover picture shows a mystique of TiO2‐supported Au nanoparticles as a photocatalyst for partial oxidations of organic substrates under sunlight irradiation and a CO2 atmosphere. In their Full Paper on p. 766 ff., Y. Ide et al. describe how the photocatalytic oxidation of aqueous phenol to hydroquinone on the catalyst under sunlight is modified to give a higher yield and selectivity if the reaction is conducted under a CO2 atmosphere. Au loading causes neither the visible light response nor the improved UV light‐induced charge separation efficiency of TiO2. A unique role of Au loading in the photocatalysis is proposed; Au nanoparticle loading drastically decreases the amount of the surface titanol, promoting the desorption of the product hydroquinone from the catalyst surface, especially if CO2 is present in the system. [ABSTRACT FROM AUTHOR]