Dang Sheng Su,*,†,‡ Siglinda Perathoner, and Gabriele Centi* †Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110006, China ‡Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany Dipartimento di Ingegneria Elettronica, Chimica ed Ingegneria Industriale, University of Messina and INSTM/CASPE (Laboratory of Catalysis for Sustainable Production and Energy), Viale Ferdinando Stagno, D’Alcontres 31, 98166 Messina, Italy

Nanocarbons for the Development of Advanced Catalysts

Nanotechnology is providing new solutions and opportunities to ensure sustainable energy and environments for the future. Materials of nanofiberous morphology are attractive to solve numerous energy and environmental issues. Nanofibers can be effectively produced by electrospinning, which is a simple and low cost technique. In addition, electrospinning allows the production of nanofibers from various materials e.g. organics and inorganics in different configurations and assemblies. This is highly beneficial for energy devices, where inorganic materials especially metal oxides can be synthesized and electrospun, improving conducting and ceramic properties. Excitonic solar cells fabricated with aligned nanofiberous metal oxide electrodes provide higher solar–electric energy conversion efficiency, whereas fuel cells made with nanofiberous electrodes enable uniform dispersion of catalysts, and thus increase electrocatalytic activity to obtain higher chemical–electric energy conversion efficiency. The nanofibers used in filtration membranes for environmental remediation, minimize the pressure drop and provide better efficiency than conventional fiber mats. The large surface area-to-volume ratio of nanofiber membranes allows greater surface adsorption of contaminants from air and water, and increases the life-time of the filtration media. This review highlights the potential and application of electrospun nanofiberous materials for solving critical energy and environmental issues.

Electrospun nanofibers in energy and environmental applications

A simple and convenient method has been demonstrated for large-scale synthesis of metal oxide (including TiO2, SnO2, In2O3, and PbO) nanowires with diameters around 50 nm and lengths up to 30 µm. In a typical procedure, tetraalkoxyltitanium, Ti(OR)4
				(with R =
				–C2H5, –iso-C3H7, or –n-C4H9), was added to ethylene glycol and heated to 170 °C for 2 h under vigorous stirring. The alkoxide was transformed into a chain-like, glycolate complex that subsequently crystallized into uniform nanowires. Similarly, nanowires made of tin glycolate were synthesized by refluxing SnC2O4·2H2O in ethylene glycol at 195 °C for 2 h, and nanowires consisting of indium and lead glycolates were prepared by adding In(OOCC7H15)(OiPr)2 and Pb(CH3COO)2 to ethylene glycol, followed by heating at 170 °C for 2 h. The nanowires could be readily collected as precipitates after the reaction solutions had been cooled down to room temperature. By calcining at elevated temperatures, each glycolate precursor could be transformed into the corresponding metal oxide without changing the wire-like morphology. Electron microscopic and XRD powder diffraction studies were used to characterize the morphology, crystallinity, and structure of these nanowires before and after calcination at various temperatures. A plausible mechanism was also proposed to account for the one-dimensional growth of such nanostructures in a highly isotropic medium. This mechanism was supported by XRD, FT-IR, solid state 13C-NMR, and TGA measurements. As a demonstration of potential applications, the polycrystalline nanowires made of SnO2 were used as functional components to fabricate sensors that could detect combustible gases (CO and H2) with greatly enhanced sensitivity under ambient conditions.

Ethylene glycol-mediated synthesis of metal oxide nanowires

Crystalline porous materials are important in the development of catalytic systems with high scientific and industrial impact. Zeolites, ordered mesoporous silica, and metal-organic frameworks (MOFs) are three types of porous materials that can be used as heterogeneous catalysts. This review focuses on a comparison of the catalytic activities of zeolites, mesoporous silica, and MOFs. In the first part of the review, the distinctive properties of these porous materials relevant to catalysis are discussed, and the corresponding catalytic reactions are highlighted. In the second part, the catalytic behaviors of zeolites, mesoporous silica, and MOFs in four types of general organic reactions (acid, base, oxidation, and hydrogenation) are compared. The advantages and disadvantages of each porous material for catalytic reactions are summarized. Conclusions and prospects for future development of these porous materials in this field are provided in the last section. This review aims to highlight recent research advancements in zeolites, ordered mesoporous silica, and MOFs for heterogeneous catalysis, and inspire further studies in this rapidly developing field.

Heterogeneous Catalysis in Zeolites, Mesoporous Silica, and Metal-Organic Frameworks.

Recent progress in synthesis, properties and potential applications of SiC nanomaterials

Two main innovations are presented in this article. (1) The first reproducible synthesis of silicon carbide nanotubes of different internal and external diameters. The method used, the shape memory synthesis, is based on the gas‐solid reaction between a vapor of SiO and nanotubes of carbon for the high diameters, and nanofibers of carbon for the small diameters. (2) A significant increase in the rate of a catalytic reaction (oxidation of H2S in S) probably due to a microscopic increase of the partial pressure of H2S inside the nanotubes, produced by condensation and microcapillarity, while the macroscopic partial pressure outside the tubes remains unchanged. This phenomenon could be extended to many other reactions, with polar gaseous reactants which are prone to condensation by capillarity at the usual temperatures of catalytic reaction, or with liquid phase reaction by an overconcentration of one of the reactants inside the tubes. c ∞ 2001 Academic Press

RESEARCH NOTE The First Preparation of Silicon Carbide Nanotubes by Shape Memory Synthesis and Their Catalytic Potential

The influence of different parameters (temperature, duration and SiO source) on the synthesis of silicon carbide SiC according to the gas-solid reaction between SiO vapors and activated charcoal was investigated. The material obtained retained the general shape of the activated charcoal, which is an advantage because of the difficulty in post shaping SiC, due to the high strength of the material. High temperature (>1250 °C) and long reaction duration led to a high C* → SiC conversion but with a relatively low surface area (20–25 m2 · g−1) due to sintering via the surface diffusion phenomenon. The combination of a lower reaction temperature (1200 °C), longer reaction duration (15 h) and high (Si + SiO2)/C* weight ratio allowed SiC to be obtained with a surface area of around 50 m2 · g−1, which can be used as a support material for heterogeneous catalysis.

Influence of the preparation conditions on the synthesis of high surface area SiC for use as a heterogeneous catalyst support

Electrocatalytic performances of nanostructured platinum–carbon materials

Gallium containing SBA-15 mesoporous materials with different Si/Ga ratio were synthesized using an in situ sol–gel procedure with an aqueous solution of Ga(NO 3 ) 3 . The materials were characterised by means of elemental analysis, BET, XRD, TEM, and H/D isotope exchange techniques. It appears that depending their loading, stable Ga-species were either anchored to the siliceous matrix of SBA-15 or introduced in the framework via isomorphous substitution, thus generating acid properties in their host material. The catalytic activity of Ga-SBA-15 materials has been evaluated in the Friedel–Crafts acylation of anisole with benzoyl chloride and in the alkylation of benzene using benzyl chloride as alkylating agent. The activity of these catalysts was compared with the one of Ga-modified SBA-15 by post-treatment. A complete conversion of benzyl chloride over Ga-SBA-15 materials has been reached after 3 h of reaction with a 75% selectivity toward diphenylmethane. In contrast to Ga-samples prepared by post-treatment, in situ Ga-SBA-15 present a lower stability in the acylation reaction. However, the catalytic results indicate that Ga-SBA-15 mesoporous materials can be used as versatile and stable acid catalysts for Friedel–Crafts reactions with appropriate behavior depending on their preparation mode.

One-pot synthesis of Ga-SBA-15 : Activity comparison with Ga-post-treated SBA-15 catalysts

Method for producing heavy metal carbides with high specific surface area, characterized in that a gas compound of said metal is reacted with a reactive carbon of high specific surface area of at least 200 m2g-1 at a temperature comprised between 900°C and 1,400°C, and carbides thus produced.

Cuong Pham-Huu

Papers

RESEARCH NOTE The First Preparation of Silicon Carbide Nanotubes by Shape Memory Synthesis and Their Catalytic Potential

Influence of the preparation conditions on the synthesis of high surface area SiC for use as a heterogeneous catalyst support

Electrocatalytic performances of nanostructured platinum–carbon materials

One-pot synthesis of Ga-SBA-15 : Activity comparison with Ga-post-treated SBA-15 catalysts

Production of heavy metal carbides of high specific surface area