Advances in the development of novel cobalt Fischer-Tropsch catalysts for synthesis of long-chain hydrocarbons and clean fuels.

This review analyses the literature from the early 1990s until the beginning of 2003 and covers the use of carbon nanotubes (CNT) and nanofibers as catalysts and catalysts supports. The article is composed of three sections, the first one explains why these materials can be suitable for these applications, the second describes the different preparation methods for supporting metallic catalysts on these supports, and the last one details the catalytic results obtained with nanotubes or nanofibers based catalysts. When possible, the results were compared to those obtained on classical carbonaceous supports and explanations are proposed to clarify the different behaviors observed.

Carbon nanotubes and nanofibers in catalysis

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

Transparent conductors as solar energy materials: A panoramic review

The chemistry of copper is extremely rich because it can easily access Cu0, CuI, CuII, and CuIII oxidation states allowing it to act through one-electron or two-electron processes. As a result, both radical pathways and powerful two-electron bond forming pathways via organmetallic intermediates, similar to those of palladium, can occur. In addition, the different oxidation states of copper associate well with a large number of different functional groups via Lewis acid interactions or π-coordination. In total, these feature confer a remarkably broad range of activities allowing copper to catalyze the oxidation and oxidative union of many substrates.

Oxygen is a highly atom economical, environmentally benign, and abundant oxidant, which makes it ideal in many ways.1 The high activation energies in the reactions of oxygen require that catalysts be employed.2 In combination with molecular oxygen, the chemistry of copper catalysis increases exponentially since oxygen can act as either a sink for electrons (oxidase activity) and/or as a source of oxygen atoms that are incorporated into the product (oxygenase activity). The oxidation of copper with oxygen is a facile process allowing catalytic turnover in net oxidative processes and ready access to the higher CuIII oxidation state, which enables a range of powerful transformations including two-electron reductive elimination to CuI. Molecular oxygen is also not hampered by toxic byproducts, being either reduced to water, occasionally via H2O2 (oxidase activity) or incorporated into the target structure with high atom economy (oxygenase activity). Such oxidations using oxygen or air (21% oxygen) have been employed safely in numerous commodity chemical continuous and batch processes.3

However, batch reactors employing volatile hydrocarbon solvents require that oxygen concentrations be kept low in the head space (typically <5–11%) to avoid flammable mixtures, which can limit the oxygen concentration in the reaction mixture.4,5,6 A number of alternate approaches have been developed allowing oxidation chemistry to be used safely across a broader array of conditions. For example, use of carbon dioxide instead of nitrogen as a diluent leads to reduced flammability.5 Alternately, water can be added to moderate the flammability allowing even pure oxygen to be employed.6 New reactor designs also allow pure oxygen to be used instead of diluted oxygen by maintaining gas bubbles in the solvent, which greatly improves reaction rates and prevents the build up of higher concentrations of oxygen in the head space.4a,7 Supercritical carbon dioxide has been found to be advantageous as a solvent due its chemical inertness towards oxidizing agents and its complete miscibility with oxygen or air over a wide range of temperatures.8 An number of flow technologies9 including flow reactors,10 capillary flow reactors,11 microchannel/microstructure structure reactors,12 and membrane reactors13 limit the amount of or afford separation of hydrocarbon/oxygen vapor phase thereby reducing the potential for explosions.

Enzymatic oxidizing systems based upon copper that exploit the many advantages and unique aspects of copper as a catalyst and oxygen as an oxidant as described in the preceding paragraphs are well known. They represent a powerful set of catalysts able to direct beautiful redox chemistry in a highly site-selective and stereoselective manner on simple as well as highly functionalized molecules. This ability has inspired organic chemists to discover small molecule catalysts that can emulate such processes. In addition, copper has been recognized as a powerful catalyst in several industrial processes (e.g. phenol polymerization, Glaser-Hay alkyne coupling) stimulating the study of the fundamental reaction steps and the organometallic copper intermediates. These studies have inspiried the development of nonenzymatic copper catalysts. For these reasons, the study of copper catalysis using molecular oxygen has undergone explosive growth, from 30 citations per year in the 1980s to over 300 citations per year in the 2000s.

A number of elegant reviews on the subject of catalytic copper oxidation chemistry have appeared. Most recently, reviews provide selected coverage of copper catalysts14 or a discussion of their use in the aerobic functionalization of C–H bonds.15 Other recent reviews cover copper and other metal catalysts with a range of oxidants, including oxygen, but several reaction types are not covered.16 Several other works provide a valuable overview of earlier efforts in the field.17 This review comprehensively covers copper catalyzed oxidation chemistry using oxygen as the oxidant up through 2011. Stoichiometric reactions with copper are discussed, as necessary, to put the development of the catalytic processes in context. Mixed metal systems utilizing copper, such as palladium catalyzed Wacker processes, are not included here. Decomposition reactions involving copper/oxygen and model systems of copper enzymes are not discussed exhaustively. To facilitate analysis of the reactions under discussion, the current mechanistic hypothesis is provided for each reaction. As our understanding of the basic chemical steps involving copper improve, it is expected that many of these mechanisms will evolve accordingly.

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Aerobic Copper-Catalyzed Organic Reactions

The physical principles of XAFS spectroscopy are given at a sufficiently basic level to enable scientists working in the field of catalysis to critically evaluate articles dealing with XAFS studies on catalytic materials. The described data-analysis methods provide the basic tools for studying the electronic and structural properties of supported metal, metal–oxide or metal–sulfide catalysts. These methods include (a) fitting in R-space, (b) application of the difference file technique and (c) control of the fit procedure with k
 1 and k
 3 weighting with the help of phase- and amplitude-corrected Fourier transforms.

/pdf/xafs-spectroscopy-fundamental-principles-and-data-analysis-41fu5eskk3.pdf

XAFS spectroscopy; fundamental principles and data analysis

Carbon nanofibres of the fishbone and parallel types were surface-oxidised by several methods. The untreated and oxidised fibres were studied with infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy (XPS). Oxidation in a mixture of concentrated nitric and sulfuric acids proved to be the most effective method for creating oxygen-containing surface groups. This treatment results not only in the formation of carboxy and carboxyic anhydride groups, but also in the generation of ether-type oxygen groups between graphitic layers that are puckered at their edges. The IR spectroscopic data clearly show that the formation of oxygen-containing surface groups occurs at defect sites on the carbon nanofibres and that oxidation proceeds via carbonyl groups and other oxides to carboxy and carboxyic anhydride groups. Owing to the presence of defects, the two types of fibre have similar surface reactivities. With parallel nanofibres, in contrast to fishbone fibres, the macroscopic structure was severely affected by treatment with HNO(3)/H(2)SO(4). The HNO(3)/H(2)SO(4)-treated fibres are highly wettable by water.

/pdf/surface-oxidation-of-carbon-nanofibres-2lhrrcizpo.pdf

Surface oxidation of carbon nanofibres

http://www.eng.uc.edu/~beaucag/Research/050913_ArgonneWorkshop/GoldParticlesonSupport/depositonzeolites2001.pdf

Preparation of Highly Dispersed Pt Particles in Zeolite Y with a Narrow Particle Size Distribution : Characterization by Hydrogen Chemisorption, TEM, EXAFS Spectroscopy, and Particle Modeling

http://www.anorg.chem.uu.nl/PDF/g98kunk.pdf

Zeolite Beta: The Relationship Between Calcination Procedure, Aluminum Configuration and Lewis Acidity

A 27Al 3Q MAS, a quantitative 27Al MAS, and a 29Si MAS NMR study has been carried out on La(x)NaY and H-USY. Assignment of the different types of Al coordinations has been done using the results of the MQ MAS experiments. The 29Si MAS and 27Al MAS NMR results obtained at high fields (14.1 T) and fast MAS up to 27 kHz made a quantitative assignment possible of the framework and nonframework Al coordinations. It is shown that highly charged octahedrally coordinated extraframework Al causes a polarization inducing a quadrupolar broadening of part of the framework Al in ultrastable Y. A similar interaction is found for the framework of La(x)NaY due to the La3+ cations. In both cases, charged extraframework species polarize the framework Al. In La(x)NaY, La3+ in a cation position and in H-USY extraframework octahedral Al are the origin of the polarization. Besides this short-range polarization effect, an additional long-range effect is observed in La(x)NaY. This long-range geometrical effect causes an increase...

Changes in Structural and Electronic Properties of the Zeolite Framework Induced by Extraframework Al and La in H-USY and La(x)NaY: A 29Si and 27Al MAS NMR and 27Al MQ MAS NMR Study

D.C. Koningsberger

Papers

XAFS spectroscopy; fundamental principles and data analysis

Surface oxidation of carbon nanofibres

Preparation of Highly Dispersed Pt Particles in Zeolite Y with a Narrow Particle Size Distribution : Characterization by Hydrogen Chemisorption, TEM, EXAFS Spectroscopy, and Particle Modeling

Zeolite Beta: The Relationship Between Calcination Procedure, Aluminum Configuration and Lewis Acidity

Changes in Structural and Electronic Properties of the Zeolite Framework Induced by Extraframework Al and La in H-USY and La(x)NaY: A 29Si and 27Al MAS NMR and 27Al MQ MAS NMR Study