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Steinfeldt N.,Leibniz Institute for Catalysis at the University of Rostock
Langmuir | Year: 2012

The temporal evolution of Pt nanoparticle formation in ethylene glycol solution from H2PtCl6·6H2O at 90 °C for different molar ratios of NaOH to Pt (84, 6.5, and 2) in the presence or absence of poly(N-vinyl-2-pyrrolidone) (PVP) as protecting agent was followed in situ by small-angle X-ray scattering (SAXS). The SAXS profiles were analyzed regarding particle size and size distribution using the Guinier approximation and the indirect Fourier transform technique (IFT). The NaOH to Pt ratio has an influence on the integral nanoparticle formation rate as well as on the metal reduction rate and the ratio of nucleation to growth reactions. The fastest nanoparticle formation rate was observed for the NaOH/Pt ratio of 6.5. The obtained results indicate that the differences in the particle formation rate might be due to differences in the reduction rate of the formed Pt complexes. In alkaline reaction media (NaOH/Pt = 84 or 6.5), small nanoparticles with a relatively narrow size distribution were formed. Therefore, it is assumed that for these NaOH/Pt ratios the particle formation is dominated by nucleation reactions. Additionally, the in situ studies point out that nanoparticles prepared at the NaOH/Pt ratio of 84 do not grow further after attaining a certain particle size. For a NaOH to Pt ratio of 2, that means in acidic medium, particle formation should be dominated by growing processes and, therefore, larger particles are formed accompanied by a broader particle size distribution. The influence of PVP on the nanoparticle formation rate is relatively low. However, in acidic medium, the presence of PVP is necessary in order to protect the formed nanoparticles from irreversible aggregation reactions. © 2012 American Chemical Society. Source


Tlili A.,Leibniz Institute for Catalysis at the University of Rostock | Billard T.,CNRS Institute of Molecular and Supramolecular Chemistry and Biochemistry
Angewandte Chemie - International Edition | Year: 2013

Modern chemistry with an old substituent: The introduction of the SCF 3 group into organic substrates is a challenging task because of harsh or specific synthetic methods. However, recent advances in the formation of C-SCF3 bonds include the trifluoromethylthiolation with transition-metal-free systems or in the presence of palladium, nickel, or copper catalysts (see scheme). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Bruckner A.,Leibniz Institute for Catalysis at the University of Rostock
Chemical Society Reviews | Year: 2010

Electron Paramagnetic Resonance (EPR) offers widespread opportunities for monitoring catalytically relevant species that contain unpaired electrons under conditions close to those of heterogeneous catalytic gas and liquid phase reactions. In this tutorial review, after introducing basic theoretical and experimental principles of the technique, selected examples of typical applications are discussed that comprise (1) transition metal ions in paramagnetic valence states such as vanadium, (2) radical anions such as O - formed on oxide surfaces and (3) electrons in ferromagnetic particles such as nickel as well as in conduction bands of organic conductors such as polyaniline. © 2010 The Royal Society of Chemistry. Source


Bentrup U.,Leibniz Institute for Catalysis at the University of Rostock
Chemical Society Reviews | Year: 2010

Several in situ techniques are known which allow investigations of catalysts and catalytic reactions under real reaction conditions using different spectroscopic and X-ray methods. In recent years, specific set-ups have been established which combine two or more in situ methods in order to get a more detailed understanding of catalytic systems. This tutorial review will give a summary of currently available set-ups equipped with multiple techniques for in situ catalyst characterization, catalyst preparation, and reaction monitoring. Besides experimental and technical aspects of method coupling including X-ray techniques, spectroscopic methods (Raman, UV-vis, FTIR), and magnetic resonance spectroscopies (NMR, EPR), essential results will be presented to demonstrate the added value of multitechnique in situ approaches. A special section is focussed on selected examples of use which show new developments and application fields. © 2010 The Royal Society of Chemistry. Source


Franke R.,Evonik Industries | Franke R.,Ruhr University Bochum | Selent D.,Leibniz Institute for Catalysis at the University of Rostock | Borner A.,Leibniz Institute for Catalysis at the University of Rostock | Borner A.,University of Rostock
Chemical Reviews | Year: 2012

Special reviews were dedicated to spectroscopic aspects of catalysts and catalytic intermediates. In 2008, Haumann and Riisager summarized recent developments in the area of hydroformylation in room-temperature ionic liquids (RTIL). Especially the production of high-boiling aldehydes or alcohols from long-chain and branched olefins remains a domain of cobalt catalysis. There are still some patent activities in this area from Shell, which indicates a renewed interest. One of the main differences between all of these large-scale rhodium-catalyzed hydroformylations is the technology used to separate the product and the catalyst with the aim of reusing the metal. The lifetime of a catalyst charge may exceed 1 year under the condition that sufficient purity of the feed and careful process control is guaranteed. Source

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