Polymerization of ethylene by the tris(pyrazolyl)borate titanium(IV) compound immobilized on MAO-modified silicas

The immobilization of soluble catalyst {Tp(Ms)}TiCl3 (Tp(Ms*)HB(3-mesityl-pyrazolyl)(2)(5-mesityl-pyrazolyl)(-)) on silica and MAO-modified silicas containing 4.0, 8.0 and 23.0 wt.% Al/SiO2 yields active supported catalysts for ethylene polymerization. Among the supported catalysts studied by XRF spectroscopy, higher titanium content was obtained using MAO-modified silica containing 8.0 wt.% Al/SiO2 as support. For the ethylene polymerization reactions carried out in hexane at 60degreesC using a combination of triisobutylaluminum (TiBA) and methylaluminoxane (MAO) (1:1), the activities varied between 24.4 and 113.5 kg of PE/mol [Ti] h. The highest activity is reached using MAO-modified silica containing 4.0 wt.% Al/SiO2 as support. The viscosity-average molecular weights ((M) over bar (v)) of the PE's produced with the supported catalysts varying from 1.44 to 9.94 x 10(5) g/mol with melting temperatures in the range of 125-140degreesC. The use of other Lewis acid cocatalysts, including TiBA, diethylaluminium chloride (DEAC), and trimethylaluminum (TMA) resulted also in the formation of active catalysts for ethylene polymerization. However, the activities are lower than that one using a combination of TiBA and MAO. The viscosity-average molecular weights (R,) of PE's are influenced by varying the cocatalysts as well as the Al/Ti molar ratio. The supported catalyst generated in situ under ethylene atmosphere is roughly four times more active than supported one containing 4.0 wt.% Al/SiO2. (C) 2003 Elsevier B.V. All rights reserved.

Effect of the balance between Co(II) and Co(0) oxidation states on the catalytic activity of cobalt catalysts for Ethanol Steam Reforming

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Synthesis of Carbon Nanomaterials through Up-Cycling Agricultural and Municipal Solid Wastes

This work addresses the synthesis of carbon nanomaterials (CNMs) by up-cycling common solid wastes. These feedstocks could supersede the use of costly and often toxic or highly flammable chemicals, such as hydrocarbon gases, carbon monoxide, and hydrogen, which are commonly used as feedstocks in current nanomanufacturing processes for CNMs. Agricultural sugar cane bagasse and corn residues, scrap tire chips, and postconsumer polyethylene (PE) and polyethylene terephthalate (PET) bottle shreddings were either thermally treated by sole pyrolysis or by sequential pyrolysis and partial oxidation. The resulting gaseous carbon-bearing effluents were then channeled into a heated reactor. CNMs, including carbon nanotubes, were catalytically synthesized therein on stainless steel meshes. This work revealed that the structure of the resulting CNMs is determined by the feedstock type, through the disparate mixtures of carbon-bearing gases generated when different feedstocks are pyrolyzed. CNM characterization was conducted by scanning and transmission electron microscopy as well as by Raman spectroscopy and by thermogravimetric analysis. Gas chromatography was used to characterize the gases in the synthesis chamber. This work demonstrated an alternative method for efficient manufacturing of CNMs using both biodegradable and nonbiodegradable agricultural and municipal carbonaceous wastes.

Design of a Dinuclear Nickel(II) Bioinspired Hydrolase to Bind Covalently to Silica Surfaces: Synthesis, Magnetism, and Reactivity Studies

Presented herein is the design of a dinuclear Ni-II synthetic hydrolase [Ni-2(HBPPAMFF)(mu-OAc)(2)(H2O)]-BPh4 (1) (H(2)BPPAMFF = 2-[(N-benzyl-N-2-pyridylmethylamine)]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl)])-4- methyl-6-formylphenol) to be covalently attached to silica surfaces, while maintaining its catalytic activity. An aldehyde-containing ligand (H(2)BPPAMFF) provides a reactive functional group that can serve as a cross-linking group to bind the complex to an organoalkoxysilane and later to the silica surfaces or directly to amino-modified surfaces. The dinuclear Ni-II complex covalently attached to the silica surfaces was fully characterized by different techniques. The catalytic turnover number (k(cat)) of the immobilized (NiNiII)-Ni-II catalyst in the hydrolysis of 2,4-bis(dinitrophenyl)phosphate is comparable to the homogeneous reaction; however, the catalyst interaction with the support enhanced the substrate to complex association constant, and consequently, the catalytic efficiency (E - k(cat)/K-M) and the supported catalyst can be reused for subsequent diester hydrolysis reactions.

Rylenfarbstoffe in nanoskopischen Systemen

ZusammenfassungDurch die Funktionalisierung des Chromophors Tetraphenoxyperylendiimid mit vier Ethinylgruppen stand ein Farbstoff zur Verfügung, welcher sich als Kernmolekül für den Aufbau von Polyphenylendendrimeren eignet. Ausgehend von dem Farbstoffkern wurden drei Dendrimergenerationen synthetisiert. Durch die Dendronisierung wird die Aggregation des zentralen Farbstoffs im Festkörper verhindert, weshalb das G1-Dendrimer als aktive Schicht in LED´s eingesetzt wurde und zur Verbesserung dieser Bauelemente führte. Weiterhin wurde auch die Oberfläche der Polyphenylendendrimere mit 4, 8 bzw. 16 Perylenmonoimidfarbstoffen funktionalisiert. Durch zeitaufgelöste Absorptions- und Emissionsmessungen und Einzelmolekülspektroskopie des G2-Dendrimers wurde ein photophysikalisches Modell des multichromophoren Systems entwickelt.Neben Polyphenylendendrimeren dienten auch Emulsionspolymerisate, Miniemulsionspolymerisate und Halbleiterkristalle als nanoskopische Trägermaterialien für Rylenfarbstoffe. Für die Anknüpfung an Lartices wurden amino- und styrylfunktionalisierte Perylen- und Terrylenchromophore dargestellt, was zu einer statistischen Verteilung der Farbstoffe auf der Oberfläche bzw. im Inneren führte. Außerdem wurden Rylenfarbstoffe als stabile Fluoreszenzmarkierung von Metallocenkatalysatoren eingesetzt. Silica- und polymergeträgerte markierte Katalysatoren wurden zur Polymerisation von Ethylen verwendet und lieferten fluoreszente PE-Produkte, ohne Einfluß auf die Polymerisation zu nehmen. Zum Einen wurde mit Hilfe der Dotierung der heterogenen Polymerisationskatalysatoren der Verbleib des fragmentierten Trägermaterials in den PE-Produktpartikeln detektiert. Zum Anderen erlaubt der Einsatz unterschiedlich fluoreszierender Markierungsgruppen die Durchführung eines kombinatorischen Verfahrens zum Testen von Polymerisationskatalysatoren.

Herstellung und physikochemische Charakterisierung von planaren gestützten Lipid-Modellmembran-Systemen

Es wurden funktionalisierte polymerunterstützte planare Phospholipid-Modellmembran-Systeme hergestellt und auf jeder Präparationsstufe eingehend charakterisiert. Dünne Polysaccharidfilme wurden in der Form von quellbaren Gelen auf oxidische Oberflächen aufgebracht und bezüglich ihres Quellungsverhaltens und der Oberflächeneigenschaften in Abhängigkeit vom Wassergehalt untersucht. Lipidmonoschichten unterschiedlicher Zusammensetzung wurden mittels Langmuir-Blodgett-Tranfer auf Polymersubstrate übertragen und bezüglich der Stärke der Lipid/Polymer Wechselwirkung, der lateralen Selbstdiffusion in Abhängigkeit von der Wasseraktivität, dem Spreitverhalten der monomolekularen Membran auf dem Substrat in Abhängigkeit von der Wasseraktivität und dem Lateraldruck der Monoschicht, sowie des Ausmaßes der Hydratation im Kopfgruppenbereich der Lipidmembran in Abhängigkeit von der Wasseraktivität mittels Fluoreszensondenmethoden (Fluoreszenzerholung nach Photobleichung (FRAP), Fluoreszenzmikroskopie und Fluoreszenzspektroskopie) untersucht. Diffusions- und Spreitverhalten von amphiphilen Monoschichten auf Polymersubstraten wurden auf der Basis von in dieser Arbeit entwickelten physikalischen Modellen diskutiert. Mittels Langmuir-Schäfer Transfer wurde auf polymerunterstützte Lipidmonoschichten eine zweite Monoschicht übertragen. Die somit erhaltenen Lipid-Doppelschichtmembranen wurden bezüglich ihrer Stabilität, der lateralen Struktur, der lateralen Selbstdiffusion, des Spreitverhaltens auf unbedeckte Bereiche sowie der Stärke der Membran/Substrat Wechselwirkung vermittels Fluoreszenzmikroskopie, FRAP und Interferenz-Kontrast-Mikroskopie (RICM) untersucht. Schließlich wurden substratgestützte Doppelschicht-Lipidmembranen mit als Protonenpumpen fungierenden integralen Membranproteinen versehen. Die laterale Selbstdiffusion der rekonstituierten Proteinmoleküle wurde mittels FRAP, die funktionale Aktivität der Protonenpumpen mit einem Ionen-sensitiven Feldeffekttransistor-Array analysiert.

Synthese und Untersuchung von neuen Alpha,Omega-funktionalisierten Lipopolymeren zum Aufbau von polymerunterstützten Lipiddoppelschichten

Ziel dieser Arbeit war es hydrophile Lipopolymere darzustellen, mit denen es möglich sein sollte polymerunterstützte Lipiddoppelschichten auf festen Substratoberflächen zu fixieren. Die Polymere sollten einen Oberflächenanker, eine lipophile Gruppe und ein hydrophiles Polymerrückgrat enthalten. Hierzu wurden Alpha,Omega-funktionalisierte Polymere ausgehend von lipophilen Initiatoren dargestellt. Ausgehend von hydrophoben 2-Brompropionsäureamiden konnte eine kontrollierte radikalische Polymerisation (ATRP) von verschiedenen Acrylamiden durchgeführt werden. So wurden verschiedene Copolymere aus Acrylamid, N-Isopropylacrylamid und N-(3-Dimethylaminopropyl)-acrylamid synthetisiert. Der Einbau des Oberflächenankers als Funktionalität erfolgte indirekt durch Polymerisation eines N-Acryloxysuccinimid Endblocks, welcher in einer anschließenden polymeranalogen Reaktion mit Cysteaminmethyldisulfid umgesetzt wurde.In Ladungsuntersuchungen (PCD) konnte das pH-abhängige Verhalten der Polymere untersucht werden. Der Knäuelkollaps (LCST) der Poly-(N-isopropylacrylamide) wurde mittels Turbidimetrie und DSC charakterisiert. Die Adsorption der Polymere auf Goldoberflächen wurde mit Hilfe der Oberflächenplasmonen Spektroskopie (SPS) aus wässriger Lösung nachgewiesen werden. Dabei bildeten sich ultradünne Filme von 15-20 Å Dicke aus. Kontaktwinkelmessungen wiesen diesen adsorbierten Polymerfilmen ein sehr hydrophiles Verhalten nach. In Lösung adsorbierten die Polymere auf Vesikeloberflächen. Auf ultradünnen Polymerfilmen adsorbierten die Vesikel, wobei mit Hilfe der SPS eine Dickenzunahme um etwa 50 Å nachgewiesen werden konnte. Die ultradünnen Filme der Poly(N-isopropylacrylamide) wiesen eine temperaturabhängige Attraktivität gegenüber Vesikeln auf. Durch gezielte Polystyrol-Entnetzung konnten strukturierte Träger erhalten werden.

Electrospinning of silica sub-microtubes mats with platinum nanoparticles for NO catalytic reduction

Silica sub-microtubes loaded with platinum nanoparticles have been prepared in flexible non-woven mats using co-axial electrospinning technique. A partially gelated sol made from tetraethyl orthosilicate was used as the silica precursor, and oil was used as the sacrificial template for the hollow channel generation. Platinum has been supported on the wall of the tubes just adding the metallic precursor to the sol–gel, thus obtaining the supported catalyst by one-pot method. The silica tubes have a high aspect ratio with external/internal diameters of 400/200 nm and well-dispersed platinum nanoparticles of around 2 nm. This catalyst showed a high NO conversion with very high selectivity to N2 at mild conditions in the presence of excess oxygen when using C3H6 as reducing agent. This relevant result reveals the potential of this technique to produce nanostructured catalysts onto easy to handle conformations.

Ni-CeO2/C Catalysts with Enhanced OSC for the WGS Reaction

In this work, the WGS performance of a conventional Ni/CeO2 bulk catalyst is compared to that of a carbon-supported Ni-CeO2 catalyst. The carbon-supported sample resulted to be much more active than the bulk one. The higher activity of the Ni-CeO2/C catalyst is associated to its oxygen storage capacity, a parameter that strongly influences the WGS behavior. The stability of the carbon-supported catalyst under realistic operation conditions is also a subject of this paper. In summary, our study represents an approach towards a new generation of Ni-ceria based catalyst for the pure hydrogen production via WGS. The dispersion of ceria nanoparticles on an activated carbon support drives to improved catalytic skills with a considerable reduction of the amount of ceria in the catalyst formulation.

Enantioselective Solvent-Free Synthesis of 3-Alkyl-3-hydroxy-2-oxoindoles Catalyzed by Binam-Prolinamides

BINAM-prolinamides are very efficient catalyst for the synthesis of non-protected and N-benzyl isatin derivatives by using an aldol reaction between ketones and isatins under solvent-free conditions. The results in terms of diastereo- and enantioselectivities are good, up to 99% de and 97% ee, and higher to those previously reported in the literature under similar reaction conditions. A high variation of the results is observed depending on the structure of the isatin and the ketone used in the process. While 90% of ee and 97% ee, respectively, is obtained by using (Ra)-BINAM-l-(bis)prolinamide as catalyst in the addition of cyclohexanone and α-methoxyacetone to free isatin, 90% ee is achieved for the reaction between N-benzyl isatin and acetone using N-tosyl BINAM-l-prolinamide as catalyst. This reaction is also carried out using a silica BINAM-l-prolinamide supported catalyst under solvent-free conditions, which can be reused up to five times giving similar results.

Zr-Laponite pillared clay-based nickel catalysts for methane reforming with carbon dioxide

Zr-Laponite pillared clays were prepared and used as supports of nickel catalysts for the methane reforming reaction with carbon dioxide to synthesis gas. The structural and textural characteristics of supports and catalysts were systematically examined by N-2 adsorption/desorption and X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron spectroscopy (TEM) techniques. The catalytic performance and carbon deposition were investigated. It is found that Zr-Laponite pillared clays are promising catalyst supports for carbon dioxide reforming of methane. The pore structure and surface properties of such supports greatly affect the catalytic behaviors of catalysts derived. Carbon deposition on catalysts was also affected by the property and structure of supports. The sintering of nickel metal and zirconia was another factor responsible for catalyst deactivation. This new-type nickel supported catalyst Ni/Zr-Laponite(8), with well-developed porosity, gave a higher initial conversion and a relatively long-term stability, and is therefore a promising catalyst for potential application to carbon dioxide reforming of methane to synthesis gas. (C) 2002 Elsevier Science B.V All rights reserved.

Synthesis and characterization of turbostratic carbons prepared by catalytic chemical vapour decomposition of acetylene

The turbostratic mesoporous carbon blacks were prepared by catalytic chemical vapour decomposition (CCVD) of acetylene using Ni/MgO catalysts prepared by co-precipitation. The relationship between deposition conditions and the nanostructures of resultant carbon black materials was investigated. It was found that the turbostratic and textural structures of carbon blacks are dependent on the deposition temperature and nickel catalyst loading. Higher deposition temperature increases the carbon crystallite unit volume V-nano and reduces the surface area of carbon samples. Moreover, a smaller V-nano is produced by a higher Ni loading at the same deposition temperature. In addition of the pore structure and the active metal surface area of the catalyst, the graphitic degree or electronic conductivity of the carbon support is also a key issue to the activity of the supported catalyst. V-nano is a very useful parameter to describe the effect of the crystalline structure of carbon blacks on the reactivity of carbon blacks in oxygen-carbon reaction and the catalytic activity of carbon-supported catalyst in ammonia decomposition semi-quantitatively. (C) 2006 Elsevier B.V. All rights reserved.

Hypervalent iodine in synthesis. 90. A mild and efficient method for the iodination of pyrazoles

The combined reagent of iodobenzene diacetate (or polymer-supported iodobenzene diacetate) with iodine was used as an effective iodinating agent of pyrazoles to the corresponding 4-iodopyrazole derivatives at room temperature with high yields.

Hypervalent iodine in synthesis 91: a mild and efficient method for the halogenation of 6-methyluracil derivatives

The combined reagent of iodobenzene diacetate (or polymer-supported iodobenzene diacetate) with iodine or bromine was used as an effective halogenative agent of 6-methyluracil derivatives to the corresponding 5-halo-6-methyluracil derivatives at room temperature with high yields.

On-chip immunoprecipitation for protein purification

Immunoprecipitation (IP) is one of the most widely used and selective techniques for protein purification. Here, a miniaturised, polymer-supported immunoprecipitation (µIP) method for the on-chip purification of proteins from complex mixtures is described. A 4 µl PDMS column functionalised with covalently bound antibodies was created and all critical aspects of the µIP protocol (antibody immobilisation, blocking of potential non-specific adsorption sites, sample incubation and washing conditions) were assessed and optimised. The optimised µIP method was used to obtain purified fractions of affinity-tagged protein from a bacterial lysate.