Corrosion protection of aluminium alloy by cerium conversion and conducting polymer duplex coatings

The corrosion protection of AA6063 aluminium alloy by cerium conversion, polyaniline conducting polymer and by duplex coatings has been investigated. The electrochemical behaviour was evaluated in aerated 3.5 wt.% NaCl. All coatings tested shifted the corrosion and pitting potentials to more positive values, indicating protection against corrosion. The duplex coatings are significantly more effective than each coating alone: corrosion and pitting potentials were shifted by +183 and +417 mV(SCE), respectively, by duplex coatings in relation to the untreated aluminium alloy. Optical microscopy and scanning electron microscopy are in agreement with the electrochemical results, reinforcing the superior performance of duplex coatings. (C) 2012 Elsevier Ltd. All rights reserved.

Cerium metal- mediated Reformatsky-type reaction with ethyl bromosuccinate for the synthesis of novel paraconic acid analogs

The treatment of cerium metal with ethyl bromosuccinate (1) forms the stabilized organolanthanoid intermediate (2), which reacts with carbonyl compounds in a Reformatsky-type reaction, under mild conditions, to produce functionalized gamma-substituted paraconic acids (4) in good yields. (C) 2012 Elsevier Ltd. All rights reserved.

Sintering and Microwave Properties of Zirconium Tin Titanate Doped with Select Oxides

Zirconium tin titanate (ZST) is often used as a dielectric resonator for the fabrication of microwave devices. Pure compositions do not sinter easily by solid state sintering; therefore, sintering ZST requires sintering aids capable of creating defects that could improve diffusion processes and/or promote liquid phase sintering. The mechanisms by which the additives influence the microstructure and, consequently, the ZSTs dielectric properties are not very clear. The effects of ZnO, Bi2O3, and La2O3, on the stoichiometry and dielectric properties of ZST sintered at different temperatures were investigated in this study.

Anaerobic oxidation of ethanol over spinel mixed oxides: the first step in the steam-iron process for H2 production

The future hydrogen demand is expected to increase, both in existing industries (including upgrading of fossil fuels or ammonia production) and in new technologies, like fuel cells. Nowadays, hydrogen is obtained predominantly by steam reforming of methane, but it is well known that hydrocarbon based routes result in environmental problems and besides the market is dependent on the availability of this finite resource which is suffering of rapid depletion. Therefore, alternative processes using renewable sources like wind, solar energy and biomass, are now being considered for the production of hydrogen. One of those alternative methods is the so-called “steam-iron process” which consists in the reduction of a metal-oxide by hydrogen-containing feedstock, like ethanol for instance, and then the reduced material is reoxidized with water to produce “clean” hydrogen (water splitting). This kind of thermochemical cycles have been studied before but currently some important facts like the development of more active catalysts, the flexibility of the feedstock (including renewable bio-alcohols) and the fact that the purification of hydrogen could be avoided, have significantly increased the interest for this research topic. With the aim of increasing the understanding of the reactions that govern the steam-iron route to produce hydrogen, it is necessary to go into the molecular level. Spectroscopic methods are an important tool to extract information that could help in the development of more efficient materials and processes. In this research, ethanol was chosen as a reducing fuel and the main goal was to study its interaction with different catalysts having similar structure (spinels), to make a correlation with the composition and the mechanism of the anaerobic oxidation of the ethanol which is the first step of the steam-iron cycle. To accomplish this, diffuse reflectance spectroscopy (DRIFTS) was used to study the surface composition of the catalysts during the adsorption of ethanol and its transformation during the temperature program. Furthermore, mass spectrometry was used to monitor the desorbed products. The set of studied materials include Cu, Co and Ni ferrites which were also characterized by means of X-ray diffraction, surface area measurements, Raman spectroscopy, and temperature programmed reduction.

From polymer precursors to metal oxides

We report on a strategy to prepare metal oxides including binary oxide and mixed metal oxide (MMO) in form of nanometer-sized particles using polymer as precursor. Zinc oxide nanoparticles are prepared as an example. The obtained zinc polyacrylate precursor is amorphous as confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The conversion from polymer precursor to ZnO nanocrystals by thermal pyrolysis was investigated by means of XRD, thermogravimetric analysis (TGA) and electron microscopy. The as-synthesized ZnO consists of many individual particles with a diameter around 40 nm as shown by scanning electron microscopy (SEM). The photoluminescence (PL) and electron paramagnetic (EPR) properties of the material are investigated, too. Employing this method, ZnO nanocrystalline films are fabricated via pyrolysis of a zinc polyacrylate precursor film on solid substrate like silicon and quartz glass. The results of XRD, absorption spectra as well as TEM prove that both the ZnO nanopowder and film undergo same evolution process. Comparing the PL properties of films fabricated in different gas atmosphere, it is assigned that the blue emission of the ZnO films is due to crystal defect of zinc vacancy and green emission from oxygen vacancy. Two kinds of ZnO-based mixed metal oxide (Zn1-xMgxO and Zn1-xCoxO) particles with very precise stoichiometry are prepared by controlled pyrolysis of the corresponding polymer precursor at 550 oC. The MMO crystal particles are typically 20-50 nm in diameter. Doping of Mg in ZnO lattice causes shrinkage of lattice parameter c, while it remains unchanged with Co incorporation. Effects of bandgap engineering are seen in the Mg:ZnO system. The photoluminescence in the visible is enhanced by incorporation of magnesium on zinc lattice sites, while the emission is suppressed in the Co:ZnO system. Magnetic property of cobalt doped-ZnO is checked too and ferromagnetic ordering was not found in our samples. An alternative way to prepare zinc oxide nanoparticles is presented upon calcination of zinc-loaded polymer precursors, which is synthesized via inverse miniemulsion polymerization of the mixture of the acrylic acid and zinc nitrate. The as-prepared ZnO product is compared with that obtained from polymer-salt complex method. The obtained ZnO nanoparticles undergo surface modification via a phosphate modifier applying ultrasonication. The morphology of the modified particles is checked by SEM. And stability of the ZnO nanoparticles in aqueous dispersion is enhanced as indicated by the zeta-potential results.

In-situ DRIFT/MS study of the conversion of ethanol on mixed Mg/Si oxides

Due to the high price of natural oil and harmful effects of its usage, as the increase in emission of greenhouse gases, the industry focused in searching of sustainable types of the raw materials for production of chemicals. Ethanol, produced by fermentation of sugars, is one of the more interesting renewable materials for chemical manufacturing. There are numerous applications for the conversion of ethanol into commodity chemicals. In particular, the production of 1,3-butadiene whose primary source is ethanol using multifunctional catalysts is attractive. With the 25% of world rubber manufacturers utilizing 1,3-butadiene, there is an exigent need for its sustainable production. In this research, the conversion of ethanol in one-step process to 1,3-butadiene was studied. According to the literature, the mechanisms which were proposed to explain the way ethanol transforms into butadiene require to have both acid and basic sites. But still, there are a lot of debate on this topic. Thus, the aim of this research work is a better understanding of the reaction pathways with all the possible intermediates and products which lead to the formation of butadiene from ethanol. The particular interests represent the catalysts, based on different ratio Mg/Si in comparison to bare magnesia and silica oxides, in order to identify a good combination of acid/basic sites for the adsorption and conversion of ethanol. Usage of spectroscopictechniques are important to extract information that could be helpful for understanding the processes on the molecular level. The diffuse reflectance infrared spectroscopy coupled to mass spectrometry (DRIFT-MS) was used to study the surface composition of the catalysts during the adsorption of ethanol and its transformation during the temperature program. Whereas, mass spectrometry was used to monitor the desorbed products. The set of studied materials include MgO, Mg/Si=0.1, Mg/Si=2, Mg/Si=3, Mg/Si=9 and SiO2 which were also characterized by means of surface area measurements.

Glycerol oxidehydration to acrylic acid on complex mixed-metal oxides

The project of this Ph.D. thesis is based on a co-supervised collaboration between Università di Bologna, ALMA MATER STUDIORUM (Italy) and Instituto de Tecnología Química, Universitat Politècnica de València ITQ-UPV (Spain). This Ph.D. thesis is about the synthesis, characterization and catalytic testing of complex mixed-oxide catalysts mainly related to the family of Hexagonal Tungsten Bronzes (HTBs). These materials have been little explored as catalysts, although they have a great potential as multifunctional materials. Their peculiar acid properties can be coupled to other functionalities (e.g. redox sites) by isomorphous substitution of tungsten atoms with other transition metals such as vanadium, niobium and molybdenum. In this PhD thesis, it was demonstrated how it is possible to prepare substituted-HTBs by hydrothermal synthesis; these mixed-oxide were fully characterize by a number of physicochemical techniques such as XPS, HR-TEM, XAS etc. They were also used as catalysts for the one-pot glycerol oxidehydration to acrylic acid; this reaction might represent a viable chemical route to solve the important issue related to the co-production of glycerin along the biodiesel production chain. Acrylic acid yields as high as 51% were obtained and important structure-reactivity correlations were proved to govern the catalytic performance; only fine tuning of acid and redox properties as well as the in-framework presence of vanadium are fundamental to achieve noteworthy yields into the acid monomer. The overall results reported herein might represent an important contribution for future applications of HTBs in catalysis as well as a general guideline for a multifaceted approach for their physicochemical characterization.

Selective oxidation of 5-hydroxymethylfurfural using monometallic and bimetallic supported nanoparticles

This work deals with the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) using metal supported catalysts. Catalysts were prepared from the immobilisation of preformed monometallic (Au, Pd) and bimetallic (AuCu, AuPd) nanoparticles on commercial oxides (TiO2, CeO2). Au-TiO2 catalyst was found to be very active for HMF oxidation; however, this system deactivated very fast. For this reason, we prepared bimetallic gold-copper nanoparticles and an increase in the catalytic activity was observed together with an increase in catalyst stability. In order to optimise the interaction of the metal active phase with the support, Au and AuCu nanoparticles were supported onto CeO2. Au-CeO2 catalyst was found to be more active than the bimetallic one, leading to the conclusion that in this case the most important feature is the interaction between gold and the support. Catalyst pre-treatments (calcination and washing) were carried out to maximise the contact between the metal and the oxide and an increase in the FDCA production could be observed. The presence of ceria defective sites was crucial for FDCA formation. Mesoporous cerium oxide was synthesised with the hard template method and was used as support for Au nanoparticles to promote the catalytic activity. In order to study the role of active phase in HMF oxidation, PdAu nanoparticles were supported onto TiO2. Au and Pd monometallic catalysts were very active in the formation of HMFCA (5-hydroxymethyl-2-furan carboxylic acid), but Pd was not able to convert it, leading to a low FDCA yield. The calcination of PdAu catalysts led to Pd segregation on the particles surface, which changed the reaction pathway and included an important contribution of the Cannizzaro reaction. PVP protected PdAu nanoparticles, synthesised with different morphologies (core-shell and alloyed structure), confirmed the presence of a different reaction mechanism when the metal surface composition changes.

Synthese von grenzflächenaktiven Monomeren zur Herstellung von funktionalen Metall-Chalkogenid,Polymer-Hybridnanopartikeln

In dieser Arbeit wurde gezeigt, wie oberflächenfunktionalisierte Polystyrolnanopartikel zur Herstellung von Metallchalkogenid/Polymer-Hybridnanopartikeln eingesetzt werden können. Dazu wurden zunächst phosphonsäure- und phosphorsäurefunktionalisierte Surfmere synthetisiert, die anschließend bei der Miniemulsionspolymerisation von Styrol verwendet wurden. Die Surfmere dienten dabei zugleich zur Stabilisierung und als Comonomer. Die oberflächenfunktionalisierten Polystyrolnanopartikel wurden anschließend als Trägerpartikel für die Kristallisation von Metalloxiden eingesetzt. Dabei wurden Metalloxid/Polymer-Hybridnanopartikel mit einer „himbeerartigen“ Morphologie erhalten. Um die vielseitige Modifizierbarkeit der phosphonat- und phosphat¬funktionalisierten Polystyrolpartikel zu demonstrieren, wurden Cer-, Eisen- sowie Zinkoxid auf der Partikeloberfläche kristallisiert. Dazu wurden sowohl wässrige als auch alkoholische Metalloxid-Präkursorlösungen eingesetzt. Die synthetisierten Metall¬oxid/Polymer-Hybridpartikel wurden detailliert mit REM, TEM und PXRD analysiert. Die Untersuchung des Kristallisationsmechanismus hatte erwiesen, dass die komplexierten Metallkationen auf der Partikeloberfläche als Nukleationszentren wirkten und die Zutropfrate des Fällungsreagenz entscheidend für die Oberflächenkristallisation ist. Durch Mischungsexperimente von Metalloxidnanopartikeln und den oberflächen¬funktionalisierten Polymerpartikeln konnte die Hybridpartikelbildung über Hetero¬koagulation ausgeschlossen werden. Außerdem wurde festgestellt, dass die Polarität der funktionellen Gruppe über die Stärke der Komplexierung der Metalloxid-Präkursor bestimmt. Darüber hinaus wurde ein Modell zur Erklärung der kolloidalen Stabilisierung der Metalloxid/Polymer-Hybridsysteme aufgestellt und ein Zusammenhang zwischen dem gemessenen Zeta-Potential und der Oberflächenbedeckung der Polymerpartikel durch Metalloxid gefunden. Mit der Methode der Oberflächenkristallisation konnten frühe Stadien der Nukleation auf der Partikeloberfläche fixiert werden. Weiterhin wurden die individuellen physikalisch-chemischen Eigenschaften der hergestellten Metall¬oxid/Polymer-Hybridnano¬partikel untersucht. Dabei zeigten die CeO2/Polymer-Hybridpartikel eine hohe katalytische Aktivität bezüglich der photokatalytischen Oxidation von Rhodamin B, die als Modellreaktion durchgeführt wurde. Des Weiteren wurde die Magnetisierung der Magnetit/Polymer-Hybridpartikel gemessen. Die Fe3O4-Hybrid¬partikelsysteme wiesen eine vergleichbare Sättigungsmagnetisierung auf. Die Zinkoxid/Polymer-Hybridsysteme zeigten eine starke Lumineszenz im sichtbaren Bereich bei Anregung mit UV-Licht. Die Metalloxid/Polymer-Hybridpartikel, die mit den phosphonat- oder phosphatfunktion¬alisierten Polystyrolpartikeln hergestellt wurden, zeigten keine signifikanten Unterschiede in ihren physikochemischen Eigenschaften. Im Allgemeinen lässt sich schlussfolgern, dass sowohl Phosphonat- als auch Phosphatgruppen gleichermaßen für die Oberflächenkristallisation von Metalloxiden geeignet sind. Die Zink¬oxid/Polymer-Hybridsysteme stellen eine Ausnahme dar. Die Verwendung der phosphonat¬funktionalisierten Polystyrolpartikel führte zur Entstehung einer Zinkhydroxidphase, die neben der Zinkoxidphase gebildet wurde. Aufgrund dessen zeigten die ZnO/RPO3H2-Hybridpartikel eine geringere Lumineszenz im sichtbaren Bereich als die ZnO/RPO4H2-Hybridsysteme.rnDie Erkenntnisse, die bei der Oberflächenkristallisation von Metalloxiden gewonnen wurden, konnten erfolgreich auf Cadmiumsulfid übertragen werden. Dabei konnte Cadmiumsulfid auf der Oberfläche von phosphonatfunktionalisierten Polystyrolpartikeln kristallisiert werden. Mit Hilfe des RPO3H2-Surfmers konnten phosphonatfunktion¬alisierte Polystyrolpartikel mit superparamagnetischem Kern synthetisiert werden, die zur Herstellung von multifunktionalen CdS/Polymer-Hybridpartikeln mit Magnetitkern verwendet wurden. Die Kristallphase und die Oberflächenbedeckung der multi¬funktionalen Hybridsysteme wurden mit den CdS/Polymer-Hybridsystemen ohne magnetischen Kern verglichen. Dabei konnte nachgewiesen werden, dass in beiden Fällen Cadmiumsulfid in der Greenockit-Modifikation gebildet wurde. Die multifunktionalen CdS/Polymer-Hybridpartikel mit superparamagnetischem Kern konnten sowohl mit einem optischen als auch einem magnetischen Stimulus angeregt werden.rnrn

Synthesis of novel ribose-based thioimidate n-oxides

This work is based on the study of new synthetic paths to obtain thioimidate N-oxides (TINOs) from D-ribose and to study their reactivity with the purpose to obtain ketonitrones. TINOs, aren’t well known molecules, but these enantiomerically pure backbones could be valuable intermediates in the synthesis of novel ketonitrones which are key intermediates in the synthesis of iminosugars. TINOs were discovered from the study of glucoraphanin, a particular glucosinolate, that unexpectedly cyclized into a TINO after desulfatation, by a spontaneous intramolecular Michael addition. The first part of this work was to synthetize the TINO 3 from D-ribose 1. The key step was the desilylative cyclisation of a suitably functionalized thiohydroximate 2. Based on precedent work developed in the laboratory, we could obtain the thiohydroximate from D-ribose. We then focused our studies on the cyclisation step trying to find the suitable substituents that could give the TINO in good yield by desilylative cyclisation. The second part of the project is to obtain ketonitrones 4 by palladiumcatalyzed coupling reaction.

Cerium oxide nanoparticle uptake kinetics from the gas-phase into lung cells in vitro is transport limited

Nowadays, aerosol processes are widely used for the manufacture of nanoparticles (NPs), creating an increased occupational exposure risk of workers, laboratory personnel and scientists to airborne particles. There is evidence that possible adverse effects are linked with the accumulation of NPs in target cells, pointing out the importance of understanding the kinetics of particle internalization. In this context, the uptake kinetics of representative airborne NPs over 30 min and their internalization after 24 h post-exposure were investigated by the use of a recently established exposure system. This system combines the production of aerosolized cerium oxide (CeO(2)) NPs by flame spray synthesis with its simultaneous particle deposition from the gas-phase onto A549 lung cells, cultivated at the air-liquid interface. Particle uptake was quantified by mass spectrometry after several exposure times (0, 5, 10, 20 and 30 min). Over 35% of the deposited mass was found internalized after 10 min exposure, a value that increased to 60% after 30 min exposure. Following an additional 24 h post-incubation, a time span, after which adverse biological effects were observed in previous experiments, over 80% of total CeO(2) could be detected intracellularly. On the ultrastructural level, focal cerium aggregates were present on the apical surface of A549 cells and could also be localized intracellularly in vesicular structures. The uptake behaviour of aerosolized CeO(2) is in line with observations on cerium suspensions, where particle mass transport was identified as the rate-limiting factor for NP internalization.