Nanosized polymer carriers for metallocene catalysts in heterogeneous olefin polymerization

Das Ziel der vorgelegten Arbeit war die Synthese von definierten, sphärischen Polystyrolpartikeln im Größenbreichen von Nanometern, die als Träger für die Immobilisierung von Metallocenkatalysatoren verwendet werden sollten. Ein wichtiger Anspruch an das System war dabei die Möglichkeit einer homogene Verteilung des Metallocenes auf dem Träger and eine homogene Fragmentierung des geträgerten Katalysators während der Polymerisation im Polymerprodukt. Für diese Zielsetzung wurden unterschiedliche Polystyrolnanopartikel hergestellt. Die Polystyrolnanopartikel waren mit unterschiedlichen funktionellen Gruppen wie Polyethylenoxid- und Polypropylenoxidketten oder Hydroxygruppen auf der Oberfläche versehen, um den Metallocenkatalysator und den Cokatalysator MAO immobilisieren zu können. In verschiedenen Experimenten wurde der Einfluss dieser Polystyrolnanopartikel als Träger auf die Katalysatoreigenschaften wie Aktivität oder Produktivität und die Eigenschaften des produzierten Polyolefins wie z.B. Molekulargewicht und Morphologie untersucht. Im Vergleich zu den PS- Nanopartikeln wurden außerdem PS-Mikropartikel, Silica und Dendrimere als Träger in der heterogenen Olefinpolymerisation eingesetzt. Von all diesen Trägersystemen wurde das Fragmentierungsverhalten durch konfocale Fluoreszenzmikroskopie untersucht. Aus den erhaltenen Ergebnissen kann geschlossen werden, dass die hergestellten Polystyrolnanopartikel neuartige und leistungsfähige Träger für heterogene Polymerisationsprozesse darstellen. Die hergestellten Polystyrolnanopartikel besaßen eine wohldefinierte sphärische Struktur, die eine homogene Verteilung des immobilisierten Metallocenkatalysators und somit auch eine vollständige Fragmentierung des geträgerten Katalysators im hergestellten Polyolefin ermöglichte. Die Katalysatorsysteme, die aus den PS- Nanopartikeln und dem Metallocenkatalysator zusammengesetzt waren, wurden in verschiedenen Polymerisationen wie der Ethylen- oder Propylenhomopolymersation und der Copolymerisation von Ethen mit α- Olefinen getestet. Die Oberflächen- funktionalisierten PS Nanopartikel immobilisierten den Metallocenkatalysator ausreichend gut, so dass kein „Leachen“ (Ablösen) des Katalysators von der Trägeroberfläche festgestellt werden konnte und deshalb Polymer von sehr guter Morphologie erhalten wurde. Um die Fragmentierung des Katalysators und den inneren Aufbau des Polymers näher untersuchen zu können, wurde die konfocale Fluoreszenzmikroskopie für das PS- Nanopartikelträgersystem angewendet. Durch farbstoffmarkierte Trägerpartikel konnte die Verteilung des fragmentierten Katalysators innerhalb des Polymers sichtbar gemacht und analysiert werden. Dabei wurde festgestellt, dass sich PS- Nanopartikel und auch Dendrimere als Träger ähnlich verhalten wie Ziegler- Natta- Katalysatoren, die auf MgCl2 immobilisiert für die heterogene Olefinpolymerisation verwendet werden. Das Fragmentierungsverhalten der Silica oder PS- Mirkopartikel geträgerten Systeme entsprach dagegen dem schichtweisen Fragmentierungsverhalten wie es bereits von Fink und Mitarbeitern beschrieben wurde.

New reactants and improved catalysts for maleic anhydride synthesis

The role of the amount of Nb, used as a dopant for VPP, and how its presence may affect the generation of the active and selective δ-VOPO4 at the VPP surface under reaction conditions, was investigated, employing ex-situ and in-situ characterisation techniques. We found that Nb indeed may favour, under specific conditions, the generation of the desired δ-VOPO4 compound; however, its effect of enhancement of catalytic behaviour was not simply proportional to its concentration. In order to better understand how Nb may affect the generation of the active phase, we prepared V/Nb mixed phosphates; the formation of a solid solution was possible only under specific conditions, with a limited reciprocal dissolution of the two elements. We concluded that even though the incorporation of small amounts of Nb5+ in the VOPO4 (and also of V5+ in NbOPO4) cannot be excluded, a phenomenon which might favour the generation of the desired δ-VOPO4 compound, however the main role of Nb5+ was related to a modification of the redox properties of V4+ in the VPP, and specifically of the redox potential associated to the couple V4+/V5+. This led to a catalyst that during reaction was more oxidized than the corresponding undoped VPP, which under specific reaction conditions allowed obtain a better selectivity to MA. Oppositely, an excessive oxidation of VPP (catalysts having high [Nb]) affected negatively the MA selectivity, because of the excessive formation of COx. A preliminary study regarding the oxidehydration of 1-butanol into MA was carried out testing various catalysts: the best catalyst resulted VPP; however the MA selectivity was lower than that obtained from n-butane. With in-situ/operando Raman study of the Nb-doped and undoped catalysts we verified that the redox cycle involves the VPP and the δ-VOPO4 compounds, that the reoxidation step of V4+ in VPP is the rate-determining one.

Electrosynthesis and characterization of structured catalysts

In this research work the optimization of the electrochemical system of LDHs as catalytic precursors on FeCrAlY foams was carried out. Preliminary sintheses were performed on flat surfaces in order to easily characterize the deposited material. From the study of pH evolution vs time at different cathodic potentials applied to a Pt electrode, the theoretical best working conditions for the synthesis of single hydroxides and LDH compounds was achieved. In order to define the optimal potential for the synthesis of a particular LDH compound, the collected data were compared with the interval of precipitation determined by titration with NaOH. However, the characterization of the deposited material on Pt surfaces did not confirm the deposition of a pure and homogeneous LDH phase during the synthesis. Instead a sequential deposition linked to the pH of precipitation of the involved elements is observed. The same behavior was observed during the synthesis of the RhMgAl LDH on FeCrAlY foam as catalytic precursor. Several parameters were considered in order to optimize the synthesis.. The development of electrochemical cells with different feature, such as the counter electrode dimensions or the contact between the foam and the potentiostat, had been carried out in order to obtain a better coating of the foam. The influence of the initial pH of the electrolyte solution, of the applied potential, of the composition of the electrolytic solution were investigated in order to improve a better coating of the catalyst support. Catalytic tests were performed after the calcination of the deposited foam for the CPO and SR reactions, showing an improve of performances along with optimization of the precursors synthesis conditions.

Investigation of heterogeneous catalysts for the synthesis of fine chemicals

In order to match the more stringent environmental regulations, heterogenization of traditional homogeneous processes is one of the main challenges of the modern chemical industry. Great results have been achieved in the fields of petrochemicals and base chemicals, whereas in fine chemical industry most of the synthetic procedures are based on multistep processes catalyzed by homogeneous catalysts mainly used in stoichiometric amounts. In the fine chemicals manufacture not so much efforts have been devoted to the investigation of suitable solid catalysts for the development of greener processes, then this sector represent a very attractive field of research. In this context, the present work deals with the extensive investigation of the possibility to heterogenize existing processes, in particular two different classes of reactions have been studied: alkylation of aromatic and heteroaromatic compounds and selective oxidation of aromatic alcohols. Traditional solid acid catalysts, such as zeolites, clays and alumina have been tested in the gas phase alkylation of 1,2-methylendioxybenzene, core building block of many drugs, pesticides and fragrances. The observed reactivity were clarified through a deep FTIR investigation complemented by ab initio calculation. The same catalysts were tested in the gas phase isopropylation of thiophene with the aim of clearly attribute the role of the reaction parameters in the reaction proceeding and verify the possibility to enhance the selectivity of one of the two possible isomers. Finally various Au/CeO2 catalysts were tested in the synthesis of benzaldehyde and piperonal, two aldehydes largely employed in the manufacture of fine chemical products, through liquid phase oxidation of the corresponding alcohols in very mild conditions.

Cinchona alkaloids and BINOL derivatives as privileged catalysts or ligands in asymmetric synthesis

During the last fifteen years organocatalysis emerged as a powerful tool for the enantioselective functionalization of the most different organic molecules. Both C-C and C-heteroatom bonds can be formed in an enantioselective fashion using many types of catalyst and the field is always growing. Many kind of chiral catalysts have emerged as privileged, but among them Proline, cinchona alkaloids, BINOL, and their derivatives showed to be particularly useful chiral scaffolds. This thesis, after a short presentation of many organocatalysts and activation modes, focuses mainly on cinchona alkaloid derived primary amines and BINOL derived chiral Brønsted acids, describing their properties and applications. Then, in the experimental part, these compounds are used for the catalysis of new transformations. The enantioselective Friedel-Crafts alkylation of cyclic enones with naphthols using cinchona alkaloid derived primary amines as catalysts is presented and discussed. The results of this work were very good and this resulted also in a publication. The same catalysts are then used to accomplish the enantioselective addition of indoles to cyclic enones. Many catalysts in combination with many acids as co-catalysts were tried and the reaction was fully studied. Selective N-alkylation was obtained in many cases, in combination with quite good to good enantioselectivities. Also other kind of catalysis were tried for this reaction, with interesting results. Another aza-Michael reaction between OH-free hydroxylamines and nitrostyrene using cinchona alkaloid derived thioureas is briefly discussed. Then our attention focused on Brønsted acid catalyzed transformations. With this regard, the Prins cyclization, a reaction never accomplished in an enantioselective fashion until now, is presented and developed. The results obtained are promising. In the last part of this thesis the work carried out abroad is presented. In Prof. Rueping laboratories, an enantioselective Nazarov cyclization using cooperative catalysis and the enantioselective desymmetrization of meso-hydrobenzoin catalyzed by Brønsted acid were studied.

Development of innovative catalysts for the hydrodechlorination to fluoroethers

In this work the hydrodechlorination of CF3OCFClCF2Cl to produce unsaturated CF3OCF=CF2 was studied over a series of supported metal catalysts. Currently this molecule is produced from the precursor CF3OCFClCF2Cl by dechlorination with zinc powder. An important cost on the economic and environmental balance is represents by the large amount of ZnCl2 produced and to be disposed of. A new approach, based on gas-phase hydrodechlorination over supported catalysts can lead to a new sustainable process. During the feasibility step of this project, substantially two kind of materials were studied: metals supported over activated carbon and Pd/Cu species supported over MCM-41 mesoporous silica. Observed catalytic performances were strongly dependent on the metal and support used. All carbon-supported Ru, Pd, and bimetallic catalysts are fairly active and yielded the target product CF3OCF=CF2, the higher selectivity being obtained with ruthenium- and palladium-based materials. Nevertheless, Ru-based catalysts showed poor stability and this deactivation may be attributed to the deposition of chlorinated organic species blocking the active sites. On the other hand, palladium-containing catalysts showed high stability. Ru/Pd and Pd/Cu bimetallic catalysts exhibited long-term selectivity and stability, highlighting the possibility for these materials to be employed in the CF3OCF=CF2 production process. During the second part of this thesis, a series of bimetallic meso-structured Pd/Cu MCM-41 catalysts were studies to overcome possible mass transfer limitations. The materials were obtained by different synthesis methods. The incorporation of Pd and Cu during MCM-41 synthesis, did not destroy the typical hexagonal array and ordered pore system of MCM-41. However, the calcination for the removal of the template provoked significant segregation of oxides. The impregnation leads to pore-occlusion and formation of Cu particles and large bimetallic PdCu species. Larger metal particles leads to lower CF3OCFClCF2Cl conversion, while the monometallic particles can decrease the selectivity to CF3OCF=CF2, fostering the dehalogenation to CF3OCH=CF2.

Sustainable processes using heterogeneous acid catalysts. Some examples of industrial interest.

In recent years the need for the design of more sustainable processes and the development of alternative reaction routes to reduce the environmental impact of the chemical industry has gained vital importance. Main objectives especially regard the use of renewable raw materials, the exploitation of alternative energy sources, the design of inherently safe processes and of integrated reaction/separation technologies (e.g. microreactors and membranes), the process intensification, the reduction of waste and the development of new catalytic pathways. The present PhD thesis reports results derived during a three years research period at the School of Chemical Sciences of Alma Mater Studiorum-University of Bologna, Dept. of Industrial Chemistry and Materials (now Dept. of Industrial Chemistry “Toso Montanari”), under the supervision of Prof. Fabrizio Cavani (Catalytic Processes Development Group). Three research projects in the field of heterogeneous acid catalysis focused on potential industrial applications were carried out. The main project, regarding the conversion of lignocellulosic materials to produce monosaccharides (important intermediates for production of biofuels and bioplatform molecules) was financed and carried out in collaboration with the Italian oil company eni S.p.A. (Istituto eni Donegani-Research Center for non-Conventional Energies, Novara, Italy) The second and third academic projects dealt with the development of green chemical processes for fine chemicals manufacturing. In particular, (a) the condensation reaction between acetone and ammonia to give triacetoneamine (TAA), and (b) the Friedel-Crafts acylation of phenol with benzoic acid were investigated.

Catalysts and processes for next-generation H2 production

The present study is focused on the development of new VIII group metal on CeO2 – ZrO2 (CZO) catalyst to be used in reforming reaction for syngas production. The catalyst are tested in the oxyreforming process, extensively studied by Barbera [44] in a new multistep process configuration, with intermediate H2 membrane separation, that can be carried out at lower temperature (750°C) with respect the reforming processes (900 – 1000°C). In spite of the milder temperatures, the oxy-reforming conditions (S/C = 0.7; O2/C = 0.21) remain critical regarding the deactivation problems mainly deriving from thermal sintering and carbon formation phenomena. The combination of the high thermal stability characterizing the ZrO2, with the CeO2 redox properties, allows the formation of stable mixed oxide system with high oxygen mobility. This feature can be exploited in order to contrast the carbon deposition on the active metal surface through the oxidation of the carbon by means of the mobile oxygen atoms available at the surface of the CZO support. Ce0.5Zr0.5O2 is the phase claimed to have the highest oxygen mobility but its formation is difficult through classical synthesis (co-precipitation), hence a water-in-oil microemulsion method is, widely studied and characterized. Two methods (IWI and bulk) for the insertion of the active metal (Rh, Ru, Ni) are followed and their effects, mainly related to the metal stability and dispersion on the support, are discussed, correlating the characterization with the catalytic activity. Different parameters (calcination and reduction temperatures) are tuned to obtain the best catalytic system both in terms of activity and stability. Interesting results are obtained with impregnated and bulk catalysts, the latter representing a new class of catalysts. The best catalysts are also tested in a low temperature (350 – 500°C) steam reforming process and preliminary tests with H2 membrane separation have been also carried out.

Investigation of the reactivity of metal oxide catalysts for the gas-phase phenol methylation

The gas-phase phenol methylation with methanol was investigated both from catalitic and spectroscopic point of view. In particular, the work focus on the behavior of metal oxide catalysts, like iron(III) vanadate and aluminum vanadate. Spectroscopic studies include: X-ray diffraction and Raman analysis for catalyst charactrerization; Diffuse reflectance infrared fourier transform spectroscopy and in-situ Infrared spectroscopy in vacuum for investigation of interactions between reactants and surface of catalysts.

From polyarylated cycloparaphenylenes to carbon nanotube segments and metallo N 4-macrocycles as fuel cell catalysts

In this work the synthesis of polyarylated cycloparaphenylenes (CPPs) is described in order to form structurally defined carbon nanotube (CNT) segments by the Scholl reaction. Therefore, polyphenylene macrocycles in different sizes and substitution patterns were synthesized. The influence of the ring-strain on the oxidative cyclodehydrogenation of these macrocycles towards CNT segments was investigated. It was demonstrated that a selective solution based bottom-up synthesis of CNT segments could be accomplished, having polyarylated CPPs, sufficient in size and with the right substituents at the critical positions. These findings mark an important step towards the bottom-up synthesis of length- and diameter defined ultrashort CNTsrnIn the second part of this work, novel non-precious metal catalysts (NPMCs) based on phenanthroline-indole macrocycles were synthesized and their electrocatalytic performance in the cathodic oxygen reduction was investigated. It could be demonstrated that all catalysts contributed to the direct 4-electron reduction of oxygen to water in alkaline media and a superior long-term stability was observed. Since these NPMCs are not heat pre-treated, the catalytically active site was structurally well-defined, allowing the investigation of the structure-property relationship. Moreover, it could be shown that these novel NPMCs act as efficient ORR catalysts and could replace the expensive and scarce platinum in fuel cell applications.rn

Synthesis, characterization and catalytic performances of ruthenium-based catalysts for the acceptorless dehydrogenative coupling of butanol

A growing interest towards new sources of energy has led in recent years to the development of a new generation of catalysts for alcohol dehydrogenative coupling (ADC). This green, atom-efficient reaction is capable of turning alcohol derivatives into higher value and chemically more attractive ester molecules, and it finds interesting applications in the transformation of the large variety of products deriving from biomass. In the present work, a new series of ruthenium-PNP pincer complexes are investigated for the transformation of 1-butanol, one of the most challenging substrates for this type of reactions, into butyl butyrate, a short-chain symmetrical ester widely used in flavor industries. Since the reaction kinetics depends on hydrogen diffusion, the study aimed at identifying proper reactor type and right catalyst concentration to avoid mass transfer interferences and to get dependable data. A comparison between catalytic activities and productivities has been made to establish the role of the different ligands bonded both to the PNP binder and to the ruthenium metal center, and hence to find the best catalyst for this type of reaction.

Supported Cu(II) polymer catalysts for aqueous phenol oxidation

Supported Cu(II) polymer catalysts were used for the catalytic oxidation of phenol at 30 degrees C and atmospheric pressure using air and H(2)O(2) as oxidants. Heterogenisation of homogeneous Cu(II) catalysts was achieved by adsorption of Cu(II) salts onto polymeric matrices (poly(4-vinylpyridine), Chitosan). The catalytic active sites were represented by Cu(II) ions and showed to conserve their oxidative activity in heterogeneous catalysis as well as in homogeneous systems. The catalytic deactivation was evaluated by quantifying released Cu(II) ions in solution during oxidation, from where Cu-PVP(25) showed the best leaching levels no more than 5 mg L(-1). Results also indicated that Cu-PVP(25) had a catalytic activity (56% of phenol conversion when initial Cu(II) catalytic content was 200 mg L(Reaction)(-1)) comparable to that of commercial catalysts (59% of phenol conversion). Finally, the balance between activity and copper leaching was better represented by Cu-PVP(25) due to the heterogeneous catalytic activity had 86% performance in the heterogeneous phase, and the rest on the homogeneous phase, while Cu-PVP(2) had 59% and CuO/gamma-Al(2)O(3) 68%.