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.

Investigation of the dipole response of nickel isotopes in the presence of a high-frequency electromagnetic field

The electric dipole response of neutron-rich nickel isotopes has been investigated using the LAND setup at GSI in Darmstadt (Germany). Relativistic secondary beams of 56−57Ni and 67−72Ni at approximately 500 AMeV have been generated using projectile fragmentation of stable ions on a 4 g/cm2 Be target and subsequent separation in the magnetic dipole fields of the FRagment Separator (FRS). After reaching the LAND setup in Cave C, the radioactive ions were excited electromagnetically in the electric field of a Pb target. The decay products have been measured in inverse kinematics using various detectors. Neutron-rich 67−69Ni isotopes decay by the emission of neutrons, which are detected in the LAND detector. The present analysis concentrates on the (gamma,n) and (gamma,2n) channels in these nuclei, since the proton and three-neutron thresholds are unlikely to be reached considering the virtual photon spectrum for nickel ions at 500 AMeV. A measurement of the stable 58Ni isotope is used as a benchmark to check the accuracy of the present results with previously published data. The measured (gamma,n) and (gamma,np) channels are compared with an inclusive photoneutron measurement by Fultz and coworkers, which are consistent within the respective errors. The measured excitation energy distributions of 67−69Ni contain a large portion of the Giant Dipole Resonance (GDR) strength predicted by the Thomas-Reiche-Kuhn energy-weighted sum rule, as well as a significant amount of low-lying E1 strength, that cannot be attributed to the GDR alone. The GDR distribution parameters are calculated using well-established semi-empirical systematic models, providing the peak energies and widths. The GDR strength is extracted from the chi-square minimization of the model GDR to the measured data of the (gamma,2n) channel, thereby excluding any influence of eventual low-lying strength. The subtraction of the obtained GDR distribution from the total measured E1 strength provides the low-lying E1 strength distribution, which is attributed to the Pygmy Dipole Resonance (PDR). The extraction of the peak energy, width and strength is performed using a Gaussian function. The minimization of trial Gaussian distributions to the data does not converge towards a sharp minimum. Therefore, the results are presented by a chi-square distribution as a function of all three Gaussian parameters. Various predictions of PDR distributions exist, as well as a recent measurement of the 68Ni pygmy dipole-resonance obtained by virtual photon scattering, to which the present pygmy dipole-resonance distribution is also compared.

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.

Structural and biochemical studies of Sporosarcina pasteurii UreE: a nickel-chaperone involved in the urease activation process

Urease is a nickel-dependent enzyme that catalyzes hydrolysis of urea in the last step of organic nitrogen mineralization. Its active site contains a dinuclear center for Ni(II) ions that must be inserted into the apo-enzyme through the action of four accessory proteins (UreD, UreE, UreF, UreG) leading to activation of urease. UreE, acting as a metallo-chaperone, delivers Ni(II) to the preformed complex of apo-urease-UreDFG and has the capability to enhance the GTPase activity of UreG. This study, focused on characterization of UreE from Sporosarcina pasteurii (SpUreE), represents a piece of information on the structure/mobility-function relationships that control nickel binding by SpUreE and its interaction with SpUreG. A calorimetric analysis revealed the occurrence of a binding event between these proteins with positive cooperativity and a stoichiometry consistent with the formation of the (UreE)2-(UreG)2 hetero-oligomer complex. Chemical Shift Perturbations induced by the protein-protein interaction were analyzed using high-resolution NMR spectroscopy, which allowed to characterize the molecular details of the protein surface of SpUreE involved in the complex formation with SpUreG. Moreover, backbone dynamic properties of SpUreE, determined using 15N relaxation analysis, revealed a general mobility in the nanoseconds time-scale, with the fastest motions observed at the C-termini. The latter analysis made it possible for the first time to characterize of the C-terminal portions, known to contain key residues for metal ion binding, that were not observed in the crystal structure of UreE because of disorder. The residues belonging to this portion of SpUreE feature large CSPs upon addition of SpUreG, showing that their chemical environment is directly affected by protein-protein interaction. Metal ion selectivity and affinity of SpUreE for cognate Ni(II) and non cognate Zn(II) metal ions were determined, and the ability of the protein to select Ni(II) over Zn(II), in consistency with the proposed role in Ni(II) cations transport, was established.

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.

Detektion von Nickel- und Cobaltspezies in einzelnen lebenden Zellen mit hoher lateraler Auflösung

Übergangsmetallen wie Nickel und Cobalt kommt meist eine große Bedeutung als Cofaktor in Enzymen oder Metallkomplexen im Metabolismus von Lebewesen zu. Da eine sehr geringe Konzentration dieser Übergangsmetalle in einer Zelle für deren Funktionalität ausreicht, ist eine konstante Konzentration der Spurenelemente in einer Zelle angestrebt. Durch meist anthropogene Einflüsse sind Pflanzen und Menschen zunehmend hohen Konzentrationen von Übergangsmetallen ausgesetzt, die in Abhängigkeit von ihrer Spezies, der Konzentration und der Lokalisation unterschiedliche Toxizitäten aufweisen können. Die Speziation von Metallen wurde bisher mittels gängiger Analyseverfahren, wie der ICP-MS und ähnlicher Verfahren, anhand von bulk-Material durchgeführt. Durch die Entwicklung von optischen Sensoren für Metallionen war es möglich, diese Metalle auch in lebenden Zellen mittels Fluoreszenzmikroskopie zu lokalisieren. Ke und Kollegen (2006, 2007) nutzten einen solchen optischen Sensor - Newport Green DCF, um die Aufnahme von Nickel in humane A543 Lungenbronchialepithelzellen nach Inkubation mit dem wasserlöslichen NiCl2 (0,5 mM und 1 mM) sowie den wasserunlöslichen Verbindungen Ni3S2 (0,5 µg/cm2 und 1 µg/cm2) und NiS (2,5 µg/cm2) nachzuweisen und zu lokalisieren und konnten damit eine Akkumulation von Nickel im Zytoplasma und im Zellkern aufzeigen. Dabei war bei wasserlöslichen und wasserunlöslichen Nickelverbindungen Nickel nach 24 h im Zytoplasma und erst nach 48 h im Zellkern zu beobachten.rnrnDa Nickel und Cobalt keine detektierbare Eigenfluoreszenz unter den gegebenen Bedingungen zeigten, wurde für den optischen Nachweis von Nickel und Cobalt mit dem konfokalen Laser-Raster Mikroskop (CLSM) nach der Zugabe der verschiedenen wasserlöslichen und wasserunlöslichen Metallverbindungen NiCl2, NiSO4, Ni3S2 und CoCl2 in einzelnen lebenden humanen Gingiva-Fibroblasten, sowie in Pflanzenzellen in dieser Arbeit ebenfalls der optische Sensor Newport Green DCF genutzt. Korrespondierend zu den Ergebnissen früherer Arbeiten von Ke et al. (2006, 2007), in denen die Nickelaufnahme bei Konzentrationen von >0,5 mM NiCl2 bzw. >0,5 µg/cm2 Ni3S2 gezeigt wurde, wurde Nickel in Fibroblasten in Abhängigkeit von der Spezies mit steigender Metallkonzentration von 100 µM bis 500 µM nach 16 h im Zytoplasma und zunehmend nach 24 h bis 48 h im Zellkern detektiert. Bei der wasserunlöslichen Verbindung Ni3S2 war der Nachweis von Nickel im Zellkern bereits nach 16 h bis 24 h erfolgreich. Zusätzlich wurden weitere Strukturen wie das Endoplasmatische Retikulum, die Mitochondrien und die Nukleoli durch eine starke Fluoreszenz des optischen Sensors bei Colokalisationsexperimenten mit Organell-spezifischen Fluoreszenzfarbstoffen als target für die Nickelbindung vermutet. Die Lokalisation von Cobalt in den Fibroblasten entsprach weitgehend der Lokalisation von Nickel. Im Zellkern war die Cobaltlokalisation jedoch auf die Nukleoli beschränkt. Weiterführende Versuche an humanen Gingiva-Fibroblasten zeigten, dass die Aufnahme der Metalle in die Fibroblasten pH-Wert abhängig war. Niedrige pH-Werte im sauren pH-Bereich verringerten die Aufnahme der Metalle in die Zellen, wobei ein pH-Wert im basischen Bereich keinen bedeutenden Unterschied zum neutralen pH-Bereich aufwies. Im Vergleich zu den Fibroblasten war in Pflanzenzellen zu jedem Zeitpunkt, auch bei geringen Konzentrationen der Metallverbindungen sowie des optischen Sensors, Nickel und Cobalt in den Zellkernen detektierbar. Durch die Eigenschaft der Pflanzenzellen eine Vakuole zu besitzen, war Nickel und Cobalt hauptsächlich in den Vakuolen lokalisiert. Weitere Strukturen wie das Endoplasmatische Retikulum, die Mitochondrien oder auch die Zellwand kamen bei Pflanzenzellen als target in Frage.rnrnDie Fluoreszenz und Lokalisation der Metalle in den Fibroblasten waren unabhängig von der Spezies sehr ähnlich, sodass in den Zellen die Spezies anhand der fluoreszenzmikroskopischen Aufnahmen kaum unterschieden werden konnten. Lambda-Scans in verschiedenen regions of interest (ROI) wurden durchgeführt, um durch die Fluoreszenzspektren Hinweise auf eine charakteristische Beeinflussung der Bindungspartner von Nickel und Cobalt oder dieser Metalle selbst in den Zellen auf den optischen Sensor zu bekommen und diese dadurch identifizieren zu können. Das Ziel der parallelen Detektion bzw. Lokalisation und gleichzeitigen Speziation bestimmter Nickel- und Cobaltpezies in einzelnen lebenden Zellen konnte in dieser Arbeit durch den optischen Sensor Newport Green DCF nicht erreicht werden.

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.