Catalysts study of adipic acid synthesis from 1,6-hexanediol

Sustainable chemicals currently have a very limited market share due to current low production but biomass is expected to become one of the major renewable energy and fine chemicals sources in the coming years. Bearing in mind the compromise of all nations to climatic change remediation, the industries will need to use efficient catalysts and green processes to meet the requirements of emissions and efficiency. This project is expected to develop new catalysts to convert 1,6-hexanediol to adipic acid through a green approach based on the “nano-catalysis” and “green chemistry” concepts. Supported Au and Pd nanoparticles were used to study one-pot reaction of HDO oxidation to AA using O2 as a final oxidant and H2O as a solvent. Catalytic results showed that under low pressure O2 atmosphere and low temperature (< 120°C) AuNPs supported on basic-supports are more active than acid and amphoteric oxides. The effect of basic oxide (MgO) addition to MgF2 was studied. The study showed that doping of MgF2 with MgO increased significantly the activity of the catalyst. The best results were obtained with the Au/0.4MgF2-0.6MgO sample, which gave the selectivity to AA of 33% at HDO conversion of 62%.

Investigation of gold-based catalysts for liquid phase oxidation of glucose to glucaric acid

Glucaric acid (GA) is one of the building block chemicals derived from sugar biomass with higher added value. Nowadays, GA is produced by oxidation of glucose (Glu) with either stoichiometric oxidants (HNO3), or by means of electrochemical or biochemical synthesis. However, these processes show drawbacks from either the environmental or economic viewpoint. For this reason, gold nanoparticles (Au NPs) supported on activated carbon (AC) have been studied as catalysts for the oxidation of Glu, using O2 as oxidant in the presence of a base. Using sol immobilization technique, Au NPs have been supported on AC following different experimental procedures. UV-Vis spectroscopy, XRD, TEM and TG analysis were utilized in the characterization of the catalysts. The operational conditions were optimized obtaining 24% of yield of GA, 37% to GO and 27% to byproducts in 1 h, 1000 rpm, 10 bar of O2 and Glu:Au:NaOH molar ratio of 1000:1:3000. Under such conditions, catalysts show relatively high Glu conversion (≥82%) with different GA yields. GO+GA yield is around 58-61%. Therefore, the oxidation reaction was performed at 15 min where Au/AC PVA0 reached the highest yield of GA (16%) and Au/AC PVA2.4 gave the lowest (8%). It is evident that the presence of PVA influences to a higher degree the reaction rate than the Au NPs size. Hence, the effect of different heat treatments where applied for the removal of PVA: washing with water at 60℃ or heat treatment (120-250℃) with Air/H2. Washing treatment and heat treatment at 120℃ with Air/H2 may have resulted in the mildest treatments for the removal of PVA. Finally, two different supports have been used in order to study the effect of metal-support interaction in the immobilization of Au NPs: ZrO2 and AC. Au/AC catalyst demonstrated a higher conversion of GO to GA at short reaction times (15.1% yield GA) compared to Au/ZrO2 (2.4% yield GA).

Theoretical and experimental studies of gold catalysts for glucose oxidation

The glucaric acid (GLA) has been identified as a “top value-added chemical from biomass” that can be employed for many uses; for instance, it could be a precursor of adipic acid, a monomer of Nylon-6,6. GLA can be synthetized by the oxidation of glucose (GLU), passing through the intermediate gluconic acid (GLO). In recent years, a new process has been sought to obtain GLA in an economic and environmental sustainable way, in order to replace the current use of HNO3 as a stoichiometric oxidant, or electrocatalysis and biochemical synthesis, which show several disadvantages. Thereby, this work is focused on the study of catalysts based on gold nanoparticles supported on activated carbon for the oxidation reaction of GLU to GLA using O2 as an oxidant agent and NaOH as base. The sol-immobilization method leads us to obtain small and well dispersed nanoparticles, characterized by UV-Vis, XRD and TEM techniques. Repeating the reaction on different batches of catalyst, both the synthesis and the reaction were confirmed to be reproducible. The effect of the reaction time feeding GLO as reagent was studied: the results show that the conversion of GLO increases as the reaction time increases; however, the yields of GLA and others increase up to 1 hour, and then they remain constant. In order to obtain information on the catalytic mechanism at the atomistic level, a computational study based on density functional theory and atomistic modeling of the gold nano-catalyst were performed. Highly symmetric (icosahedral and cubo-octahedral) and distorted Au55 nanoparticles have been optimized along with Au(111) and Au(100) surfaces. Distorted structures were found to be more stable than symmetrical ones due to relativistic effects. On these various models the adsorptions of various species involved in the catalysis have been studied, including OH- species, GLU and GLO. The study carried out aims to provide a method for approaching to the study of nanoparticellary catalytic systems.

Ossidazione elettrocatalitica di glucosio su schiume di nickel per la produzione selettiva di acido gluconico e acido glucarico

The selective electro-oxidation of D-glucose represents a promising way for the synthesis of many platform molecules, currently produced from non-renewable fossil fuels. Electrocatalysis is gaining considerable interest as an alternative to the thermochemical process, since it allows the process to be sustainable by operating at room temperature and pressure as well as using green solvents and electricity produced from renewable sources. In this work, the activity of three electrocatalysts, based on open cell Ni foams, towards the electrochemical oxidation of glucose to gluconic acid and glucaric acid was initially compared: a Ni bare foam, and Ni foams calcined at 500 °C for one hour and electrodeposited with Ni NP nanoparticles. The calcined foam turned out to be the most efficient. Then, the performance of this Ni calcined electrocatalyst was studied varying the reaction conditions, such as the potential applied (from 0,5V to 1,0V vs SCE), D-glucose concentration (0,01M, 0,05M and 0,10M) and NaOH concentration (0,10M and 1,0M). The activity of the electrocatalysts was evaluated in terms of glucose conversion, gluconic and gluconic acid selectivity and faradic efficiency. The best results were obtained over a Ni calcined foam with a 0,05M solution of D-glucose and 0,10M of NaOH at a 0,80V vs SCE potential.

Synthesis and characterisation of electrospun gold on ceria catalysts

Cerium oxide in catalysis can be used both as support and as a catalyst itself. Ceria catalyses many oxidations reactions, its excellent catalytic properties are due to its store oxygen storage capacity (OSC) and the reticular defects present on its surface. Different morphologies expose different reticular planes, and different reticular planes can expose different amounts of defects. The preparation method of cerium oxide can influence the surface area, morphology, and the number of defects in the sample. This work is focused on different preparation methods for gold nanoparticles supported on 1D nanostructures of cerium oxide prepared via electrospinning, their XRD, DRUV-Vis and Raman characterizations, and their catalytic performance on the oxidation reaction of HMF to FDCA.

Nickel dependent carcinogenesis and infections: structural and biophysical characterization of NDRG1 and SgSrnR

In prokaryotic organisms, lower eukaryotes and plants, some important biological reactions are catalyzed by nickel-dependent enzymes, making this metal ion essential microelement for their life. On the other hand, excessive concentration of nickel into the cell, or prolonged exposure to nickel compounds, has toxic effects in living organisms. In addition, nickel has been classified by IARC as Group I human carcinogen, because of the correlation between its inhalation and increased incidence of nasal and lung cancers. The aim of this work was to investigate the nickel impact on human health, considering both its direct role on human cells and its indirect effect as essential element for human important bacteria. In humans, nickel induces N-myc downstream regulated gene 1 (NDRG1) expression, recently proposed as new target in cancer therapy. CD, light scattering and ITC were applied on the recombinant full-length protein and its C-terminal intrinsically disordered domain, for studying the NDRG1 structural and functional properties. In particular, the fold and dynamics of the C-terminal region were examined by NMR spectroscopy and site-directed spin labeling coupled to EPR, showing the features of an intrinsically disordered region. In nickel-dependent bacteria, nickel metabolism is strictly regulated, through the activity of different transcription factors. In Streptomyces griseus the expression of two superoxide dismutases (SODs) is antagonistically regulated by nickel thanks to the transcriptional complex SgSrnR/SgSrnQ. The SgSrnR protein was heterologously expressed and its activity as possible nickel sensor studied. DNaseI footprinting and β-galactosidase gene reporter assays revealed that SgSrnR functions as transcriptional activator, prompting the hypothesis of a new model to describe the activity of this complex. In addition, ITC, NMR and X-ray crystallography demonstrated that SgSrnR presents the fold typical of ArsR/SmtB transcription factors and low metal binding affinity, non compatible with a role as a nickel-sensor, function probably played by its partner SgSrnQ.

Aquivion-based spray freeze-dried composite catalysts for the cascade conversion of furfural to γ-valerolactone

Furfural is one of the most promising biomass derived platform molecules. It is to this day produced in volumes above 300 ktons per year from the hydrolysis and dehydration of hemicellulose, one of the main components of lignocellulosic biomass. While the majority of the yearly production is destined to selective reduction to furfuryl alcohol for the production of furan resins, these molecules hold great potential for the production of more valuable chemicals, fuels, fuel additives and solvents. Among these products are alkyl levulinates and γ-valerolactone. To convert furfural to these target products, a cascade process involving Lewis acidity-catalysed reduction steps and Brønsted acidity-catalysed steps. In order to develop catalysts capable of promoting the one-pot domino reaction from furfural to γ-valerolactone, the two kinds of acidity must both be present. To this end, in this work, the spray freeze-drying technique is employed to combine the high activity and strong Brønsted acidity of Aquivion with the structural properties and Lewis acidity of different supporting metal oxide, forming composite catalysts. The flexibility of the spray freeze-drying technique and the modulable composition of the catalysts allowed a thorough study of the complex network of equilibria underlying the cascade reaction, while achieving high selectivities towards the final product.

New catalytic strategies for the manipulation of arenes

The aim of this Doctoral Thesis is the development of new catalytic synthetic methodologies in the context of the modern organic chemistry setting, with special focus on the use of cheap, sustainable catalytic materials. Specifically, during the course my PhD, I focused my research on two main distinct catalytic strategies, namely: the use of carbonaceous materials as catalysts (carbocatalysis) and nickel catalysis, also investigating a synergistic combination of the two. These methodologies were explored as means for the manipulation of (hetero)aromatic cores, representing ubiquitous, easily accessible and privileged scaffolds in medicinal or natural products chemistry. Both polar and radical reaction manifolds were engaged as complementary reactivities, capitalizing on metal- as well as organo-based activation modes. Particular attention has been devoted to addressing modern synthetic challenges or highly sought- after methodologies. Specifically, protocols for direct substitution of alcohols, dearomatization of arene nuclei, formation of C-S bonds, carbon dioxide fixation, C-C bond activation and fluoroalkylation were successfully achieved under carbo- or nickel catalyzed conditions.

Valorization and recycling of waste biomass and bioplastics into molecules, polymers and catalysts

The enormous amount of goods that world societies consume every day, derives from an immense consumption of energy and raw materials, and leads to an unthinkable amount of wastes. The abuse of fossil-based resources and the mismanaged waste is leading to big environmental pollution and climate change, with consequences on all living beings. To solve this issue and start living in equilibrium with nature, modern societies must stop using fossil fuels massively in favor to clean renewable energies, recycling, and biomass and waste utilization for materials and chemical production. Moreover, bioplastic recycling must be prioritized over their biodegrading and composting. This work is dedicated to the study of new synthetic strategies that fall into these fields.

Investigation on the role of polymeric ligands in heterogeneous nanocatalysis towards the development of hybrid metal-polymer catalysts

The relationship between catalytic properties and the nature of the active phase is well-established, with increased presence typically leading to enhanced catalysis. However, the costs associated with acquiring and processing these metals can become economically and environmentally unsustainable for global industries. Thus, there is potential for a paradigm shift towards utilizing polymeric ligands or other polymeric systems to modulate and enhance catalytic performance. This alternative approach has the potential to reduce the requisite amount of active phase while preserving effective catalytic activity. Such a strategy could yield substantial benefits from both economic and environmental perspectives. The primary objective of this research is to examine the influence of polymeric hydro-soluble ligands on the final properties, such as size and dispersion of the active phase, as well as the catalytic activity, encompassing conversion, selectivity towards desired products, and stability, of colloidal gold nanoparticles supported on active carbon. The goal is to elucidate the impact of polymers systematically, offering a toolbox for fine-tuning catalytic performances from the initial stages of catalyst design. Moreover, investigating the potential to augment conversion and selectivity in specific reactions through tailored polymeric ligands holds promise for reshaping catalyst preparation methodologies, thereby fostering the development of more economically sustainable materials.

Study of the activity and enantioselectivity of alginate-based catalysts in Friedel-Crafts reactions

This thesis is part of a long-term project which aims to demonstrate for the first time that alginate gel beads can be used as chiral heterogeneous catalysts for enantioselective reactions. Alginate barium beads were prepared as previously optimized and applied to the Friedel-Crafts reaction between indoles and nitroalkenes. New substrates were tested, showing that the reaction can accommodate different nitroalkenes and indoles, affording the corresponding products with moderate yields and good enantioselectivities. However, aliphatic nitroalkenes cannot be used as they degrade under the catalytic reaction conditions. Preliminary study on the recyclability of the heterogeneous catalyst indicated a moderate stability of the catalyst, which can be used for few cycles with a slight erosion of enantioinducing power. Some directions for future improvements (storage and work-up solvent, use of ultrasonic bath) have been suggested.

Direct C–H silylation and borylation of biomass derivatives by iridium heterogeneous catalysts

Furfural and its derivatives represent renewable and readily available platforms for a wide range of chemicals. Much attention has been devoted to their functionalization over the last years. TM-catalysed C–H activation has emerged as a powerful tool for synthesizing new C–C and C–X bonds. Moreover, it provides a sustainable way to obtain molecules by reducing waste and saving steps. At the same time, iridium catalysts have proven to be very active in some C–H functionalizations of several (hetero)arenes. Although very promising, this technique is still poorly applied on an industrial scale due to the severe conditions required. Continuous flow chemistry using heterogeneous catalysts appears to be a valuable way to overcome these problems. In this work, we present different solutions for the immobilization of homogeneous iridium complexes on silica gels, using bidentate amines and phosphines as anchoring ligands. We successfully employed the catalysts in C–H silylation and borylation of furfural, using C2 located directing group. In this way, we finally obtained a suitable catalyst that could be potentially applied in continuous-flow chemistry.