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.

Bis-Alkoxycarbonylation And Difunctionalization Of Alkenes Employing Palladium(II) Or Nickel(II) Complexes As Catalysts

Section 1 is focused on the bis-alkoxycarbonylation reaction of olefins, catalyzed by aryl α-diimine/Pd(II) complexes, for the synthesis of succinic acid ester derivatives, important compounds in many industrial fields. The opening chapter (Chapter 1) of this thesis presents an overview of the basic chemistry of organopalladium compounds and carbonylation reactions, focusing on oxidative bis-alkoxycarbonylation processes. In Chapter 2 the results obtained in the bis-alkoxycarbonylation of 1,2-disubstituted olefins are reported. The reaction proceeds under very mild reaction conditions, using an aryl α-diimine/Pd(II) catalyst and p-benzoquinone as oxidant, in the presence of a suitable alcohol. This process proved to be very efficient, selective and diastereospecific and various 2,3-disubstituted succinic esters have been obtained in high yields. In Chapter 3 the first bis-alkoxycarbonylation reaction of acrylic esters and acrylic amides, leading to the synthesis of 2-alkoxycarbonyl and 2-carbamoyl succinates respectively, is reported. Remarkably, the utilized aryl α-diimine/Pd(II) catalyst is able to promote the carbonylation of both the β- and the generally non-reactive α- positions of these alkenes. The proposed catalytic cycle is supported by DFT calculations. Section 2 is mainly focused on the Ni-catalyzed difunctionalization of unactivated alkenes tethered to unstabilized ketones. This reaction allows for a wide range of pharmaceutically useful cyclic architectures to be obtained. Chapter 4 consists of an introduction to the difunctionalization reactions of unactivated olefins. In particular, intramolecular reactions will be discussed in detail. In Chapter 5 the results obtained from the Ni-catalyzed difunctionalization of unactivated alkenes tethered to unstabilized ketones are reported. The reaction proceeds through the formation of a zinc-enolate compound, followed by a cyclization/cross-coupling reaction, which takes place in the presence of a phosphine/Ni(II) complex and an (hetero)aryl electrophile, leading to different cyclic and bicyilc architectures. In Chapter 6, preliminary results concerning the anionic cyclization of zinc enolates tethered to unactivated alkenes are presented.

Study of new Catalysts for the Selective Oxidation of n-Butane to Maleic Anhydride: The Role of Catalysts Thermal Treatment

Maleic anhydride (MA) is a very versatile molecule, indeed, with three functional groups (two carbonyl groups and one double bond C=C) it is an excellent joining and cross-linking material. It is obtained via selective oxidation of n-butane, using vanadyl pyrophosphate as a catalyst. The catalytic system has been largely studied over the years and it is normally used in the industrial production of MA, but the main open problem is to completely control its preparation. This thesis reports the effect of different preparation parameters employed during the calcination procedure for the transformation of precursor into the active catalyst. The thermal treatment is already known to be favoured in the presence of water, hence the first study was on the role of different amount of water co-fed with air, leading to obtain catalysts with an higher crystallinity. This is not the only parameter to control: the molar ratio of oxygen has also an important role, to obtain an active and selective catalyst. Some tests decreasing the “oxidizing power” of the mixture were carried out and it was observed a progressive development of VPP phase instead of oxidized V/P/O systems. Established the role of water and oxygen, the optimal conditions have been found when a mixture composed of air, water and nitrogen was used for the calcination, in the molar ratio of 30:10:60% respectively. Also at the lower temperature tested, i.e. 400°C, the catalyst presents the higher conversion of n-butane and MA yield compared to all other samples. The important conclusion we have reached is that not higher amount of water is necessary to obtain the most performing catalyst, thus leading to economic savings. Performing the same experiments on two different precursors, give catalysts with different activity but the mixture previously descripted is always the one that leads to the best performance.

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.

Study and implementation of control strategies for polymerization processes assisted by atmospheric pressure plasma jets

In recent years, polymerization processes assisted by atmospheric pressure plasma jets (APPJs) have received increasing attention in numerous industrially relevant sectors since they allow to coat complex 3D substrates without requiring expensive vacuum systems. Therefore, advancing the comprehension of these processes has become a high priority topic of research. This PhD dissertation is focused on the study and the implementation of control strategies for a polymerization process assisted by an atmospheric pressure single electrode plasma jet. In the first section, a study of the validity of the Yasuda parameter (W/FM) as controlling parameter in the polymerization process assisted by the plasma jet and an aerosolized fluorinated silane precursor is proposed. The surface characterization of coatings deposited under different W/FM values reveals the presence of two very well-known deposition domains, thus suggesting the validity of W/FM as controlling parameter. In addition, the key role of the Yasuda parameter in the process is further demonstrated since coatings deposited under the same W/FM exhibit similar properties, regardless of how W/FM is obtained. In the second section, the development of a methodology for measuring the energy of reactions in the polymerization process assisted by the plasma jet and vaporized hexamethyldisiloxane is presented. The values of energy per precursor molecule are calculated through the identification and resolution of a proper equivalent electrical circuit. To validate the methodology, these energy values are correlated to the bond energies in the precursor molecule and to the properties of deposited thin films. It is shown that the precursor fragmentation in the discharge and the coating characteristics can be successfully explained according to the obtained values of energy per molecule. Through a detailed discussion of the limits and the potentialities of both the control strategies, this dissertation provides useful insights into the control of polymerization processes assisted by APPJs.

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.