Langellotti, Vincenzo (2026) Chemocatalytic conversion of biomass for sustainable production of high-added value chemicals and vectors for energy. [Tesi di dottorato]

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Abstract

The use of biomass, like agricultural residues or waste oils, as raw materials for fine products and vectors for energy is a crucial factor in the transition to a circular economy model and a sustainable chemical industry. A key instrument to achieve this is catalysis because, thanks to efficient, active and selective systems, it can convert the plethora of molecules obtainable from biomass into something useful and with added value. This PhD project is part of the frame, with the idea of investigating two big classes of ligands, salen- and pyridine-based, to use them, by complexation with different metals, for the valorization of molecules from biomass. Starting from the salen moiety, two families of salen-based iron(III) complexes were developed. The µ-oxo-dinuclear Fe(III)-salen complexes showed very high activity in the transesterification of methyl levulinate, in mild conditions and absence of solvent, leading to a complete formation of esters of industrial interest. Instead, iron(III) salphen complexes were successfully applied to the production of biodiesel from waste vegetable oils, at very low loadings and under favourable conditions. An evolution of this ligand scheme was developed by enhancing the π-conjugation across the ligand core, with the aim of unlocking new applications in the fields of electrocatalysis and photophysics (via corresponding boron complexes). The π-extended salphen ligands themselves were preliminarily tested as electrocatalysts for carbon dioxide valorization, obtaining a metal-free system that produces a good amount of CO. The boron complexes were used as photosensitizers for singlet oxygen generation and oxidative cleavage of the double bond. They represented the first example of salen-type boron complexes applied as photocatalysts, offering an alternative to more dangerous ozonolysis and very competitive conditions. About pyridine-based ligands, two glucose-based picolinamidate Ir(III) complexes and one with an aliphatic chain were evaluated with excellent results in the dehydrogenation of formic acid. Their catalytic activity was analyzed towards different parameters, underlining the importance of the sugar substituent in achieving remarkable values of TOF, TON, and conversion. Following the same idea, two sugar-based imino-pincer-(N,N,N) Ru(II) complexes, one functionalized with glucose and the other with galactose, and one decorated with an aliphatic cycle were tested in the Guerbet reaction of 1-phenylethanol and benzyl alcohol. Their catalytic activity was evaluated by screening diverse factors, developing a very active and versatile system, able to produce long-chain alcohols under sustainable conditions.

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