Characterization and catalytic activity of hydrotalcites as basic catalysts for the coupling of CO₂ and glycidol toward glycerol carbonate

The potential as high value, biobased chemical, and its capacity to valorize glycerol waste, glycerol carbonate became more interesting in the last years. Previous studies demonstrated interesting results regarding the synthesis of glycerol carbonate from epoxides through different kind of catalysts. The chemical conversion of carbon dioxide into valuable products is a sustainable approach to reduce atmospheric CO₂ levels. Among various strategies, reacting CO₂ with epoxides is particularly efficient, producing useful cyclic carbonates and polycarbonates with 100% atom efficiency. This process can be enhanced using glycidol, a bio-based byproduct from biodiesel production. Different applications of glycerol carbonate range from its use in materials such as coatings and adhesives, to solvent, to additive in battery technology up to the synthesis of polymers. The use of hydrotalcites as heterogeneous catalysts for the coupling of CO2 and glycidol is the main topic of this thesis. Hydrotalcites are anionic clays organized in layered structures; they are derivatives of brucite (Mg(OH)2), in which some Mg2+ ions are replaced with Al3+ ions. These clays have been historically studied due to their interesting acid-base properties and their tunable composition. The focus of the work is to understand what are the factors that tune the reactivity of the catalysts, studying its structure and its activity, before and after thermal treatment, understanding how the properties influence the catalytic activity. Doing different types of analysis is possible to understand what is the best design of the catalyst, in terms of ratio of the elements in the crystal, its degree of cristallinity, that is linked to the total surface area of the catalyst. After studying the structure and the activity of the catalysts, another key aspect to focus on, especially in view of future industrial applications aligned with green chemistry, is the recovery and reuse of the catalyst.