Development of new decarboxylation catalysts for CO₂ capture

In carbonate-based CO₂ capture, Na₂CO₃ and K₂CO₃ absorb CO₂ to form NaHCO₃ and KHCO₃. Regeneration requires thermal decarboxylation of the bicarbonates (2HCO₃⁻ → CO₃²⁻ + CO₂ + H₂O), releasing CO₂ and regenerating the carbonate sorbent. The regeneration step typically requires temperatures above 120 °C, making it one of the most energy-intensive steps in carbonate-based CO₂ capture. New decarboxylation catalysts, MgCO₃ and CaCO₃, have been shown to lower the regeneration temperature, potentially improving the energy efficiency of CO₂ capture and acid gas treatment technologies. However, the kinetics and mechanisms of these catalysts are not yet fully understood. This work investigates alkaline earth metal bicarbonate or/and bicarbonato complexes with commercial ligands as potential decarboxylation catalysts. Complexes were synthesised and then characterised using X-ray crystallography (powder and single crystal), ¹H & ¹³C NMR, and FT-IR spectroscopy. Decarboxylation performance was evaluated using aqueous sodium and potassium bicarbonate slurries. The effects of commercial diamines, e.g., tetramethyl ethylene diamine, and new amine-based salts were also examined. Both MgCO₃ and CaCO₃ enhanced bicarbonate decarboxylation, with MgCO₃ showing greater activity due to its higher solubility. Increased solubility of Mg and Ca salts, particularly acetates and citrates, compared to carbonate analogues, improved reaction kinetics. A newly synthesised amine-based salt (TMID) also increased the decarboxylation rate. Experimental optimisation highlighted the importance of water purity, stirring efficiency, and temperature control. Complex synthesis using solvent diffusion methods was a better approach for obtaining purer crystals. Although Mg- and Ca-based crystals proved difficult to synthesise, these findings provide insight for future catalyst design and optimisation for CO₂ capture applications.