Advancing CCU Technologies and LOHCs: Synergies of Ionic Liquids and Ru-PNP Catalysts for Efficient CO₂ Hydrogenation and Dehydrogenation Under Ambient Conditions. Towards a Low-Carbon Future

This thesis presents a comprehensive exploration of catalytic hydrogenation and dehydrogenation of CO₂ using various ionic liquids (ILs) and Ru-PNP homogenous catalysts, delivering significant advancements in our understanding of these processes and their potential applications in carbon capture and utilization (CCU). Across eight chapters, the research uncovers critical insights into the roles of cations and anions in ILs through Kamlet–Taft (KAT) and Gutman Donor Number (DN) parameters; the influence of bases and acids; the selection and optimization of catalysts; and the conversion rates for Liquid Organic Hydrogen Carriers (LOHCs) production, such as formic acid (FA), under ambient conditions of 30°C and 1 bar pressure. The study also introduces innovative uses of supported ionic liquid phases (SILPs) in CO₂ hydrogenation, contributing to the development of more efficient and sustainable catalytic systems with broad industrial and environmental applications.
Through detailed kinetic analysis and catalyst evaluation, the combination of Ru-PNP homogenous catalyst with EMIM-propionate demonstrated outstanding performance in both batch and continuous flow CO₂ hydrogenation and its subsequent dehydrogenation experiments, achieving high convertion rates.
A particularly striking achievement is the development of a synergetic system using the same IL and commercial catalyst, which not only demonstrated real-world Direct Air Capture (DAC) success through ¹³CO₂-labelled experiments at 500 ppm but also achieved a remarkable 75% conversion of CO₂ into FA from real biogas samples at just 1 bar and 30 °C. This system allows for the continuous addition and transformation of CO₂, enabling multiple conversion cycles. Additionally, the combination of a base (Et₃N) and a weak acid (e.g. H3PO4) with the IL in CO₂ hydrogenation significantly reduced the reaction time by more than half—from 18 hours to less than 10 hours—at an ambient temperature of 30 °C. The research also demonstrates that methanol can be produced with yields exceeding 30% at near-room temperature, showcasing the versatility and efficiency of the catalytic systems developed.
In terms of dehydrogenation, the research shows that the process can be effectively conducted at temperatures as low as 70 °C without any CO formation, yielding only CO₂ and H₂ as products, which is a significant improvement in reaction conditions. Additionally, the switch to SILPs enabled the transformation of 2000 ppm of CO₂ into FA under a continuous flow system, with the added benefits of SILP catalysts being both recyclable and reusable. These findings collectively advance the field of CCU technologies, offering scalable, efficient, and environmentally sustainable solutions that could significantly impact industrial applications.