Harnessing the Synergistic Effect of Acidic and Basic Sites in Nitrogen-Enriched α-TiP for Co-Catalyst-Free Selective CO ₂ Cycloaddition

The development of environmentally benign catalysts for the valorization of CO₂ remains a crucial challenge in sustainable chemistry. In this work, we report a nitrogen-enriched acid-base bifunctional titanium phosphate catalyst (CC-3A-TiP), synthesized via intercalation of layered α-TiP with aminosilanes and cyanuric chloride. The resulting material features dual active sites, including Lewis acidic centers (Ti⁴⁺, -OH) and Lewis basic functionalities (-NH-, -C═N-), which facilitate the cooperative activation of epoxides and CO₂ molecules. Comprehensive structural and spectroscopic characterization confirmed the presence and accessibility of these active sites. The synergistic acid-base interactions enabled highly efficient catalytic performance, achieving >99% conversion, 99% yield, and 100% selectivity toward cyclic carbonates under mild, solvent-free conditions, remarkably, without the use of halogenated cocatalysts such as TBAB, commonly employed in conventional systems. The catalyst demonstrated excellent stability and recyclability, maintaining ∼92% yield over five consecutive cycles. A plausible mechanism involving direct cycloaddition of epoxide and CO₂ without any cocatalyst was proposed, highlighting the intrinsic bifunctional nature of the catalyst. DFT studies confirm that the bifunctional nature of the catalyst, offering both acidic and basic sites, drastically lowers the activation energy to 7.21 kcal mol⁻¹, much lower than literature values, highlighting its vital role in facilitating CO₂ cycloaddition with epoxides, which is further supported by experimental kinetics showing an activation energy of 9.06 kcal mol⁻¹ in excellent agreement with the DFT results. The cocatalyst-free and solvent-free operational profile, along with high activity and recyclability, underscores the potential of CC-3A-TiP for sustainable CO₂ conversion applications.