Unlocking the Potential of Acidic–Basic Catalytic Sites in Nitrogen-Rich Multifunctional Zirconium Phosphate-Based Hybrid Material for Selective CO2 Chemical Transformation

Abstract

Rational design and development of an acid–base multifunctional catalyst is a difficult task. Here, a multifunctional zirconium phosphate-based inorganic–organic hybrid catalyst (ZPCC), incorporating both acidic and basic sites, was synthesized by exfoliating α-ZrP and subsequently functionalizing it with 3-aminopropyltriethoxysilane (APTES) and cyanuric chloride. The as-synthesized catalyst exhibits outstanding catalytic performance for the transformation of carbon dioxide into cyclic carbonates with high selectivity using a low cocatalyst dose under solvent-free conditions. The catalyst ZPCC features Zr⁴⁺ and P–OH groups as acidic sites, and N-containing moieties [secondary amine (−NH−) and triazine ring (−C═N−)] impart basic nature to the catalyst. This combination of acid and base sites enacts a synergetic effect on the activation of epoxide and CO₂, respectively, and also increases the cocatalyst activity to open or close the epoxide ring. The functionalized catalyst, ZPCC, exhibited 50% conversion, 49% yield, and 95% selectivity toward cyclic carbonate without any cocatalyst, and it shows almost 100% conversion, 99% yield, and 99% selectivity at optimized conditions (including a minimal amount of cocatalyst and short reaction period). Nuclear magnetic resonance and GC–MS techniques were used to find a plausible mechanism and reveal the direct preparation of cyclic carbonates without any byproduct formation. The characterization of the used catalyst, easy recoverability, and the ability to be recycled over five times with more than 90% conversion demonstrate its ability to be used as a suitable catalyst for industrial purposes.