Rational design of bifunctional catalyst from KF and ZnO combination on alumina for cyclic urea synthesis from CO₂ and diamine

This study is mainly focused on the design of stable, active and selective catalyst for direct synthesis of 2-imidazolidinone (cyclic urea) from ethylenediamine and CO₂. Based on the rationale for the catalyst properties needed for this reaction, KF, ZnO and Al₂O₃ combination was selected to design the catalyst. ZnO/KF/Al₂O₃ catalyst was prepared by stepwise wet-impregnation followed by the removal of physisorbed KF from the surface. High product yield could be achieved by tuning acid-base sites by varying the composition and calcination temperature. The catalysts were characterized by various techniques like XRD, N₂-sorption, NH₃-TPD, CO₂-TPD, TEM, XPS and FT-IR measurements. It is shown that acidic and basic properties of the solvent can influence the activity and product selectivity for this reaction. Under optimized condition; 180 °C, 10 bar and 10 wt.% catalyst in batch mode, 96.3 % conversion and 89.6 % selectivity towards the 2-imidazolidinone were achieved.