Highly efficient synthesis of cyclic ureas from CO2 and diamines by a pure CeO2 catalyst using a 2-propanol solventElectronic supplementary information (ESI) available. See DOI: 10.1039/c3gc40495a

Pure cerium oxide (CeO 2 ) acts as an effective and reusable heterogeneous catalyst for direct synthesis of cyclic ureas from CO 2 and diamines even at a low CO 2 pressure of 0.3 MPa. 2-Propanol is the most preferable solvent to provide good selectivity. The system composed of a CeO 2 catalyst and a 2-propanol solvent is applied to various diamines to provide the corresponding cyclic ureas in high yields (7898%), including six-membered-ring ureas that are difficult to be synthesized from CO 2 . Based on the kinetic studies on the effect of CO 2 pressure and amine concentration and FTIR studies on adsorption of ethylenediamine and CO 2 onto CeO 2 , the following mechanism for the synthesis of cyclic urea is proposed: (1) formation of carbamic acid and carbamate species on CeO 2 , (2) decomposition of carbamic acid to a free amino group and CO 2 , (3) nucleophilic attack of the amino group on the carbamate on CeO 2 to produce the cyclic urea and (4) desorption of the product and regeneration of CeO 2 . Pure cerium oxide (CeO 2 ) acts as an effective and reusable heterogeneous catalyst for direct synthesis of cyclic ureas from CO 2 and diamines even at a low CO 2 pressure of 0.3 MPa.