Frustrated Lewis pairs on facet-engineered CeO2 boost the conversion of low-concentration CO2 into cyclic ureas with assistance of diamine platforms

The development of efficient processes for value-added utilization of low-concentration CO₂ is an on-going challenge. In this work, we present a sequential system based on diamine platforms for the direct utilization of low-concentration sources of CO₂ (≤15%) in the production of cyclic ureas. Specifically, the low-concentration CO₂ is captured by ethylenediamine to form ethylenediamine carbamate (EDA-CA), which subsequently undergoes the intramolecular dehydration to give ethyleneurea (EU) in the presence of frustrated Lewis pairs (FLPs) on the facet-engineered CeO₂. Remarkably, the productivity of EU obtained from EDA-CA in the sequential system (9.5 mmol·g_cat⁻¹·h⁻¹) is ∼4 times higher compared to the traditional catalytic system (2.4 mmol·g_cat⁻¹·h⁻¹) using ethylenediamine and pure CO₂ (3 MPa). Density functional theory calculations demonstrated that the FLPs on facet-engineered CeO₂ significantly reduce the energy barrier for the nucleophilic attack of N-containing segment towards the carbonyl carbon in EDA-CA (rate-limiting step), ultimately optimizing the intramolecular cyclization efficiency of EDA-CA. This work not only provides an innovation tandem approach that enables the production of cyclic ureas from low-concentration CO₂, but also opens up a promising avenue for the direct utilization of low-concentration CO₂ for value-added applications in the future.