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

Abstract

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·gcat−1·h−1) is ∼4 times higher compared to the traditional catalytic system (2.4 mmol·gcat−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.

Keywords

• CO2 capture and utilization
• Frustrated Lewis pairs
• Facet engineering
• CeO2 nanorods
• Cyclic ureas