Boosting catalytic activity of δ-MnO₂ through potassium incorporation for efficient carbonylation of amines by carbon dioxide

The synthesis of N,N′-dialkylurea from carbonylation of amines with CO₂ over δ-MnO₂ catalyst is a highly attractive green route, however, the catalytic performance of δ-MnO₂ is still far from satisfied. Here, we report a new strategy for fine tuning the physicochemical properties of δ-MnO₂ through KOH hydrothermal activation, resulting in superior catalytic performance with N,N′-dialkylurea yield as high as 77.09% using NMP as solvent at 160 °C for 4 h, as compared to only 43.41% for the pristine δ-MnO₂. The yield is further boosted to 92.02 % by using PEG 400 as solvent. Systematic analysis based on characterization techniques reveals such superior catalytic performance is closely related to, on the one hand, the potassium-incorporation and catalysis induced modification of the concentration of vacancies of both oxygen and Mn, on the other hand, PEG 400 as solvent is favorable to both absorbance of CO₂ and stability of carbamic acids intermediates.