《Table 2 Reaction conditions optimizationa)》

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《Choline-based ionic liquids for CO_2 capture and conversion》

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a) Reaction conditions:morpholine，1.0 mmol；Ch-IL，0.5 mmol；P（CO2）=3 MPa，total pressure of 8 MPa after charging H2，24 h.b) Determined by GC analysis.

The resultant Ch-ILs could chemically absorb CO2with high capacity，and they are thus expected to be capable of catalyzing the further conversion of CO2.In this work，these ChILs were applied in the N-formylation of amines with CO2and H2，which is a green route to produce formamides.It was indicated that these Ch-ILs could not individually catalyze the N-fomylation of morpholine with CO2/H2，and CuCl only showed low catalytic activity（Table 2，entries 1 and 2）.Interestingly，the combination of Ch-IL with CuCl showed high performance for catalyzing this reaction，as shown in Table 2.Especially，[Ch][Im]in combination with CuCl displayed the best performance compared to other Ch-ILs under the similar conditions，affording a product yield of>99.9%.These results indicate that Ch-ILs and CuCl cooperated and realized the formylation of amine with CO2/H2.As described above，the Ch-ILs could chemically absorb CO2to form carbamates or carbonic acid，which may reduce the activation energy of CO2，facilitating its further conversion.Though the ILs[Ch][2-OP]and[Ch][PhO]had higher CO2capture capacities than[Ch][Im]，they displayed lower activity in the N-formylation reaction（Table 2，entries 3，7and 8），suggesting that the anion considerably affected the catalytic activity of the CuCl-IL system.The good coordination ability of imidazolate with CuCl may be responsible for its high activity[41].Moreover，it was also observed that the ILs with substituted imidazolate anions exhibited similar activities to the IL with imidazolate anion（Table 1，entries 3–6），suggesting the cooperation effect from imidazolate anions and CuCl played the key role in catalyzing the reaction.