A Biomass-Ligand-Based Ru(III) Complex as a Catalyst for Cycloaddition of CO2 and Epoxides to Cyclic Carbonates and a Study of the Mechanism

Aiming highly efficient conversion of greenhouse gas CO2 to cyclic carbonates, a biomass Ru(III) Schiff base complex catalyst (SalRu) was constructed by employing a derivative of Lignin degradation (5-aldehyde vanillin). The SalRu catalyst had a remarkable conversion for epoxides into corresponding cyclic carbonates even at atmospheric pressure of CO2 without the presence of co-catalyst. As the condition at 120 degrees C and 2 MPa CO2 the conversion reached to 94 % with selectivity at 99 % after 8 h. 32 % cyclic carbonate production was obtained even under 0.2 MPa CO2 pressure. The epoxide activation and ring opening, CO2 insertion and cyclic carbonate formation were illuminated explicitly through the of characteristic absorption peaks changing, which further providing direct and visual evidence for the mechanism proposing. This study has important theoretical significance for the comprehensive utilization of environmental pollutants and energy.

Automated summary

A Ru(III) Schiff base complex catalyst (SalRu) was constructed using a derivative of lignin degradation to efficiently convert CO2 to cyclic carbonates. The SalRu catalyst showed remarkable conversion even at atmospheric pressure of CO2 without co-catalyst, reaching 94% conversion and 99% selectivity at 120 degrees C and 2 MPa CO2 after 8 hours. This study provided direct evidence for the mechanism proposing epoxide activation, ring opening, CO2 insertion, and cyclic carbonate formation, and has important theoretical significance for the utilization of environmental pollutants and energy.