Metalloporphyrin and triazine integrated nitrogen-rich frameworks as high-performance platform for CO2 adsorption and conversion under ambient pressure

Abstract

The development of multi-site integrated nanomaterials with remarkable properties and their application to selective CO2 capture and utilization have attracted extensive research interest. In this study, several metalloporphyrin and triazine integrated nitrogen-rich frameworks (M ⊂ PPTFs; where “M” stands for metal) were constructed and structurally characterized. These frameworks’ tendency to adsorb CO2 and their catalytic performance in the conversion of CO2 to cyclic carbonates were then investigated. The cycloaddition between CO2 and epichlorohydrin to produce chloropropene carbonate was selected as model reaction to screen the various catalysts and optimize the reaction conditions. The recycling performance and substrate scope were also evaluated. Evidence indicated that Zn ⊂ PPTF15 has dual functions: CO2 adsorption and its synergistic conversion. The CO2 adsorption capacity reached values of 2315 μmol/g and 1883 μmol/g at 273 K and 298 K, respectively. Under conditions of synergistic catalysis with tetrabutylammonium bromide (TBAB), Zn ⊂ PPTF15 afforded 96% yield of chloropropene carbonate with 99% selectivity at 60 °C and 0.1 MPa CO2 pressure for 15 h. The catalytic conditions and activity were investigated by comparison with reported triazinyl-based polymers. Notably, the catalytic system also displayed satisfactory applicability to other epoxides. Furthermore, Zn ⊂ PPTF15 was easily recyclable and did not become deactivated after repeated use. Based on the multi-site structure of the catalyst and the experimental results, a possible mechanism was proposed for the cycloaddition reaction.