Coupling hydrogen bond donors and atomically dispersed Zn–N4 sites in porous N-doped carbon for CO2 fixation to cyclic carbonates

Abstract

Introducing dual Lewis acidic and basic sites into carbon is a promising way to improve the catalytic efficiency of carbon-based catalysts for CO₂ fixation into epoxides to produce cyclic carbonates. Here, a simple and one-step method is proposed to couple atomically dispersed Zn–N₄ sites and abundant –OH/–COOH groups as hydrogen bond donor (HBD) sites in porous nitrogen-doped carbon via pyrolysis of a mixture of tea saponin, melamine and Zn(NO₃)₂. These HBD sites, together with atomically dispersed Zn sites, serve as Lewis acids to activate epoxides, while N-doping provides a Lewis base, favouring CO₂ activation. As a result, the resulting carbon (ZNC-800) displayed high yields of >99% at 12 h for CO₂ cycloaddition with different epoxides, such as epichlorohydrin, epibromohydrin, benzyl(R)-(−)-glycidyl ether, 1,2-epoxyhexane and glycidyl phenyl ether, at 80 °C and 0.1 MPa CO₂. In addition, owing to its good photothermal ability, ZNC-800 can also drive CO₂ cycloaddition reactions with high catalytic efficiency under light irradiation, which makes ZNC-800 a promising biomass-derived catalyst for both thermally and photothermally driven CO₂ conversion.