N-doped porous carbon-anchored zinc single-atom as an efficient and robust heterogeneous catalyst for glycerol carbonylation with urea

Constructing highly efficient and stable heterogeneous catalysts for glycerol carbonylation is a very significant subject for its importance in promoting the development of biodiesel industry. Herein, a carbon-based single-Zn-atom catalyst (Zn1/NC) was prepared by using N-doped porous carbon material (NC) as support via a wet impregnation technique, following a thermal treatment at 600 °C. Various characterization results demonstrate that Zn2+ cations are atomically dispersed on the surface of NC support by coordination with the existed N- and O-containing groups. The Zn1/NC catalyst exhibited outstanding catalytic activity, selectivity and stability for glycerol carbonylation with urea at mild conditions. Operando ReactIR spectra results show that urea molecules could be easily activated by the single-atom Zn catalyst then react with glycerol molecules to generate the main product of glycerol carbonate via an intermediate of 2,3-dihydroxypropyl carbamate. Density functional theory calculations reveal that NC support could provide a unique coordination environments for the single-atom site of Zn2+, which can guarantee the preferential adsorption of urea molecule (rather than glycerol) and effectively inhibit the generation of the unfavorable Zn-glycerol complex, thus leading to the formation of highly efficient and robust heterogeneous catalyst for glycerol carbonylation with urea.