Nitrogen-doped graphene supported copper catalysts for methanol oxidative carbonylation: Enhancement of catalytic activity and stability by nitrogen species

Nitrogen-doped graphene (NG) has recently attracted much interest because of its ability to fix the metal nanoparticles (NPs). In this study, NG materials with a nitrogen content of 4.5–7.6 wt% were prepared by hydrothermal method and then used to support Cu catalysts for dimethyl carbonate (DMC) synthesis via the oxidative carbonylation of methanol. The Cu/NG catalysts showed significantly enhanced catalytic activity and stability as compared with copper/reduced graphene oxide (rGO) catalyst. The characterization results show that the enhancing effect of nitrogen doping can be attributed to the decrease in size of Cu NPs and the increase in density of carrier for efficient charge transfer. Density functional theory calculations gave further evidence that the energy barrier for the rate-limiting step for DMC formation (CO insertion) is 89.6 to 67.5 kJ/mol, and that the energies of binding between Cu and the substrate on Cu/rGO and Cu/NG catalysts are 723.1 and 922.7 kJ/mol, respectively.