The promotion and stabilization effects of surface nitrogen containing groups of CNT on cu-based nanoparticles in the oxidative carbonylation reaction

Abstract

N-doped carbon nanotubes (NCNTs) with different contents of N were prepared by pre-oxidation and subsequent N-doping strategy and employed as the supports to fabricate Cu-based catalysts for oxidative carbonylation of methanol. The supports and their corresponding catalysts were characterized thoroughly by BET, XPS, XRD, H2-TPR, TEM, N2O chemisorption, CO-TPD, CH3OH-TPD and ICP-OES measurements. It is found that the increase of oxygen containing groups generated by pre-oxidation can effectively improve the content of the nitrogen containing groups during the subsequent N-doping process. The nitrogen containing groups, especially the pyridine N groups, serving as the preferred anchoring site, significantly promotes the dispersion of Cu species. With the increased content of N from 0 to 5.2%, the dispersion of Cu species increases from 11.0 to 21.6% and the space time yield of DMC increases from 150.5 to 1789.6 mg g−1h−1. Moreover, the incorporation of nitrogen containing groups enhances the interaction between Cu species and CNT support, which suppresses the auto-reduction of Cu2+ to Cu+ and Cu0, while improves the anti-agglomeration, anti-oxidation and anti-leaching properties of Cu species. From the perspective of stability, the space time yield of DMC for Cu/CNT decreases from 150.5 to 86.9 mg g−1 h−1 after four consecutive runs, while that of Cu/NCNT200 slightly decreases from 1789.6 to 1557.9 mg g−1 h−1, and the declined degrees are 42.3% and 12.9%, respectively. The superior dispersion, anti-agglomeration, anti-oxidation and anti-leaching properties of Cu species as well as the promotion effect of pyridine N groups are contributed to the increased activity and stability of the Cu/NCNT200 catalyst.