Ultrahigh-Content Nitrogen-doped Carbon Encapsulating Cobalt NPs as Catalyst for Oxidative Esterification of Furfural

It is an attractive and challenging topic to endow non-noble metal catalysts with high efficiency via a nitrogen-doping approach. In this study, a nitrogen-doped carbon catalyst with high nitrogen content encapsulating cobalt NPs (CoO _x @N-C(g)) was synthesized, and characterized in detail by XRD, HRTEM, N ₂ -physisorption, ICP, CO ₂ -TPD, and XPS techniques. g-C ₃ N ₄ nanosheets act as nitrogen source and self-sacrificing templates, giving rise to an ultrahigh nitrogen content of 14.0 %, much higher than those using bulk g-C ₃ N ₄ (4.4 %) via the same synthesis procedures. As a result, CoO _x @N-C(g) exhibited the highest performance in the oxidative esterification of biomass-derived platform furfural to methylfuroate under base-free conditions, achieving 95.0 % conversion and 97.1 % selectivity toward methylfuroate under 0.5 MPa O ₂ at 100 °C for 6 h, far exceeding those of other cobalt-based catalysts. The high efficiency of CoO _x @N-C(g) was closely related to its high ratio of pyridinic nitrogen species that may act as Lewis basic sites as well as its capacity for the activation of dioxygen to superoxide radical O ₂ ^.− .