Study On Active Sites And Applications Of CoNC And FeNC Catalysts In Catalytic Oxidation And Hydrogenation Reactions

MeNC catalysts have shown excellent catalytic activity in the electrocatalytic reduction of oxygen(ORR). Recently, the MeNC catalyst also showed good catalytic activity and stability for the synthesis of chemicals in liquid phase. However, so far the active site of MeNC catalyst has not been understood accurately, which hampered a rational design of the efficient catalyst. In this context, we prepared a series of CoNC/CNT, CoNC and FeNC/CNT catalysts by a hightemperature pyrolysis method. We identified the active sites of CoNC/CNT and FeNC/CNT and expanded the application of CoNC as an efficient catalyst for organic synthesis.(1) CoNC/CNT was synthesized by impregnation and pyrolysis method. Subsequently, we unravel the real active sites of this catalyst through a combination of XRD, XPS, HRTEM, EELS and poisoning experiments with sulfur-containing compounds. The oxidative esterification of benzyl alcohol, nitrobenzene hydrogenation and hydrogenated coupling of nitrobenzene with benzaldehyde were used as probe reactions. By comparing the catalytic performance before and after HCl washing, it was demonstrated that particulate Co3O4 has marginal effect on the catalysis, and the highly dispersed CoNx on carbon nanotubes created during the pyrolysis is responsible for the activity. It was proposed that cobalt chelate complexes bonded to 2 to 3 nitrogens in graphene lattice, probably like the pyridinic vacancy, might be responsible for the activity.(2) CoNC catalysts were synthesized by an economic and facile method by the hydrothermal carbonization of glucose, ammonium chloride and cobalt salt. The catalyst was washed by acids to distinguish the contributions of Co particles and CoNx. The active sites of CoNC were determined probably as CoNx based on the characterization results from TEM, STEM mapping, XRD and XPS. The CoNC has a wide applications in various organic reactions in liquid phase, including the oxidative esterification of benzyl alcohols, oxidation of aromatic alcohols to aldehydes and hydrogenation of aromatic nitro compounds.(3) FeNC/CNT was synthesized by impregnation and pyrolysis method. Nitrobenzene hydrogenation was used as a probe reaction. The active site of FeNC/CNT for the nitrobenzene hydrogenation was studied by catalytic activity, apparent kinetics experiments, poisoning experiments and catalyst characterizations. It was proposed that the active sites of FeNC/CNT were connected with Fe, Fe2O3 and FeNx species.