Metal-Free Nitrogen- and Boron-Codoped Mesoporous Carbons for Primary Amides Synthesis from Primary Alcohols via Direct Oxidative Dehydrogenation

Abstract

Metal-free catalysts show environmental friendliness and cost-effectiveness, as well as less susceptibility to poisoning over metal and metal oxide catalysts. In this respect, we present the synthesis and characterization of metal-free mesoporous nitrogen- and boron-codoped nanocarbon (meso-N,B/C), which exhibits good catalytic performance with conversion of 89% and selectivity of 83% toward amide synthesis from primary alcohols using NH4OAc as an ammonia resource under an oxygen atmosphere. The facile codoping synthetic strategy was executed by pyrolysis of nitrogen-enriched ligand 4,5-diazafluorene-9-one azine (DAA) and H3BO3 as a nitrogen and boron content modulator, respectively. Significantly, control experiments revealed that the reaction proceeded through direct oxidative dehydrogenation of hemiaminal after aldehyde-ammonia condensation, which was remarkably different from that in the previous literature. Density functional theory (DFT) calculations further demonstrate that the selective preference for benzamide largely benefits from the strong adsorption and enhanced activity of oxygen molecules via the interaction with a B atom doped in the catalyst. The active sites in the meso-N,B/C catalyst are proposed to be B atom bonded with N within the graphitic carbon sheets. This founding opens up avenues for the development of modified carbon materials on metal-free catalysis.