Cotton Fiber-Anchored Nb Single-Site Catalyst for Selective Oxidation of Anilines to Azoxybenzenes

Abstract

This work demonstrated a facile methodology to construct single Nb site catalysts with merely 0.63 wt% Nb by employing α-hydroxy carboxylic acid-functionalized cotton fiber as green and sustainable supporting material. The as-synthesized catalysts exhibited a superior catalytic activity for selective oxidation of aniline into azoxybenzene under mild and green conditions, demonstrating the highest TOF (4806 h-1) among the reported heterogeneous catalysts. Moreover, the catalyst has steadily been operated under continuous-flow conditions. The activity test and catalyst characterization indicated that the atomically dispersed Nb-peroxo coordination centers were actually catalytic sites. Moreover, 1H MAS NMR spectra verified that there exists an acid-base interaction between arylamines and free α-hydroxy carboxylic acid groups covalently grafted on cotton fiber, which was favorable for adsorption and activation of the substrates. The work provides an economical and environmentally friendly approach to construct single–site catalysts for the oxidation reaction.

Keywords: Cotton fiber, Nb, Single-site, Arylamine, Azoxybenzene