Ultrafine metallic cobalt nanoparticle encapsulated in N‐doped carbon as high‐efficiency catalysts for reduction of 4‐nitrophenol

Abstract

Novel and efficient ultrafine metallic cobalt nanoparticles encapsulated in N‐doped carbon catalysts are prepared via a facile method from pyrolysis of ZIF‐67‐x%CTAB, which is modified by CTAB (cetyltrimethyl ammonium bromide). The content of surfactant CTAB can control the crystal size of ZIF‐67, which further determines the Co particle size of Co@CN‐x%CTAB. The as‐prepared ZIF‐67‐x%CTAB and Co@CN‐x%CTAB were characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), Brunauer−Emmett−Teller (BET), and X‐ray photoelectron spectroscopy (XPS). Co@CN‐0%CTAB could not maintain the primary morphologies of ZIF‐67‐0%CTAB with the collapse of skeleton. However, the Co@CN‐3%CTAB and Co@CN‐5%CTAB catalysts inherit the original morphologies with skeleton constriction. It indicated that Co@CN catalysts could maintain the skeleton structure of ZIF‐67 by adding CTAB during the preparation process. The particle size of Co@CN decreased with the increasing of CTAB content. Moreover, the addition of CTAB facilitated the formation of Co‐Nx species on catalyst surface. The kinetic rate constant of Co@CN‐5%CTAB catalyst was 0.99 min−1, which is 2.5 times as high as that of Co@CN‐0%CTAB catalyst for 4‐nitrophenol reduction. The excellent catalytic performance of Co@CN‐5%CTAB may be due to the presence of Co (0) species generated in situ during the calcination process, the smaller Co nanoparticles and more Co‐Nx site on the surface of the catalyst.