Regulation of the Co–Nx Active Sites of MOF-Templated Co@NC Catalysts via Au Doping for Boosting Oxidative Esterification of Alcohols

Abstract

The Co–Nx active sites play a critical role over the Co@NC catalyst in the heterogeneous catalysis. However, the effective methods for the regulation of the content and electronic structure of Co–Nx active sites to enhance the catalytic efficiency of heterogeneous catalysts are still insufficient. Herein, a nitrogen-doped porous carbon-encapsulated Au-doped Co nanoparticle catalysts with abundant and electron-rich Co–Nx sites in the outer carbon layer was designed by a Au doping strategy through pyrolysis of the HAuCl4-modified ZIF-67 metal organic framework precursor. The optimal catalyst exhibits improved catalytic performance in alcohol selective oxidative esterification. The linear relationship between the ester yield and Co–Nx species content, combined with a series of control experiments, indicated that the Co–Nx active sites are crucial for achieving the excellent catalytic activity (yield: 99.9%). In situ diffuse reflectance infrared Fourier transform spectroscopy, O2-temperature-programed desorption characterizations, active oxygen species quenching experiments together with density functional theory calculations results indicate that Au doping in the Co nanoparticle core increases the content and the electron density of Co–Nx species on the outer carbon shell, which enhanced the chemical adsorption and activation of molecular O2 for producing reactive O2•– species. This study demonstrated a novel Co–Nx active site regulation strategy for the efficient selective oxidative esterification of alcohols under mild reaction conditions.