The Co–N
x
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–N
x
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–N
x
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–N
x
species
content, combined with a series of control experiments, indicated
that the Co–N
x
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–N
x
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–N
x
active site regulation strategy for the efficient
selective oxidative esterification of alcohols under mild reaction
conditions.
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