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

Abstract

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.

Selective hydrodeoxygenation of α, β-unsaturated carbonyl compounds to alkenes

“…In the initial step, it was observed that the presence of either base or acid led to a reduction in CAL conversion, emphasising the significance of Lewis acid-base sites for the reaction (Supplementary Table 4 , Entry 2 and 3). KSCN, a recognised poison reagent capable of deactivating single atomic or metal sites 46 , resulted in a substantial decrease in CAL conversion from 95.0% to 53.7% when 20 mg KSCN was added to the reaction (Supplementary Table 4 , Entry 4). In the subsequent step, both pyridine and KSCN reduced the conversion of COL, while the impact of boric acid was minimal (Supplementary Table 4 , Entry 6–8).…”

Additive- and base-free tandem aerobic oxidative cleavage of olefins to esters using bifunctional mesoporous copper-incorporated Al-SBA-15

“…Esters contribute to many fruits' characteristic aroma and flavor, also often used as solvents, plasticizers, and raw materials for perfumery. 3,4 Hence, esters are produced through different methods, including the esterification of acids and oxidative esterification of aldehydes and alcohols (Scheme 1). Traditionally, this conversion has involved the use of stoichiometric amounts of oxidizing agents like KMnO 4 , O 3 , TBHP, and H 2 O 2 .…”

Influence of Oxide Coating Layers on the Stability of Gold Catalysts for Furfural Oxidative Esterification to Methyl Furoate

“…Heterogeneous catalysts such as noble metal catalysts (i.e., Au [22][23][24], Pt [25], Pd [26], etc.) as well as transition metal catalysts (i.e., Co [27,28], etc.) have shown great potential in the oxidative esterification process due to their capability of converting O 2 molecules into highly active atomic O or other reactive oxygen species [29].…”