Defective Auδ−-Ov interfacial sites boost C-H bond activation for enhanced selective oxidation of amino alcohols to amino acids

Abstract

Designing efficient active sites to facilitate the oxidation of hydroxyl group to carboxylic acid under the influence of nitrogen-containing functional groups is worth exploring, but it is rarely investigated. Herein, we construct defective Au-ZrO2 interfacial structures by tuning the calcination temperature of ZrO2 support to boost the oxidation of amino alcohols to amino acids. Interestingly, the modification of calcination temperature induces the escape of saturated coordination oxygen atoms in ZrO2 support, leaving behind abundant surface oxygen vacancy (Ov). The as-formed Auδ−-Ov interfacial site displays the unique synergistic adsorption effect and electron transfer ability. Specifically, the Ov site voluntarily adsorbs the –NH2 group of amino alcohol, thus ensuring that the electron-rich Auδ− nearby Ov site adsorbs the hydroxyl groups and activates the C-H bond activation of NH2CH2CH2O* intermediates. Consequently, Au/ZrO2-600 catalyst with more defective Auδ−-Ov interfacial sites exhibits 98.8 % product yield for the oxidation of diethanolamine to iminodiacetic acid at only 30 °C. The catalyst system is further extended to the oxidation of other amino alcohols, involving monoethanolamine and triethanolamine, to their corresponding amino acids with excellent catalytic performance.