Density regulation of surface hydroxyl on porous carbons as efficient catalytic supports

Abstract

Oxygen-containing functional groups play a crucial role in anchoring active metals on supported catalysts, especially hydroxyl groups, which hold advantages in regulating the electronic structure and optimizing the dispersion of metal species through their lone electron pairs. However, the coexistence of various oxygen-containing groups (e.g., CO, C–O–C, C–OH) on carbon support is intractable in identifying the role of hydroxyl groups and revealing structure-activity relationships in the construction of effective supported catalysts. Herein, we established a regulation method for enriching hydroxyl groups of porous carbons by selective removal of ether oxygen-containing species via Diels-Alder (DA) reaction. This results in an increase in the proportion of hydroxyl from 30 % up to 54 %. The high proportion of hydroxyl on the obtained sample ET(200)-Air-HCM serves as an effective site for anchoring Pd species, thus leading to high dispersion of Pd nanoparticles featuring Pd²⁺ with an electron-deficient state. The highly dispersed Pd²⁺ species provides abundant active sites for the selective oxidation of benzyl alcohol with 99.7 % conversion and 99.6 % selectivity of benzaldehyde attained over Pd@ET(200)-Air-HCM at 363 K and 1 atm oxygen atmosphere. This study offers a facile method for the selective regulation of the proportion of hydroxyl groups on porous carbon-based materials for catalysis applications.