Metal-Support Synergy in Nitrogen-Doped Carbon-Supported Ru Nanoparticles Enables Base-Free Aerobic Oxidation of Isononanol to Isononanoic Acid.

Abstract

Selective aerobic oxidation of long-chain primary aliphatic alcohols to the corresponding carboxylic acids remains a fundamental yet industrially challenging transformation, particularly under base-free conditions. Herein, we report a systematic investigation of Ru nanoparticles supported on nitrogen-doped carbon (Ru/NC) for the oxidation of isononanol to isononanoic acid using molecular oxygen as the sole oxidant. By tailoring the thermal treatment atmosphere and temperature, the particle size and surface oxidation state of Ru were precisely regulated. Among the catalysts examined, Ru/NC reduced in H₂ at 523 K exhibited optimal performance, affording 98% conversion and 88% selectivity to isononanoic acid at 393 K and 0.8 MPa O₂ after 24 h without any added base. Structure-activity correlation reveals a volcano-type dependence of activity on Ru particle size with an optimum around 1.3 nm, and a strong positive correlation between surface Ru° fraction and catalytic performance. The N-doped carbon support not only stabilizes highly dispersed Ru nanoparticles but also modulates their electronic structure via metal-support interactions. Catalyst deactivation is primarily attributed to Ru leaching and nanoparticle sintering. This study provides mechanistic insight into Ru-catalyzed oxidation of high-carbon aliphatic alcohols and highlights the critical role of controlled reduction in achieving efficient, base-free oxidation systems.