Unraveling the hydrogenation of α-ketoglutaric acid on Pd through active sites, substrate structure, and kinetics

α-Ketoglutaric acid (α-KGA) is an upcoming platform molecule in bio-based industries, with catalytic valorization strategies currently being explored. This study investigates the aqueous-phase hydrogenation of α-KGA using hydrogen gas in a batch reactor, focusing on the role of catalyst properties, substrate structure, and kinetics that affect catalytic activity. 5% Pd/C was the most suitable catalyst (at 40°C and 50 bar) with high turnover frequencies (4.3–7.9 s⁻¹), while other metals (Pt, Rh, Ru, Ni, Cu, and Mo) were inferior. The main product, α-hydroxyglutaric acid, was typically produced in high yield (95%), with minor formation of γ-carboxyl butyrolactone (3%). Furthermore, the α-COOH group in the substrate enhanced the activity on Pd whereas inhibition occurred on oxophilic Ru. Finally, a two-step addition of hydrogen to α-KGA on Pd emerged as the most plausible surface reaction pathway. These findings provide a thorough understanding of aqueous-phase hydrogenation of activated α-ketoacids, which is useful for other biomass-derived oxygenates.