Pt Loading-Dependent Glucaric Acid Formation in Aerobic Oxidation of Glucose over Pt/HAP Catalysts

Abstract The selective aerobic oxidation of glucose to glucaric acid represents a sustainable route for producing renewable dicarboxylic acids, yet the efficient oxidation of the terminal C6 hydroxymethyl group remains challenging. Herein, hydroxyapatite-supported Pt catalysts (Pt/HAP) with different Pt loadings were prepared by wet impregnation and evaluated for the one-pot aerobic oxidation of glucose in aqueous NaHCO3 using O2 as the terminal oxidant. Increasing the Pt loading enhanced glucose conversion and promoted deeper oxidation toward glucaric acid, whereas the improvement in glucaric acid yield became limited when the Pt loading exceeded 3 wt %. Although Pt5/HAP afforded the highest glucaric acid yield of 32.73% after 1 h, Pt3/HAP achieved the highest apparent Pt-normalized glucaric acid productivity of 304.8 mmol·gPt–1·h–1, together with the highest total yield of quantified C6 acids of 91.78%. XRD and TEM analyses revealed substantial Pt particle growth at a loading of 5 wt %, suggesting that excessive Pt loading compromises the effective utilization of Pt species. Under the optimized reaction conditions, Pt3/HAP achieved complete glucose conversion and a 57.27% glucaric acid yield after 8 h, while maintaining high activity over five cycles. These findings identify Pt loading as a key parameter for balancing glucaric acid formation and Pt utilization in sustainable glucose oxidation.