Rare-Earth Metal Yttrium-Modified Composite Metal Oxide Catalysts for High Selectivity Synthesis of Biomass-Derived Lactic Acid from Cellulose

Lactic acid is a versatile and potential building block for generating biodegradable plastics and polylactic acid, as well as in chemical and pharmaceuticals industry. Nevertheless, the achievement of lactic acid production in large quantities remains an enormous challenge. Herein, a series of yttrium-modified composite metal oxide catalysts were synthesized for production of lactic acid starting from renewable biomass cellulose. Interestingly, Y₂O₃/Al₂O₃ showed outstanding chemoselectivity towards lactic acid due to its predominant Lewis acid sites (Y³⁺) and weak Brønsted acid sites (hydroxyl group) together with appropriate total surface acidity. The structure-activity relationship was systematically investigated by a combination of XRD, BET, NH₃-TPD, PyIR, SEM, FTIR, and XPS characterization techniques. A nearly complete conversion of cellulose and as high as 72.8 % yield of lactic acid could be achieved under the optimum conditions. Importantly, the resultant catalysts were reusable without appreciable loss in catalytic activity after five consecutive cycles. This study provides an efficient, cost-efficient and facile strategy for fabricating promising heterogeneous catalysts for conversion of biomass resources to highly valuable chemicals.