Acidity tuning of beta zeolite for efficient one-step lactide synthesis from lactic acid

Lactide (LD) is a key monomer for producing biodegradable polylactic acid (PLA) and critically influences the material’s performance and range of applications. Compared with the conventional two-step route from lactic acid (LA) to LD, the one-step liquid-phase process provides milder reaction conditions and greater industrial potential. β zeolites, featuring a unique three-dimensionally interconnected pore structure, have demonstrated considerable promise in catalyzing the conversion of LA to LD. However, the synergistic roles of Brønsted and Lewis acid sites (i.e., BASs and LASs) in enhancing LD yield and selectivity remain insufficiently explored. In this study, steaming treatment was employed to tailor the density, strength and ratio of BASs and LASs in β zeolite catalysts, aiming to elucidate their cooperative effects on LA-to-LD conversions. Characterization results indicated that the steaming treatment has minimal impact on the structural integrity of the zeolite while enabling effective regulation of their acidic properties. Catalytic performance assessments revealed that the optimally treated catalyst, Hβ-300–3h (steamed at 300 °C for 3 h), achieved a high LA conversion of 96% and an LD yield of 90%, with stereoselectivity toward L -LD exceeding 99%. These results surpass those of most previously reported zeolite catalysts. The enhanced catalytic activity can be attributed to the optimized concentration and strength of BASs and LASs, which facilitate synergistic catalysis across multiple reaction steps and promote the efficient conversion of LA to LD.