Efficient Brønsted Acid Sites Accessibility of ZSM-5 Nanosheets Promoting One-Step Lactide Synthesis

Graphical N-ZSM-5–40 nanosheet zeolites prepared by seed-induced growth coupled with mineralization agent assisted method exhibited remarkable activity and stability in conversion of lactic acid to lactide. Enhanced diffusion and accessible Brønsted acid sites amount benefit the production of lactide. Lactide (LD) is the key building block of high-quality polylactic acid (PLA), a biodegradable polymer with broad industrial applications. Developing an efficient catalyst for one-step conversion of lactic acid to LD is critical for the PLA industry. Herein, N-ZSM-5–40 nanosheets with a thickness of about 20 nm were successfully synthesized and first applied to this esterification reaction. The yield of LD over N-ZSM-5–40 reaches 60.5% after reaction at an oil bath temperature of 140 °C for 5 h. Systematic characterization revealed that reducing the b-axis thickness of MFI-type nanosheet zeolites improves Brønsted acid sites (BASs) accessibility, which was identified as a critical factor governing the yield of LD. Time-dependent product distribution experiments demonstrate that the nanosheet structure of N-ZSM-5–40 facilitates faster cyclization of L 2 A to LD, compared to commercial C-ZSM-5–40. In-situ FTIR results reveal that N-ZSM-5–40 nanosheets have a strong ability to adsorb and activate carbonyl groups, which promotes the rapid conversion of lactic acid to LD. Given the aforementioned advantages, ZSM-5 nanosheets hold great potential for guiding the development of industrial catalysts for sustainable LD synthesis.