Efficient Synthesis of Methyl Lactate from Glucose over Postsynthesized Sn-Beta Zeolites: Switching Selectivity by Tuning Surface Acidity

In this contribution, several Sn-β zeolites with variable Sn content and acid characteristics were prepared by regulated postsynthetic incorporation of Sn into predealuminated Beta zeolites and investigated in detail in terms of their surface properties, namely, using FTIR pyridine and deuterated acetonitrile, as well as XPS. The obtained zeolites were applied to the catalytic conversion of glucose in methanol to yield methyl lactate. Precise regulation of the tin amount (close to stoichiometric Si/Sn ratio) allowed us to obtain catalysts which afforded up to 63.5% yield of methyl lactate even without additional alkaline treatments. No clear correlations of the yield of methyl lactate on the concentration of Brønsted acid sites and LAS/BAS were observed, while a decrease in the fraction of silanol groups was beneficial for the selective formation of the desired product. An increase in site density (the ratio of the framework Sn concentration from FTIR CD₃CN to mesopore specific surface area) resulted in elevated catalytic performance of the Sn-Beta zeolites.