Solid Lewis Acids with Sn Catalyzing Fructose into Methyl Lactate

With the increasing demand of lactic acid (LA), a highly value-added platform chemical, catalytic conversion of biomass to produce LA and its ester is more economical and efficient relative to the fermentative route. We describe here a catalytic process for the formation of methyl lactate (ML) directly from fructose, and ML can be easily hydrolyzed to LA. A series of solid Lewis acids with Sn as active sites were prepared via the pyrolyzing coordinated polymer (PCP) method, converting fructose into ML in methanol. The results of XRD, SEM, ICP-MS, XPS, BET, NH₃-TPD and Py-IR show that our customized catalysts are microporous-mesoporous materials and their acidities are strong; the Sn₃-CN catalyst with an optimal Sn loading of 6.39 wt% is rich in Lewis acidic sites and contains almost no Brønsted acidic sites. The catalytic evaluation showed that Sn₃-CN catalyst completely converted fructose for 20 h at 160 °C, and the yield of ML was 52%. In the repeated use of Sn₃-CN, ML selectivity remained at about 52% after 6 cycles, and fructose conversion decreased by about 10%, indicating that it had the promising stability.

Graphical Abstract