Directing the Simultaneous Conversion of Hemicellulose and Cellulose in Raw Biomass to Lactic Acid

The production of lactic acid (LaA) directly from actual biomass via a one-step reaction without pretreatment by chemocatalysis has shown high potential for satisfying its enormous demand in widespread applications. Here, we developed an integrated catalytic strategy using Y(III) as the catalyst, enabling the simultaneous conversion of hemicellulose and cellulose components in the actual biomass and selectively yielding LaA with a yield up to 66.3%. The evaluated turnover frequency was 9.7 h–1, the highest value using the actual biomass as the feedstock as far as we know. Combining the result of the experiment with density functional theory studies, we revealed that in the present system, H+, [Y(OH)2(H2O)2]+ species derived from Y3+ hydrolysis cooperatively contributed to the production of LaA. H+ was primarily responsible for the selective fractionation of hemicellulose and cellulose from actual lignocelluloses to soluble polysaccharide fragments as well as the next polysaccharide conversion to the monosaccharide. [Y(OH)2(H2O)2]+ species predominantly contributed to the next monosaccharide conversion to LaA, particularly favoring the electron outflow from C3 to C4–O of fructose derived from glucose isomerization and leading to the accumulation of electronic density on the O atom in C4–O, thereby significantly weakening the C3–C4 bond and directing the selective cleavage of the C3–C4 bond in fructose to LaA. This work might provide a potential strategy for the simultaneous conversion of C5 and C6 sugars in the actual biomass selectively yielding LaA in a cost-effective and environment-friendly way.