Aluminum-based Metal-Organic Framework as Water-tolerant Lewis Acid Catalyst for Selective Dihydroxyacetone Isomerization to Lactic Acid

Lactic acid is a renewable and versatile chemical for food, pharmaceuticals, cosmetics, and other chemicals. Lactic acid can be produced from biomass-derived dihydroxyacetone. However, selective and recyclable water-tolerant acid catalysts need to be developed for the specific production of lactic acid. Here we show that the MIL-101(Al)−NH₂ metal-organic framework (MOF) is a water-tolerant and selective solid Lewis acid catalyst for dihydroxyacetone isomerization to lactic acid. The Lewis acidic MIL-101(Al)−NH₂ catalyst promoted a high lactic acid selectivity of 91 % at 96 % dihydroxyacetone conversion at 120 °C in water. The reaction proceeded by temperature and/or MIL-101(Al)−NH₂ MOFs mediated dihydroxyacetone dehydration to pyruvaldehyde. Subsequently, the MIL-101(Al)−NH2 facilitated rehydration of the pyruvaldehyde to lactic acid. The Lewis acidic MIL-101(Al)−NH₂ catalyst was stable and reusable four times without any decrease in catalytic performance.