Aluminum phosphotungstate as a promising bifunctional catalyst for biomass carbohydrate transformation to methyl levulinate under mild conditions

Abstract

To develop an efficient and sustainable catalytic process for the transformation of biomass-derived carbohydrates into methyl levulinate (ML), a series of phosphotungstates, MPW12O40 (MPW, where M = Al3+, In3+, Cr3+, Fe3+) with bifunctional Brønsted and Lewis acidities were investigated. Among these catalysts, aluminum phosphotungstate (AlPW12O40, AlPW) showed superior activity, affording 45–70 mol% yield of ML from various carbohydrates at 160 °C, with an extremely low solvent-to-substrate ratio (7.5 g/g) for 20–30 min under both exterior and microwave heating. The bifunctional Brønsted and Lewis acidic sites of MPWs exhibited synergistic effects, which facilitated the transformation of glucose to ML at mild temperatures. Product analyses indicated that the introduction of metal ions affected the product selectivity and provided insights into the reaction pathway. The formation of the pseudoliquid phase of AlPW improved the accessibility of the active catalyst sites, contributing to its high efficiency. Furthermore, AlPW had excellent reusability with little loss of catalytic activity after five recycle runs. In general, the use of the AlPW catalyst offers a promising approach to sustainable, clean, and highly efficient ML production.