Coupled Transfer Hydrogenation and Alcoholysis of Furfural To Yield Alkyl Levulinate over Multifunctional Zirconia-Zeolite-Supported Heteropoly Acid

Alkyl levulinate as one kind of fuel additive and versatile biomass-based platform molecule has attracted significant interests in the field of sustainable chemistry, which can be harvested straight from furfural (FAL), an important industrial chemical derived from agricultural residues. The development of a high-efficiency and low-cost catalytic system is highly desirable toward this challenging valorization process. In this contribution, bifunctional zirconia-zeolite-supported heteropoly acid catalysts with adjustable Lewis and Bronsted acid sites were successfully designed via an in situ synthetic method and attempted to couple transfer hydrogenation and alcoholysis for one-pot conversion of FAL to alkyl levulinate. The catalyst characterization and catalytic behavior were systematically combined for insight into the structure-function relationship and reaction mechanism. Selectivity toward alkyl levulinate was found to be strongly dependent upon the distribution of acid sites. As-prepared HPMo(20)/Zr-MCM-41 with a Si/Zr molar ratio of 60 and H-3[P(Mo3O10)(4)] (HPMo) impregnation concentration of 20 g/L was uniquely effective using isopropanol as a hydrogen donor and reaction medium, leading to a high isopropyl levulinate yield of 79.6%. This monolithic catalyst exhibited good stability and could be reused at least 5 times without any substantial change in the product yield after plain thermal regeneration.

Automated summary

In this study, a bifunctional zirconia-zeolite-supported heteropoly acid catalyst was successfully designed to convert furfural to alkyl levulinate through a one-pot conversion combining transfer hydrogenation and alcoholysis. The selectivity towards alkyl levulinate was observed to be strongly influenced by the distribution of acid sites, with the HPMo(20)/Zr-MCM-41 catalyst showing high efficiency with isopropanol as a hydrogen donor. This monolithic catalyst exhibited good stability and could be reused multiple times without significant change in product yield.