Full potential of microwave-assisted processes: From synthesis of high-quality MIL-101(Fe) catalyst to furfural valorization

Abstract

Metal-organic frameworks (MOFs) have emerged as promising catalysts in biomass valorization processes, due to mainly their high structural and chemical flexibility when compared to other catalytic materials. However, it is still challenging to achieve perfect control in the synthetic method to obtain high-quality MOF particles containing uniform active sites, which will strongly influence their further catalytic performance. Herein, we have demonstrated that microwaves (MWs) can play a key role not only in the preparation of the MOF catalyst, specifically MIL-101(Fe), but also in performing the MOF-catalyzed oxidative esterification of furfural to methyl-2-furoate under mild conditions and in the absence of a base. MIL-101(Fe) exhibited a high conversion of furfural (>90 %) and excellent selectivity to methyl-2-furoate (>95 %) in just 1 h of reaction and at a moderate temperature (60 °C). A series of control experiments and DFT-mechanistic studies revealed the pivotal role played by the MIL-101(Fe) particles to drive the preferential formation of the target compound methyl-2-furoate, and evidenced that the MOF behaves as a truly heterogeneous catalyst. Overall, this work demonstrates that the potential of MW energy is underexploited, and highlights that there is still a long way to go in the development of new MOF-based catalytic approaches for biomass transformations.