Sunlight-driven photocatalytic conversion of furfural and its derivatives

Abstract

Furfural (mainly furfural and 5-hydroxymethylfurfural) and its derivatives stand out as an important platform for C5 and C6 compounds from lignocellulosic biomass. Catalytic valorization of these renewable carbohydrates not only enables the manufacture of various high-valued chemicals but also enriches routes and theories for the direct use of crude biomass. Photocatalytic conversion of furfural and its derivatives using solar energy has recently received great attention. Such an environmentally friendly and energy-saving approach enables activation and transformation of the target chemical bonds under very mild reaction conditions using photoexcited charge carriers or photogenerated reactive species. However, highly selective photocatalysts are somewhat lacking and the reaction mechanisms usually remain obscure. Herein, this review article aims to systematically summarize the recent advances in sunlight-driven photocatalytic conversion of furfural and 5-hydroxymethylfurfural to sustainable building-block chemicals. In particular, the strategies of catalyst design and the unique roles of reactive species (i.e., photogenerated electrons and holes, hydroxyl and superoxide radicals, and singlet oxygen) are discussed. This allows insights into the catalytic mechanisms. In addition, the latest progress in the combination of such photooxidation with H₂ evolution or CO₂ reduction, as well as photo(electro)chemical conversion, is also reviewed. In addition to the common oxidation and reduction reactions, some nontraditional reaction paths (i.e., reductive coupling, oxidative decarboxylation and ring-opening) and promising products are introduced. Finally, challenges and future opportunities from the perspective of green chemistry are also analyzed. Therefore, a bright prospect can be foreseen in the near future for many more photocatalytic valorizations of furfural-like molecules.