High production of furfural by flash pyrolysis of C6 sugars and lignocellulose by Pd-PdO/ZnSO₄ catalyst

Furfural (C₅H₄O₂) is an important platform chemical for the synthesis of next-generation bio-fuels. Herein, we report a novel and reusable heterogeneous catalyst, Pd-PdO/ZnSO₄ with 1.1 mol% palladium (Pd), for the production of furfural by flash pyrolysis of lignocelluloses at 400 °C. For both dry and wet C6 cellulose and its monomers, the furfural yields reach 74–82 mol%, relative to 96 mol% from C5 xylan and 23–33 wt% from sugarcane bagasse and corncob. The catalyst has a well-defined structure and bifunctional property, comprising a ZnSO₄ support for the dehydration and isomerization of glucose, and a local core-shell configuration for metallic Pd⁰ encapsulated by an oxide (PdO) layer. The PdO layer is active for the Grob fragmentation of formaldehyde (HCHO) from glucose, which is subsequently in-situ steam reformed into syn-gas (i.e. H₂ and CO), whereas the Pd⁰ core is active in promoting the last dehydration step for the formation of furfural.