Efficient decarbonylation of 5-hydroxymethylfurfural over an Pd/Al2O3 catalyst: Preparation via electrostatic attraction between Pd(II) complex and anionic Al2O3

- Highly dispersed Pd/Al2O3 was prepared based on electrostatic attraction strategy.
- Action mechanism of pH of impregnation solution was explored.
- Catalysts with small Pd nanoparticles showed superior catalytic performance.
- Structure sensitive behavior of catalysts was discussed.
- Surface properties of catalysts were characterized by in situ FTIR.

Decarbonylation of 5-hydroxymethylfurfural (HMF) provides a potential way to utilize the abundant natural hexoses derived from cellulose or hemicellulose. Herein, we propose for the first time that a Pd/Al2O3 prepared based on an electrostatic attraction strategy can efficiently convert HMF into furfuryl alcohol (FOL). Ammonia solution with high pH value could realize the electrostatic attraction assumption in the interface of support and palladium complex, while diluted hydrochloric acid with low pH value could cause the instability of H+ ions on Al2O3 surface, leading to larger Pd nanoparticles (NPs) of the catalyst and lowering the decarbonylation activity. A structure-sensitive behavior was discussed that the intrinsic activity of catalyst rised with the decreased size of Pd NPs, which could be illustrated by that the smaller particles exposed more defective Pd sites, on which the decarbonylation adsorption mode of η2(C, O) was preferred. FOL yield of 95% was obtained through modulation of reaction conditions.