Double-metal cyanide-supported Pd catalysts for highly efficient hydrogenative ring-rearrangement of biomass-derived furanic aldehydes to cyclopentanone compounds

The hydrogenative ring-rearrangement of biomass-derived furanic aldehydes (furfural or 5-hydroxymethyl furfural) to cyclopentanone compounds (cyclopentanone or 3-hydroxymethyl cyclopentanone) is of great significance for high-value chemicals. The Brønsted acid in metal-support bifunctional catalysts causes a serious carbon loss, and the weak Lewis acid is difficult to induce hydrolysis reaction steps. Here, a double-metal cyanide (DMC) catalyst with pure moderate Lewis acid sites was investigated for solving the above problems. The crystal structure and the Lewis acidity of the catalyst are controlled by different kinds of metals, and the surface properties are changed by a complexing effect. Pd clusters of 8 nm are uniformly dispersed on the surface after impregnation on the double-metal cyanide. For the reaction of furanic aldehydes, the Pd/FeZn-DMC catalyst with a moderate Lewis acidity shows a high efficiency for the synthesis of cyclopentanone compounds, whereas the Pd/FeNi-DMC and Pd/FeCo-DMC catalysts with a weak Lewis acidity result in a yield above 90.2% of furanic alcohols (furfuryl alcohol or 2,5-bis(hydroxymethyl)furan). The catalytic activity of Pd/FeZn-DMC is controlled by the surface area based on the accessibility of the Lewis acid sites, and the highest yields of 96.6% and 87.5% are obtained for cyclopentanone and 3-hydroxymethyl cyclopentanone, respectively. Furthermore, the catalyst is resistant to leaching and performs stably after 6 runs. This study not only provides a promising route for efficient production of cyclopentanone compounds but also shows the excellent advantage of DMC-based bifunctional catalysis in biomass conversion reactions.