Zeolite-Encapsulated Cu Nanoparticles for the Selective Hydrogenation of Furfural to Furfuryl Alcohol

Catalytic hydrogenation of furfural (FFL) to furfuryl alcohol (FAL) is one of the pivotal reactions for biomass valorization. Herein, well-defined Cu nanoparticles of similar to 1.8 nm encapsulated within titanium silicalite-1 (TS-1) have been successfully prepared by an in situ encapsulation approach, which possesses significant advantages in metal dispersion and uniformity compared to the traditional wet impregnation method. After a Na ion-exchange process for modulation of the zeolite microenvironment, the obtained Na-Cu@TS-1 catalyst affords an enhanced activity and selectivity in the selective hydrogenation of FFL into FAL, with a FFL conversion of 93.0% and a FAL selectivity of 98.1% at 110 degrees C, 10 bar H-2, after a reaction time of 2 h. A turnover frequency value of 55.2 h(-1) has been achieved, reflecting some of the highest activity for Cu-based heterogeneous catalysts under similar conditions. Comprehensive characterization studies reveal that the confined environment of the zeolite could not only provide the spatial restriction for metal particles but also induce an electronic interaction between encapsulated Cu nanoparticles and Ti species in Na-Cu@TS-1, which both lead to effective suppression of the metal aggregation and leaching during catalysis. Na species, added by the ion exchange, not only mediate the acid/basic property of the zeolite for suppressing the side reactions but also modulate the encapsulated Cu species into an electronic-rich state, facilitating the FFL hydrogenation. Deactivation of Na-Cu@TS-1 is primarily caused by Na leaching into the liquid phase, but activity can be almost restored after a Na readdition process.