Nitrogen‐Doped Carbon Xerogels Supporting Palladium Nanoparticles for Selective Hydrogenation Reactions: The Role of Pyridine Nitrogen Species.

Abstract: Nitrogen‐doped carbon xerogels (NDCX) functionalized with various nitrogen functionalities are synthesized and used as supports for Pd nanoparticles (NPs) for selective hydrogenation reactions. The nitrogen doping not only induces the formation of surface basic sites that can connect with the Pd NPs by donating electrons to the unoccupied d orbital of Pd atoms and improve the Pd dispersion, but it also leads to C–N–C hybrid rings that can interact with substrates containing electron‐rich carbon rings, increasing the reaction activity. So far, the Pd/NDCX shows >95 % 1,5‐cyclooctadiene (COD) conversion and cyclooctene (COE) selectivity within 90 min for selective hydrogenation of COD to COE, and the activity can be recovered after washing the catalyst. Moreover, the catalyst can be applied to various substrates containing C=C and/or −NO₂ groups with considerable conversion and selectivity. Experimental results and DFT theoretical calculations suggest that the pyridinic nitrogen plays an important role in the reaction, as it is not only the adsorption site of Pd NPs for H₂ activation, but it also serves as the active site for COD activation. On these bases, a mechanism for the reaction is proposed. [ABSTRACT FROM AUTHOR]