ChemCatChem 2018-01-27

Nitrogen doped carbon xerogels supporting Pd nanoparticles for selective hydrogenation reactions: the role of pyridine nitrogen species

Duihai Tang, Xue Sun, Dan Zhao, Junjiang Zhu, Wenting Zhang, Xuelian Xu, Zhen Zhao

Index: 10.1002/cctc.201702007

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Abstract

Nitrogen doped carbon xerogels (NDCX) functionalized with various nitrogen functionalities are synthesized and used as supports of 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 also forms 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% COD conversion and COE selectivity within 90 min for selective hydrogenation of 1,5-cyclooctadiene (COD) to cyclooctene (COE), and the activity can be recovered after washing the catalyst. Moreover, the catalyst can be applied to varied substrates containing C=C and/or -NO2 groups with considerable conversion and selectivity. Experimental results and DFT theoretical calculations suggest that the pyridine nitrogen plays an important role in the reaction, which is not only the adsorption site of Pd NPs for H2 activation, but also the active site for COD activation. On these bases, a mechanism for the reaction is proposed.