Enhanced catalytic hydrodechlorination of 2,4-dichlorophenol over Pd catalysts supported on nitrogen-doped graphene

Pd catalysts supported on graphene and N-doped graphene (GN-1, GN-2 and GN-3) with varied N-doping amounts were prepared using the deposition-precipitation method, and liquid phase catalytic hydrodechlorination (HDC) of 2,4-dichlorophenol (2,4-DCP) was investigated over these catalysts. The catalysts were characterized by X-ray diffraction, elementary analysis, N-2 adsorption-desorption isotherms, transmission electron microscopy, and X-ray photoelectron spectroscopy. Characterization results showed that graphene could be successfully doped by N using the heat treatment method with melamine as precursor, and N doping amounts were determined to be 5.7, 8.6 and 11.3% for GN-1, GN-2 and GN-3, respectively. Additionally, Pd2+/Pd-0 ratios and Pd dispersions in the Pd/GN catalysts were much higher than those in Pd/graphene. For a similar Pd loading, the Pd dispersion of Pd/GN first increased and then decreased with the increase of N-doping amount, and the highest Pd dispersion was observed on Pd(2.9)/GN-2. Accordingly, GN supported Pd catalysts exhibited much higher catalytic activities than Pd/graphene, the catalytic reaction first increased and then decreased slightly in activity with the increase of nitrogen doping amount, and the highest activity was identified on Pd(2.9)/GN-2. Moreover, the dechlorination of 2,4-DCP over supported Pd catalysts proceeded via both a stepwise and concerted pathway, and the concerted pathway became predominant upon N doping.