Insight into the low-temperature decomposition of Aroclor 1254 over activated carbon-supported bimetallic catalysts obtained with XANES and DFT calculations

Novel bimetallic catalysts supported on activated carbon (AC) with high metal loadings were synthesized by carbonizing an ion-exchange resin. AC-supported Ni-Cu (Ni-Cu/C) and Ni-Zn (Ni-Zn/C) bimetallic catalysts with different Ni:Cu(Zn) ratios were used to decompose Aroclor 1254, which is a commonly used commercial mixture of polychlorinated biphenyls. Characterization with scanning electron microscopy and energydispersive X-ray spectroscopy showed that the metals were uniformly distributed on the surfaces and inside the catalysts. After 30 min reaction over the Ni-Cu/C catalyst at a low temperature of 250 °C, the efficiencies of Hexa-CBs decomposition present in Aroclor 1254 exceeded 97%, which were higher than those achieved over Ni-Zn/C. These efficiencies increased with Cu content in Ni-Cu/C, and decreased with the amount of Zn in Ni-Zn/C. X-ray photoelectron spectra and X-ray absorption near-edge structure spectra of Ni-Cu/C and Ni-Zn/C before and after the reaction indicated that Ni and Cu were oxidized during the reaction. However, Zn showed no significant change, suggesting that Ni and Cu are the active components to promote reaction with Aroclor 1254, whereas Zn is only a spectator. The efficiencies of Aroclor 1254 decomposition over bimetallic catalysts were greater than those over monometallic catalysts, which was confirmed by density functional theory calculations.