Effect of NiFe sub(2)O sub(4) on PCDF byproducts formation during thermal degradation of decachlorobiphenyl

Formation of 2,3,7,8-PCDD/Fs during the catalytic decomposition of decachlorobiphenyl over spinel NiFe sub(2)O sub(4) was evaluated at 300 degree C and compared with that over Fe sub(2)O sub(3) and in a catalyst-free system. The total concentration of 2,3,7,8-PCDFs, dominated by OCDF and then 2,3,7,8-HpCDF, were significantly formed, being 6-53 times higher than the total concentration of 2,3,7,8-PCDD in all three reaction systems studied. Time-dependent distribution profile of 2,3,7,8-PCDF indicated that the degradation and formation of PCDF occurred concurrently. The initial hydrodechlorination of OCDF preferentially occurred at the 1- and 9-position than at the 4- and 6-position (thus, higher amounts of 1,2,3,4,6,7,8-HpCDF were generated relative to 1,2,3,4,7,8,9-HpCDF), followed by further major hydrodechlorination pathway of 1,2,3,4,6,7,8-HpCDF arrow right 1,2,3,6,7,8-HxCDF arrow right 1,2,3,7,8-PeCDF arrow right 2,3,7,8-TCDF. Relative to the catalyst-free reaction system, the concentration and total toxic equivalent values of 2,3,7,8-PCDFs decreased by 24.1-99.7% and 86-98.4%, respectively, in the NiFe sub(2)O sub(4) catalyst system, while initial increases by 744.5% and 426.3%, respectively, followed by reduction up to 81.6% and 90.7%, respectively, were observed in the Fe sub(2)O sub(3) catalyst system. Current findings indicate that NiFe sub(2)O sub(4) hindered PCDF formation, which was attributed to its chemical structural stability and high activity towards degradation of biphenyl-like constituents in PCBs.