Electrocatalytic reduction of 2-chlorobiphenyl in contaminated water using palladium-modified electrode

Enhanced electrocatalytic hydrodechlorination of 2,4-dichlorophenoxyacetic acid by a Pd-Co3O4/Ni foam electrode

A new Pd-Co3O4/Ni foam electrode was synthesized by a facile two-step method comprising co-electrodeposition and calcination. Compared with Ni foam-supported Pd electrodes obtained by electrodeposition or chemical deposition, the new Pd-Co3O4/Ni foam electrode exhibited greatly enhanced catalytic hydrodechlorination activity. The introduction of Co3O4 reduced the amount of Pd required. For the same degree of dechlorination of 2,4-D, only 25% of the Pd was required in the Pd-Co3O4/Ni foam electrode compared with the Ni foam electrode prepared by chemical deposition. Various characterizations indicated that Co3O4 on the surface of the Ni foam enhanced catalytic performance through accelerated generation of atomic H*. In addition, the good distribution of macropores, providing a larger specific surface area and lower electron transfer impedance, enabled more adsorption of atomic .

Electrocatalytic Hydrogenolysis of Chlorophenolic Compounds by Modified Electrodes in Aqueous Medium in the Absence and the Presence of Ionic Surfactant

The electrocatalytic hydrogenolysis of different chlorophenolic compounds, namely 2-chlorophenol (2CP) and pentachlorophenol (PCP) was performed on nickel-silica (Ni-SiO2) and nickel-clay (Ni-CY) electrode catalyts. The influence of the catalytic support and the surfactant agent was studied in aqueous media at different pH. Results demonstrated that different regioselectivities were observed according to the used catalytic support. The cyclohexanone was obtained as the major product. In presence of ionic surfactants (SDS and CTAB), the investigated electrodes exhibited a promising dechlorination and hydrogenation potential of aromatic halides with high electrocatalytic activity and good stability.

Effect of silver or copper middle layer on the performance of palladium modified nickel foam electrodes in the 2-chlorobiphenyl dechlorination

To enhance the activity of chemi-deposited palladium/nickel foam (Pd/Ni) electrodes used for an electrochemical dechlorination process, silver or copper was deposited electrochemically onto the nickel foam substrate (to give Ag/Ni or Cu/Ni) before the chemical deposition of palladium. The physicochemical properties of the resulting materials (Pd/Ni, Pd/Ag/Ni and Pd/Cu/Ni) were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and their electrochemical catalytic activities were evaluated by monitoring the electrochemical dechlorination of 2-chlorobiphenyl (2-CB) in strongly alkaline methanol/water solution. The results show that the Pd/Ag/Ni and Pd/Cu/Ni electrodes had consistently higher electrocatalytic activities and current efficiencies (CEs) compared with the untreated Pd/Ni electrode. The Pd/Ag/Ni electrode exhibited the highest activity. The dechlorination was also studied as a function of Pd loading, the Ag or Cu interlayer loadings, and the current density. The Pd loading and the interlayer loadings both had positive effects on the dechlorination reaction. Increasing the current density increased the reaction rate but reduced the CE. The improvement of the electrocatalytic activities of the Pd/Ni electrode by applying the interlayer of Ag or Cu resulted from the enlargement of the effective surface area of the electrode and the adjustment of the metal-H bond energy to the appropriate value, as well as the effective adsorption of 2-CB on Ag. Moreover, the high catalytic activity of the Pd/Ag/Ni electrode was maintained after six successive cyclic experiments, whereas Pd/Cu/Ni electrodes deactivate severely under the same conditions.

Co-detoxification of transformer oil-contained PCBs and heavy metals in medical waste incinerator fly ash under sub- and supercritical water

The simultaneous detoxification processes of transformer oil-contained PCBs and heavy metals in medical waste incinerator (MWI) fly ash were developed under sub- and supercritical water. The addition of MWI fly ash to transformer oil-contained PCBs was found to increase the destruction efficiency of PCBs, at the same time, it facilitated reducing the leaching concentration of toxic metals from residues (obtained after reaction) for harmless disposal. In this study, we elucidated primarily the catalysis possibility of heavy metals in raw MWI fly ash for PCBs degradation by adopting the sequential extraction procedure. For both MWI fly ashes, more than 90% destruction efficiency of PCBs was achieved at ≥375 °C for 30 min, and trichlorobenzene (TCB) existing in the transformer oil was also completely decomposed. The correlation of catalytic performance to PCBs degradation was discussed based on structural characteristics and dechlorinated products. Likewise, such process rendered residues innocuous through supercritical water treatment for reuse or disposal in landfill.

Bimetallic Pd/Al particles for highly efficient hydrodechlorination of 2-chlorobiphenyl in acidic aqueous solution

Pd-based bimetallic materials have been widely studied for the effective hydrodechlorination (HDC) of aqueous chloroorganic compounds. However, the reaction functions of metal substrates and mechanism responsible for changes in reactivity have not been fully elucidated. Here, we synthesized Pd-based bimetals with Mg, Al, Mn, Zn, Fe, Sn, and Cu to explore the influence of metal substrates on HDC reactivity of 2-chlorobiphenyl (2-PCB). Bimetals exhibited disparate reactivity toward 2-PCB in acidic solution. Among these bimetals, Pd/Al particles presented the highest stability and relatively high reactivity to remove 2-PCB. The maintenance and regeneration of Al substrate are attributed to its particular corrosion properties which provide an efficient recycling between Al element and its oxide layer. The fresh and reacted Pd/Al samples were characterized by ICP-OES, SEM, XRD, and BET. The investigation of the pH effect on 2-PCB HDC further revealed the particular behaviour of Al surface. The effect of Pd loading amount on the HDC indicated that the optimal Pd content in terms of catalytic activity was related to the Pd dispersion degree. Finally, a mechanism for 2-PCB HDC on the Pd/Al surface was proposed.