Catalytic Hydrodehalogenation And Hydrogenation Of 2,4-Dichlorophenol And 2,2’,4,4’-Tetrabrominated Diphenyl Ether Over Supported Pd-Rh Bimetallic Catalysts

Halogenated organic compounds(HOCs)have been widely used in industry,agriculture and pharmacy.For example,chlorophenols are the important raw materials for the production of antibacterial agents and insecticides;Poly brominated diphenyl ethers(PBDEs)are the main ingredients of fire retardants which could be found in many living goods,such as plastic,electronic device,textile,etc.However,HOCs were also well known as typical environmental pollutions due to their high biotoxicities such as bioaccumulation and carcinogenicity.Recent decades,a lot of efforts have been devoted into the removal and degradation of HOCs.Among the disposal stratergies,liquid phase catalytic hydrodehalogenation attracted tremendous interests as a highly efficient,energy-saving water treatment technique.Liquid catalytic hydrodehalogenation could effectively remove the halogen atoms in the HOC moleculars and thus sharply reduce the toxicity of HOCs.However,for many HOCs such as chlorophenols,the dechloried products are still toxic for human because of the existence of benzene rings.Hydrogenation of phenol to cyclohexanone provides an effective way to futher reduce the toxicity and produce products with value added.However,to the best of our knowledge,researches about the relevant were still limited.In this work,we prepared bimetallic Pd-Rh/Al2O3 catalysts with varied Pd/Rh ratio using impregnation method and studied their catalytic properties for the hydrodehalogenation and hydrogenation of 2,4-Dichlorophenol and 2,2’,4,4’-Tetrabrominated diphenyl ether.The intermediate,dehalogated and hydrogenated products were identified using high performance liquid chromatography,gas chromatography,and gas chromatography-mass spectrometry,the reaction path were thus proposed.The catalysts were characterized by Inductive coupled plasma emission spectrometer,X-Ray Diffraction,Transmission Electronic Microscope,X-ray Photoelectron Spectroscopy to investigate their structural properties.Additionally,we systematically studied the influence of catalyst supports,catalyst preparation methods,active metals,catalyst dosages,the initial concentrations of reactants,solution pH and solvents on the catalytic activities.For the hydrodechlorination and hydrogenation of 2,4-Dichlorophenol,Al2O3 as catalyst support performed better that SiO2 and CeO2.Catalyst prepared using impregnation method exhibited higher catalytic activities than that prepared using deposition-precipitation method.Pd/Al2O3 was more effective for the catalytic hydrodechlornation of 2,4-DCP,while Rh/Al2O3 exhibited better activity for the hydrogenation of phenol.Accordingly,bimetallic catalyst with Pd/Rh ratio of 0.05:0.93 had the best catalytic performance.The intermediate products of hydrodechlorination were 2-Chlorophenol,dechlorinated products were phenol,and the hydrogenated products were cyclohexanone and cyclohexanol.For the hydrodebromination and hydrogenation of 2,2’,4,4’-Tetrabrominated diphenyl ether Pd-Rh bimetallic catalysts,we found that the increase of Pd content was beneficial for the hydrodebromination and the increase of Rh content could promote hydrogenation.According to the gas chromatography-mass spectrometry results,the intermediate products of hydrodebromination were three Low brominated diphenyl ethers,debrominated products were diphenyl ethers,and the hydrogenated products were oxydicyclohexane.