Catalytic Hydrodechlorination Of2-chlorophenol And2,4-dichlorophenol Over Pd Catalyst Supported On Nitrogen Doped Carbon Nanotubes

Chlorophenols are commonly identified organic contaminants in water environment. Due to their high toxicity and refractory, chlorophenols have attracted extensive attention. The liquid phase catalytic hydrodechlorination (HDC) is an efficient, clean method for the reductive removal of chlorophenol from waters in combination with the advantages of resource recovery.Because of their unique thermal, optical, electrical, mechanics properties, carbon nanotubes have aroused widespread concern and research interests from in the catalysis study. Carbon nanotubes have large surface area, regular bore structure, stable chemical properties and tunable surface chemical properties, making carbon nanotubes as catalyst carriers.In this study, multi-walled carbon nanotubes were purified and modified by nitrogen doping, and supported Pd catalysts were synthesized by the impregnation method. The catalysts are characterized by elements analysis, transmission electron microscopy (TEM), inductively coupled plasma emission spectrometer (ICP), X-ray powder diffraction (XRD), N2adsorption (BET), X-ray photoelectron spectroscopy (XPS). The catalytic activities of the catalysts and the factors influencing the HDC of2-chlorophenol and2,4-dichlorophenol were investigated, and the reaction kinetics of2,4-DCP over the catalysts was also evaluated.Nitrogen doped carbon nanotube supported Pd catalysts exhibited good repeatability and high catalytic reduction reactivity for the HDC of2-CP and2,4-DCP. The activity of the catalyst is influenced by nitrogen doping, reduction temperature, dosage of the catalyst and initial concentration of the pollutants. The doping of nitrogen resulted in small Pd particle due to effective Pd particle dispersion, thus giving rise to enhanced catalytic activity. High reduction temperature decreased the content of oxygen-containing functional groups on the surface of the carrier, and the interaction between Pd particles and carrier. Accordingly, low catalytic activity was obtained. The initial consumption rate of pollutants increased with the catalyst dosage, while the rate was remained unchanged when normalized by the catalyst dosage, indicating the absence of the mass transport limitation in the HDC reaction. The initial consumption rate was enhanced first with initial concentration of the pollutant, but remained unchanged when the increase of the initial pollutant concentration further increased, indicating that the reaction is controlled by adsorption of the reactant on the catalyst surface.The result of the reaction kinetics of2,4-DCP showed that the catalytic reduction reactivity was significantly improved upon the modification of carbon nanotube by nitrogen doping. The results of catalyst reuse showed that after three times cycle the catalytic activity slightly decreased, but remained highly active for the HDC of2,4-DCP.Nitrogen doped carbon nanotube supported Pd catalysts displayed high catalytic activities for the HDC of2-CP and2,4-DCP, reflecting that the catalytic performance of the catalyst could be optimized by nitrogen doping.