Catalytic Hydrodechlorination Of Triclosan And 2,2’4,4’-tetrabromodiphenyl Ether Over Pd/TiO₂

Triclosan (TCS) is widely used in human life as a broad-spectrum antibacterial agent. Recent studies have shown that it produces damage to the soil ecosystem, aquatic biological, mammals and potential threat to human’s health. Polybrominated diphenyl ethers (PBDEs) is often used as a flame retardant added to the equipment and plastics such as textile, electrical and electronic components.It has thyroid gland toxicity, nervous system toxicity and reproductive development toxicity. Due to their high stability, and low biodegradation, it is highly demanded to develop effective treatment methods to eliminate their pollution. Liquid phase catalytic hydrogenation has been wildly used to eliminate the toxicity of many organic and inorganic compounds, because of its low cost and environmentally friendly.It is a very important aspect to explore effective catalysts in catalytic hydrogenation. Because noble metals usually has a good ability of activation of H2, so noble metal such as Pd, Pt, Rh, Ru is usually used in the liquid phase catalytic hydrogenation, and metallic Pd based catalyst is widely used because of its good ability of activation H2. In this thesis, supported Pd catalysts were prepared by the deposition-precipitation method, and were characterized by TEM, XRD and ICP-AES. The liquid phase catalytic hydrodechlorination of triclosan and 2,2’,4,4’-tetrabromodiphenyl ether (BDE-47) over the catalysts was investigated. Results showed that the catalytic activity of the catalysts with different supports decreased as:TiO2 support> Al2O3 support> SiO2 support; Pd/TiO2 catalysts showed good catalytic performance in hydrodechlorination process, and the catalytic activity increased with Pd loading.At an initial TCS concentration of 0.016 mmol·L-1, pH of 10 and catalyst dosage of 50 mg, complete hydrodechlorination of TCS was achieved within 70 min. During the catalytic hydrodechlorination process of TCS, many intermediate products were formed, and the final product was 2-phenoxyphenol. Under alkaline conditions, increasing pH hindered the reaction. The initial activity normalized by catalysts mass was found to be nearly identical when the amount of catalyst used varied within 15-25 mg, indicative of the absence of mass transport limitations. Finally, the initial activity markedly enhanced with the initial concentration of TCS when the concentration was in the range of 0.009 mmol·L-1-0.02 mmol·L-1; while it remained constant with further increasing the initial concentration, reflecting that the catalytic hydrodechlorination of TCS over Pd/TiO2 followed the Langmuir-Hinshelwood model, and the catalytic hydrodechlorination was controlled by TCS adsorption.At initial BDE-47 concentration of 0.028 mmol·L-1, and a dosage of 10 mg of 0.36% Pd/TiO2 catalyst, complete hydrodebromination of BDE-47 was achieved within 30 min. There are many intermediate products in the process, and the final product was diphenyl ether. The initial activity normalized by catalyst mass was found to be nearly identical when the amount of catalyst used varied within 5—15 mg, indicative of the absence of mass transport limitations. Finally, the initial activity markedly increased with the initial concentration of BDE-47 when the concentration was in the range of 0.01 mmol·L-1-0.03 mmol·L-1; reflecting that the catalytic hydrodechlorination of BDE-47 over Pd/TiO2 followed the Langmuir-Hinshelwood model, and the catalytic hydrodebromination was controlled by BDE-47 adsorption on the catalyst surface.