Effective liquid phase hydrodechlorination of diclofenac catalysed by Pd/CeO2

Abstract

Palladium catalysts supported on Al₂O₃, activated carbon (AC), SiO₂ and CeO₂ were prepared using the impregnation and deposition–precipitation methods. The liquid phase catalytic hydrodechlorination of diclofenac on the catalysts was investigated, and the toxicity of the original and treated diclofenac solutions was evaluated using Daphnia magna. Characterization results indicated that the Pd catalyst supported on CeO₂ had a higher Pd dispersion than those supported on Al₂O₃, AC and SiO₂. The binding energy of Pd 3d_5/2 in Pd/CeO₂ was higher than Pd/Al₂O₃ with a similar Pd loading amount. Additionally, for Pd/CeO₂ prepared by the deposition–precipitation method the binding energy of Pd 3d_5/2 slightly decreased with the Pd loading amount. As for catalytic diclofenac reduction, Pd/SiO₂ exhibited a nearly negligible catalytic activity, whereas diclofenac concentration decreased by 100, 86, and 29% within 50 min of reaction on Pd/CeO₂, Pd/Al₂O₃, and Pd/AC, respectively, indicative of a catalytic activity order of Pd/CeO₂ > Pd/Al₂O₃ > Pd/AC > Pd/SiO₂. The hydrodechlorination of diclofenac on Pd/CeO₂ could be well described using the Langmuir–Hinshelwood model. Diclofenac hydrodechlorination processed via a combined stepwise and concerted pathway, and increasing Pd loading amount in Pd/CeO₂ favoured the concerted pathway. In comparison with original diclofenac, catalytic hydrodechlorination of diclofenac led to markedly decreased toxicity to Daphnia magna.