Effective liquid phase hydrodechlorination of diclofenac catalysed by Pd/CeO2

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.