HYDRODECHLORINATION OF DICLOFENAC IN AQUEOUS SOLUTION OVER PD/ZRO2 AND PD/ZRO2SIO2 CATALYSTS

Abstract

Pd/ZrO2 and Pd/ZrO2SiO2 catalysts prepared by wet impregnation and reduced with H2 under mild (30 °C, aqueous suspension) or harsh (320 °C) conditions were compared in the hydrodechlorination of the microecotoxicant diclofenac in aqueous solution at 30 оС. According to TPR and XPS data, the addition of SiO2 to the support reduces the degree of metal-support interaction and facilitates the reduction of palladium. Despite the lower Pd0 fraction, the Pd/ZrO2 catalyst was more active in the batch reactor: after reduction at 320 °С, it slightly, and after mild reduction, signi cantly (7 times) exceeded Pd/ZrO2SiO2 in catalytic activity. XRD and TEM showed a wider size distribution of palladium nanoparticles in the Pd/ZrO2 sample, while low-temperature N2 adsorption, XPS, and TPR demonstrated better accessi-bility of palladium on the Pd/ZrO2 surface due to reduced decoration with support components and increased pore size. These features explain the increased activity of Pd/ZrO2. Testing in the ow system demonstrated higher DCF conversion in the presence of catalysts reduced at 320°C and higher stability of Pd/ZrO2SiO2 compared to Pd/ZrO2. The stability is ensured by the increased reducibility of Pd2+ with H2 and by the developed surface of Pd/ZrO2SiO2, which prevents deactivation under the action of HCl released in hydrodechlorination.