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Vera V. Shishova, Ekaterina S. Lokteva, Grigory S. Maksimov, Konstantin I. Maslakov, Igor Y. Kaplin, Sergey V. Maksimov, Elena V. Golubina
Hydrodechlorination of diclofenac in
aqueous solution over Pd/ZrO2 AND Pd/ZrO2SiO2 catalysts
Abstract
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 oC. 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 °C, it slightly, and after mild reduction,
significantly (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 accessibility 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 flow 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.
Key words: palladium,
zirconia, silica, hydrodechlorination, diclofenac, H2 reduction
Copyright (C) Chemistry Dept., Moscow State University, 2002
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