The hydrodechlorination of 4-chlorophenol in an aqueous phase was studied in a semicontinuous basket stirred tank reactor using Pd, Pt, and Rh on γ-alumina commercial catalysts (0.5% w/w) under mild reaction conditions. The catalytic activity was studied in the temperature range of 20-40 °C. Pd and Rh showed a higher catalytic activity than Pt. From consumption of 4-chlorophenol and evolution of the reaction products, phenol, cyclohexanone, and cyclohexanol, a reaction scheme based on a parallel-series pathway and a kinetic model based on pseudo-first-order dependence on 4-chlorophenol have been proposed. Hydrodechlorination of 4-chlorophenol to phenol exhibits the largest apparent kinetic constant for Pd (k 1 ) 0.42-0.73 h -1 ) and Pt (k 1 ) 0.20-0.42 h -1 ) catalysts, while in the case of Rh, the three reactions, hydrodechlorination of 4-chlorophenol to phenol (k 1 ) 0.43-0.64 h -1 ) and hydrogenation of phenol to cyclohexanone (k 3 ) 0.42-0.78 h -1 ) and to cyclohexanol (k 4 ) 0.38-0.65 h -1 ), have comparable values of the kinetic constant. The apparent activation energy for 4-chlorophenol disappearance was determined, and values of 21.0, 26.2, and 15.3 kJ/ mol were obtained for Pd, Pt, and Rh, respectively.

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Two different activated carbons were treated with nitric acid and were used as supports to prepare 0.5 wt % Pd/C catalysts. The supports were characterized by N 2 adsorption, elemental analysis, X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD) in order to study the modifications in the porous structure and in the surface chemistry composition. Both XPS and transmission electron microscopy (TEM) were employed to study the dispersion of Pd on the catalysts. Oxidation of the activated carbon led to a substantial increase in oxygen surface groups, whereas the porous structure was not modified significantly. All the catalysts were tested in the hydrodechlorination of 4-chlorophenol in aqueous phase at mild conditions. It was observed that an increase in the CO 2 /(CO + CO 2 ) ratio obtained from TPD of the carbon supports is accompanied by a better dispersion of Pd and an increase in the catalyst activity and the selectivity toward cyclohexanol, which is less toxic than the other products, cyclohexanone and phenol.

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