Chitosan-Supported Palladium Catalyst. II. Chlorophenol Dehalogenation

Preliminary treatment with glutaraldehyde increased the stability of chitosan in acidic solution and the sorption of palladium from HCl solutions at high loading. A reduction procedure was used to partially reduce the palladium. The resulting chitosan-supported palladium catalyst was efficiently used for the hydrodehalogenation and partial dehydrodearomatization of 2-chlorophenol (2-CP). The reaction proceeds via hydrogen transfer using sodium formate. The optimum pH for the degradation of 2-CP was close to pH 3. The effects of catalyst dosage, formate concentration, 2-CP concentration, and temperature were studied to define the optimum conditions for the conversion of 2-chlorophenol into phenol and cyclohexanone. A limit on the formate/2-CP molar ratio was found to be required to achieve the complete dehalogenation of 2-CP: The formate excess needed to be higher than 50 times the 2-CP concentration. Increasing the temperature from 20 to 60 °C continuously increased the degradation rate, and the activation energy ranged between 20 and 25 kJ mol -1 under nonlimiting experimental conditions (formate excess at the required level and pH 2.7).