Chitosan-supported palladium catalyst. 3. Influence of experimental parameters on nitrophenol degradation

Glutaraldehyde cross-linked chitosan was loaded with palladium and then reduced by means of an in situ hydrogen generation procedure (Zn in sulfuric acid solution) to prepare a chitosan-supported palladium catalyst. This catalyst was successfully used to degrade nitrophenol in dilute solutions in the presence of sodium formate as the hydrogen donor. The optimum initial pH was below pH 4. The pH strongly increased during the reaction. The influence of the initial concentration of nitrophenol and sodium formate was studied in order to determine the minimum molar ratio between these compounds to achieve the complete conversion of the nitrogenous product. The pseudo-first-order equation was shown to fit degradation kinetics in most cases; however, in some cases it was necessary to use a variable-order equation in order to model the kinetics. Decreasing catalyst particle size increased degradation rate; the kinetic parameter varied linearly with the reciprocal of the diameter, indicating that film diffusion may partially contribute to the kinetic control of the reaction. The kinetic parameter linearly increased with catalyst dosage, while increasing the palladium loading in the catalyst slightly increased degradation kinetics but the catalytic activity did not increase proportionally. Catalytic activity appears to be restricted to external catalyst layers.