MODELING OF THE DEACTIVATION OF POLYMER-SUPPORTED PALLADIUM CATALYSTSIN THE HYDROGENATION OF 4-NITROTOLUENE

The kinetics of the hydrogenation of 4-nitrotoluene over Pd catalysts supported on sulfonated polystyrene and simultaneous deactivation of t hese catalysts were investigated. Reaction rates of both the hydrogena tion and the dissolution of Pd crystallites were related to the total Pd surface. The average radius of ideal spherical crystallites, as det ermined by X-ray powder diffraction analysis, was taken as the startin g value of the crystallite size. Stability of the polymer network was checked by Inverse Steric Exclusion Chromatography (ISEC). The ESR and Static Gradient field Spin Echo (SGSE) NMR spectroscopies were used t o assess the accessibility and diffusivity before and after deactivati on experiments. Langmuir-Hinshelwood type kinetic models were applied to describe the hydrogenation of 4-nitrotoluene. The kinetic law was i ncorporated into a more comprehensive model involving also diffusion o f reactants inside catalytic particles. Simultaneous treatment of a fe w sets of kinetic data from batch hydrogenation carried our at 0.25-0. 75 MPa yielded reliable values of model parameters. The model showed a n increasing rate of dissolution of palladium with decreasing concentr ation of hydrogen and increasing concentration of 4-nitrotoluene. The latter fact supports the hypothesis that the nitro compound is the oxi dant responsible for the dissolution of palladium.