Collect. Czech. Chem. Commun. 1998, 63, 1074-1088

Modelling of the Deactivation of Polymer-Supported Palladium Catalysts in the Hydrogenation of 4-Nitrotoluene

Milan Králika, Roman Fišeraa, Marco Zeccab, Angelo A. D'Archivioc, Luciano Galantinic, Karel Jeřábekd and Benedetto Corainc

a Department of Organic Technology, Slovak University of Technology, Radlinského 9, 812 37 Bratislava, Slovak Republic
b Dipartimento di Chimica Inorganica, Metallorganica e Analitica, via Marzolo 1, 35131 Padova, Italy
c Dipartimento di Chimica, Ingegneria Chimica e Materiali, Università dell'Aquila, Coppito Due - Via Vetoio, 67010 L'Aquila, Italy
d Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, 165 02 Prague 6, Czech Republic


The kinetics of the hydrogenation of 4-nitrotoluene over Pd catalysts supported on sulfonated polystyrene and simultaneous deactivation of these catalysts were investigated. Reaction rates of both the hydrogenation and the dissolution of Pd crystallites were related to the total Pd surface. The average radius of ideal spherical crystallites, as determined by X-ray powder diffraction analysis, was taken as the starting 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 to assess the accessibility and diffusivity before and after deactivation experiments. Langmuir-Hinshelwood type kinetic models were applied to describe the hydrogenation of 4-nitrotoluene. The kinetic law was incorporated into a more comprehensive model involving also diffusion of reactants inside catalytic particles. Simultaneous treatment of a few sets of kinetic data from batch hydrogenation carried out at 0.25-0.75 MPa yielded reliable values of model parameters. The model showed an increasing rate of dissolution of palladium with decreasing concentration of hydrogen and increasing concentration of 4-nitrotoluene. The latter fact supports the hypothesis that the nitro compound is the oxidant responsible for the dissolution of palladium.

Keywords: Hydrogenation; 4-Nitrotoluene; Ion-exchange polymers; Polymer-supported palladium catalysts; Catalyst deactivation; Heterogeneous catalysis.