Evaluation of the metal-support interactions -: Case of platinum-supported catalysts:: effect of the support nature and the metallic dispersion

The potentials of platinum oxidation according to the metallic particle size and the nature of the support have been evaluated. The use of the Fe3+/Fe2+ redox system potentials of platinum oxidation to be defined according to the dispersion of platinum and the nature of the support. By the use of the Gibbs-Helmoltz law (DeltaG = -zF Delta E), the comparison with bulk platinum allows the platinum excess free energy to be calculated. It thus appears that the platinum-support interaction decreases following the sequence: Al2O3 > C > SiO2. However, the most important parameter seems to be the size of the particle. Thus, the small particles are oxidised more easily by the Fe3+/Fe2+ redox system. At the end of the process, the size of the most stable particles is defined by a compromise between a decrease of the stability when the dispersion increases and an increase of the metal-support interaction when the particle size decreases. (C) 2002 Elsevier Science B.V. All rights reserved.