PREPARATION OF PT GAMMA-AL2O3 PELLETS WITH INTERNAL STEP-DISTRIBUTIONOF CATALYST - EXPERIMENTS AND THEORY/

Step-type Pt/gamma-Al2O3 catalyst pellets were prepared by coimpregnat ion and sequential impregnation of hexachloroplatinic and citric acids . A diffusion-adsorption model based on Fickian diffusion and Langmuir adsorption was formulated. The parameters of the model were determine d from separate experiments. Adsorption constants were obtained in the absence of diffusional resistances, while effective diffusivities wer e obtained in the absence of adsorption or desorption. In order to ext end the Langmuir adsorption equations to the multicomponent system, tw o new parameters were introduced, which accounted for solution effects and steric hinderances. Catalyst distribution inside the pellet and t he effects of various impregnation parameters were predicted satisfact orily by the multicomponent diffusion-adsorption model. The platinum d istribution of pellets prepared by the two impregnation techniques was similar, although sequential impregnation gave thinner catalyst step widths. (C) 1996 Academic Press, Inc.