Heat-Treated Carbon-Blacks as Supports for Platinum Catalysts

Abstract

The effect of the degree of graphitization of the support on the dispersion, sintering resistance, and catalytic activity of a series of platinum catalysts supported on heat-treated carbon blacks has been determined. The supports were prepared by heat treatment of a furnace carbon black in an inert atmosphere at temperatures up to 2473 K. The resulting samples were characterized by physical adsorption (nitrogen at 77 K and carbon dioxide at 273 K), X-ray diffraction, and surface acidity measurements. Platinum catalysts were prepared by impregnating the supports with aqueous hexachloroplatinic acid; metal dispersions were measured by hydrogen and carbon monoxide chemisorption at room temperature and by transmission electron microscopy. Benzene hydrogenation was used as a test reaction to assess the possible effect of the support on the catalytic behavior of platinum. Platinum dispersions as high as 0.99 were achieved, and they can be well correlated with the surface acidity characteristics of the supports. The only sample not following the observed trend is the catalyst prepared with the less pregraphitized support. On the other hand, the highest resistance to sintering was found for the catalyst supported on the carbon black with the highest degree of graphitization, and this is attributed to an interaction between the metal particles and the π sites on the support. However, this interaction is not strong enough to affect the catalytic behavior for benzene hydrogenation. Thus, the metallic dispersion seems to be the result of, at least, two factors: (a) an adequate metal precursor support interaction during the impregnation step and (b) a high sintering resistance under the reduction conditions which hinders the metal particle growth during this stage of the catalyst preparation.