HEAT-TREATED CARBON-BLACKS AS SUPPORTS FOR PLATINUM CATALYSTS

The effect of the degree of graphitization of the support on the dispe rsion, sintering resistance, and catalytic activity of a series of pla tinum catalysts supported on heat-treated carbon blacks has been deter mined. The supports were prepared by heat treatment of a furnace carbo n black in an inert atmosphere at temperatures up to 2473 K. The resul ting samples were characterized by physical adsorption (nitrogen at 77 K and carbon dioxide at 273 K), X-ray diffraction, and surface acidit y measurements. Platinum catalysts were prepared by impregnating the s upports with aqueous hexachloroplatinic acid; metal dispersions were m easured by hydrogen and carbon monoxide chemisorption at room temperat ure 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 pregraphiti zed support. On the other hand, the highest resistance to sintering wa s found for the catalyst supported on the carbon black with the highes t degree of graphitization, and this is attributed to an interaction b etween the metal particles and the pi sites on the support. However, t his interaction is not strong enough to affect the catalytic behavior for benzene hydrogenation. Thus, the metallic dispersion seems to be t he result of, at least, two factors: (a) an adequate metal precursor s upport interaction during the impregnation step and (b) a high sinteri ng resistance under the reduction conditions which hinders the metal p article growth during this stage of the catalyst preparation. (C) 1995 Academic Press, Inc.