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STEPHEN F. ADLERA N D J a a r ~ sJ. KEAVKEY
T-ol. 64
THE PHYSICAL NATURE OF SUPPORTED PLATISUN BY STEPHEN F. ADLERAND JAMESJ. KEAVNEY Stamford Laboratories, American Cyanamid Company, Stamford, Connecticut Received August IS, 1959
Two types of platinum-alumina reforming catalysts, impregnated and cogelled, have been examined by means of HI adsorption and X-ray line-broadening techniques. The catalysts were examined (1) fresh, ( 2 ) coked, (3) regenerated, (4) mildly sintered, ( 5 )severely sintered and (6) reactivated after the two levels of sintering. The adsorption was shown to decline after coke had been deposited in a naphtha reforming reactor. A careful burn-off of the coke restored the adsorption to at least one-half of its original level. Mild sintering, in a partial steam atmosphere, caused a large decrease in adsorption which was partially recovered after reactivation under a high pressure of oxygen. On the other hand, sintering at one atmosphere of steam caused a decrease in adsorption which was essentially irreversible despite attempts a t reactivation. The adsorption results on fresh, sintered and reactivated catalyst are interpreted by assuming (1) the existence of two types of platinum aggregation-monolayer for impregnated catalyst, pseudo-spherical for cogelled catalyst, and (2) that Hz is adsorbed as atoms a t the surface interstices between platinum atoms. Platinum particle sizes are derived that are in good agreement with X-ray line-broadening values. The adsorption of Hz per gram of platinum was found to be virtually independent of platinum concentration within either of the two groups of catalysts investigated.
Introduction It has been of interest to this LTboratory to study the nature of platinum supported on alumina, in the concentration range appropriate for a reforming catalyst. One of the properties which most obviously affects the performance of any heterogeneous catalyst is the surface area of the active mnteriul. A study was therefore started to determine the surface area of platinum available in supported catalysts of the type used in reforming. Determination of the surface area of one component in a multiple component catalyst has been done previously by Emmett and Brunauer' for iron on a promoted ammonia-synthesis catalyst, by means of carbon monoxide adsorption, and later2J by the same method for cobalt on kieselguhr and for nickel on aluminum oxide. These determinations were made on catalysts in which the active component occupied a large percentage of the surface. Boreskov and I
