The effect of Sn on the reactions of n-hexane and cyclohexane over polycrystalline Pt foils

The modification of the catalytic properties of a polycrystalline platinum foil by the addition of tin was studied by the reactions of n-hexane and cyclohexane in excess H-2. The reactions were studied at 13.3 kPa of n-hexane, 450 kPa of H-2 and 740 K, and 6.7 kPa of cyclohexane, 450 kPa of H-2 and 573 K. The Pt-Sn catalyst was characterized by Auger electron spectroscopy and by temperature-programmed desorption of CO before and after the reactions. The sites that bind CO most strongly on the Pt foil also have the highest initial turnover rate and are the first ones to be poisoned by carbon deposits from hydrocarbon reactions or by sulfur when a sulfur-containing compound (thiophene) is present in the feed. The addition of tin can block these sites preferentially, thus decreasing the undesirable high initial hydrogenolysis rate of platinum catalysts in reforming reactions and eliminating the need for presulfiding the catalyst. Also, tin suppressed the hydrogenolysis reaction preferentially to the isomerization and cyclization reactions thus increasing the selectivities to isomerization and cyclization. The amount of carbon deposited was smaller on tin containing platinum catalysts during the dehydrogenation of cyclohexane and n-hexane, (C) 1998 Academic Press.