HYDROGENOLYSIS AND ISOMERIZATION OF N-BUTANE ON LOW-INDEX PT SINGLE-CRYSTALS AND POLYCRYSTALLINE PT FOIL

The hydrogenolysis and isomerization of n-butane over Pt(100) and Pt(1 11) single crystals and a polycrystalline Pt foil have been studied ov er a wide range of reaction temperatures (510-610 K) and hydrogen part ial pressures (7.5-250 Torr), The activity and selectivity have both b een determined as a function of temperature and hydrogen partial press ure, The more open Pt(100) surface was an order of magnitude more acti ve than the close-packed Pt(111) surface, Hydrogenolysis selectivities were invariant with reaction temperature over the range studied, Hydr ogen partial pressure affected both the activity and product distribut ion. Both single-crystal surfaces exhibit a decrease in the activity a s the H-2 pressure is decreased below a critical amount and this decre ase is directly attributable to the formation of a carbonaceous surfac e residue, The amount of isomerization was always less than the amount of hydrogenolysis regardless of the n-butane to hydrogen ratio or the reaction temperature. (C) 1996 Academic Press, Inc.