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S. J. STEPHENS
Vol. 62
CHEMISORPTION AND SURFACE REACTIONS OF ETHYLENE ON EVAPORATED PALLADIUM FILMS BY S. J. STEPHENS Bell Telephone Laboratories, Inc., Murray Hill,New Jersey Received February
io, 1 Q68
The chemisorption and self-hydrogenation of ethylene on evaporated palladium films and the reaction of the adsorbed hydrocarbon layer with hydrogen have been studied. At O", ethylene is chemisorbed with low residual rasure until a surface coverage of about 70% (assuming four-site adsorption) is reached, after which self-hydrogenation gegins and continues until the surface is almost completely covered with acetylenic residues (C2Hg). The products of self-hydrogenation are ethane and about 3% butane. If the amount of ethylene added is insufficient for complete self-hydrogenation of the surface layer, desorption of ethane from the surface will take place after the rapid self-hydrogenation reaction. This indicates that reaction can occur among adsorbed species, and is not necessarily confined to reaction between gas phase ethylene and adsorbed hydrogen. Presence of butane among the reaction products also supports this idea, since butane is formed by polymerization of adsorbed hydrocarbon radicals on the surface. At -78" only 10% of the adsorbed layer undergoes self-hydrogenation, and there is no noticeable desorption. About 80% of the adsorbed hydrocarbon residues can be removed with hydrogen a t a pressure of
