Dehydrogenation processes on nickel and platinum surfaces. Conversion of cyclohexane, cyclohexene, and cyclohexadiene to benzene

Abstract

Described is the surface coordination chemistry of cyclohexane, 1,3- and 1,4-cyclohexadiene, and cyclohexene on the low Miller index planes and a stepped surface of nickel and on the platinum (111) and stepped 6(111)X(111) surfaces as established by thermal desorption spectroscopy, chemical displacement reactions, and isotopic labeling studies. Cyclohexane did not react with Ni(111) at 0 to 70/sup 0/C, Ni(110) at 20-90/sup 0/C, Ni(100) at 25-200/sup 0/C, and Ni(9(111)X(111)) at 20-70/sup 0/C. A similar behavior was observed for Pt(111) at -35 to +135/sup 0/C, although a small degree of dehydrogenation was evident on this surface. Definite evidence for cyclohexane conversion to benzene was obtained for the stepped platinum surface; the reactivity of this stepped surface toward cyclohexane was substantially higher than that of the platinum (111) plane. Cyclohexene and 1,3- and 1,4-cyclohexadiene were converted, at least partially, to benzene on all of the nickel and platinum surfaces. Hydrogen-deuterium (C-H) exchange during the conversion of a mixture of chemisorbed C/sub 6/H/sub 10/ and C/sub 6/D/sub 10/ and of a mixture of chemisorbed cyclochexadiene and deuterium atoms to benzene was evident only for the platinum surfaces. Carbon significantly altered the cyclochexene chemistry on Ni(110);Ni(110)-C was far more effective than the clean surface formore » dehydrogenation of cyclohexene to benzene. A substantial carbon effect of the chemistry of the other surfaces was not evident.« less