Hydrogenation of olefins. Part 5.—Hydrogenation of but-1-ene catalyzed by iridium-alumina

Abstract

But-1-ene hydrogenation catalyzed by iridium-alumina has been studied over the range 20–170°C. Isomerization of but-1-ene to but-2-ene accompanied hydrogenation, and the kinetics of both processes are reported. The formation of chemisorbed butyl groups was rate-determining both in hydrogenation and in isomerization. Some 40 % of the product was but-2-ene under favourable conditions at 150°C, but the rate of isomerization, relative to hydrogenation, declined as the temperature was lowered and became minimal at 20°C. Iridium is unique among metal catalysts in showing a marked preference for the formation of but-2-ene in the cis-configuration under all isomerization conditions. But-2-ene formed early in reactions contained 60–90 % of the cis-isomer. Iridium is compared briefly with other noble group 8 metals from the standpoint of activity for but-1-ene isomerization during hydrogenation.