Olefin isomerization catalyzed by group 8 metals in absence of molecular hydrogen. Part 3.—Butene isomerization over iridium-alumina

Abstract

Butene isomerization catalyzed by iridium supported on hydrated alumina has been studied at 100°C. Molecular hydrogen is not required as a reactant. Overall relative rate constants for the three-component system have been determined using Wei and Prater theory. Isomerization occurs by an addition-abstraction mechanism, the intermediates being chemisorbed secondary butyl groups. When the availability of surface hydrogen atoms is low, butene desorption is rate-controlling, and products are formed in equilibrium proportions. Under conditions of relatively high hydrogen atom availability, desorption is not rate-controlling, and but-1-ene isomerizes to give but-2-ene predominantly (∼70 %) in the cis-configuration. This selectivity for cis-isomer formation may result from the operation of a particularly restrictive geometric factor.