Isomerization of n-Butenes 

n-Butene could be isomerized to isobutene using Shell FER catalyst which is active and selective. n-Butene mixture from steam cracker or FCC after removal of C₅ olefins via selective hydrogenation step passes to the isomerization unit. It has been proposed that after the formation of a butyl carbocation, a cyclopropyl carbocation is formed which gives a primary carbenium ion that produces isobutene :