n-Butanol to iso-butene in one-step over zeolite catalysts Original Research Article

The conversion of n-butanol to iso-butene in one-step has been studied over zeolite catalysts (Theta-1, ZSM-2, Ferrierite, ZSM-5, SAPO-11 and Y). The zeolites were characterized by XRF, XRD, BET, and NH3-TPD. Coke formation on the spent catalysts was measured by TGA. The unidirectional channel zeolites Theta-1 and ZSM-23 gave high yields of iso-butene and showed high stability. In contrast, ferrierite, although initially active, deactivated due to the presence of water from dehydration giving progressively lower yields of iso-butene. ZSM-5 showed high activity but low selectivity to iso-butene; SAPO-11 was structurally unstable under the reaction conditions. Ferrierite deactivation was studied in more detail by NH3-TPD, 27Al MAS NMR and by a comparison of 1-butene isomerisation with and without the presence of added steam. A similar comparison was made for ZSM-23 and Theta-1 which further emphasised their stability and showed that for these catalysts under the reaction conditions used, the product steam from n-butanol dehydration promoted iso-butene yield by acting as a diluent.