Comparison of butene skeletal isomerization selectivity over a pair of commercial H-ferrierites

The conversion of butenes to isobutene was compared at atmospheric pressure and 250–350 °C over two commercial H-ferrierite catalysts having different chemical compositions, crystal morphologies, and diffusional resistance (DR). The Si/Al ratio affects the number of Brönsted acidic (BA) sites but not their intrinsic acid strength. These equally strong BA sites are thought to be active sites for the skeletal isomerization. Catalyst selectivity seems mainly depend on the diffusional resistance of micropores and the reaction conditions. The DR is affected by the presence of extra-framework species in the 10MR channels of the zeolite which might include charge compensating cations, Al-containing species, and coke. To see their effect on the selectivity for i-butene versus oligomerization products we tested zeolites with basic exchanged cations and removed Al-containing debris from the transport channels with EDTA solutions. A proper balance of the extra-framework species and the reaction conditions allowed nearly 100% isobutene selectivity at relatively high branched butene yield.