The reversible skeletal isomerization between n-butenes and iso-butene over solid acid catalysts

Abstract

The reversibility of skeletal isomerization between n-butenes and iso-butene has been studied over various solid acid catalysts including ferrierite and ZSM-5 zeolites, mesoporous materials and amorphous alumina in order to identify the cause for their different selectivities for skeletal isomerization. A remarkable selectivity for the reverse skeletal isomerization of iso-butene to n-butenes is found from ferrierite, fluorinated alumina with low fluorine loading and the KIT-1 mesoporous material with low aluminium content; which also demonstrate high selectivity for forward skeletal isomerization. Catalysts that are not selective for forward isomerization exhibit poor selectivity for reverse isomerization. The preference for multimolecular oligomerization due to high concentrations of activated reactants in the pores of nonselective catalysts reduces their selectivity for skeletal isomerization. Thus, the suppression of oligomerization over the selective catalyst makes the cracking of oligomers impossible and increases selectivity. This is achieved by a sparse distribution of activated reactants caused by specific pore structures or low concentrations of strong acid sites. The reversibility of skeletal isomerization and the adsorbed state of butenes are discussed in relation to the monomolecular reaction path.