Shape-Selective Catalysis Determined by the Volume of a Zeolite Cavity and the Reaction Mechanism for Propylene Production by the Conversion of Butene Using a Proton-Exchanged Zeolite

The role of the zeolite cavity in the production of C3H6 from butene was investigated using various zeolites with pore structures of 8-, 10-, and 12-membered rings (MRs). The reaction mechanism is discussed on the basis of which octyl carbocations produced C3H6 at low conversions of butene. The selectivity for C3H6 was highly dependent on the volume of the zeolite cavity but not on the entrance pore diameter. The optimum cavity volumes of zeolites with 8-, 10-, and 12-MR entrance pore structures were similar, while the highest C3H6 selectivity among the zeolites was different. The most selective production of C3H6 can be accomplished by matching the volume of the specific octyl carbocation to that of the zeolite cavity. This concept can be employed to explain the selective production of C3H6 according to a proposed reaction model. Furthermore, the reaction mechanism for the production of C3H6 from C2H4 was also investigated at low conversion of C2H4. C3H6 was produced by the beta-scission of the same specific octyl carbocations in the conversions of both butene and C2H4.