FTIR and UV-vis spectroscopic study of interaction of 1-butene on H-ferrierite zeolite

The interaction of 1-butene with zeolite H-ferrierite has been studied at increasing temperatures (between 300 and 670 K) by using IR and UV-vis spectroscopies, with the aim to isolate in situ the species precursors to isobutene and high-temperature coke. The bimolecular mechanism of conversion of butene to isobutene on the fresh catalyst has been confirmed, since low branched C8 chains are observed. At 300 It, the main products of the interaction are the butene isomers 2-cis- and 2-trans-butene. At temperatures between 300 and 393 K, the presence of monoenic allylic carbocations is observed, and at temperatures between 473 and 573 K, neutral and carbocationic polyenes are present. At temperatures greater than or equal to 623 KI the polyenyl unsaturated chains cyclize to form mono- and polycyclic aromatics. These experimental features are explained on the basis of mechanisms in which the protonated intermediates (formed by protonation of butene) can produce, by further reaction with butene molecules, mainly two kinds of products: (i) polyenyl allyl carbocations (by a butene hydride abstraction) and (ii) octane carbocations (by dimerization), which then evolve (by cracking) to isobutene.