Spectroscopic studies of butane isomerization over platinum supported on chlorinated alumina

Abstract

U.v.-visible reflectance spectroscopy and mass spectrometry have been used to study the interaction of n-butane with chlorinated alumina with and without platinum. On pure alumina no reaction is detected except at high temperatures, where coking of the catalysts takes place. Chlorinated alumina reveals strong acidic sites; on this catalyst isomerization occurs but coking is not inhibited. Platinum deposited on the alumina exhibits hydrogenolysis properties at high reaction temperatures. In the chlorination of Pt/Al₂O₃ by CCl₄, oxidation of the metal occurs in the first stage accompanied by the appearance of strong Lewis-acid sites on the support. Then a complex between PtCl₂ and AlCl₃ is formed and is dispersed on the alumina. The system obtained is active in the isomerization of n-butane. At 300 °C under a mixture of n-butane and H₂ the complex is reduced, with chlorine leaving the surface. Once the chlorine is removed coking cannot be prevented.