Spectroscopic studies of benzene hydrogenation on platinum-loaded zeolites. Part 1.—Benzene adsorption on supports

Abstract

U.v. diffuse reflectance and i.r. spectroscopies have been used to study the benzene adsorption on silica, alumina, silica—alumina and Y zeolites containing cations or protons. C₆H₆ is strongly adsorbed on the zeolite support especially in the case of cation-exchanged zeolites.

U.v. measurements show that benzene molecules are perturbed by the zeolite surface and that the aromatic ring is no longer planar. I.r. spectra confirm this observation and also show the presence of two types of adsorbed benzene. The first type, more or less strongly held, is directly bonded to the cation by formation of a π-complex and the second type corresponds to benzene molecules in interaction with the cation–C₆H₆ complex. This latter type might explain the new extra u.v. band observed at 215 nm which is assigned to a charge-transfer complex. In both cases, adsorption leads to a decrease in the aromatic character.