Unusual manifestation of benzene radical cations in ESR spectra on sulfated zirconia

A narrow singlet has been observed in the ESR spectra after benzene adsorpt ion on sulfated zirconia, with its evacuation and freezing leading to the r eversible formation of benzene dimer radical cations. The singlet has been proposed to result from the delocalization of the electron density througho ut several benzene rings due to fast electron exchange. This distinguishes sulfated zirconia catalysts from zeolites where this effect is not observed because of the small size of channels. (C) 2000 Elsevier Science B.V. All rights reserved.