Effect of light on reactions over sulfated zirconia

The effect of illumination with visual and near-UV light on the isomerization and cracking of n-pentane and formation of radical cations from benzene and its derivatives over sulfated zirconia has been studied. Sulfated zirconia proved to have very strong acceptor sites capable of ionizing benzene and methylbenzenes to corresponding radical cations. The ionization of aromatic molecules could be initiated with visual light. The presence of oxygen in the gas phase appeared to strengthen the acceptor sites and shift the photoreaction red edge to longer wavelengths. Electron donor-acceptor complexes are shown to be key intermediates in the ionization of aromatic molecules on sulfated zirconia. A qualitative correlation between the presence of the strongest acceptor sites and the isomerization activity was observed. Illumination with visual light significantly increased the pentane cracking selectivity with little effect on the isomerization activity. Pentane cracking is proposed to proceed via dimerization initiated by the charge transfer with the formation of unstable radical cations. (C) 1998 Academic Press.