Formation of carbonium ions on zeolite surfaces

Abstract

The adsorption and thermal desorption of carbonium ions from surfaces of zeolites, Al 2O 3 and TiO 2 have been investigated spectroscopically. The formation of stable carbonium ions (Φ 3C +) of triphenylmethyl compounds (Φ 3CCl and Φ 3COH) occurred at relatively low temperatures, e.g. 100°C. No Φ 3C + ions could be detected after adsorption of triphenylmethane. These findings are in agreement with prior mass spectrometric results. Intensities of the respective IR bands indicate that the molecules (Φ 3CCl, Φ 3COH, Φ 3CH) penetrate into the interior of the zeolite grains, where they are adsorbed. The experiments show that acidic Lewis sites are responsible for the carbonium ion formation in the present system.