ADSORPTION AND DECOMPOSITION OF ALIPHATIC-ALCOHOLS ON TIO2

Methanol, ethanol, 1-propanol, and 2-propanol were adsorbed at ambient temperature on TiO//2 anatase powders. Temperature-programmed desorption spectra were obtained by using two different experimental apparatuses: a carrier-gas flow reactor system and a high-vacuum microbalance system. Two adsorption states were observed: molecular alcohol and alkoxide. Molecular alcohols desorbed intact upon slight heating (at 350 K) while alkoxides were removed from the surface via two channels: recombination at 390 K and decomposition at higher temperatures. The concentration of alkoxide species was equal for all of the primary alcohols but was less for the secondary alcohol due to steric effects. Temperatures at which the maximum rate of alkoxide decomposition occurred decreased in the sequence methoxide greater than ethoxide greater than n-propoxide greater than isopropoxide. The selectivity of alkoxide decomposition depended on both intramolecular bond energies and intermolecular interactions, suggesting that the interpretation of the selectivity in terms of surface acid-base properties alone is inadequate.