PRODUCT SELECTIVITY DURING CH3OH DECOMPOSITION ON TIO2 POWDERS

We show that the product selectivity during the temperature-programmed decomposition of CH//3OH on TiO//2 is a strong function of the initial CH//3OH coverage. For low coverages, the dissociated CH//3OH protons react with residual HO//(//a//) groups on the TiO//2 surface, leading to the desorption of H//2O and leaving behind isolated CH//3O//(//a//) groups that are stable to 673 K. For higher coverages a range of additional products is observed, including recombined CH//3OH, CH//3OCH//3, and CH//2O below 673 K and CO, CO//2, and CH//4 at higher temperature. We propose a model in which the decomposition selectivity is determined by the coverage of neighboring HO//(//a//), CH//3O//(//a//), and O**2** minus //(//a //) species. In the case of HO//(//a//) species, evidence suggests that surface diffusion of protons from non-nearest-neighbor sites also affect the decomposition selectivity.