Temperature programmed desorption study of pre-irradiated TiO$_2$ anatase in the presence of ethanol. Effect of conduction band electrons on reaction selectivity

The work addresses one of the fundamentals of photocatalytic reactions, the fate of conduction-band (CB) electrons of a photo-excited TiO$_2$-anatase. Some of these CB-electrons are self-trapped as large-polarons. We have studied by Infrared-spectroscopy these polarons upon UV-excitation in the presence and absence of O$_2$. Moreover, the effect of CB-electrons on chemical reactions was investigated by temperature-programmed-desorption. Over the non-irradiated TiO$_2$, the dehydration and oxidation products dominated, while over that prior UV-irradiated in the presence of ethanol the dehydrogenation product increased and the oxidation pathway was partly suppressed. These changes are attributed to CB-electrons that made the near-surface more metallic.