Thermal and Photochemical Reactions of Methanol, Acetaldehyde, and Acetic Acid on Brookite TiO2 Nanorods

The catalytic and photocatalytic activity of brookite TiO2 nanorods toward methanol, acetaldehyde, and acetic acid was studied using temperature-programmed desorption (TPD). For thermally activated reactions, the brookite nanorods were found to exhibit catalytic properties similar to those reported previously for the ruffle and anatase phases of TiO2. In particular, methanol adsorbed dissociatively on 5-fold coordinate surface Ti cations and underwent dehydrogenation to formaldehyde and deoxygenation to methane near 650 K; acetaldehyde adsorbed on these sites underwent aldol condensation to produce crotonaldehyde and to a lesser extent reductive coupling to butene between 460 and 600 K; acetic acid adsorbed dissociatively to produce acetate species that decomposed to produce ketene at 630 K. The brookite nanorods were also found to be photocatalytically active for the coupling of methanol to methyl formate and the photo-oxidation of acetaldehyde to acetate. Lastly, the photocatalytic activity of the brookite nanorods was found to be length-dependent, with longer rods exhibiting higher activity. This length dependence is attributed to enhanced delocalization of the photoexcited electrons in the longer rods, thereby decreasing the rate of electron-hole recombination.