A fundamental reaction
in industries for producing aldehydes and
ketones is the partial oxidation of alcohols. As a model reaction,
we investigated the photo-oxidation of 2-propanol on rutile titania, which is a promising chemically nontoxic photocatalyst.
Photochemical infrared reflection absorption spectroscopy (PC-IRRAS)
was used to study the reaction on powder catalysts in the liquid phase
(neat liquid and dissolved in dichloromethane). We compare these results
with polarized Fourier transform (FT)-IRRAS and temperature-programmed
desorption (TPD) experiments on rutile TiO2(110) single
crystals in ultrahigh vacuum (UHV). Our in situ liquid-phase experiments
showed that 2-propanol converts into acetone on rutile powders, which
is in accordance with previous ex situ studies. Mass transport limitations
are the key to avoid total oxidation. However, the yield of acetone
is limited. We identified water formed as a byproduct and suspected
that water might block the active sites. To elucidate possible reaction
mechanisms, further experiments were performed on rutile TiO2(110) single crystals in the presence and absence of oxygen and UV
irradiation under UHV conditions. Here, we obtained further insights
into the elementary steps of the different 2-propanol reactions. We
demonstrated that acetone desorbs from a diolate species, which forms
in the presence of oxygen under UV irradiation at temperatures around
200 K. Furthermore, propane was identified for the first time as a
new thermally activated deoxygenation product besides the simultaneously
formed, formally reported, propene. Propene formation is quenched
by UV irradiation. Active site blocking by water is confirmed by TPD
and polarized FT-IRRAS measurements.