The partial oxidation of acetaldehyde and propionaldehyde on a TiO2 supported VOx catalyst in the presence of water vapor was investigated at temperatures from 120 to 280 degrees C. Depending on the kind of aldehyde and reaction temperature, the selective oxidation to the appropriate carboxylic acid and an oxidative splitting to lower carboxylic acids took place. Acetaldehyde was oxidized to acetic acid with selectivities up to 82% at similar to 200 degrees C whereas propionic acid was formed only with selectivities of about 20% at similar to 140 degrees C in the oxidation of propionaldehyde. The oxidative cleavage of propionaldehyde led to the formation of more acetic acid than formic acid, which was in agreement with the higher formation of COx compared to that in the acetaldehyde oxidation. The presence of water and the increasing concentration of oxygen in the feed was found to enhance the selectivity towards the formation of C-1 to C-3 carboxylic acids by inhibiting the total oxidation of aldehydes and carboxylic acids.