Transient isotopic studies on 1-butene oxidation over a VOx-TiO2 catalyst in presence of water vapor

The catalytic oxidation of 1-butene was studied in the temperature range of 390-553 K in presence and absence of O2 and water vapor. An increase in acetic acid yield was observed with increasing temperature up to a maximum at 520 K. The addition of water promoted the formation of acetic acid and suppressed total oxidation reactions. Transient isotopic experiments with 18O2/16O2 and H218O/H216O were carried out to investigate the role of gas oxygen and water in the formation of acetic acid. In absence of water the isotopic exchange was slow and complete at high temperatures. On the contrary, a fast but incomplete isotopic exchange in acetic acid was observed in presence of water. Isotopic transient experiments with 18O2 and H218O revealed that 18O from H218O was more readily incorporated into acetic acid than 18O from 18O2 pointing to a role of water as a reactant.