The partial oxidation of C-5 hydrocarbons was investigated over unprom
oted and alkali-promoted V2O5 catalysts. Products of this mild oxidati
on reaction include both maleic and phthalic anhydride. The apparent e
ffect of alkali promotion is to facilitate the loss of surface oxygen
species which are important in the activation of alkanes and the compl
ete oxidation of intermediate species. Studies performed using l-pente
ne as feed have indicated that once the first oxidative dehydrogenatio
n step is eliminated, pentene oxidation proceeds readily towards malei
c and phthalic anhydride formation. The use of 1-pentene in the feed s
tream caused a bulk reduction of the catalyst from V2O5 to VO2 in the
presence of gas phase oxygen.