New information has been provided about the reaction pathway for n-butane partial oxidation to maleic anhydride over vanadyl pyrophosphate (VPO) catalysts using FTIR spectroscopy under transient conditions. Adsorption studies of n-butane, 1,3-butadiene, and related oxygenates were performed to gain information about reaction intermediates. n-Butane was found to adsorb on the VPO catalyst to form olefinic species at low temperatures. Unsaturated, noncyclic carbonyl species were determined to be precursors to maleic anhydride.