Publisher Summary This chapter discusses the suboxides of vanadia catalysts used in pentane, pentene, dicyclopentadiene, and cyclopentane oxidation reactions. The role of alkali promoters on the catalyst selectivity has also been discussed. The catalysts were reduced in situ at different temperatures and the effect of prereduction temperature was investigated. Controlled-atmosphere characterization of prereduction, postreduction, and postreaction catalysts were performed, using X-ray diffraction, X-ray photoelectron spectroscopy, laser Raman spectroscopy, and temperature programmed desorption experiments. The objectives of this study were to determine the activity and selectivity of different suboxides of vanadia in maleic and phthalic anhydride formation reactions and to examine the effect of alkali promoters on the product distribution. The chapter discusses the results from the transient response and temperature programmed desorption experiments performed, using dicyclopentadiene and phthalic anhydride, as probe molecules. Dicyclopentadiene was used as a probe molecule in this phase of the study. Although an optimization procedure was not followed to maximize the yield, a prereduction temperature of 400°C, coupled with a reaction temperature of 400°C, gave the best results with a combined anhydride yield (maleic+phthalic) of about 22% under the conditions used in these experiments.