The reaction of methanol to formaldehyde on both V2O3 and V2O5 films supported on CeO2(111) was studied by temperature programmed desorption (TPD). Methanol was found to react on monolayer and submonolayer vanadia films to produce formaldehyde, while multilayer films were found to be inactive for this reaction. The kinetics and mechanism of the dehydrogenation of adsorbed methoxides was found to be dependent on the oxidation state of the vanadium cations in the supported vanadia layer. On films that contained V3+ (i.e. V2O3), adsorbed methoxy species produced via dissociative adsorption of methanol underwent dehydrogenation to formaldehyde at 600 K. In contrast, on films that contained predominantly V5+ (i.e., V2O5), adsorbed methoxy species underwent dehydrogenation to produce formaldehyde at 540 K. Kinetic parameters for the methoxide dehydrogenation to formaldehyde on both V2O3 and V2O5 films were determined from the TPD data. The TPD results also provide insight into the thermal stability of supported vanadia films and the role of adsorbed oxygen in the oxidation of methanol to formaldehyde.