Silica-supported vanadium oxides modified by alkali ions (Na+ K+, or Rb+) comprise two types of surface active species, which have been elucidated by phosphorescent emission and excitation spectra and the results of photoadsorption of gaseous propane and oxygen. One is the same as that on V2O5/SiO2 excited by light with wavelengths 310 < lambda < 390 nn and the other is that interacting with alkali ions excited by light with wavelengths lambda > 390 nm. Propanone is selectively formed by the photooxidation of propane over alkali-ion-modified catalysts. The active species excited by the light of wavelengths lambda > 390 nm have been found to be effective for the activation of the secondary C-H bonds of propane.