Density functional theory (DFT) calculations are carried out to investigate partial oxidation of propylene over neutral VO3 clusters. C=C bond cleavage products CH3CHO + VO2CH2 and HCHO + VO2CHCH3 can be formed overall barrierlessly from the reaction of propylene with VO3 at room temperature. Formation of hydrogen transfer products H2O + VO2C3H4, CH2=CHCHO + VO2H2, CH3CHCHO + VO2, and (CH3)(2)CO + VO2 is subject to tiny (0.01 eV) or small (0.06 eV, 0.19 eV) overall free energy barriers, although their formation is thermodynamically more favorable than the formation of C=C bond cleavage products. These DFT results are in agreement with recent experimental observations. VO3 regeneration processes at room temperature are also investigated through reaction Of 02 with the C=C bond cleavage products VO2CH2 and VO2CHCH3. The following barrierless reaction channels are identified: VO2CH2 + O-2 -> VO3 + CH2O; VO2CH2 + O-2 - VO3C + H2O, VO3C + O-2 -> VO3 + CO2; VO2CHCH3 + O-2 -> VO3 + CH3CHO; and VO2CHCH3 + O-2 -> VO3C + CH3OH, VO3C + O-2 -> VO3 + CO2. The kinetically most favorable reaction products are CH3CHO, H2O, and CO2 in the gas phase model catalytic cycles. The results parallel similar behavior in the selective oxidation of propylene over condensed phase V2O5/SiO2 catalysts.