Abstract: Chemical trapping experiments with H₂, NH₃, and CH₃I as the trapping agents were used for studying the adsorption of propylene over MoO₃or r-Bi₂MoO₆The results show that fragmentation of carbon chain takes place during the adsorption of propylene through breaking C=C double bond and C-Cbond on Mo²⁺and the adjacent lattice oxygen, leading to formation of the oxygen-or nitrogen-containing by-products of C₁and C₂species. Diffuse-Reflection Fourier Transform Infrared (DRFTIR) spectroscopy was used to study the surface species formed during the chemisorption and reaction of propylene over r-Bi₂MoO₆at a lower temperature. The results that C₁, C₂species were detected by DRFTIR at 175℃ are consistent with the results of chemical trapping experiments, while the results at 50℃ support the mechanism of selective propylene oxidation proposed by Grasselli et al.

Key words: Selective oxidation of propylene, Ammoxidation, Mechanism of by-products formation, Chemical trapping, DRFTIR