The Formation of Gas-Phase ?-Allyl Radicals from Propylene over Bismuth Oxide and γ-Bismuth Molybdate Catalysts

Article abstract of DOI:10.1021/ja00403a019

Gas-phase ?-allyl radicals were produced when propylene reacted over Bi2O3 and γ-bismuth molybdate catalysts at 723 K.The pressure in the catalyst zone was varied between 5 * 10^-3 and 1 torr.The radicals were detected by EPR spectroscopy together with a matrix isolation technique in which argon was used as the diluent.The matrix was formed on a sapphire rod at 12 K which was located 33-cm downstream from the catalyst.Bismuth oxide was more effective in the production of gas-phase allyl radicals than γ-bismuth molybdate.By contrast α-bismuth molybdate was ineffective in forming allyl radicals and MoO3 acted as a sink for radicals which were produced elsewhere in the system.Comparison of the ?-allyl radical and the stable product concentrations over Bi2O3 revealed that gas-phase radical recombination reactions served as a major pathway for the formation of 1,5-hexadiene.Addition of small amounts of gas-phase oxygen increased the concentration of allyl radicals, and at greater oxygen levels allyl peroxy radicals were detected.Because of the effect of temperature on the equilibrium between allyl and allyl peroxy radicals, the latter product must be formed in the cooler part of the system.