(535e) Mechanistic Details of Propylene Oxidation on Alpha-Bismuth Molybdate: Origins of Unselective Oxidation Products

Application of Wojciechowski’s product stability analysis [1] to the partial oxidation of propylene with gas phase oxygen on α-bismuth molybdate (Bi₂Mo₃O₁₂) at 623 K revealed acrolein, acetaldehyde, and acetone to be primary unstable products, while acrylic acid, acetic acid, ethylene, butadiene, and benzene were identified as secondary products. Co-processing water with the reaction feed mixture increased the formation rate of acetone 10-fold at low propylene conversion (<5%) and increased the formation rate of acetaldehyde at higher propylene conversion (>10%), illustrating the direct participation of water in the formation of acetone from propylene and in the formation of acetaldehyde from a primary unstable product which is proposed to be acrolein. Independent co-feed experiments of acetone and acetaldehyde demonstrated the formation pathways of acetic acid from these two compounds and revealed acetone as the primary precursor of acetic acid. Propylene oxide was observed to be rapidly and quantitatively converted to acetaldehyde, CO, and CO₂, suggesting that a surface peroxide-like intermediate from propylene is the precursor of acetaldehyde. A pseudo-first-order kinetic model is shown to quantitatively describe the formation and consumption of all observed products. A detailed reaction network with proposed surface intermediates and reaction mechanisms for the conversion of propylene to all products will be presented.

1. Best, D.; Wojciechowski, B. H., Journal of Catalysis, 47, pp. 11-27 (1977)