Mechanisms for C[sbnd]C bond cleavage and formation during acrolein production on a mixed metal oxide catalyst

Abstract

We report a reaction network detailing the mechanistic origins of 20 C2–C6 byproducts observed during the oxidation of propylene to acrolein at 623K on a molybdenum-based catalyst promoted with cobalt and nickel used in the industrial production of acrolein. The carbon backbone of propylene is preserved in the sequential oxidation of propylene to allyl alcohol, acrolein, and acrylic acid, as well as propylene oxidation to acetone and propanal via water-mediated pathways. Transient kinetic measurements in conjunction with co-feed experiments of C2 and C3 aldehydes and carboxylic acids show that decarbonylation and decarboxylation reactions, reactions of organic compounds with surface-adsorbed oxygen species, and total combustion reactions are the three mechanisms for CC bond cleavage. CC bond formation reactions that result in C4–C6 byproducts occur via: (i) the addition reaction of a propylene-derived surface allyl species with formaldehyde to form C4 products and with propylene and allyl alcohol to form C6 products, or (ii) the addition reaction of an acrolein (acrylic acid)-derived surface ethenyl intermediate with propylene to form pentadiene and with acrolein to form C5 cyclic oxygenates.