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

We report a reaction network detailing the mechanistic origins of 20 C-2-C-6 byproducts observed during the oxidation of propylene to acrolein at 623 K 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 C-2 and C-3 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 C-C bond cleavage. C-C bond formation reactions that result in C-4-C-6 byproducts occur via: (i) the addition reaction of a propylene-derived surface allyl species with formaldehyde to form C-4 products and with propylene and allyl alcohol to form C-6 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 C-5 cyclic oxygenates.