Steady State Isotopic Transient Kinetic Analysis of the acrolein oxidation on Mo-V-W-mixed oxide catalysts

Mixed oxide catalysts on the basis of molybdenum and vanadium are industrially important catalysts for the partial oxidation of acrolein to acrylic acid. For a better understanding of the oxygen pathways for an optimised model catalyst with the stoichiometric composition Mo7.5V2.5W0.5Ox, the so-called Steady State Isotopic Transient Kinetic Analysis (SSITKA) method was employed. After switching from 16O2 to 18O2 the formation of 18O-labelled acrolein was observed. Acrolein exchanges its carbonyl oxygen with oxygen from the solid catalyst. This exchange is also reflected in the isotopic distribution of the oxidation products (acrylic acid and combustion products). Subsequent desorption of acrolein, as well as further reaction to the oxidation products, can take place. Compared to the partial oxidation the incorporation of the isotopic tracer oxygen into the combustion by-products is much slower. This might be an indicator of an intermediate layer in the combustion pathway. To obtain activation parameters SSITKA experiments were performed over a temperature range between 322 and 391 °C. Based on the observations, a macro kinetic model was adapted upon. The activation energy for the exchange of the carbonyl oxygen of acrolein was found to be approximately 30 kJ mol−1.