Mechanistic Study on the Selective Oxidation of Acrolein to Acrylic Acid concerning the Role of Water

The activity of Mo/V/W mixed oxide catalyst in the gas phase oxidation of acrolein to acrylic acid is tremendously influenced by addition of fed water. This effect of water is investigated and connected to the catalytic mechanism by several stationary kinetic measurements and transient response methods, such as temperature‐programmed reduction, oxidation and desorption experiments, special concentration‐programmed methods as well as H218O‐SSITKA and D2O‐SSITKA experiments. Furthermore, kinetic modeling, based on results of H218O‐SSITKA experiments in a wide temperature and feed water content range gives access to kinetic parameters of single reaction steps in the catalytic mechanism. The developed mechanism is not only able to describe conversion and selectivities, inclusively the effect of water, but also describes the 18O‐degree of labeling of all reaction components quantitatively. Water as co‐catalyst: Feeding of additional water in the Mo/V/W mixed oxide catalyzed partial oxidation of acrolein to acrylic acid tremendously enhances the catalytic activity or acrolein conversion, respectively. This effect is caused by a direct intervention of water in the catalytic mechanism. The role of water is investigated by several steady state kinetic measurements and transient response methods. Kinetic modeling confirms the catalytic mechanism and delivers quantitative information.