In situ XAS-Untersuchungen zur Partialoxidation von Acrolein an Mischoxidkatalysatoren

Vanadium molybdenum mixed oxides have proven to be active and selective catalysts for the partial oxidation of unsaturated aldehydes. They are widely used in Megaton-scale industrial processes like the partial oxidation of acrolein to acrylic acid. The macroscopic reaction kinetics of vanadium molybdenum oxide catalysts for partial oxidation reactions are well established, and numerous promoters, e.g. tungsten, are available for improving performance and stability. However, little is known about the structure and dynamics of the microscopic mechanisms during catalyst operation. A detailed understanding of the partial oxidation mechanism, including the role of the different metal centers, the defect structure and the oxygen transport in this material, is necessary for further improvement and development of these important catalysts. In situ X-ray absorption spectroscopy (XAFS) was used to determine the change of average charge states of all the metal ions, i.e. molybdenum, vanadium and tungsten, in the catalyst during temperature and concentration programmed reduction and oxidation experiments, as well as for steady state operating conditions. A chemical relaxation model was then employed to determine kinetic data on the instationary transitions. Finally, this data yields an operational model for the steady-state kinetics of the catalyst