Preparation and characterization of iron–molybdate thin films

Mixed Fe–Mo oxides are used in industrial catalytic processes of selective oxidation of methanol to formaldehyde. For better understanding of the structure-reactivity relationships of these catalysts we aim to prepare well-ordered iron–molybdate thin films as model catalysts. Here we have studied Mo deposition onto Fe3O4 (111) thin films produced on Pt(111) as a function of Mo coverage and annealing temperature using LEED, AES, STM and IRAS. At low temperatures, the iron oxide film is covered by Mo = O terminated molybdena nanoparticles. Upon oxidation at elevated temperatures (T > 900 K), Mo species migrate into the film and form new bonds with oxygen in the film. The resulting films maintain the crystal structure of Fe3O4, and the surface undergoes a (√3 × √3)R30° reconstruction. The structure is rationalized in terms of Fe substitution by Mo in the surface layers.