Metal Oxide−Support Interactions in Fe/ZrO2Catalysts

To reveal the metal oxide−support interactions in ZrO 2 -supported Fe oxide catalysts as a function of calcination temperature, 5 wt % Fe/ZrO 2 was characterized by means of 57 Fe Mössbauer spectroscopy, IR, XRD, and thermogravimetric analysis. The catalytic activity of Fe/ZrO 2 was examined at 523 K for NO−CO reaction. It is shown that when Fe/ZrO 2 is calcined below 573 K, small particles of hydrated Fe 3+ oxyhydroxides (superparamagnetic at 297 K) are formed together with Fe 3+ paramagnetic species ion-exchanged with the surface OH groups of ZrO 2 . In addition to the Fe 3+ ion-exchanged species, Fe 3+ oxide clusters and crystalline α-Fe 2 O 3 particles are formed by successive dehydration of the oxyhydroxides on calcination at 973 K. When Fe/ZrO 2 is calcined at 1073 or 1173 K, the Mössbauer spectroscopic results suggest the formation of Fe 3+ cations trapped in surface vacant sites of ZrO 2 at the expense of the Fe 3+ oxide clusters. On the calcination at a higher temperature, crystalline α-Fe 2 O 3 predominates with a small portion of the Fe 3+ cations being in surface vacant sites. With 2 wt % Fe/ZrO 2 prepared by a coprecipitation method and calcined at 1173−1373 K, Fe 3+ cations dissolved in a ZrO 2 lattice are formed in addition to a small amount of magnetically split component.