The state of the iron promoter in tungstated zirconia catalysts

The activity and selectivity of tungstated zirconia (WZ) for the conversion of n- into isopentane are dramatically enhanced when the catalyst is modified with Pt and Fe. The state of iron in these catalysts was hitherto only poorly characterized. Therefore, in the present work we investigated the structural and electronic properties of iron in WZ catalysts containing 1 wt% Pt and 1 wt% Fe2O3, by a combination of spectroscopic techniques, namely X-ray absorption spectroscopy (XAS), in situ electron paramagnetic resonance (EPR), and Mossbauer spectroscopy. In the oxidized catalyst, iron is present as Fe-III and predominantly forms a surface solid solution in which the isolated Fe-III ions are located in a distorted octahedral environment. A small amount of the total iron (around 10%) is present in the form of small iron oxide particles. Both iron species can be reduced in H-2 and then easily reoxidized on exposure to air at room temperature. We infer that the promoter action of iron in these catalysts is intimately related to its redox properties and specifically affects the dehydrogenation activity of the materials.