Iron-Based Dehydrogenation Catalysts Supported on Zirconia. I. Preparation and Characterization

Abstract

Zirconia-supported iron oxide catalysts were prepared by incipient wetness impregnation, followed by drying and calcination in air. Characterization of the catalysts was performed with electron microscopy combined with element analysis (HR-TEM/EDAX), X-ray diffraction (XRD), temperature-programmed reduction (TPR), and thermomagnetic analysis. A homogeneous distribution of the iron containing phase can be obtained by using the metal complexes ammonium iron (III) citrate or ammonium (III) iron EDTA. A simple salt, such as iron nitrate, proved to be less suitable for this purpose. By HR-TEM/EDAX, it was shown that coverage of the zirconia support had been accomplished. XRD showed that crystalline Fe2O3particles were formed at loadings ≥3 wt% Fe. TPR studies point to a bi-modal particle size distribution for the catalysts with 3 wt% Fe. Above this loading (>3 wt%) bulk properties prevail in TPR, whereas at lower loadings (<3 wt%) no distinct iron oxide species could be indicated. Magnetization measurements confirmed the results obtained by TPR. Catalysts prepared by coimpregnation of iron and potassium were also studied. TEM and XRD results show that a well-dispersed phase is obtained, but from XRD only potassium carbonate and no iron oxide or ferrite is evident. It was also found that the presence of potassium increases the onset of reduction of the iron phase by about 100°C.