IRON-BASED DEHYDROGENATION CATALYSTS SUPPORTED ON ZIRCONIA .1. PREPARATION AND CHARACTERIZATION

Zirconia-supported iron oxide catalysts were prepared by incipient wet ness impregnation, followed by drying and calcination in air. Characte rization of the catalysts was performed with electron microscopy combi ned with element analysis (HR-TEM/EDAX), X-ray diffraction (XRD), temp erature-programmed reduction (TPR), and thermomagnetic analysis. A hom ogeneous 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 su itable for this purpose. By HR-TEM/EDAX, it was shown that coverage of the zirconia support had been accomplished. XRD showed that crystalli ne Fe2O3 particles were formed at loadings greater than or equal to 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 propert ies prevail in TPR, whereas at lower loadings (<3 wt%) no distinct iro n oxide species could be indicated. Magnetization measurements confirm ed the results obtained by TPR. Catalysts prepared by coimpregnation o f iron and potassium were also studied. TEM and XRD results show that a well-dispersed phase is obtained, but from XRD only potassium carbon ate and no iron oxide or ferrite is evident, It was also found that th e presence of potassium increases the onset of reduction of the iron p hase by about 100 degrees C. (C) 1996 Academic Press, Inc.