Autori: Radu Craciun

Editorial: Solid State Ionics, 110(1-2), p.83-93, 1998.

Rezumat:

Various analyses techniques were employed for characterization of mixed amorphous/crystalline CeO2 supported on SiO2 catalysts prepared by incipient wetness using i) Ce4+-ammonium nitrate (CeqN) aqueous solution, and by grafting using ii) Ce4+-methoxyethoxide (CeqA) alcoholic solution. X-ray diffraction (XRD), temperature programmed reduction (TPR), and transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDX) were used to obtain information about CeO2 dispersion and crystallinity on the SiO2. After calcination at 500C, XRD analysis indicated formation of larger CeO2 crystallites in the of CeqN compared to CeqA catalysts. Calcination at 800C led to a high degree of crystallinity and large CeO2 particles. TEM electron diffraction revealed that cerium is present on CeqA catalysts mostly as an amorphous phase, whereas in CeqN catalysts as crystalline CeO2. The small CeO2 particle size shown by XRD data, low temperature TPR profile, and relatively high XPS ICe3d/ISi2p intensity ratio, indicate a better cerium dispersion on the SiO2 support in the case of CeqA than in CeqN catalysts. EPR data showed the presence of paramagnetic Ce3+ as defects in the CeO2 crystalline structure only in CeqN catalysts. Calcination at 800C of CeqA catalysts led to formation of more crystalline CeO2 phase. XPS analysis have indicated only the presence of Ce4+-species on CeqN and CeqA catalysts surface. The observed differences between CeqA and CeqN catalysts structure were correlated with the activity data obtained in ethylbenzene oxidative dehydrogenation and CO oxidation.

Cuvinte cheie: CeO2/SiO2 catalysts, XRD, XPS, TEM-EDX, EPR, TPR, ethylbenzene oxidative dehidrogenation