Characterization of mixed amorphous/crystalline cerium oxide supported on SiO2

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 the CeO2, dispersion and crystallinity supported on SiO2. After calcination at 500 degrees C, XRD analysis indicated formation of larger CeO2, crystallites on CeqN catalysts compared to CeqA catalysts. Catalysts calcination at 800 degrees C led to a higher degree of crystallinity and larger particles of CeO2, compared with the catalysts calcined at 500 degrees C. TEM electron diffraction revealed that ceria is present on CeqA catalysts mostly as an amorphous phase, whereas on CeqN catalysts as crystalline CeO2. The CeO2 particle size calculated from XRD data, the TPR profile, and the XPS I-Ce3d/I-Si2p intensity ratio, indicated a better ceria dispersion on the SiO2 support for CeqA than for CeqN catalysts. EPR data showed the presence of paramagnetic Ce3+ as defects in the CeO2, crystalline structure only in CeqN catalysts. XPS analysis indicated that cerium is present on CeqN and CeqA catalysts surface as Ce4+. The observed differences between the CeqA and CeqN catalysts structure were presented in correlation with activity data obtained from ethylbenzene oxidative dehydrogenation and CO oxidation. (C) 1998 Elsevier Science B.V. All lights reserved.