Ceria on silica and alumina catalysts: dispersion and surface acid-base properties as probed by X-ray diffractometry, UV-Vis diffuse reflectance and in situ IR absorption studies

Zaki, Mohamed I.; Hussein, G.A.M.; Mansour, S.A.A.; Ismail, Hamdy M.; Mekhemer, Gamal A. H.

doi:10.1016/s0927-7757(96)03943-x

Cited by 83 publications

(36 citation statements)

References 27 publications

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“…The spectrum of the CeO 2 /Al 2 O 3 supports present an intense absorption band with maximum at about 307 nm, which is ascribed to the overlapping of theCe 4þ O 2À charge transfer and interband transitions, reported in pure CeO 2 at 278 and 313 nm, respectively [16,17]. The introduction of gold in the samples induces a shift of this maximum to higher wavenumbers.…”

Section: Resultsmentioning

confidence: 85%

“…The band gap observed for the gold samples are different each other, thus pointing to the existence of differences in the electronic and acid/base properties among them. It has been proposed that the energy of the band gap carry information about the average crystalline domain size of the oxide (CeO 2 in our case) particles, in such a way that the domain size increase when the band gap energy decreases [16,17], however as the measured band gap for the supported ceria particles is quite close to that measured for the bulk oxide, 3.1 eV [16,25], it should be considered that all the observed modifications are due to the presence of gold levels being independent of the domain size of ceria particles.…”

Section: Resultsmentioning

confidence: 96%

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Gold supported CeO2/Al2O3 catalysts for CO oxidation: influence of the ceria phase

et al. 2005

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A series of low loading gold supported ceria/alumina catalysts have been prepared by the deposition-precipitation method, varying the pH of the synthesis. The catalysts were characterised by means of XRD, TEM, S BET , XRF and UV-Vis techniques, and their catalytic activity towards CO oxidation in the absence and in presence of water in the stream, were tested. It has been found that in this low loading gold catalysts, where the metallic particles are far away one from another and the oxygen transportation is not the limiting step of the reaction, the electronic properties of the ceria phase and the structure of the metal-support perimeter more than the diameter of the gold nanoparticles is the determinant factor in the catalytic performances of the solid.

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Section: Resultsmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 96%

Gold supported CeO2/Al2O3 catalysts for CO oxidation: influence of the ceria phase

et al. 2005

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“…However, this technique has limitations due to the difficulty in interpreting large bandwidths and specular reflectance often observed in the spectra [36]. According to Bensalem et al [45], the wavelength corresponding to the UV absorption edge of a semiconducting powder such as CeO 2 can be safely used to probe the presence of nano-crystallites (\5 nm), which cannot be detected by XRD [46]. The DR spectra of C, CZ and CH samples are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Catalytic Efficiency of Ceria–Zirconia and Ceria–Hafnia Nanocomposite Oxides for Soot Oxidation

et al. 2008

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The catalytic oxidation of soot particulates has been investigated over CeO 2 , CeO 2 -ZrO 2 and CeO 2 -HfO 2 nanocomposite oxides. These oxides were synthesized by a modified precipitation method employing dilute aqueous ammonia solution. The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and BET surface area methods. The soot oxidation has been evaluated by a thermogravimetric method under 'tight contact' conditions. The XRD results revealed formation of cubic CeO 2 , Ce 0.75 Zr 0.25 O 2 and Ce 0.8 Hf 0.2 O 2 phases in case of CeO 2 , CeO 2 -ZrO 2 and CeO 2 -HfO 2 samples, respectively. TEM studies confirm the nanosized nature of the catalysts. Raman measurements suggest the presence of oxygen vacancies, lattice defects and oxide ion displacement from normal ceria lattice positions. UV-Vis DRS studies show presence of charge transfer transitions Ce 3+ /O 2-and Ce 4+ /O 2-respectively. The catalytic activity studies suggest that the oxidation of soot could be enhanced by incorporation of Zr 4+ and Hf 4+ into the CeO 2 lattice. The CeO 2 -HfO 2 combination catalyst exhibited better activity than the CeO 2 -ZrO 2 . The observed high activity has been related to the nanosized nature of the composite oxides and the oxygen vacancy created in the crystal lattice.

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“…It has been reported that the formation of the stronger Lewis acid (Zr 4 or Ce 4 ) and base (surface O 2À ) sites is favorable for CO 2 activation. 12,13 The more pronounced intensity attributed to the formation of planar polydentate carbonates (1466 and 1406 cm À1 ) on Ce-ZrO 2 indicates the closeness of cations, which is characteristic of the tetragonal structure of ZrO 2 . 14 For zirconia the bands assigned to bidentate carbonates (1550 and 1331 cm À1 ) and hydrogen carbonates (1630, 1427, and 1219 cm À1 ) disappear after evacuation at 300°C, whereas the bands due to hydrogen carbonates (1653, 1431, and 1200 cm À1 ) appear on supported Fe 3 O 4 catalyst after evacuation at 300°C.…”

Section: Resultsmentioning

confidence: 99%

CO2 utilization for the formation of styrene from ethylbenzene over zirconia-supported iron oxide catalysts

Noh

Chang

Park

et al. 2000

Appl. Organometal. Chem.

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Dehydrogenation of ethylbenzene with carbon dioxide has been carried out over zirconia-based catalysts. Carbon dioxide in this reaction was found to play a beneficial role as an oxidant for promoting catalytic activity. The addition of a ceria promoter to zirconia improved the catalytic activity significantly, which was attributed to increasing basicity as well as oxygen vancancies. The loading of iron oxide onto only zirconia among zirconia-related materials is effective for improving the activity.

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Ceria on silica and alumina catalysts: dispersion and surface acid-base properties as probed by X-ray diffractometry, UV-Vis diffuse reflectance and in situ IR absorption studies

Cited by 83 publications

References 27 publications

Gold supported CeO2/Al2O3 catalysts for CO oxidation: influence of the ceria phase

Gold supported CeO2/Al2O3 catalysts for CO oxidation: influence of the ceria phase

Catalytic Efficiency of Ceria–Zirconia and Ceria–Hafnia Nanocomposite Oxides for Soot Oxidation

CO2 utilization for the formation of styrene from ethylbenzene over zirconia-supported iron oxide catalysts

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