Oxygen storage capacity (OSC) of aged Pt/CeO2/Al2O3 catalysts: roles of Pt and CeO2 supported on Al2O3

Kakuta, Noriyoshi; Morishima, Naoto; Kotobuki, Masashi; Iwase, Takemasa; Mizushima, Takeshi; Sato, Yasunori; Matsuura, Shinji

doi:10.1016/s0169-4332(97)00346-2

Cited by 41 publications

(23 citation statements)

References 8 publications

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“…So that CO 2 may be formed from the reaction of adsorbed CO and oxidized noble metal (PtO, Rh 2 O 3 ). Similar enhancement of the reducibility of CeO 2 by supporting Pt was observed and the strong Pt-CeO 2 interactions was estimated [3]. The reason for increase in the reducibility of CeO 2 by supporting noble metals is not clear, however, we tentatively suppose that the supported noble metals would give partial negative charge to Ce 4+ ions, and the slightly reduced CeO 2 ions may be more reducible than pure CeO 2 .…”

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confidence: 83%

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Redox properties of CeO2 and Pt-Rh/CeO2 studied by TAP method

et al. 2006

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Redox properties of CeO 2 and Pt-Rh/CeO 2 were studied by temporal analysis of products (TAP) method using alternative pulses of CO and O 2 . A portion of pulsed CO was oxidized to CO 2 and a portion of CO was adsorbed on the surface. Pulsing 18 O 2 onto the catalyst which has surface species derived from CO, evolved CO 2 contained no 18 O suggesting that the surface species will be carbonate ions.KEY WORDS: redox property; ceria; temporal-analysis-of-products; noble metal; promotion effect.Ceria has been widely used as a catalyst support for three-way catalysts in order to enlarge the efficient operating air/fuel (A/F) window. Fast redox character of CeO 2 is expected to work as an oxygen reservoir [1,2] usually; TPR and TPD are used for evaluation of oxidation activity and oxygen storage capacity of catalysts. However, it takes several 10 min to obtain a spectrum and data contains surface and bulk information. The data is sometimes far from the actual situation of catalysis. Temporal analysis of products (TAP) reactor system, an important tool for investigating 'gas-solid' reactions, adopts shots of different gases with a very short interval. Therefore, TAP analysis would be helpful to analyze catalytic reaction on metal oxides. CeO 2 was provided by (Anan Chem. Co., Japan). The loading of Pt and Rh for Pt-Rh/CeO 2 are 0.19 wt% and 0.56 wt%, respectively. The Pt-Rh/SiO 2 was also prepared with same loading amount of Pt and Rh (SiO 2 , Degussa, Aerosil, OX-50). CeO 2 and Pt-Rh/CeO 2 are confirmed to be cubic fluorite-type structure. The BET surface specific areas (SSA) of CeO 2 , Pt-Rh/CeO 2 and Pt-Rh/SiO 2 are 118, 116 and 50 m 2 /g, respectively.TAP reactor system was used for CO-O 2 pulse reaction. Four solenoid-operating gas-valves are arranged to supply a small amount of gas pulse. A quartz tube reactor with an internal diameter of 4 mm is used. Samples were pressed, crushed, and sieved with the size of 32-60 mesh. About 50 mg of a sample was packed in the reactor located in the center of an electrical furnace. The reactor was evacuated to 10 )2 $ 10 )3 Pa by a rotary pump. A capillary tube, of which one end is located just after the catalyst bed, is used for introducing gaseous products into a mass spectrometer. The chamber of mass spectrometer was kept high vacuum ($10 )6 Pa) by a turbo-molecular pump. Prior to measurements, the catalysts are evacuated at 500°C for 3 h and then fully oxidized by O 2 pulses. The accurate amount of each pulse is determined by measuring the pressure of gases in a vessel with known volume after injecting 50 $ 100 pulses with a high accuracy pressure gauge. And the accurate amount of CO (and O 2 ) consumed and CO 2 formed upon each pulse are determined by mass spectrometer. Peaks of CO (m/e = 28), O 2 (m/e = 32), and CO 2 (m/e = 44) are monitored. The relative sensitivity of CO, O 2 and CO 2 are calibrated using each gas. Since CO 2 gave m/e = 28 peak as a fragment peak, which is 11% of the parent peak area of m/e = 44, the amount of CO was corrected by this amount.Approaching...

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confidence: 83%

“…CO 2 was evolved upon the pulses of 18 O 2 , and no 18 O was observed in the formed CO 2 . This result strongly suggested that the CO was adsorbed as CO 3 2) on the ceria surface. If CO was adsorbed as CO or carbon atom(s) on the ceria, when it was oxidized by gaseous 18 O 2 , it would choose the added 18 O atom rather than lattice oxygen ions.…”

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confidence: 85%

Redox properties of CeO2 and Pt-Rh/CeO2 studied by TAP method

et al. 2006

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“…2,3 In the last few years, nanostructured CeO 2 in powder form has been broadly studied. [4][5][6] Furthermore, CeO 2 nanomaterials have attracted wide interest to the research community due to their potential applications in various fields such as ultra violet filter and blocker, 7,8 luminescent material, 9 polishing material, 10 skin cancer treatment, 11 solar cell, 12 catalytic material, 13 oxygen storage capacitor 14 and oxygen sensor. 15 In recent decade, diluted magnetic semiconductor (DMS) has attracted great attention from the worldwide scientists to investigate origin of ferromagnetism and its size dependence.…”

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confidence: 99%

Controlled synthesis and magnetic properties of monodispersed ceria nanoparticles

et al. 2015

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In the present study, monodispersed CeO2 nanoparticles (NPs) of size 8.5 ± 1.0, 11.4 ± 1.0 and 15.4 ± 1.0 nm were synthesized using the sol-gel method. Size-dependent structural, optical and magnetic properties of as-prepared samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscopy (HR-TEM), ultra-violet visible (UV-VIS) spectroscopy, Raman spectroscopy and vibrating sample magnetometer (VSM) measurements. The value of optical band gap is calculated for each particle size. The decrease in the value of optical band gap with increase of particle size may be attributed to the quantum confinement, which causes to produce localized states created by the oxygen vacancies due to the conversion of Ce4+ into Ce3+ at higher calcination temperature. The Raman spectra showed a peak at ∼461 cm-1 for the particle size 8.5 nm, which is attributed to the 1LO phonon mode. The shift in the Raman peak could be due to lattice strain developed due to variation in particle size. Weak ferromagnetism at room temperature is observed for each particle size. The values of saturation magnetization (Ms), coercivity (Hc) and retentivity (Mr) are increased with increase of particle size. The increase of Ms and Mr for larger particle size may be explained by increase of density of oxygen vacancies at higher calcination temperature. The latter causes high concentrations of Ce3+ ions activate more coupling between the individual magnetic moments of the Ce ions, leading to an increase of Ms value with the particle size. Moreover, the oxygen vacancies may also produce magnetic moment by polarizing spins of f electrons of cerium (Ce) ions located around oxygen vacancies, which causes ferromagnetism in pure CeO2 samples.

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“…A great deal of research has been devoted to understanding the interaction between metals and different metal oxide supports in order to design better catalysts [9][10][11][12]. Recently, cerium oxide (CeO 2 ) has become a very attractive candidate as a metal oxide support [13][14][15]. CeO 2 has extensively documented oxygen storage capacity (OSC) [16][17][18] and results in strong metal-metal oxide interactions [19].…”

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confidence: 99%

Catalytic properties of Pt cluster-decorated CeO2 nanostructures

et al. 2010

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Uniform clusters of Pt have been deposited on the surface of capping-agent-free CeO 2 nanooctahedra and nanorods using electron beam (e-beam) evaporation. The coverage of the Pt nanocluster layer can be controlled by adjusting the e-beam evaporation time. The resulting e-beam evaporated Pt nanocluster layers on the CeO 2 surfaces have a clean surface and clean interface between Pt and CeO 2 . Different growth behaviors of Pt on the two types of CeO 2 nanocrystals were observed, with epitaxial growth of Pt on CeO 2 nanooctahedra and random growth of Pt on CeO 2 nanorods. The structures of the Pt clusters on the two different types of CeO 2 nanocrystals have been studied and compared by using them as catalysts for model reactions. The results of hydrogenation reactions clearly showed the clean and similar chemical surface of the Pt clusters in both catalysts. The supportdependent activity of these catalysts was demonstrated by CO oxidation. The Pt/CeO 2 nanorods showed much higher activity compared with Pt/CeO 2 nanooctahedra because of the higher concentration of oxygen vacancies in the CeO 2 nanorods. The structure-dependent selectivity of dehydrogenation reactions indicates that the structures of the Pt on CeO 2 nanorods and nanooctahedra are different. Thes differences arise because the metal deposition behaviors are modulated by the strong metal-metal oxide interactions.

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Oxygen storage capacity (OSC) of aged Pt/CeO2/Al2O3 catalysts: roles of Pt and CeO2 supported on Al2O3

Cited by 41 publications

References 8 publications

Redox properties of CeO2 and Pt-Rh/CeO2 studied by TAP method

Redox properties of CeO2 and Pt-Rh/CeO2 studied by TAP method

Controlled synthesis and magnetic properties of monodispersed ceria nanoparticles

Catalytic properties of Pt cluster-decorated CeO2 nanostructures

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