Ceria and Other Oxygen Storage Components in Automotive Catalysts

Shelef, M.; Graham, George W.; McCabe, Robert W.

doi:10.1142/9781860949654_0010

Cited by 60 publications

(45 citation statements)

References 27 publications

(32 reference statements)

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“…Ce(NO 3 ) 3 •6H 2 O (Aldrich 99.99 %) was dissolved in distilled water, after which the solution was added drop wise to a 10% NH 4 OH solution under vigorous stirring. H 2 O 2 (35%) was then added to the suspension and the mixture was stirred for 40 min before filtering.…”

Section: Samplesmentioning

confidence: 99%

“…Ceria-based materials have been used for many years in automotive emissions control for Oxygen-Storage Capacitance (OSC) [1][2][3] and are finding many new applications as supports for water-gas-shift catalysts [4][5][6][7][8][9][10][11][12], supports for reforming catalysts [13,14], and as hydrocarbon oxidation catalysts in diesel emissions [15,16]. In all of these applications, it is likely that the ability of cerium to cycle between Ce +3 and Ce +4 is crucial.…”

Section: Introductionmentioning

confidence: 99%

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Oxidation enthalpies for reduction of ceria surfaces

et al. 2007

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The thermodynamic properties of surface ceria were investigated through equilibrium isotherms determined by flow-titration and coulometric-titration measurements on high-surface-area ceria and ceria supported on La-modified alumina (LA). While the surface area of pure ceria was found to be unstable under redox conditions, the extent of reduction at 873 K and a P(O 2 ) of 1.6x10 -26 atm increased with surface area. Because ceria/LA samples were stable, equilibrium isotherms were determined between 873 and 973 K on a 30-wt% ceria sample. Oxidation enthalpies on ceria/LA were found to vary with the extent of reduction, ranging from -500 kJ/mol O 2 at low extents of reduction to near the bulk value of -760 kJ/mol O 2 at higher extents. To determine whether +3 dopants could affect the oxidation enthalpies for ceria, isotherms were measured for Sm +3 -doped ceria (SDC) and Y +3 -doped ceria. These dopants were found to remove the phase transition observed in pure ceria below 973 K but appeared to have minimal effect on the oxidation enthalpies. Implications of these results for catalytic applications of ceria are discussed. AbstractThe thermodynamic properties of surface ceria were investigated through equilibrium isotherms determined by flow-titration and coulometric-titration measurements on high-surfacearea ceria and ceria supported on La-modified alumina (LA). While the surface area of pure ceria was found to be unstable under redox conditions, the extent of reduction at 873 K and a P(O 2 ) of 1.6x10 -26 atm increased with surface area. Because ceria/LA samples were stable, equilibrium isotherms were determined between 873 and 973 K on a 30-wt% ceria sample. Oxidation enthalpies on ceria/LA were found to vary with the extent of reduction, ranging from -500 kJ/mol O 2 at low extents of reduction to near the bulk value of -760 kJ/mol O 2 at higher extents.To determine whether +3 dopants could affect the oxidation enthalpies for ceria, isotherms were measured for Sm +3 -doped ceria (SDC) and Y +3 -doped ceria. These dopants were found to remove the phase transition observed in pure ceria below 973 K but appeared to have minimal effect on the oxidation enthalpies. Implications of these results for catalytic applications of ceria are discussed.

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Section: Samplesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Oxidation enthalpies for reduction of ceria surfaces

et al. 2007

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“…The addition of 1 wt % Pd is too small to provide electronic conductivity directly; however, Pd could affect the average oxidation state of the ceria due to the fact that its presence is expected to dramatically increase the rate of ceria reduction. [26][27][28][29][30] An increased rate of reduction could affect the average oxidation state of the ceria at higher current densities if the rate of ceria oxidation by ions coming through the electrolyte is significant compared to the rate of reduction of ceria by the fuel gas. It is also possible that there is a contribution to the increase in ohmic resistance under current loadings due to an increase in the diffusion pathway for oxygen ions, since a less active catalyst would require more surface area to consume the same number of ions.…”

Section: B696mentioning

confidence: 99%

An Examination of SOFC Anode Functional Layers Based on Ceria in YSZ

Gross

Vohs

Gorte

2007

J. Electrochem. Soc.

109

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The properties of solid oxide fuel cell ͑SOFC͒ anode functional layers prepared by impregnation of ceria and catalytic metals into porous yttria-stabilized zirconia ͑YSZ͒ have been examined for operation at 973 K. By varying the thickness of the functional layer, the conductivity of the ceria-YSZ composite was determined to be only 0.015-0.02 S/cm. The initial performance of anodes made with ceria loadings of 40 or 60 wt % were similar but the anodes with lower loadings lost conductivity above 1073 K due to sintering of the ceria. The addition of dopant levels of catalytic metals was found to be critical. The addition of 1 wt % Pd or Ni decreased the anode impedances in humidified H 2 dramatically, while the improvement with 5 wt % Cu was significant but more modest. Pd doping also decreased the anode impedance in dry CH 4 much more than did Cu doping; however, addition of either Pd or Cu led to similar improvements for operation in n-butane. Based on these results, suggestions are made for ways to improve SOFC anode functional layers.

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“…Consistent with this, CeO 2 single crystals, which by definition have been heated to high temperatures in their preparation, are difficult to reduce except by very harsh treatments such as ion sputtering [14,15]. Deactivation of the oxygen storage capacity of ceria by high temperatures in automotive applications is well known, and it is necessary to stabilize the reducibility of ceria for that application by mixing it with zirconia [16].…”

Section: Introductionmentioning

confidence: 98%