Mixed oxides of the type MO2 (fluorite)—M2O3—I oxygen dissociation pressures and phase relationships in the system CeO2Ce2O3 at high temperatures

Bevan, D. J. M.; Kordis, J.

doi:10.1016/0022-1902(64)80038-5

Cited by 364 publications

(164 citation statements)

References 23 publications

Supporting

Mentioning

143

Contrasting

Order By: Relevance

“…In the least reducing Gas 2 reduction also began at about 700 o C and the final value of n was 1.88. The difference in the level of reduction in Gases 2 and 3 became appreciable at about 750 o C. These values of n are in reasonable agreement with experimental values published by Bevan and Kordis (1964) results using Gas 1 (most highly reducing) while Figure 17 presents data in Gas 2 (least reducing). The electrobalance response curves appear somewhat variable because of the extremely small weight losses associated with reduction.…”

Section: Sorbent Reductionsupporting

confidence: 89%

High Efficiency Desulfurization of Synthesis Gas

Yi¹,

Podlaha²,

Harrison³

2002

View full text Add to dashboard Cite

Mixed metal oxides containing CeO 2 and ZrO 2 are being studied as high temperature desulfurization sorbents capable of achieving the DOE Vision 21 target of 1 ppmv or less H 2 S. The research is justified by recent results in this laboratory that showed that reduced CeO 2 , designated CeO n (1.5 < n < 2.0), is capable of achieving the 1 ppmv target in highly reducing gas atmospheres. The addition of ZrO 2 has improved the performance of oxidation catalysts and three-way automotive catalysts containing CeO 2 , and should have similar beneficial effects on CeO 2 desulfurization sorbents.An electrochemical method for synthesizing CeO 2 -ZrO 2 was developed and the products were characterized by XRD and TEM during year 01. Nanocrystalline particles having a diameter of about 5 nm and containing from approximately 10 mol% to 80 mol% ZrO 2 were prepared. XRD showed the product to be a solid solution at low ZrO 2 contents with a separate ZrO 2 phase emerging at higher ZrO 2 levels. Unfortunately, the quantity of CeO 2 -ZrO 2 that could be prepared electrochemically was too small to permit full testing in our desulfurization reactor.Also during year 01 a laboratory-scale fixed-bed reactor was constructed for desulfurization testing. All components of the reactor and analytical systems that may be exposed to low concentrations of H 2 S are constructed of quartz, Teflon, or silcosteel. Reactor product gas composition as a function of time is determined using a Varian 3800 gas chromatograph equipped with a pulsed flame photometric detector (PFPD) for measuring low H 2 S concentrations (<~10 ppmv) and a thermal conductivity detector (TCD) for higher concentrations of H 2 S.Larger quantities of CeO 2 -ZrO 2 mixtures from other sources, including mixtures prepared in this laboratory using a coprecipitation procedure, have been obtained. Characterization and desulfurization testing of these sorbents began in year 02 and is continuing. To properly evaluate the effect of ZrO 2 addition on desulfurization capability, the physical properties of the sorbent mixtures must be similar. That is, a CeO 2 -ZrO 2 mixture from source A would not necessarily be superior to pure CeO 2 from source B if the properties were dissimilar. Therefore, current research is concentrating on CeO 2 and CeO 2 -ZrO 2 mixtures prepared in this laboratory using the coprecipitation procedure. The structure of these sorbents is similar and the effect of ZrO 2 addition can be separated from other effects.X-ray diffraction tests of the sorbents prepared in house have confirmed the existence of a solid solution of ZrO 2 in CeO 2 . Reduction tests using an electrobalance reactor have confirmed that CeO 2 -ZrO 2 mixtures are more easily reduced than pure CeO 2 . Reduction of CeO 2 -ZrO 2 begins at a lower temperature and the final value of n in CeO n (1.5

show abstract

Section: Sorbent Reductionsupporting

confidence: 89%

High Efficiency Desulfurization of Synthesis Gas

Yi¹,

Podlaha²,

Harrison³

2002

View full text Add to dashboard Cite

show abstract

“…The ultimate degree of reduction, i.e., the equilibrium value of n, depends on temperature and the oxygen partial pressure of the reducing gas, as described by Bevan and Kordis (1964) and Sorensen (1976). Reduction experiments in this laboratory using CeO 2 and an electrobalance reactor showed that the level of reduction, i.e., the experimental value of n, is in reasonable agreement with the results of Bevan and Kordis.…”

Section: High Temperature Gas Desulfurizationsupporting

confidence: 84%

High Efficiency Desulfurization of Synthesis Gas

Yi¹,

Mukherjee²,

Podlaha³

et al. 2004

View full text Add to dashboard Cite

Mixed metal oxides containing ceria and zirconia have been studied as high temperature desulfurization sorbents with the objective of achieving the DOE Vision 21 target of 1 ppmv or less H 2 S in the product gas. The research was justified by recent results in this laboratory that showed that reduced CeO 2 , designated CeO n (1.5 < n < 2.0), is capable of achieving the 1 ppmv target in highly reducing gas atmospheres. The addition of ZrO 2 has improved the performance of oxidation catalysts and three-way automotive catalysts containing CeO 2 , and was postulated to have similar beneficial effects on CeO 2 desulfurization sorbents.An electrochemical method for synthesizing CeO 2 -ZrO 2 mixtures was developed and the products were characterized by XRD and TEM during year 01. Nanocrystalline particles having a diameter of about 5 nm and containing from approximately 10 mol% to 80 mol% ZrO 2 were prepared. XRD analysis showed the product to be a solid solution at low ZrO 2 contents with a separate ZrO 2 phase emerging at higher ZrO 2 levels. Unfortunately, the quantity of CeO 2 -ZrO 2 that could be prepared electrochemically was too small to permit desulfurization testing.Also during year 01 a laboratory-scale fixed-bed reactor was constructed for desulfurization testing. All components of the reactor and analytical systems that were exposed to low concentrations of H 2 S were constructed of quartz, Teflon, or silcosteel. Reactor product gas composition as a function of time was determined using a Varian 3800 gas chromatograph equipped with a pulsed flame photometric detector (PFPD) for measuring low H 2 S concentrations from approximately 0.1 to 10 ppmv, and a thermal conductivity detector (TCD) for higher concentrations of H 2 S.Larger quantities of CeO 2 -ZrO 2 mixtures from other sources, including mixtures prepared in this laboratory using a coprecipitation procedure, were obtained. Much of the work during year 02 consisted of characterization and desulfurization testing of materials obtained from commercial sources. Most of the commercial CeO 2 and CeO 2 -ZrO 2 materials were capable of reducing H 2 S concentration from 5000 ppmv in highly reducing feed gas to less than 1 ppmv in the product gas. However, to properly evaluate the effect of ZrO 2 addition on desulfurization capability, the physical properties of the sorbent must be similar. That is, a CeO 2 -ZrO 2 mixture from source A would not necessarily be superior to pure CeO 2 from source B if the properties of the pure CeO 2 were superior. Therefore, research during year 03 concentrated on CeO 2 and CeO 2 -ZrO 2 mixtures prepared in this laboratory using a coprecipitation procedure. The structural properties of these sorbents were similar and the effect of ZrO 2 addition could better be separated from the structural effects.X-ray diffraction tests of the sorbents prepared in house confirmed the formation of a solid solution of ZrO 2 in CeO 2 . Crystallite sizes ranged from 12.7 to 18.8 nm and surface areas from 75 to 85 m 2 /g. Reduction tests us...

show abstract

“…For bulk ceria, most oxidation occurs over a very narrow range of P(O 2 ) in this temperature range because there are two ceria phases, a reduced phase and a more oxidized phase, in equilibrium at 973 K and below [42]. For ceria oxidation at temperatures above 1073 K, there is only a single ceria phase with a varying oxygen stoichiometry.…”

Section: High-surface-area Ceria and Ceria/lamentioning

confidence: 98%

Oxidation enthalpies for reduction of ceria surfaces

et al. 2007

View full text Add to dashboard Cite

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.

show abstract

Mixed oxides of the type MO2 (fluorite)—M2O3—I oxygen dissociation pressures and phase relationships in the system CeO2Ce2O3 at high temperatures

Cited by 364 publications

References 23 publications

High Efficiency Desulfurization of Synthesis Gas

High Efficiency Desulfurization of Synthesis Gas

High Efficiency Desulfurization of Synthesis Gas

Oxidation enthalpies for reduction of ceria surfaces

Contact Info

Product

Resources

About