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EnglishThe 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(O2) of 1.6 × 10-26 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 O2 at low extents of reduction to near the bulk value of -760 kJ/mol O2 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.
| Titolo: | Oxidation Enthalpies for Reduction of Ceria Surfaces |
| Autori: | |
| Data di pubblicazione: | 2007 |
| Rivista: | |
| Abstract: | 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(O2) of 1.6 × 10-26 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 O2 at low extents of reduction to near the bulk value of -760 kJ/mol O2 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. |
| Handle: | http://hdl.handle.net/11368/1694281 |
| Digital Object Identifier (DOI): | http://dx.doi.org/10.1016/j.susc.2007.04.238 |
| Appare nelle tipologie: | 1.1 Articolo in Rivista |
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