Ceria-containing mixed oxides for oxygen storage
The present disclosure is directed to compositions comprising Ce-containing mixed oxides, especially those having a stoichiometry of Ln y Ce x M w O z ; where 0.15≤x≤0.5, y≤0.25, w=(1−x−y)≥0.5, and z=(2x+2w+1.5y); M is Zr, Hf, Ti, Sn or Ge or a combination thereof; Ln is Y and/or one or more rare earth metals, exclusive of Ce, and the uses of these compositions. These compositions are characterized by the even distribution of the Ce in the lattice of the mixed oxide.
1. A composition comprising a crystalline mixed oxide having
a stoichiometry of Ln y Ce x M w O z ; where
0.15≤x≤0.5, y≤0.25, w=(1−x−y)≥0.5, and z=(2x+2w+1.5y);
M is Zr, Hf, Ti, Sn, Ge, or a combination thereof;
Ln is Y and/or one or more rare-earth metals, exclusive of Ce;
wherein the Ce is evenly distributed through the lattice; and
wherein the crystalline mixed oxide has a crystallite size in a range of from about 1 nm to about 100 nm.
2. The composition of claim 1 , wherein M is or comprises Zr, Hf, or a mixture or combination thereof.
3. The composition of claim 1 , wherein Ln is La, Nd, Pr and/or Y.
4. The composition of claim 1 , wherein the crystalline mixed oxide is present as mesoporous or macroporous aggregates or agglomerates.
5. The composition of claim 1 , wherein the crystalline mixed oxide has a surface area in a range of from about 10 m 2 g −1 to about 100 m 2 g −1 .
6. The composition of claim 1 , wherein the crystalline mixed oxide is present in a tetragonal phase, a cubic phase, or a combination thereof.
7. The composition of claim 1 , wherein the crystalline mixed oxide exhibits a powder X-Ray Diffraction (PXRD) pattern, wherein the ratio of diffraction line intensities at 2θ=14.5±0.5° and 2θ=29.5±1° (I 14.5 /I 29.5 ) is less than 0.02.
8. The composition of claim 1 , wherein the crystalline mixed oxide has a Ce—Ce coordination number (CN) that is within 20% of the theoretical minimum value for the corresponding composition assuming perfect Ce distribution.
9. A method of preparing the crystalline mixed oxide of claim 1 , the method comprising:
(a) subjecting oxide precursors of the Ce, the one or more of Zr, Hf, Ti, Sn or Ge and the optional Y and/or one or more other rare-earth metals, exclusive of Ce to reduction conditions to form a reduced form of the crystalline mixed oxide; and
(b) optionally oxidizing the reduced form of the crystalline mixed oxide to form the crystalline mixed oxide.
10. The method of claim 9 , wherein the reduction conditions are a carbothermal reduction or a hydrogen reduction.
11. The method of claim 10 , wherein the oxide precursors of the Ce, the one or more of Zr, Hf, Ti, Sn or Ge and the optional Y and/or one or more other rare-earth metals, exclusive of Ce are deposited onto a high surface carbon support before subjecting the supported oxide precursors to the carbothermal reduction conditions.
12. The composition of claim 1 is useful in (a) a gasoline after-treatment system, including a Three-Way Catalyst (TWC) or (coated) gasoline or diesel particulate or soot filter; (b) a lean NO x trap for diesel after-treatment system; (c) a passive NO x adsorber (PNA); (d) a diesel oxidation catalyst (DOC); (e) a Water-Gas Shift catalyst; (f) a hydrocarbon reforming catalyst, including as a steam reforming and/or partial oxidation catalyst; and/or (g) a high-temperature water splitting catalyst to give H 2 .
13. A catalyst article comprising the composition of claim 1 , wherein the catalyst article is a TWC, a (coated) gasoline or diesel particulate or soot filter, a lean NO x trap for diesel after-treatment, a PNA, a DOC, Water-Gas Shift catalyst, a hydrocarbon reforming catalyst, a steam reforming catalyst, a partial oxidation catalyst; and/or a high-temperature water splitting catalyst.
14. A composition comprising a crystalline mixed oxide having
a stoichiometry of Ln y Ce x M w O z ; where
0.15≤x≤0.5, y≤0.25, w=(1−x−y)≥0.5, and z=(2x+2w+1.5y);
M is Zr, Hf, Ti, Sn, Ge, or a combination thereof;
Ln is Y and/or one or more rare-earth metals, exclusive of Ce;
wherein the Ce is evenly distributed through the lattice; and
wherein the crystalline mixed oxide exhibits a powder X-Ray Diffraction (PXRD) pattern,
wherein the ratio of diffraction line intensities at 2θ=14.5±0.5° and 2θ=29.5±1° (I 14.5 /I 29.5 ) is less than 0.02.
15. A composition comprising a crystalline mixed oxide having
a stoichiometry of Ln y Ce x M w O z ; where
0.15≤x≤0.5, y≤0.25, w=(1−x−y)≥0.5, and z=(2x+2w+1.5y);
M is Zr, Hf, Ti, Sn, Ge, or a combination thereof;
Ln is Y and/or one or more rare-earth metals, exclusive of Ce;
wherein the Ce is evenly distributed through the lattice; and
wherein the crystalline mixed oxide has a Ce—Ce coordination number (CN) that is within 20% of the theoretical minimum value for the corresponding composition assuming perfect Ce distribution.