Mixed-phase ceramic oxide three-way catalyst formulations and methods for preparing the catalysts

• US 7,641,875 B1
• Filed: 11/03/2008
• Issued: 01/05/2010
• Est. Priority Date: 11/15/2000
• Status: Expired due to Fees

• Current Assignee: Catalyst Health Solutions Incorporated (UnitedHealth Group Incorporated)
• Original Assignee: Catalyst Health Solutions Incorporated (UnitedHealth Group Incorporated)
• Inventors: Golden, Stephen J.
• Primary Examiner(s): Nguyen; Cam N
• Application Number:
  US12/290,775
• Time in Patent Office: 428 Days
• Field of Search: 502/104, 502/113, 502/302, 502/303, 502/304, 502/306, 502/308, 502/309, 502/311, 502/312, 502/313, 502/314, 502/315, 502/316, 502/317, 502/318, 502/319, 502/320, 502/321, 502/322, 502/323, 502/324, 502/326, 502/327, 502/328, 502/330, 502/331, 502/332, 502/333, 502/334, 502/335, 502/336, 502/337, 502/338, 502/339, 502/341, 502/344, 502/345, 502/346, 502/347, 502/525, 502/527.12, 423/213.5, 423/239.1, 423/245.1, 423/247
• US Class Current: 423/213.5
• CPC Class Codes: B01D 2255/1021 Platinum
• CPC Class Codes: B01D 2255/1023 Palladium
• CPC Class Codes: B01D 2255/1025 Rhodium
• CPC Class Codes: B01D 2255/202 Alkali metals
• CPC Class Codes: B01D 2255/204 Alkaline earth metals
• CPC Class Codes: B01D 2255/206 Rare earth metals
• CPC Class Codes: B01D 2255/402 Perovskites
• CPC Class Codes: B01D 2255/407 Zr-Ce mixed oxides
• CPC Class Codes: B01D 2255/9022 Two layers
• CPC Class Codes: B01D 2258/014 Stoichiometric gasoline engines
• CPC Class Codes: B01D 53/945 characterised by a specific catalyst
• CPC Class Codes: B01J 23/002 Mixed oxides other than spinels, e.g. perovskite
• CPC Class Codes: B01J 23/6562 Manganese
• CPC Class Codes: B01J 2523/00 Constitutive chemical elements of heterogeneous catalysts
• CPC Class Codes: B01J 2523/24 Strontium
• CPC Class Codes: B01J 2523/37 Lanthanides
• CPC Class Codes: B01J 2523/3706 Lanthanum
• CPC Class Codes: B01J 2523/3712 Cerium
• CPC Class Codes: B01J 2523/72 Manganese
• CPC Class Codes: B01J 2523/824 Palladium
• CPC Class Codes: B01J 37/0036 : Grinding
• CPC Class Codes: B01J 37/0234 : Impregnation and coating simultaneously
• CPC Class Codes: B01J 37/0242 : Coating followed by impregnation
• CPC Class Codes: B01J 37/0244 : Coatings comprising several layers
• CPC Class Codes: B01J 37/031 : Precipitation
• CPC Class Codes: B01J 37/08 : Heat treatment B01J37/0009, B01J37/0018 take precedence
• CPC Class Codes: C01B 13/32 : by oxidation or hydrolysis of elements or compounds in the liquid or solid state or in non-aqueous solution, e.g. sol-gel process
• CPC Class Codes: C01G 25/006 : Compounds containing, besides zirconium, two or more other elements, with the exception of oxygen or hydrogen
• CPC Class Codes: C01G 45/006 : Compounds containing, besides manganese, two or more other elements, with the exception of oxygen or hydrogen manganates, manganites or permanganates C01G45/12
• CPC Class Codes: C01G 49/009 : Compounds containing, besides iron, two or more other elements, with the exception of oxygen or hydrogen
• CPC Class Codes: C01G 51/006 : Compounds containing, besides cobalt, two or more other elements, with the exception of oxygen or hydrogen cobaltates C01G51/40
• CPC Class Codes: C01G 53/006 : Compounds containing, besides nickel, two or more other elements, with the exception of oxygen or hydrogen nickelates C01G53/40
• CPC Class Codes: C01G 55/00 : Compounds of ruthenium, rhodium, palladium, osmium, iridium, or platinum
• CPC Class Codes: C01P 2002/34 : perovskite-type (ABO3)
• CPC Class Codes: C01P 2004/80 : Particles consisting of a mixture of two or more inorganic phases
• CPC Class Codes: C01P 2006/16 : Pore diameter
• CPC Class Codes: C04B 2235/3213 : Strontium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3225 : Yttrium oxide or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3227 : Lanthanum oxide or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3229 : Cerium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3289 : Noble metal oxides
• CPC Class Codes: C04B 35/016 : based on manganites
• CPC Class Codes: C04B 35/486 : Fine ceramics
• CPC Class Codes: Y02A 50/20 : Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies
• CPC Class Codes: Y10S 502/525 : Perovskite

Abstract

A multi-phase catalyst for the simultaneous conversion of oxides of nitrogen, carbon monoxide, and hydrocarbons is provided. A catalyst composition comprising the multi-phase catalyst and methods of making the catalyst composition are also provided. The multi-phase catalyst may be represented by the general formula of Ce_yLn_1-xA_x+sMO_Z, wherein Ln is a mixture of elements originally in the form of single-phase mixed lanthanides collected from natural ores, a single lanthanide, or a mixture of lanthanides; A is an element selected from a group consisting of Mg, Ca, Sr, Ba, Li, Na, K, Cs, Rb, or any combination thereof; and M is an element selected from the group consisting of Fe, Mn, Cr, Ni, Co, Cu, V, Zr, Pt, Pd, Rh, Ru, Ag, Au, Al, Ga, Mo, W, Ti, or any combination thereof; x is a number defined by 0≦x<1.0; y is a number defined by 0≦y<10; s is a number defined by 0≦s<10; where s=0 only when y>0 and y=0 only when s>0. The multi-phase catalyst can have an overlayer of an oxide having the fluorite structure with a combination of platinum and/or rhodium.

Claims

1. A multi-phase catalyst for simultaneous conversion of oxides of nitrogen, carbon monoxide, and hydrocarbons represented by the general formula:

Ce_yLn_1-xA_x+sMO_z,

wherein;

A is an element selected from the group consisting of Mg, Ca, Sr, Ba, Li, Na, K, Cs, Rb, and any combination thereof;

Ln is a mixture of elements originally in the form of single-phase mixed lanthanides collected from natural ores, a single lanthanide, or a mixture of artificial lanthanides;

M is an element selected from the group consisting of Fe, Mn, Cr, Ni, Co, Cu, V, Zr, Pt, Pd, Rh, Ru, Ag, Au, Al, Ga, Mo, W, Ti, and any combination thereof;

x is a number defined by 0≦

x<

1.0;

y is a number defined by 0≦

y<

10;

s is a number defined by 0≦

s<

10; and

z is a number defined by z>

0,

where s=0 only when y>

0 and y=0 only when s>

0.

2. The multi-phase catalyst of claim 1, wherein said multi-phase catalyst comprises a perovskite phase and a non-perovskite phase.

3. The multi-phase catalyst of claim 2, wherein the perovskite phase is represented by a general formula Ln_1-xA_xMO₃.

4. The multi-phase catalyst of claim 3, wherein the perovskite phase has a cation formula selected from the group consisting of Ln_0.8Sr_0.2Mn_0.88Pd_0.12, Ln_0.8Sr_0.2Mn_0.94Pd_0.6, Ln_0.60Sr_0.40Mn_0.95Pd_0.05, Ln_0.64Sr_0.36Mn_0.72Pd_0.28, and Ln_0.80Sr_0.20Mn_0.65Pd_0.35.

5. The multi-phase catalyst of claim 2, wherein the non-perovskite phase is selected from the group consisting of cerium oxide, an alkaline earth metal oxide represented by a formula AO, an alkali metal oxide represented by the formula A₂O, an alkaline earth metal carbonate, and combinations thereof.

6. The multi-phase catalyst of claim 5, wherein the non-perovskite phase is cerium oxide.

7. The multi-phase catalyst of claim 5, wherein the non-perovskite phase is an alkaline earth metal oxide represented by a formula AO.

8. The multi-phase catalyst of claim 7, wherein the alkaline earth metal oxide is SrO.

9. The multi-phase catalyst of claim 5, wherein the multi-phase catalyst comprises a first non-perovskite phase of cerium oxide, and a second non-perovskite phase of an alkaline earth metal oxide represented by a formula of AO.

10. The multi-phase catalyst of claim 9, wherein the alkaline earth metal oxide is SrO.

11. The multi-phase catalyst of claim 10, wherein the perovskite phase has a cation formula selected from the group consisting of Ln_0.64Sr_0.36Mn_0.72Pd_0.28 and Ln_0.80Sr_0.20Mn_0.65Pd_0.35.

12. The multi-phase catalyst of claim 1, wherein Ln is obtained from lanthanum concentrate.

13. The multi-phase catalyst of claim 1, wherein Ln is a mixture of elements originally in the form of single-phase mixed lanthanides collected from bastnasite.

14. The multi-phase catalyst of claim 1, wherein z is approximately 2y−

1/2x+s+3.

15. A catalyst composition, comprising:

(a) a substrate;

(b) a washcoat; and

(c) a multi-phase catalyst represented by the general formula;

Ce_yLn_1-xA_x+sMO_z,

wherein;

Ln is a mixture of elements originally in the form of single-phase mixed lanthanides collected from natural ores, a single lanthanide, or a mixture of artificial lanthanides;

A is an element selected from the group consisting of Mg, Ca, Sr, Ba, Li, Na, K, Cs, Rb, and combinations thereof;

M is an element selected from the group consisting of Fe, Mn, Cr, Ni, Co, Cu, V, Zr, Pt, Pd, Rh, Ru, Ag, Au, Al, Ga, Mo, W, Ti, and combinations thereof;

x is a number defined by 0≦

x<

1.0;

y is a number defined by 0≦

y<

10;

s is a number defined by 0≦

s<

10; and

z is a number defined by z>

0,

where s=0 only when y>

0 and y=0 only when s>

0.

16. The catalyst composition of claim 15, wherein the substrate is a metal or ceramic honeycomb support.

17. The catalyst composition of claim 15, wherein the washcoat comprises alumina and a cerium oxide-based material.

18. The catalyst composition of claim 17, wherein the washcoat comprises gamma-alumina, Ce_0.24Zr_0.67La_0.09O₂, SrO, and Ln₂O₃.

19. The catalyst composition of claim 15, wherein the alumina is gamma-alumina.

20. The catalyst composition of claim 15, wherein the cerium oxide-based material is selected from the group consisting of Ce_1-aZr_aO_2-δ

1 and Ce_1-c-dZr_cLan_dO<sub>2-δ

2</sub>, wherein

0<

a<

1;

Lan is at least one rare earth selected from the group consisting of Y, La, Pr, Nd, Sm, Eu, and Yb;

c>

0.15;

0.15>

d>

0.01;

and

δ

1 and δ

2 are oxygen deficiencies.

21. The catalyst composition of claim 20, wherein the cerium oxide-based material is selected from the group consisting of Ce_0.68Zr_0.32O₂ and Ce_0.24Zr_0.67La_0.09O₂.

22. The catalyst composition of claim 15, wherein the multi-phase catalyst comprises a perovskite phase and a non-perovskite phase.

23. The catalyst composition of claim 22, wherein the perovskite phase is represented by a general formula of Ln_1-xA_xMO₃.

24. The catalyst composition of claim 23, wherein the perovskite phase has a cation formula selected from the group consisting of Ln_0.8Sr_0.2Mn_0.88Pd_0.12, Ln_0.8Sr_0.2Mn_0.94Pd_0.06, Ln_0.60Sr_0.40 Mn_0.95Pd_0.05, Ln_0.64Sr_0.36Mn_0.72Pd_0.28, and Ln_0.80Sr_0.20 Mn_0.65Pd_0.35.

25. The catalyst composition of claim 22, wherein the non-perovskite phase is selected from the group consisting of cerium oxide, an alkaline earth metal oxide represented by a formula AO, an alkali metal oxide represented by the formula A₂O, an alkaline earth metal carbonate, and combinations thereof.

26. The catalyst composition of claim 25, wherein the non-perovskite phase is cerium oxide.

27. The catalyst composition of claim 25, wherein the non-perovskite phase is an alkaline earth metal oxide represented by a formula of AO.

28. The catalyst composition of claim 27, wherein the alkaline earth metal oxide is SrO.

29. The catalyst composition of claim 25, comprising a first non-perovskite phase of cerium oxide, and a second non-perovskite phase of SrO.

30. The catalyst composition of claim 29, wherein the perovskite phase has a cation formula selected from the group consisting of Ln_0.8Sr_0.2Mn_0.88Pd_0.12, Ln_0.8Sr_0.2Mn_0.94Pd_0.06, Ln_0.60Sr_0.40Mn_0.95Pd_0.05, Ln_0.64Sr_0.36Mn_0.72Pd_0.28, and Ln_0.80Sr_0.20Mn_0.65Pd_0.35.

31. The catalyst composition of claim 15, further comprising at least one precious metal component selected from the group consisting of platinum, rhodium, palladium, iridium, ruthenium, osmium, and silver.

32. The catalyst composition of claim 31, wherein said at least one precious metal component is introduced into said catalyst composition by impregnating said catalyst composition with a solution of a water-soluble salt of said at least one precious metal component.

33. The catalyst composition of claim 15, further comprising at least one base metal.

34. The catalyst composition of claim 33, wherein said at least one base metal is introduced into said catalyst composition by impregnating said catalyst composition with a water solution of a water-soluble salt of said at least one base metal or by co-mulling at least one compound comprising said at least one base metal with at least one component of said catalyst composition.

35. The catalyst composition of claim 15, further comprising a layer comprising as a non-precious metal component a cerium oxide-based material with the formula:

Ce_1-c-dZr_cLan_dO<sub>2-δ

2</sub>, where;

Lan is at least one of Y, La, Pr, Nd, Sm, Eu, Gd, Ho, or Yb;

c>

0.15;

0.15>

d>

0.01; and

δ

2 is an oxygen deficiency,

where the cerium oxide-based material has the fluorite crystal structure.

36. The catalyst composition of claim 35, wherein said layer is an overlayer.

37. The catalyst composition of claim 35, wherein said layer further comprises at least one precious metal component selected from the group consisting of palladium, platinum, and rhodium.

38. The catalyst composition of claim 35, wherein said layer comprises platinum and rhodium precious metal components.

39. The catalyst composition of claim 38, wherein a weight ratio of the platinum precious metal component to the rhodium precious metal component in said layer is between about 0.3:

1 and about 3;

1.

40. The catalyst composition of claim 38, wherein a weight ratio of the platinum precious metal component to the rhodium precious metal component in said layer is approximately 1:

1.

41. The catalyst composition of claim 38, wherein a loading of said layer in said catalyst composition is more than about 20 g/liter and less than about 130 g/liter.

42. The catalyst composition of claim 38, wherein a loading of said platinum precious metal component in said catalyst composition is between about 1 g/ft³ and about 10 g/ft³ and a loading of said rhodium precious metal component in said catalyst composition is between about 2 g/ft³ and about 8 g/ft³.

43. The catalyst composition of claim 35, wherein said layer comprises a rhodium precious metal component.

44. The catalyst composition of claim 37, wherein said layer further comprises alumina as a non-precious metal component.

45. The catalyst composition of claim 44, wherein a weight ratio of said alumina to said cerium oxide-based material in said layer is between approximately 0.1:

1 and approximately 1;

0.4.

46. The catalyst composition of claim 37, wherein said at least one precious metal component is introduced into said layer by combining at least water-soluble salt of said at least one precious metal component with at least one non-precious metal component of said layer.

47. The catalyst composition of claim 46, wherein said at least one water-soluble salt is selected from the group consisting of platinum nitrate and rhodium nitrate.

48. The catalyst composition of claim 46, wherein said at least one water-soluble salt is selected from the group consisting of platinum nitrate and rhodium chloride.

49. The catalyst composition of claim 15, further comprising a layer comprising alumina as a non-precious metal component.

50. The catalyst composition of claim 49, wherein said layer further comprises platinum as a precious metal component.

51. A method of making a catalyst composition, the method comprising the steps of:

(a) providing a substrate;

(b) providing at least one carrier material for forming a washcoat on the substrate;

(c) providing a solution for forming a multi-phase catalyst supported by the substrate, wherein the solution has a general cation formula of

Ce_yLn_1-xA_x+sM, wherein;

Ln is a single lanthanide, a mixture of artificial lanthanides, or a mixture of elements originally in the form of single-phase mixed lanthanides collected from natural ores;

A is an element selected from the group consisting of Mg, Ca, Sr, Ba, Li, Na, K, Cs, Rb, and combinations thereof; and

M is an element selected from the group consisting of Fe, Mn, Cr, Ni, Co, Cu, V, Zr, Pt, Pd, Rh, Ru, Ag, Au, Al, Ga, Mo, W, Ti and combinations thereof;

x is a number defined by 0≦

x<

1.0;

y is a number defined by 0≦

y<

10;

s is a number defined by 0≦

s<

10, and

z is a number defined by z>

0,

where s=0 only when y>

0 and y=0 only when s>

0;

and

(d) forming the catalyst composition comprising the substrate, the washcoat, and the multi-phase catalyst.

52. The method of claim 51, wherein step (d) comprises:

(i) slurry depositing the carrier material onto the substrate to form a layer of washcoat;

(ii) impregnating the solution into the washcoat; and

(iii) calcining the substrate, washcoat, and the impregnated solution to form the multi-phase catalyst on the substrate.

53. The method of claim 52, further comprising drying the washcoat and impregnated solution before calcining.

54. The method of claim 51, wherein step (d) comprises:

(i) forming the multi-phase catalyst in a bulk form from the solution;

(ii) forming a slurry suspension of the carrier material and the bulk multi-phase catalyst; and

(iii) depositing the slurry suspension onto the substrate to form the multi-phase catalyst on the substrate.

55. The method of claim 54, wherein forming said multi-phase catalyst in a bulk form comprises calcining said solution.

56. The method of claim 54, wherein forming said multi-phase catalyst in a bulk form comprises co-precipitating a multi-phase catalyst precursor from said solution and calcining said multi-phase catalyst precursor.

57. The method of claim 56, wherein co-precipitating said multi-phase catalyst precursor comprises contacting said solution with oxalic acid.

58. The method of claim 51, wherein step (d) comprises

(i) impregnating the solution onto the carrier material;

(ii) calcining the carrier material impregnated with the solution to form the multi-phase catalyst in the form of a dispersed multi-phase catalyst on the carrier material; and

(iii) slurry depositing the carrier material with the dispersed multi-phase catalyst onto the substrate to form the multi-phase catalyst on the substrate.

59. The method of claim 51, wherein the substrate is a metal or ceramic honeycomb support.

60. The method of claim 51, wherein more than one carrier material is provided, and wherein the washcoat comprises alumina and a cerium oxide-based material.

61. The method of claim 60, wherein the alumina is gamma-alumina.

62. The method of claim 60, wherein the cerium oxide-based material is selected from the group consisting of Ce_1-aZr_bO_2-δ

1 and Ce_1-c-dZr_cLan_dO<sub>2-δ

2</sub> wherein

0<

a<

1;

Lan is at least one rare earth selected from the group consisting of Y, La, Pr, Nd, Sm, Eu, and Yb;

c>

0.15;

0.15>

d>

0.01;

and

δ

1 and δ

2 are oxygen deficiencies.

63. The method of claim 62, wherein the cerium oxide-based material is selected from the group consisting of Ce_0.68Zr_0.32O₂ and Ce_0.24Zr_0.67La_0.09O₂.

64. The method of claim 60, wherein the washcoat comprises gamma-alumina, Ce_0.24Zr_0.67La_0.09O₂, SrO, and Ln₂O₃.

65. The method of claim 51, wherein the multi-phase catalyst comprises a perovskite phase and a non-perovskite phase.

66. The method of claim 65, wherein the perovskite phase is represented by a general formula of Ln_1-xA_xMO₃.

67. The method of claim 66, wherein the non-perovskite phase is an alkaline earth metal oxide represented by a formula of AO.

68. The method of claim 65, wherein the perovskite phase has a cation formula selected from the group consisting of Ln_0.8Sr_0.2Mn_0.88Pd_0.12, Ln_0.8Sr_0.2Mn_0.94Pd_0.06, Ln_0.60Sr_0.40Mn_0.95Pd_0.05, Ln_0.64Sr_0.36Mn_0.72Pd_0.28, and Ln_0.80Sr_0.20Mn_0.65Pd_0.35.

69. The method of claim 65, wherein the non-perovskite phase is selected from the group consisting of cerium oxide, an alkaline earth metal oxide represented by a formula of AO, an alkali metal oxide represented by the formula A₂O, an alkaline earth metal carbonate, and combinations thereof.

70. The method of claim 69, wherein the non-perovskite phase is cerium oxide.

71. The method of claim 69, wherein the alkaline earth metal oxide is SrO.

72. The method of claim 69, wherein the non-perovskite phase comprises a first non-perovskite phase of cerium oxide, and a second non-perovskite phase of SrO.

73. The method of claim 51, further comprising forming a layer on said catalyst composition, wherein said layer comprises as a non-precious metal component a cerium oxide-based material having a formula:

Ce_1-c-dZr_cLan_dO<sub>2-δ

2</sub>, where;

Lan is at least one of Y, La, Pr, Nd, Sm, Eu, Gd, Ho, or Yb;

c>

0.15;

0.15>

d>

0.01; and

δ

2 is an oxygen deficiency,

where the cerium oxide-based material has a fluorite crystal structure.

74. The method of claim 73, wherein said layer is an overlayer.

75. The method of claim 73, wherein said layer further comprises at least one precious metal component selected from the group consisting of palladium, platinum, and rhodium.

76. The method of claim 75, wherein said layer further comprises alumina as a non-precious metal component.

77. The method of claim 76, wherein a weight ratio of said alumina to said cerium oxide-based material is between approximately 0.1:

1 and approximately 1;

0.4.

78. The method of claim 76, wherein said precious metal component is introduced into said layer by impregnating a solution of at least water-soluble salt of said at least one precious metal component into at least one non-precious metal component of said layer.

79. The method of claim 78, wherein said at least one water-soluble salt is selected from the group consisting of platinum nitrate and rhodium nitrate.

80. The method of claim 78, wherein said at least one water-soluble salt is selected from the group consisting of platinum nitrate and rhodium chloride.

81. The method of claim 73, wherein said layer further comprises at least one precious metal component selected from the group consisting of platinum and rhodium.

82. The method of claim 81, wherein a weight ratio of a platinum precious metal component to a rhodium precious metal component in said layer is between about 0.3:

1 and about 3;

1.

83. The method of claim 81, wherein a weight ratio of a platinum precious metal component to a rhodium precious metal component in said layer is about 1:

1.

84. The method of claim 81, wherein a loading of said platinum precious metal component on said catalyst composition is between about 1 g/ft³ and about 10 g/ft³ and a loading of said rhodium precious metal component in said catalyst composition is between about 2 g/ft³ and about 8 g/ft³.

85. The method of claim 73, wherein a loading of said layer in the catalyst composition is between about 20 g/liter and about 130 g/liter.

86. A method for simultaneous conversion of oxides of nitrogen, carbon monoxide, and hydrocarbons in motor vehicle exhaust comprising:

(a) providing a catalyst composition, wherein said catalyst composition comprises;

(i) a substrate;

(ii) a washcoat; and

(iii) a multi-phase catalyst represented by the general formula;

Ce_yLn_1-xA_x+sMO_z,

wherein;

Ln is a mixture of elements originally in the form of single-phase mixed lanthanides collected from natural ores, a single lanthanide, or a mixture of artificial lanthanides;

A is an element selected from the group consisting of Mg, Ca, Sr, Ba, Li, Na, K, Cs, Rb, and combinations thereof;

M is an element selected from the group consisting of Fe, Mn, Cr, Ni, Co, Cu, V, Zr, Pt, Pd, Rh, Ru, Ag, Au, Al, Ga, Mo, W, Ti, and combinations thereof;

x is a number defined by 0≦

x<

1.0;

y is a number defined by 0≦

y<

10;

s is a number defined by 0≦

s<

10; and

z is a number defined by z>

0,

where s=0 only when y>

0 and y=0 only when s>

0; and

(b) contacting said exhaust with said catalyst composition.

87. The method of claim 86, wherein said contacting is at a temperature of at least 150°

Centigrade and at approximately one atmosphere pressure.

88. The method of claim 86, wherein said catalyst composition further comprises a layer comprising a cerium oxide-based material having a formula:

Ce_1-c-dZr_cLan_dO<sub>2-δ

2</sub>, where;

Lan is at least one of Y, La, Pr, Nd, Sm, Eu, Gd, Ho, or Yb;

c>

0.15;

0.15>

d>

0.01; and

δ

2 is an oxygen deficiency,

where the cerium oxide-based material has a fluorite crystal structure.

89. The method of claim 88, wherein said layer is an overlayer.

90. The method of claim 88, wherein said layer further comprises at least one precious metal component selected from the group consisting of palladium, platinum, and rhodium.