WO2018130569A1

WO2018130569A1 - Catalysts for treating exhaust gas

Info

Publication number: WO2018130569A1
Application number: PCT/EP2018/050559
Authority: WO
Inventors: Qinghua Yin; Xiwang Qi; Bryant KEARL; Maximillian A. Biberger
Original assignee: Umicore Ag & Co. Kg
Priority date: 2017-01-10
Filing date: 2018-01-10
Publication date: 2018-07-19

Abstract

The present disclosure discloses catalysts for treating exhaust gas, including exhaust gas resulting from the combustion of natural gas, combustible hydrocarbon liquids, oil, kerosene, coal, or wood, and other organic fuels. An exemplary catalyst comprises a substrate, a first washcoat layer comprising porous micron-sized particles comprising palladium on ceria, and alumina derived from boehmite, and a second washcoat layer comprising porous micron-sized particles comprising platinum on alumina, and alumina derived from boehmite. Additional components which can be used in the washcoat layers are also disclosed.

Description

CATALYSTS FOR TREATING EXHAUST GAS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority benefit of U.S. Provisional Patent Application

No. 62/444,727 filed January 10, 2017. The entire contents of that application are hereby incorporated by reference herein.

FIELD OF THE INVENTION

[0002] The present disclosure relates to the field of catalysts for treating exhaust gas, including exhaust gas resulting from the combustion of natural gas, combustible hydrocarbon liquids, oil, kerosene, coal, or wood and other organic fuels.

BACKGROUND OF THE INVENTION

[0003] Indoor stoves, furnaces, fireplaces, and generators present significant hazards due to the resulting exhaust that results from the combustion of fuel, including natural gas, combustible hydrocarbon liquids, oil, kerosene, coal, or wood. Carbon monoxide poisoning is a frequent cause of hospital-related visits, and frequently occurs from insufficient ventilation of a gas- burning furnace. Sufficient ventilation of carbon monoxide generating sources is often challenging, particularly in densely populated urban areas. Additionally, carbon monoxide is an odorless and colorless gas, making detection of the gas difficult.

[0004] One solution to reduce pollutants in exhaust gas is to treat the exhaust gas with a catalyst (also referred to as a catalytic combustor). Catalysts for treating exhaust gas generally use platinum group metals to oxidize or reduce gases in the exhaust gas. For example, carbon monoxide can be oxidized to less harmful carbon dioxide. However, platinum group metals are expensive, and significant amounts of platinum group metal can make the cost of a catalyst for treating exhaust gas to be unaffordable for many consumers.

[0005] The disclosures of all publications, patents, and patent applications referred to herein are each hereby incorporated herein by reference in their entireties. To the extent that any reference incorporated by references conflicts with the instant disclosure, the instant disclosure shall control.

SUMMARY OF THE INVENTION

[0006] In one aspect, there is provided a catalyst comprising a substrate coated with a first washcoat layer and a second washcoat layer; the first washcoat layer comprising porous micron- sized particles comprising ceria impregnated with palladium, and alumina derived from boehmite particles; and the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum, and alumina derived from boehmite particles. In some embodiments, the micron-sized particles comprising ceria in the first washcoat layer are impregnated with palladium by wet-chemistry methods. In some embodiments, the micron-sized particles comprising alumina in the second washcoat layer are impregnated with platinum by wet-chemistry methods.

[0007] In some embodiments, the boehmite particles used to derive the alumina in the first washcoat layer have an average dispersed particle size of about 60 nm or less. In some embodiments, the boehmite particles used to derive the alumina in the first washcoat layer have a BET surface area of about 120 m²/e or more. In some embodiments, the boehmite particles used to derive the alumina in the second washcoat layer have an average dispersed particle size of about 150 nm or more. In some embodiments, the boehmite particles used to derive the alumina in the second washcoat layer have a BET surface area of about 250 m²/g or less.

[0008] In some embodiments, the micron-sized particles comprising alumina in the second washcoat layer are stabilized with lanthana.

[0009] In some embodiments, the first washcoat layer further comprises porous micron-sized particles comprising alumina. In some embodiments, the porous micron-sized particles comprising alumina in the first washcoat layer are impregnated with palladium. In some embodiments, the porous micron-sized particles comprising alumina in the first washcoat layer are impregnated with palladium by wet-chemistry methods. In some embodiments, the porous micron-sized particles comprising alumina in the first washcoat layer are substantially free of palladium. In some embodiments, the micron-sized particles comprising alumina are stabilized with lanthana. In some embodiments, the micron-sized particles comprising alumina in the first washcoat layer make up about 2 wt% to about 10 wt% of the solids in the first washcoat layer.

[0010] In some embodiments, the alumina derived from boehmite in the first washcoat layer makes up about 2 wt% to about 15 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the second washcoat layer makes up about 1 wt% to about 8 wt% of the solids in the second washcoat layer.

[0011] In some embodiments, the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1.

[0012] In some embodiments, the first washcoat layer has a palladium loading of about 0.1 g/1 to about 0.5 g/1. In some embodiments, the second washcoat layer has a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1.

[0013] In some embodiments, the micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer.

[0014] In some embodiments, the micron-sized particles comprising alumina in the second washcoat layer make up about 85 wt% to about 99 wt% of the solids in the second washcoat layer.

[0015] In some embodiments, the substrate comprises cordierite. In some embodiments, the substrate has a honeycomb structure. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0016] In another aspect, there is provided an exhaust treatment system comprising a conduit for exhaust gas and any one of the catalysts described above. In some embodiments, the catalyst is fluidly connected to an exhaust gas source. In some embodiments, the exhaust gas source burns natural gas, a combustible hydrocarbon liquid, oil, kerosene, coal, or wood. In some

embodiments, the exhaust gas source is a stove, a furnace, a fireplace, or a generator.

[0017] In another aspect, there is provided a method of treating an exhaust gas comprising contacting the exhaust gas with any one of the catalysts described above. [0018] In another aspect, there is provided a method of making a catalyst comprising (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, or comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles. In some embodiments, the first washcoat composition comprises porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles. In some embodiments, the first washcoat composition comprises porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles. In some embodiments, the second washcoat composition comprises porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles. In some embodiments, the second washcoat composition comprises porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles.

[0019] In some embodiments, the method further comprises drying the first washcoat composition after it has been coated onto the substrate. In some embodiments, the method further comprises calcining the substrate after the first washcoat composition has been coated onto the substrate. In some embodiments, the method comprises drying the second washcoat composition after it has been coated onto the substrate. In some embodiments, the method comprises calcining the substrate after the second washcoat composition has been coated onto the substrate.

[0020] In some embodiments of the method of making a catalyst, the substrate is coated with the first washcoat composition prior to being coated with the second washcoat composition.

[0021] In some embodiments of the method of making a catalyst, the boehmite particles in the first washcoat composition have an average dispersed particle size of about 60 nm or less. In some embodiments, the boehmite particles in the first washcoat composition have a BET surface area of about 120 m²/s or more. In some embodiments, the boehmite particles in the second washcoat layer have an average dispersed particle size of about 150 nm or more. In some embodiments, the boehmite particles in the second washcoat layer have a BET surface area of about 250 m²/g or less.

[0022] In some embodiments of the method of making a catalyst, the micron-sized particles comprising alumina in the second washcoat composition are stabilized with lanthana.

[0023] In some embodiments of the method of making a catalyst, the first washcoat composition further comprises porous micron-sized particles comprising alumina. In some embodiments, the micron-sized particles comprising alumina in the first washcoat composition are stabilized with lanthana. In some embodiments, the micron-sized particles comprising alumina in the first washcoat composition make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition.

[0024] In some embodiments of the method of making a catalyst, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition.

[0025] In some embodiments of the method of making a catalyst, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids.

[0026] In some embodiments, the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1. In some embodiments, the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1.

[0027] In some embodiments of the method of making a catalyst, the micron-sized particles comprising ceria make up about 80 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition.

[0028] In some embodiments of the method of making a catalyst, the substrate comprises cordierite. In some embodiments, the substrate has a honeycomb structure. In some embodiments, the substrate is about 1 cm to about 4 cm thick. In some embodiments, the substrate has a transverse profile of about 100 to about 600 cm².

[0029] Further provided is a catalyst made according to any one of the methods described above.

[0030] Hence, the present invention pertains to a catalyst comprising:

a substrate coated with a first washcoat layer and a second washcoat layer;

the first washcoat layer comprising porous micron-sized particles comprising ceria impregnated with palladium, and alumina derived from boehmite particles; and the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum, and alumina derived from boehmite particles.

[0031] In this catalyst, preferably, the micron-sized particles comprising ceria in the first washcoat layer are impregnated with palladium by wet-chemistry methods.

[0032] In this catalyst, preferably, the micron-sized particles comprising alumina in the second washcoat layer are impregnated with platinum by wet-chemistry methods.

[0033] In the above mentioned catalyst, preferably, the boehmite particles used to derive the alumina in the first washcoat layer have an average dispersed particle size of about 60 nm or less. More preferably the boehmite particles used to derive the alumina in the first washcoat layer have a BET surface area of about 120 m2/g or more.

[0034] In the above mentioned catalyst, preferably, the boehmite particles used to derive the alumina in the second washcoat layer have an average dispersed particle size of about 150 nm or more. More preferably, the boehmite particles used to derive the alumina in the second washcoat layer have a BET surface area of about 250 m2/g or less.

[0035] In the above mentioned catalyst, preferably, the micron-sized particles comprising alumina in the second washcoat layer are stabilized with lanthana.

[0036] In the above mentioned catalyst, preferably, the first washcoat layer further comprises porous micron-sized particles comprising alumina. More preferably, the porous micron-sized particles comprising alumina in the first washcoat layer are impregnated with palladium. Even more preferably, the porous micron-sized particles comprising alumina in the first washcoat layer are impregnated with palladium by wet-chemistry methods. [0037] In the above mentioned catalyst, also preferably, the porous micron-sized comprising alumina in the first washcoat layer are substantially free of palladium.

[0038] In the above mentioned catalyst, preferably, the micron-sized particles of the first washcoat layer comprising alumina are stabilized with lanthana.

[0039] In the above mentioned catalyst, preferably, the micron-sized particles comprising alumina in the first washcoat layer make up about 2 wt% to about 10 wt% of the solids in the first washcoat layer. Further preferably, the alumina derived from boehmite in the first washcoat layer makes up about 2 wt% to about 15 wt% of the solids in the first washcoat layer.

[0040] In the above mentioned catalyst, preferably, the alumina derived from boehmite in the second washcoat layer makes up about 1 wt% to about 8 wt% of the solids in the second washcoat layer.

[0041] In the above mentioned catalyst, preferably, the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1.

[0042] In the above mentioned catalyst, preferably, the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1.

[0043] In the above mentioned catalyst, preferably, the first washcoat layer has a palladium loading of about 0.1 g/1 to about 0.5 g/1.

[0044] In the above mentioned catalyst, preferably, the second washcoat layer has a platinum loading of about 0.2 g/1 to about 0.7 g/1.

[0045] In the above mentioned catalyst, preferably, the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1.

[0046] In the above mentioned catalyst, preferably, the micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer.

[0047] In the above mentioned catalyst, preferably, the micron-sized particles comprising alumina in the second washcoat layer make up about 85 wt% to about 99 wt% of the solids in the second washcoat layer. [0048] In the above mentioned catalyst, preferably, the substrate comprises cordierite. Further preferably, the substrate has a honeycomb structure. Also further preferably, the substrate is about 0.5 cm to about 6 cm thick. Also preferably, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0049] The present invention pertains to an exhaust treatment system comprising a conduit for exhaust gas and the catalyst as mentioned above. Preferably, in this exhaust treatment system the catalyst is fluidly connected to an exhaust gas source. More preferably, the exhaust gas source burns natural gas, a combustible hydrocarbon liquid, oil, kerosene, coal, or wood. Still more preferably, the exhaust gas source is a stove, a furnace, a fireplace, or a generator.

[0050] The present invention also pertains to a method of treating an exhaust gas comprising contacting the exhaust gas with the catalyst as mentioned above.

[0051] Further, the present invention pertains to a method of making a catalyst comprising: i. coating a substrate with a first washcoat composition comprising:

porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, or porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles; and

ii. coating the substrate with a second washcoat composition comprising:

porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles.

[0052] In this method, preferably, the first washcoat composition comprises porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles. More preferably, the first washcoat composition comprises porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles.

[0053] In this method, preferably, the second washcoat composition comprises porous micron- sized particles comprising ceria impregnated with palladium, and boehmite particles. [0054] More preferably, the second washcoat composition comprises porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles.

[0055] This method, preferably, further comprises drying the first washcoat composition after it has been coated onto the substrate. More preferably, the method further comprises calcining the substrate after the first washcoat composition has been coated onto the substrate.

[0056] This method, preferably, further comprises drying the second washcoat composition after it has been coated onto the substrate. More preferably, the method further comprises calcining the substrate after the second washcoat composition has been coated onto the substrate.

[0057] In this method, preferably, the substrate is coated with the first washcoat composition prior to being coated with the second washcoat composition.

[0058] In this method, preferably, the boehmite particles in the first washcoat composition have an average dispersed particle size of about 60 nm or less. Also preferably, the boehmite particles in the first washcoat composition have a BET surface area of about 120 m2/g or more.

[0059] In this method, preferably, the boehmite particles in the second washcoat layer have an average dispersed particle size of about 150 nm or more. Also preferably, the boehmite particles in the second washcoat layer have a BET surface area of about 250 m2/g or less.

[0060] In this method, preferably, the micron-sized particles comprising alumina in the second washcoat composition are stabilized with lanthana.

[0061] In this method, preferably, the first washcoat composition further comprises porous micron-sized particles comprising alumina. More preferably, the micron-sized particles comprising alumina in the first washcoat composition are stabilized with lanthana.

[0062] In this method, preferably, the micron-sized particles comprising alumina in the first washcoat composition make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition. More preferably, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition.

[0063] In this method, preferably, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. [0064] In this method, preferably, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids.

[0065] In this method, preferably, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids.

[0066] In this method, preferably, the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1.

[0067] In this method, preferably, the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1.

[0068] In this method, preferably, the micron-sized particles comprising ceria make up about 80 wt% to about 95 wt% of the solids in the first washcoat composition.

[0069] In this method, preferably, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition.

[0070] In this method, preferably, the substrate comprises cordierite. Also preferably, the substrate has a honeycomb structure. Also preferably, the substrate is about 1 cm to about 4 cm thick. Still further preferably, the substrate has a transverse profile of about 100 cm² to about 600 cm 2.

[0071] In a further aspect, the present invention pertains to a catalyst made according to the method mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIG. 1 A illustrates one method of forming the catalyst in accordance with some embodiments of the present invention.

[0073] FIG. IB illustrates one embodiment of a catalyst including a substrate coated with the first washcoat layer and the second washcoat layer.

[0074] FIG. 2 shows the amount of carbon monoxide exiting a reference catalyst (Catalyst A) and two embodiments of the catalyst described herein (Catalyst B and Catalyst C) plotted against the temperature of the exhaust gas. DETAILED DESCRIPTION OF THE INVENTION

[0075] Described herein is a substrate coated with a first washcoat layer and a second washcoat layer; the first washcoat layer comprising porous micron-sized particles comprising ceria impregnated with palladium, and alumina derived from boehmite particles; and the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum, and alumina derived from boehmite particles. The boehmite particles used to derive the alumina in the first washcoat layer and the second washcoat layer can be the same or different. For example, in some embodiments, the boehmite particles used to derive the alumina in the first washcoat layer have an average dispersed particle size of about 60 nm or less or a BET surface area of about 120 m²/s or more, and the boehmite particles used to derive the alumina in the second washcoat layer have an average dispersed particle size of about 150 nm or more or a BET surface area of about 250 m²/g or less. In some embodiments, the micron-sized particles comprising ceria in the first washcoat layer are impregnated with palladium by wet- chemistry methods. In some embodiments, the micron-sized particles comprising alumina in the second washcoat layer are impregnated with platinum by wet-chemistry methods. In some embodiments, the first washcoat layer further comprises micron-sized particles comprising alumina. In some embodiments, the first washcoat layer has a palladium loading of about 0.1 g/1 to about 0.5 g/1. In some embodiments, the first washcoat layer is substantially free of platinum. In some embodiments, the second washcoat layer has a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the second washcoat layer is substantially free of palladium.

[0076] Also described herein is an exhaust treatment system comprising a conduit for exhaust gas and the catalyst described herein. In some embodiments, the catalyst is fluidly connected to an exhaust gas source, such as a stove, a furnace, a fireplace, or a generator. In some

embodiments, the exhaust gas source is an indoor exhaust gas source. In some embodiments, the exhaust gas source is not a vehicle. In some embodiments, the exhaust gas source burns natural gas, combustible hydrocarbon liquids, oil, kerosene, coal, or wood.

[0077] Further described herein is a method of treating an exhaust gas comprising contacting the exhaust gas with the catalyst described herein. In some embodiments, the exhaust gas comprises carbon monoxide, hydrocarbons (including non-methane hydrocarbons), or methane. In some embodiments, the exhaust gas is emitted by an indoor exhaust gas source, such as an indoor stove, furnace, fireplace, or generator. In some embodiments, the exhaust gas source is not a vehicle. In some embodiments, the exhaust gas source burns natural gas, combustible hydrocarbon liquids, oil, kerosene, coal, or wood.

[0078] Additionally, there is described herein a method of making a catalyst comprising (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, or a first washcoat composition comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or a second washcoat composition comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles. The boehmite particles in the first washcoat composition and the second washcoat composition can be the same or different. In some embodiments, the method comprises drying the first washcoat composition after it has been coated onto the substrate. In some embodiments, the method comprises calcining the substrate after the first washcoat composition has been coated onto the substrate. In some embodiments, the method comprises drying the second washcoat composition after it has been coated onto the substrate. In some embodiments, the method comprises calcining the substrate after the second washcoat composition has been coated onto the substrate. In some embodiments of the method, the substrate is coated with the first washcoat composition prior to being coated with the second washcoat composition.

Definitions

[0079] As used herein, the singular forms "a," "an," and "the" include the plural reference unless the context clearly dictates otherwise.

[0080] Reference to "about" a value or parameter herein includes (and describes) variations that are directed to that value or parameter per se. For example, description referring to "about X" includes description of "X".

[0081] It is generally understood by one of skill in the art that the unit of measure "g/1" or "grams per liter" is used as a measure of density of a substance in terms of the mass of the substance in any given volume containing that substance. When referring to a thickness of a washcoat or washcoat layer coated on a substrate, "g/1" is used to refer to the mass of solids in the washcoat or washcoat layer per the volume of the substrate. When referring to an amount of material "loaded" onto a substrate, "g/1" is used to refer to the mass of that material per the volume of the substrate. For example, "platinum loaded onto a substrate at 4.0 g/1" refers to 4.0 grams of platinum for each liter of a coated substrate. Similarly, "a washcoat layer thickness of 100 g/1" refers to a washcoat layer having 100 grams of solids for each liter of the coated substrate.

[0082] The term "platinum group metals" (abbreviated "PGM") refers to the collective name for the metals ruthenium, rhodium, palladium, osmium, iridium, and platinum.

[0083] A "portion" of a material is understood to mean at least some of the material and may include all of that material.

[0084] The word "substantially" does not exclude "completely." For example, a composition which is "substantially free" from Y may be completely free from Y. The term "substantially free" permits trace or naturally occurring impurities. It should be noted that, during fabrication, or during operation (particularly over long periods of time), small amounts of materials present in one washcoat layer may diffuse, migrate, or otherwise move into other washcoat layers. Accordingly, use of the terms "substantial absence of and "substantially free of is not to be construed as absolutely excluding minor amounts of the materials referenced. Where necessary, the word "substantially" may be omitted from the definition of the invention.

[0085] "Treating" an exhaust gas refers to having the exhaust gas proceed through an exhaust system, thereby catalyzing at least a portion of the gasses in the exhaust gas into some other chemical form prior to release into the environment.

[0086] A "washcoat composition" refers to a suspension of one or more solid components, such as particles, in a liquid. The washcoat composition can also include one or more salts dissolved in the liquid. A "washcoat layer" refers to a washcoat composition after the composition has been applied to a substrate, either before or after the washcoat composition has been dried or calcined. [0087] The term "wet-chemistry method" is used herein to describe any technique whereby a solution of a metal salt is deposited on or in a material, and the metal salt is converted into a metallic form.

[0088] The term "wt%" is used herein to refer to a weight percentage. Weight percentages of materials in a solution or suspension (such as a washcoat composition) refer to the weight percentages of solids in that solution or suspension after removing liquid components. Salts (such as barium slats) or other materials dissolved in the liquid are included as solids if the salts or other materials would be solids upon evaporation of the liquid.

[0089] It should be noted that, during fabrication or during operation (particularly over long periods of time), small amounts of materials present in one layer may diffuse, migrate, or otherwise move into other layers.

[0090] It is understood that reference to relative weight percentages in a composition assumes that the combined total weight percentages of all components in the composition add up to 100. It is further understood that relative weight percentages of one or more components may be adjusted upwards or downwards such that the weight percent of the components in the composition combine to a total of 100, provided that the weight percent of any particular component does not fall outside the limits of the range specified for that component.

[0091] Various aspects of the disclosure can be described through the use of flowcharts. Often, a single instance of an aspect of the present disclosure is shown. As is appreciated by those of ordinary skill in the art, however, the protocols, processes, and procedures described herein can be repeated continuously or as often as necessary to satisfy the needs described herein. In addition, it is contemplated that certain method steps can be performed in alternative sequences to those disclosed in the flowcharts.

[0092] It is understood that aspects and embodiments of the invention described herein include the "comprising," the "consisting," and/or the "consisting essentially of aspects and

embodiments. For all methods, systems, compositions, and devices described herein, the methods, systems, compositions, and devices can either comprise the listed components or steps, or can "consist of or "consist essentially of the listed components or steps. When a system, composition, or device is described as "consisting essentially of the listed components, the system, composition, or device contains the components listed, and may contain other components which do not substantially affect the performance of the system, composition, or device, but either do not contain any other components which substantially affect the

performance of the system, composition, or device other than those components expressly listed; or do not contain a sufficient concentration or amount of the extra components to substantially affect the performance of the system, composition, or device. When a method is described as "consisting essentially of the listed steps, the method contains the steps listed, and may contain other steps that do not substantially affect the outcome of the method, but the method does not contain any other steps which substantially affect the outcome of the method other than those steps expressly listed.

[0093] With respect to numerical ranges disclosed in the present description, any disclosed upper limit may be combinable with any disclosed lower limit to provide a range. Each of these combinations of disclosed upper and lower limits are explicitly envisaged herein. For example, if ranges for the amount of a particular component are given as 50 g/L - 200 g/L, and 90 g/L - 170 g/L, the ranges 50 g/L - 170 g/L and 90 g/L - 200 g/L are also envisaged.

[0094] In the general description herein, the proposal of general preferences and options with respect to different features of the invention constitutes the proposal of general combinations of those general preferences and options for the different features, insofar as they are combinable and compatible.

[0095] This disclosure provides several examples and embodiments. It is contemplated that any features from any embodiment can be combined with any features from any other embodiment where possible. In this fashion, hybrid configurations of the disclosed features are within the scope of the present invention. The systems, compositions, substrates, and methods described herein, including any embodiment of the invention as described herein, may be used alone or may be used in combination with other systems, compositions, substrates, and methods.

Catalysts

[0096] The catalyst includes at least two washcoat layers coating a substrate. The first washcoat layer includes micron-sized particles comprising ceria impregnated with palladium. The second washcoat layer includes micron-sized particles comprising alumina impregnated with platinum. Alumina derived from boehmite particles is also present in the first washcoat layer and the second washcoat layer, although the boehmite particles used to derive the boehmite in the first washcoat layer and the second layer may be the same or different (for example, different average dispersed particles size or BET surface area). Preferably, the first washcoat layer is disposed underneath the second washcoat layer (that is, the first washcoat layer is more proximal to the substrate than the second washcoat layer). Nevertheless, in some embodiments, the second washcoat layer is disposed underneath the first washcoat layer. It is further contemplated that one or more additional layers can coat the substrate above or below the first washcoat layer or the second washcoat layer (including between the first washcoat layer and the second washcoat layer).

[0097] In some embodiments, the micron-sized particles comprising ceria have an average diameter of about 0.5 micrometers to about 20 micrometers (such as about 1 micrometer to about 15 micrometers, about 2 micrometers to about 10 micrometers, about 3 micrometers to about 8 micrometers, or about 4 micrometers to about 6 micrometers). Exemplary micron-sized particles comprising ceria are HSA20 particles, available from Grace Division, Rhodia. The micron-sized particles comprising ceria are porous, which allows a high surface area to contact exhaust gas flowing through the particles.

[0098] The micron-sized particles comprising ceria are impregnated with palladium, for example by wet-chemistry methods. A palladium salt solution can be combined with porous micron-sized particles comprising ceria, and the palladium salt can be converted into metallic palladium that impregnates the micron-sized particles. For example, the micron-sized particles comprising ceria and wetted with the palladium salt solution can be calcined (or dried and then calcined), which converts the palladium salt to the metallic palladium. In some embodiments, the palladium salt solution is free or substantially free of a platinum salt or metallic platinum.

Chloropalladic acid, FbPdCle, and palladium (II) nitrate, Pd(N0₃)2, are exemplary salts that can be used to impregnate the porous micron-sized particles comprising ceria. The micron-sized particles comprising ceria can be impregnated with palladium by wet-chemistry methods either before or after being combined with the other washcoat ingredients. For example, in some embodiments, the porous micron-sized particles comprising ceria are combined with a palladium salt and calcined (with an optional drying step prior to the calcining step), thereby converting the palladium salt into metallic palladium to impregnate the micron-sized particles with the palladium. The micron-sized particles comprising ceria and impregnated with the palladium can then be combined with any other washcoat composition ingredients (such as boehmite or micron- sized particles comprising alumina) to form the washcoat composition, which can be coated onto the substrate. In some embodiments, the porous micron-sized particles comprising ceria are combined with the palladium salt and the other washcoat composition ingredients (such as boehmite or micron-sized particles comprising alumina) to form the washcoat composition. The washcoat composition comprising the micron-sized particles comprising ceria and the palladium salt (and any other washcoat composition ingredients) is then coated onto the substrate and calcined (with an optional drying step before the calcining step), thereby converting the palladium salt, which had impregnated the micron-sized particles in the washcoat composition, into metallic palladium.

[0099] In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% or more (such as about 70 wt% or more, about 80 wt% or more, or about 90 wt% or more) of the solids in the first washcoat layer. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% (such as about 60 wt% to about 95 wt%, about 70 wt% to about 95 wt%, about 80 wt% to about 95 wt%, about 88 wt%, or about 89 wt%) of the solids in the first washcoat layer.

[00100] In some embodiments, the first washcoat layer further comprises micron-sized particles comprising alumina. In some embodiments, the micron-sized particles comprising alumina are porous, which allows a high surface area to contact exhaust gas flowing through the particles. The micron-sized particles comprising alumina can have an average diameter of about 0.5 micrometers to about 20 micrometers (such as about 1 micrometer to about 15 micrometers, about 2 micrometers to about 10 micrometers, about 3 micrometers to about 8 micrometers, or about 4 micrometers to about 6 micrometers). Exemplary micron-sized particles comprising alumina are MI-386 particles, available from Grace Division, Rhodia. Optionally, the micron- sized particles comprising alumina are stabilized with lanthana. For example, the micron-sized particles comprising alumina can comprise about 2 wt% to about 4 wt% lanthana. In some embodiments, the micron-sized particles comprising alumina make up about 2 wt% to about 10 wt% (such as about 3 wt% to about 8 wt%, or about 4 wt% to about 6 wt%) of the solids in the first washcoat layer. [00101] In some embodiments, the micron-sized particles comprising alumina in the first washcoat layer are impregnated with palladium, for example by wet-chemistry methods. The micron-sized particles comprising alumina in the first washcoat layer can be impregnated with palladium in a similar manner as the micron-sized particles comprising ceria in the first washcoat layer. A palladium salt solution can be combined with porous micron-sized particles comprising alumina, and the palladium salt can be converted into metallic palladium that impregnates the micron-sized particles. For example, the micron-sized particles comprising alumina and wetted with the palladium salt solution can be calcined (or dried and then calcined), which converts the palladium salt to the metallic palladium. In some embodiments, the palladium salt solution is free or substantially free of a platinum salt or metallic platinum. Chloropalladic acid, bPdCle, and palladium (II) nitrate, Pd(N0₃)2, are exemplary salts that can be used to impregnate the porous micron-sized particles comprising alumina. The micron-sized particles comprising alumina can be impregnated with palladium by wet-chemistry methods either before or after being combined with the other washcoat ingredients. For example, in some embodiments, the porous micron-sized particles comprising alumina are combined with a palladium salt and calcined (with an optional drying step prior to the calcining step), thereby converting the palladium salt into metallic palladium to impregnate the micron-sized particles with the metallic palladium. The micron-sized particles comprising alumina and impregnated with the palladium can then be combined with any other washcoat composition ingredients (such as the micron- sized particles comprising ceria and impregnated with palladium) to form the washcoat composition, which can be coated onto the substrate. In some embodiments, the porous micron- sized particles comprising alumina are combined with the palladium salt and the other washcoat composition ingredients (such as boehmite or micron-sized particles comprising ceria) to form the washcoat composition. The washcoat composition comprising the micron-sized particles comprising alumina and the palladium salt (and any other washcoat composition ingredients, including the micron-sized particles comprising ceria) is then coated onto the substrate and calcined (with an optional drying step before the calcining step), thereby converting the palladium salt, which had impregnated the micron-sized particles comprising ceria and the micron-size particle comprising alumina in the washcoat composition, into metallic palladium.

[00102] In some embodiments, the first washcoat layer comprises alumina derived from boehmite. Boehmite converts to alumina upon calcination of the boehmite. Therefore, boehmite can be included in the washcoat composition and, after coating the washcoat composition including the boehmite on the substrate, the substrate can be calcined, thereby converting the boehmite into alumina. Inclusion of the boehmite in the washcoat composition further stabilizes the washcoat layer coated on the substrate. In some embodiments, the alumina derived from boehmite in the first washcoat layer comprises about 2 wt% to about 15 wt% (such as about 4 wt% to about 14 wt%, about 5 w% to about 12 wt%, about 6 wt% to about 8 wt%, about 8 wt% to about 10 wt%, about 10 wt% to about 12 wt%, or about 1 1 wt%) of the solids in the first washcoat layer. The boehmite is generally in the form of particles that can be dispersed in solution. In some embodiments, the boehmite has an average dispersed particle size of about 10 nm to about 400 nm (such as about 10 nm to about 30 nm, about 30 nm to about 60 nm, about 60 nm to about 100 nm, about 100 nm to about 150 nm, about 150 nm to about 250 nm, or about 250 nm to about 400 nm). In some embodiments, the boehmite has an averaged dispersed particle size of about 60 nm or less. In some embodiments, the boehmite has an average dispersed particle size of about 150 nm or more. The average dispersed particle size of the boehmite can be measured after forming a 10 wt% boehmite dispersion in water using laser diffraction spectroscopy techniques. In some embodiments, the BET surface area of the boehmite is about 80 m²/g to about 300 m²/g (such as about 100 m²/g to about 260 m²/g, such as about 100 m²/g to about 140 m²/g, about 140 m²/g to about 180 m²/g, about 180 m²/g to about 220 m²/g, or about 220 m²/g to about 260 m²/g). In some embodiments, the BET surface area of the boehmite is about 250 m²/g or less (such as about 200 m²/g or less, or about 160 m²/g or less). In some embodiments, the BET surface area of the boehmite is about 120 m²/g or more (such as about 160 m²/g or more, or about 180 m²/g or more). The BET surface area of the boehmite is measured after calcining the boehmite at 550 °C for three hours and measuring the surface are of the resulting alumina using BET nitrogen adsorption techniques. Exemplary boehmite particles that can be used to for the first washcoat layer are DISPERAL® P2 boehmite particles, available from Sasol (Hamburg, Germany). DISPERAL® P2 boehmite particles have an average dispersed particle size of about 25 nm and a BET surface area of about 260 m²/g. DISPAL® 11N7-80 boehmite particles can also or alternatively be used in the first washcoat layer.

[00103] In some embodiments, the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1 (such as about 100 g/1 to about 120 g/1, about 120 g/1 to about 140 g/1, about 140 g/1 to about 160 g/1, about 160 g/1 to about 180 g/1, about 180 g/1 to about 200 g/1, about 200 g/1 to about 220 g/1, about 220 g/1 to about 240 g/1, about 240 g/1 to about 270 g/1, or about 270 g/1 to about 300 g/1). In some embodiments, the first washcoat layer has a palladium loading of about 0.1 g/1 to about 0.5 g/1, ( such as about 0.15 g/1 to about 0.3 g/1, or about 0.2 g/1). In some embodiments, the first washcoat layer is substantially free of platinum. In some embodiments, the first washcoat layer is substantially free of any platinum group metal other than palladium.

[00104] The second washcoat layer comprises micron-sized particles comprising alumina impregnated with platinum, such as by wet-chemistry methods. In some embodiments, the micron-sized particles comprising alumina in the second washcoat layer are porous, which allows a high surface area to contact exhaust gas flowing through the particles. The micron- sized particles comprising alumina can have an average diameter of about 0.5 micrometers to about 20 micrometers (such as about 1 micrometer to about 15 micrometers, about 2

micrometers to about 10 micrometers, about 3 micrometers to about 8 micrometers, or about 4 micrometers to about 6 micrometers). Exemplary micron-sized particles comprising alumina are MI-386 particles, available from Grace Division, Rhodia. Optionally, the micron-sized particles comprising alumina are stabilized with lanthana. For example, the micron-sized particles comprising alumina can comprise about 2 wt% to about 4 wt% lanthana. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% (such as about 90 wt% to about 97 wt%, about 94 wt% to about 96 wt%, or about 95 wt%) of the solids in the second washcoat layer.

[00105] To impregnate the micron-sized particles comprising alumina in the second washcoat layer with platinum, a platinum salt solution can be combined with porous micron- sized particles comprising alumina, and the platinum salt can be converted into metallic platinum that impregnates the micron-sized particles. For example, the micron-sized particles comprising alumina and wetted with the platinum salt solution can be calcined (or dried and then calcined), which converts the platinum salt to the metallic platinum. In some embodiments, the platinum salt solution is free or substantially free of a palladium salt or metallic palladium. Chloroplatinic acid, H₂PtCl6, is an exemplary salt that can be used to impregnate the porous micron-sized particles comprising ceria. The micron-sized particles comprising ceria can be impregnated with platinum by wet-chemistry methods either before or after being combined with the other washcoat ingredients used to form the second washcoat layer. For example, in some embodiments, the porous micron-sized particles comprising alumina are combined with a platinum salt and calcined (with an optional drying step prior to the calcining step), thereby converting the platinum salt into metallic platinum to impregnate the micron-sized particles with the platinum. The micron-sized particles comprising alumina and impregnated with the platinum can then be combined with any other washcoat composition ingredients (such as boehmite) to form the washcoat composition, which can be coated onto the substrate. In some embodiments, the porous micron-sized particles comprising alumina are combined with the platinum salt and the other washcoat composition ingredients (such as boehmite) to form the washcoat composition. The washcoat composition comprising the micron-sized particles comprising alumina and the platinum salt (and any other washcoat composition ingredients) is then coated onto the substrate and calcined (with an optional drying step before the calcining step), thereby converting the platinum salt, which had impregnated the micron-sized particles in the washcoat composition, into metallic platinum.

[00106] In some embodiments, the second washcoat layer comprises alumina derived from boehmite. In some embodiments, the alumina derived from boehmite in the second washcoat layer comprises about 1 wt% to about 10 wt% (such as about 2 wt% to about 8 wt%, about 3 w% to about 6 wt%, or about 4 wt% to about 5 wt%) of the solids in the second washcoat layer. The boehmite is generally in the form of particles that can be dispersed in solution. In some embodiments, the boehmite has an average dispersed particle size of about 10 nm to about 400 nm (such as about 10 nm to about 30 nm, about 30 nm to about 60 nm, about 60 nm to about 100 nm, about 100 nm to about 150 nm, about 150 nm to about 250 nm, or about 250 nm to about 400 nm). In some embodiments, the boehmite has an averaged dispersed particle size of less than about 60 nm. In some embodiments, the boehmite has an average dispersed particle size of about 150 nm or more. The average dispersed particle size of the boehmite can be measured after forming a 10 wt% boehmite dispersion in water using laser diffraction spectroscopy techniques. In some embodiments, the BET surface area of the boehmite is about 80 m²/g to about 300 m²/g (such as about 100 m²/g to about 260 m²/g, such as about 100 m²/g to about 140 m²/g, about 140 m²/g to about 180 m²/g, about 180 m²/g to about 220 m²/g, or about 220 m²/g to about 260 m²/g). In some embodiments, the BET surface area of the boehmite is about 250 m²/g or less (such as about 200 m²/g or less, or about 160 m²/g or less). In some embodiments, the BET surface area of the boehmite is about 120 m²/g or more (such as about 160 m²/g or more, or about 180 m²/g or more). The BET surface area of the boehmite is measured after calcining the boehmite at 550 °C for three hours and measuring the surface are of the resulting alumina using BET nitrogen adsorption techniques. Exemplary boehmite particles that can be used to for the second washcoat layer are DISPAL® 11N7-80 boehmite particles, available from Sasol (Hamburg, Germany). DISPAL® 11N7-80 boehmite particles have an average dispersed particle size of 220 nm and a BET surface area of about 100 m²/g. DISPERAL® P2 boehmite particles, can also or alternatively be used in the second washcoat layer.

[00107] In some embodiments, the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1 (such as about 40 g/1 to about 120 g/1, about 40 g/1 to about 100 g/1, about 50 g/1 to about 80 g/1, or about 60 g/1). In some embodiments, the second washcoat layer has a platinum loading of about 0.2 g/1 to about 0.7 g/1, ( such as about 0.3 g/1 to about 0.6 g/1, about 0.4 g/1 to about 0.5 g/1, or about 0.45 g/1). In some embodiments, the second washcoat layer is substantially free of palladium. In some embodiments, the second washcoat layer is substantially free of any platinum group metal other than platinum.

[00108] In some embodiments, the catalyst has a platinum group metal loading (that is, total loading of the first washcoat layer, second washcoat layer, and any other washcoat layer coated on the substrate) of about 0.3 g/1 to about 1.2 g/1 (such as about 0.3 g/1 to about 1 g/1, about 0.4 g/1 to about 0.8 g/1, about 0.5 g/1 to about 0.7 g/1, or about 0.67 g/1).

[00109] The substrate preferably demonstrates good thermal stability, including resistance to thermal shock, and to which the described washcoat compositions can be affixed in a stable manner. Suitable substrates include, but are not limited to, substrates formed from cordierite or other ceramic materials, and substrates formed from metal. The substrates may include a honeycomb structure, which provides numerous channels and results in a high surface area. The high surface area of the coated substrate with its applied washcoat layers in the catalytic converter provides for effective treatment of the exhaust gas flowing through the catalyst.

[00110] In some embodiments, the substrate has a thickness (i.e., dimension in the direction of gas flow through the substrate) of about 0.5 cm to about 6 cm (for example, about 1 cm to about 4 cm, about 1.5 cm to about 3 cm, or about 2 cm). The transverse profile (that is, the profile of the substrate transverse or perpendicular relative to the gas flow) of the substrate can be square, rectangular, circular, oval, or any other suitable shape. In some embodiments, the transverse profile is about 100 cm² to about 600 cm² (such as about 100 cm² to about 400 cm², about 150 cm² to about 300 cm², or about 175 cm² to about 220 cm²). In some embodiments, the transverse profile is rectangular with a length of about 15 cm to about 30 cm (such as about 17 cm to about 28 cm, about 20 cm to about 25 cm, or about 22.5 cm) and a width of about 5 cm to about 12 cm (such as about 7 cm to about 10 cm, or about 8.5 cm).

[00111] In some embodiments, a catalyst comprises a substrate coated with a first washcoat layer and a second washcoat layer; the first washcoat layer comprising porous micron- sized particles comprising ceria impregnated with palladium, and alumina derived from boehmite particles; and the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum, and alumina derived from boehmite particles. In some embodiments, the first washcoat layer further comprises porous micron-sized particles comprising alumina. In some embodiments, the porous micron-sized particles comprising alumina are impregnated with palladium by wet-chemistry methods. In some embodiments, the porous micron-sized particles in the first washcoat layer make up about 2 wt% to about 10 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the first washcoat layer makes up about 2 wt% to about 15 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the second washcoat layer makes up about 1 wt% to about 8 wt% of the solids in the second washcoat layer. In some embodiments, the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1. In some embodiments, the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1 (such as about 0.5 g/1 to about 0.8 g/1). In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[00112] In some embodiments, a catalyst comprises a substrate coated with a first washcoat layer and a second washcoat layer; the first washcoat layer comprising porous micron- sized particles comprising ceria impregnated with palladium by wet-chemistry methods, and alumina derived from boehmite particles; and the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum by wet-chemistry methods, and alumina derived from boehmite particles. In some embodiments, the first washcoat layer further comprises porous micron-sized particles comprising alumina. In some

embodiments, the porous micron-sized particles comprising alumina are impregnated with palladium by wet-chemistry methods. In some embodiments, the porous micron-sized particles in the first washcoat layer make up about 2 wt% to about 10 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the first washcoat layer makes up about 2 wt% to about 15 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the second washcoat layer makes up about 1 wt% to about 8 wt% of the solids in the second washcoat layer. In some embodiments, the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1. In some embodiments, the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1 (such as about 0.5 g/1 to about 0.8 g/1). In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[00113] In some embodiments, a catalyst comprises a substrate coated with a first washcoat layer and a second washcoat layer; the first washcoat layer comprising porous micron- sized particles comprising ceria impregnated with palladium by wet-chemistry methods, and alumina derived from boehmite particles having an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum by wet-chemistry methods, and alumina derived from boehmite particles. In some embodiments, the first washcoat layer further comprises porous micron-sized particles comprising alumina. In some

[00114] In some embodiments, a catalyst comprises a substrate coated with a first washcoat layer and a second washcoat layer; the first washcoat layer comprising porous micron- sized particles comprising ceria impregnated with palladium by wet-chemistry methods, and alumina derived from boehmite particles; and the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum by wet-chemistry methods, and alumina derived from boehmite particles; wherein the first washcoat layer has a palladium loading of about 0.1 g/1 to about 0.5 g/1, and the second washcoat layer has a platinum group loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the first washcoat layer further comprises porous micron-sized particles comprising alumina. In some embodiments, the porous micron-sized particles comprising alumina are impregnated with palladium by wet- chemistry methods. In some embodiments, the porous micron-sized particles in the first washcoat layer make up about 2 wt% to about 10 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the first washcoat layer makes up about 2 wt% to about 15 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the second washcoat layer makes up about 1 wt% to about 8 wt% of the solids in the second washcoat layer. In some embodiments, the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1. In some embodiments, the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1 (such as about 0.5 g/1 to about 0.8 g/1). In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm². [00115] In some embodiments, a catalyst comprises a substrate coated with a first washcoat layer and a second washcoat layer; the first washcoat layer comprising porous micron- sized particles comprising ceria impregnated with palladium by wet-chemistry methods, and alumina derived from boehmite particles having an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum by wet-chemistry methods, and alumina derived from boehmite particles; wherein the first washcoat layer has a palladium loading of about 0.1 g/1 to about 0.5 g/1, and the second washcoat layer has a platinum group loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the first washcoat layer further comprises porous micron-sized particles comprising alumina. In some embodiments, the porous micron-sized particles comprising alumina are impregnated with palladium by wet- chemistry methods. In some embodiments, the porous micron-sized particles in the first washcoat layer make up about 2 wt% to about 10 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the first washcoat layer makes up about 2 wt% to about 15 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the second washcoat layer makes up about 1 wt% to about 8 wt% of the solids in the second washcoat layer. In some embodiments, the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1. In some embodiments, the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1 (such as about 0.5 g/1 to about 0.8 g/1). In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 80 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[00116] In some embodiments, a catalyst comprises a substrate coated with a first washcoat layer and a second washcoat layer; the first washcoat layer comprising porous micron- sized particles comprising ceria impregnated with palladium by wet-chemistry methods, and alumina derived from boehmite particles having an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum by wet-chemistry methods, and alumina derived from boehmite particles having an average dispersed particle size of about 150 nm or more (such as about 180 nm to about 240 nm). In some embodiments, the first washcoat layer further comprises porous micron-sized particles comprising alumina. In some embodiments, the porous micron-sized particles comprising alumina are impregnated with palladium by wet-chemistry methods. In some embodiments, the porous micron-sized particles in the first washcoat layer make up about 2 wt% to about 10 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the first washcoat layer makes up about 2 wt% to about 15 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the second washcoat layer makes up about 1 wt% to about 8 wt% of the solids in the second washcoat layer. In some embodiments, the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1. In some embodiments, the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1 (such as about 0.5 g/1 to about 0.8 g/1). In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[00117] In some embodiments, a catalyst comprises a substrate coated with a first washcoat layer and a second washcoat layer; the first washcoat layer comprising porous micron- sized particles comprising ceria impregnated with palladium by wet-chemistry methods, and alumina derived from boehmite particles having an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum by wet-chemistry methods, and alumina derived from boehmite particles having an average dispersed particle size of about 150 nm or more (such as about 180 nm to about 240 nm) ; wherein the first washcoat layer has a palladium loading of about 0.1 g/1 to about 0.5 g/1, and the second washcoat layer has a platinum group loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the first washcoat layer further comprises porous micron-sized particles comprising alumina. In some embodiments, the porous micron-sized particles comprising alumina are impregnated with palladium by wet-chemistry methods. In some embodiments, the porous micron-sized particles in the first washcoat layer make up about 2 wt% to about 10 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the first washcoat layer makes up about 2 wt% to about 15 wt% of the solids in the first washcoat layer. In some embodiments, the alumina derived from boehmite in the second washcoat layer makes up about 1 wt% to about 8 wt% of the solids in the second washcoat layer. In some embodiments, the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1. In some embodiments, the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1 (such as about 0.5 g/1 to about 0.8 g/1). In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[00118] In some embodiments, a catalyst comprises a substrate coated with a first washcoat layer and a second washcoat layer; the first washcoat layer comprising about 85 wt% to about 90 wt% porous micron-sized particles comprising ceria impregnated with palladium by wet-chemistry methods, about 3 wt% to about 7 wt% porous micron-sized particles comprising alumina, and about 5 wt% to about 10 wt% alumina derived from boehmite particles having an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and the second washcoat layer comprising about 90 wt% to about 99 wt% porous micron-sized particles comprising alumina impregnated with platinum by wet-chemistry methods, and about 1 wt% to about 10 wt% or about 1 wt% to about 8 wt% alumina derived from boehmite particles having an average dispersed particle size of about 150 nm or more (such as about 180 nm to about 240 nm); wherein the first washcoat layer has a palladium loading of about 0.1 g/1 to about 0.5 g/1, and the second washcoat layer has a platinum group loading of about 0.2 g/1 to about 0.7 g/1; and wherein the substrate is about 1 cm to about 4 cm thick and has a transverse profile of about 100 cm² to about 400 cm². In some embodiments, the porous micron-sized particles comprising alumina are impregnated with palladium by wet-chemistry methods. In some embodiments, the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1. In some embodiments, the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1 (such as about 0.5 g/1 to about 0.8 g/1). Methods of Making a Catalyst

[00119] A method of making a catalyst comprises (1) coating a substrate with A) a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, andboehmite particles; or B) a first washcoat composition comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles; and (2) coating the substrate with C) a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles; or D) a second washcoat composition comprising porous micron-sized particles comprising alumina impregnated with platinum, andboehmite particles. The first and second washcoat compositions can be selected from the pairs A) and C), A) and D), B) and C), or B) and D). The boehmite particles in the first washcoat composition and the second washcoat composition may be the same or different (for example, different average dispersed particles size or BET surface area). In some embodiments the first washcoat composition further comprises micron-sized particles comprising alumina. In some embodiments the substrate is coated with the first washcoat composition before the substrate is coated with the second washcoat composition.

[00120] The first washcoat composition can be applied to the substrate (which may already have one or more previously-applied washcoat layers) by coating the substrate with a washcoat composition, for example by dip coating the substrate. Excess washcoat composition can be blown off the substrate (and optionally collecting and recycling the excess washcoat blown off the substrate). Once coated with a first washcoat composition, the coated substrate can be dried and/or calcined. The substrate can be coated in the second washcoat compositions, for example by dip coating the substrate. Excess washcoat composition can be blown off the substrate (and optionally collecting and recycling the excess washcoat blown off the substrate). Once coated with the second washcoat composition, the coated substrate can be dried and/or calcined. In some embodiments one or more additional washcoat compositions are coated onto the substrate, either before or after the application of the first washcoat composition or the second washcoat composition.

[00121] Drying of the washcoat layers can be performed at room temperature or elevated temperature (for example, from about 30°C to about 95°C, preferably about 60°C to about 70°C), at atmospheric pressure or at reduced pressure (for example, from about 1 pascal to about 90,000 pascal, or from about 7.5 mTorr to about 675 Torr), in ambient atmosphere or under an inert atmosphere (such as nitrogen or argon), and with or without passing a stream of gas over the substrate (for example, dry air, dry nitrogen gas or dry argon gas). In some embodiments, the drying process is a hot-drying process. A hot drying process includes any way to remove the solvent at a temperature greater than room temperature, but at a temperature below a standard calcining temperature. In some embodiments, the drying process may be a flash drying process, involving the rapid evaporation of moisture from the substrate via a sudden reduction in pressure or by placing the substrate in an updraft of warm air. It is contemplated that other drying processes may also be used. In some embodiments, the washcoat layer is dried for about 2 hours to about 48 hours (such as about 4 hours to about 36 hours, about 6 hours to about 24 hours, or about 8 hours to about 12 hours).

[00122] After drying the washcoat onto the substrate, the washcoat may then be calcined onto the substrate. Calcining takes place at elevated temperatures, such as from 400°C to about 700°C, preferably about 500°C to about 600°C, more preferably at about 540°C to about 560°C or at about 550°C. In some embodiments, calcining occurs at atmospheric pressure. In some embodiments, calcining occurs in ambient atmosphere, an oxidizing atmosphere, a non-oxidizing atmosphere, or a reducing atmosphere. In some embodiments, the washcoat layer is calcined for about 1 hour to about 24 hours (such as about 2 hours to about 18 hours, about 3 hours to about 12 hours, about 4 hours to about 8 hours, or about 6 hours).

[00123] FIG. 1 A illustrates one method of forming the catalyst in accordance with some embodiments of the present invention. The method comprises coating the substrate with a first washcoat composition to form a first washcoat layer, and coating the substrate with a second washcoat composition to form a second washcoat layer. At step 105, a first washcoat composition is applied to the substrate to from the first washcoat layer. In some embodiments, the first washcoat composition comprises micron-sized particles comprising ceria impregnated with palladium. In some embodiments, the first washcoat composition comprises micron-sized particles comprising ceria and a palladium salt. The first washcoat composition can further include micron-sized particles comprising alumina and/or boehmite particles. In some embodiments, the boehmite is in the form of particles with an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm). In some embodiments, the boehmite has a BET surface area of about 180 m²/s or more (such as about 220 m²/g to about 300 m²/g). At step 110, a first drying process is performed on the substrate. Examples of such drying processes include, but are not limited to, a hot-drying process, or a flash drying process. At step 115, a first calcining process is performed on the substrate.

[00124] At step 120, the second washcoat composition is applied to the substrate to coat the substrate with a second washcoat layer on top of the first washcoat layer. In some embodiments, the second washcoat composition comprises micron-sized particles comprising alumina impregnated with platinum. In some embodiments, the second washcoat composition comprises micron-sized particles comprising alumina and a platinum salt. In some

embodiments, the second washcoat composition further comprises boehmite particles. In some embodiments, the boehmite is in the form of particles with an average dispersed particle size of about 150 nm or more (such as about 180 nm to about 240 nm). In some embodiments, the boehmite has a BET surface area of about 160 m²/g or less (such as about 80 m²/g to about 140 m²/g. At step 125, a second drying process is performed on the substrate. Examples of such drying processes include, but are not limited to, a hot-drying process, or a flash drying process. At step 130, a first calcining process is performed on the substrate.

[00125] FIG. IB illustrates one embodiment of a catalyst including a substrate 135 coated with the first washcoat layer 140 and the second washcoat layer 145.

[00126] Washcoat compositions are prepared by suspending the designated materials in an aqueous solution. The pH of the resulting suspension can be adjusted to between about 2 and about 7 (such as between about 3 and about 5, or to about 4). The viscosity can also be adjusted, if desired, for example by adding cellulose, cornstarch, or other rheology modifiers to the washcoat composition. In some embodiments, the viscosity is adjusted to between about 300 cP and about 1200 cP.

[00127] In some embodiments, the first washcoat composition comprises micron-sized particles comprising ceria impregnated with palladium, for example by wet-chemistry methods. In some embodiments, the first washcoat composition further comprises boehmite particles. In some embodiments, the first washcoat composition further comprises micron-sized particles comprising alumina. In some embodiments, the first washcoat composition is substantially free of platinum or a platinum salt.

[00128] In some embodiments, the first washcoat composition comprises micron-sized particles comprising ceria and palladium salt. In some embodiments, the first washcoat composition further comprises boehmite particles. In some embodiments, the first washcoat composition further comprises micron-sized particles comprising alumina. In some

embodiments, the first washcoat composition is substantially free of platinum or a platinum salt.

[00129] In some embodiments, the micron-sized particles comprising ceria in the first washcoat composition have an average diameter of about 0.5 micrometers to about 20 micrometers (such as about 1 micrometer to about 15 micrometers, about 2 micrometers to about 10 micrometers, about 3 micrometers to about 8 micrometers, or about 4 micrometers to about 6 micrometers). Exemplary micron-sized particles comprising ceria are HSA20 particles, available from Grace Division, Rhodia. The micron-sized particles comprising ceria are porous, which allows a high surface area to contact exhaust gas flowing through the particles.

[00130] In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% or more (such as about 70 wt% or more, about 80 wt% or more, or about 90 wt% or more) of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% (such as about 60 wt% to about 95 wt%, about 70 wt% to about 95 wt%, about 80 wt% to about 95 wt%, about 88 wt%, or about 89 wt%) of the solids in the first washcoat composition.

[00131] In some embodiments, the first washcoat composition further includes micron- sized particles comprising alumina. In some embodiments, the micron-sized particles comprising alumina are porous, which allows a high surface area to contact exhaust gas flowing through the particles. The micron-sized particles comprising alumina can have an average diameter of about 0.5 micrometers to about 20 micrometers (such as about 1 micrometer to about 15 micrometers, about 2 micrometers to about 10 micrometers, about 3 micrometers to about 8 micrometers, or about 4 micrometers to about 6 micrometers). Exemplary micron-sized particles comprising alumina are MI-386 particles, available from Grace Division, Rhodia. Optionally, the micron-sized particles comprising alumina are stabilized with lanthana. For example, the micron-sized particles comprising alumina can comprise about 2 wt% to about 4 wt% lanthana. In some embodiments, the micron-sized particles comprising alumina make up about 2 wt% to about 10 wt% (such as about 3 wt% to about 8 wt%, or about 4 wt% to about 6 wt%) of the solids in the first washcoat composition. [00132] In some embodiments, the first washcoat composition comprises boehmite particles. In some embodiments, the boehmite in the first washcoat composition comprises about 2 wt% to about 15 wt% (such as about 4 wt% to about 14 wt%, about 5 w% to about 12 wt%, about 6 wt% to about 8 wt%, about 8 wt% to about 10 wt%, about 10 wt% to about 12 wt%, or about 1 1 wt%) of the solids in the first washcoat composition. The boehmite is generally in the form of particles that can be dispersed in the washcoat composition. In some embodiments, the boehmite has an average dispersed particle size of about 10 nm to about 400 nm (such as about 10 nm to about 30 nm, about 30 nm to about 60 nm, about 60 nm to about 100 nm, about 100 nm to about 150 nm, about 150 nm to about 250 nm, or about 250 nm to about 400 nm). In some embodiments, the boehmite has an averaged dispersed particle size of less than about 60 nm. In some embodiments, the boehmite has an average dispersed particle size of about 150 nm or more. In some embodiments, the BET surface area of the boehmite is about 80 m²/g to about 300 m²/g (such as about 100 m²/g to about 260 m²/g, such as about 100 m²/g to about 140 m²/g, about 140 m²/g to about 180 m²/g, about 180 m²/g to about 220 m²/g, or about 220 m²/g to about 260 m²/g). In some embodiments, the BET surface area of the boehmite is about 250 m²/g or less (such as about 200 m²/g or less, or about 160 m²/g or less). In some embodiments, the BET surface area of the boehmite is about 120 m²/g or more (such as about 160 m²/g or more, or about 180 m²/g or more). Exemplary boehmite particles that can be used for the first washcoat composition are DISPERAL® P2 boehmite particles, available from Sasol (Hamburg,

Germany), which have an average dispersed particle size of about 25 nm and a BET surface area of about 260 m²/g.

[00133] In some embodiments, the first washcoat composition is coated onto the substrate to obtain a thickness of about 100 g/1 to about 300 g/1 (such as about 100 g/1 to about 120 g/1, about 120 g/1 to about 140 g/1, about 140 g/1 to about 160 g/1, about 160 g/1 to about 180 g/1, about 180 g/1 to about 200 g/1, about 200 g/1 to about 220 g/1, about 220 g/1 to about 240 g/1, about 240 g/1 to about 270 g/1, or about 270 g/1 to about 300 g/1). In some embodiments, the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1, ( such as about 0.15 g/1 to about 0.3 g/1, or about 0.2 g/1). In some embodiments, the first washcoat composition is substantially free of platinum. In some embodiments, the first washcoat composition is substantially free of any platinum group metal other than palladium. [00134] In some embodiments, the first washcoat composition comprises micron-sized particles comprising ceria impregnated with palladium. In some embodiments, the first washcoat composition further comprises boehmite particles. In some embodiments, the micron-sized particles comprising ceria makes up about 85 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite makes up about 5 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite has an average dispersed particle size of about 10 nm to about 30 nm. In some embodiments, the boehmite has an average BET surface area of 120 m²/g or more (such as about 220 m²/g to about 300 m²/g). In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1.

[00135] In some embodiments, the first washcoat composition comprises micron-sized particles comprising ceria impregnated with palladium, boehmite, and micron-sized particles comprising alumina. In some embodiments, the micron-sized particles comprising ceria makes up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite makes up about 5 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite has an average dispersed particle size of about 10 nm to about 30 nm. In some embodiments, the boehmite has an average BET surface area of about 120 m²/e or more (such as about 220 m²/g to about 300 m²/g). In some embodiments, the micron-sized particles comprising alumina make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1.

[00136] In some embodiments, the first washcoat composition comprises micron-sized particles comprising ceria and a palladium salt. In some embodiments, the first washcoat composition further comprises boehmite particles. In some embodiments, the micron-sized particles comprising ceria makes up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite makes up about 5 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite has an average dispersed particle size of about 10 nm to about 30 nm. In some embodiments, the boehmite has an average BET surface area of about 120 m²/g or more (such as about 220 m²/g to about 300 m²/g). In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1.

[00137] In some embodiments, the first washcoat composition comprises micron-sized particles comprising ceria, a palladium salt, boehmite, and micron-sized particles comprising alumina. In some embodiments, the micron-sized particles comprising ceria makes up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite makes up about 5 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite has an average dispersed particle size of about 10 nm to about 30 nm. In some embodiments, the boehmite has an average BET surface area of about 120 m²/g or more (such as about 220 m²/g to about 300 m²/g). In some embodiments, the micron- sized particles comprising alumina make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1. In some embodiments, the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1.

[00138] In some embodiments, the second washcoat composition comprises micron-sized particles comprising alumina impregnated with platinum, for example by wet chemistry methods. In some embodiments, the second washcoat composition further comprises boehmite particles. In some embodiments, the second washcoat composition is substantially free of palladium or a palladium salt.

[00139] In some embodiments, the second washcoat composition comprises micron-sized particles comprising alumina and a platinum salt. In some embodiments, the second washcoat composition further comprises boehmite particles. In some embodiments, the second washcoat composition is substantially free of palladium or a palladium salt.

[00140] In some embodiments, the micron-sized particles comprising alumina can have an average diameter of about 0.5 micrometers to about 20 micrometers (such as about 1 micrometer to about 15 micrometers, about 2 micrometers to about 10 micrometers, about 3 micrometers to about 8 micrometers, or about 4 micrometers to about 6 micrometers). Exemplary micron-sized particles comprising alumina are MI-386 particles, available from Grace Division, Rhodia. Optionally, the micron-sized particles comprising alumina are stabilized with lanthana. For example, the micron-sized particles comprising alumina can comprise about 2 wt% to about 4 wt% lanthana. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% (such as about 90 wt% to about 97 wt%, about 94 wt% to about 96 wt%, or about 95 wt%) of the solids in the second washcoat composition.

[00141] In some embodiments, the second washcoat composition comprises boehmite particles. In some embodiments, the boehmite in the second washcoat composition makes up about 1 wt% to about 10 wt% (such as about 2 wt% to about 8 wt%, about 3 w% to about 6 wt%, or about 4 wt% to about 5 wt%) of the solids in the second washcoat composition. The boehmite is generally in the form of particles that can be dispersed in the composition. In some embodiments, the boehmite has an average dispersed particle size of about 10 nm to about 400 nm (such as about 10 nm to about 30 nm, about 30 nm to about 60 nm, about 60 nm to about 100 nm, about 100 nm to about 150 nm, about 150 nm to about 250 nm, or about 250 nm to about 400 nm). In some embodiments, the boehmite has an averaged dispersed particle size of less than about 60 nm. In some embodiments, the boehmite has an average dispersed particle size of about 150 nm or more. In some embodiments, the BET surface area of the boehmite is about 80 m²/g to about 300 m²/g (such as about 100 m²/g to about 260 m²/g, such as about 100 m²/g to about 140 m²/g, about 140 m²/g to about 180 m²/g, about 180 m²/g to about 220 m²/g, or about 220 m²/g to about 260 m²/g). In some embodiments, the BET surface area of the boehmite is about 250 m²/g or less (such as about 200 m²/g or less, or about 160 m²/g or less). In some embodiments, the BET surface area of the boehmite is about 120 m²/g or more (such as about 160 m²/g or more, or about 180 m²/g or more). Exemplary boehmite particles that can be used for the second washcoat composition are DISPAL® 11N7-80 boehmite particles, available from Sasol (Hamburg, Germany). DISPAL® 1 1N7-80 boehmite particles have an average dispersed particle size of 220 nm and a BET surface area of about 100 m²/g.

[0100] In some embodiments, the second washcoat composition comprises micron-sized particles comprising alumina impregnated with platinum. In some embodiments, the second washcoat composition further comprises boehmite particles. In some embodiments, the micron- sized particles comprising alumina makes up about 90 wt% to about 99 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite makes up about 1 wt% to about 10 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite has an average dispersed particle size of about 150 nm to about 250 nm. In some embodiments, the boehmite has an average BET surface area of about 250 m²/g or less (such as about 160 m²/g or less, or about 80 m²/g to about 140 m²/g). In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1. In some embodiments, the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1.

[0101] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, or comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm². [0102] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0103] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina

impregnated with platinum, and boehmite particles. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm 2.

[0104] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, or comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and (2) coating the substrate with a second washcoat composition comprising porous micron- sized particles comprising alumina, a platinum salt, and boehmite particles, or comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0105] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0106] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0107] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, or comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles, wherein the boehmite particles in the first washcoat composition have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite, wherein the boehmite particles in the second washcoat composition have an average dispersed particle size of about 150 nm or more. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm². [0108] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, wherein the boehmite particles in the first washcoat composition have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, wherein the boehmite particles in the second washcoat composition have an average dispersed particle size of about 150 nm or more. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0109] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles, wherein the boehmite particles in the first washcoat composition have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite, wherein the boehmite particles in the second washcoat composition have an average dispersed particle size of about 150 nm or more. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm 2.

[0110] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, porous micron-sized particles comprising alumina, and boehmite particles, or comprising porous micron-sized particles comprising ceria impregnated with palladium, porous micron-sized particles comprising alumina, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles. In some embodiments, the micron-sized particles comprising alumina make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0111] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, porous micron-sized particles comprising alumina, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles. In some embodiments, the micron-sized particles comprising alumina make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0112] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria impregnated with palladium, porous micron-sized particles comprising alumina, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm); and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles. In some embodiments, the micron-sized particles comprising alumina make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0113] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, or comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles, wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite, wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm 2.

[0114] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0115] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles, wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite, wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0116] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, or comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite, wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some

embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0117] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0118] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina impregnated with platinum, andboehmite, wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm 2. [0119] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, or comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles, wherein the boehmite particles in the first washcoat composition have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles, wherein the boehmite particles in the second washcoat composition have an average dispersed particle size of about 150 nm or more, and wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0120] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, wherein the boehmite particles in the first washcoat composition have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, wherein the boehmite particles in the second washcoat composition have an average dispersed particle size of about 150 nm or more, and wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0121] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles, wherein the boehmite particles in the first washcoat composition have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles, wherein the boehmite particles in the second washcoat composition have an average dispersed particle size of about 150 nm or more, and wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm 2.

[0122] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, porous micron-sized particles comprising alumina, and boehmite particles, or comprising porous micron-sized particles comprising ceria impregnated with palladium, porous micron-sized particles comprising alumina, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles. In some embodiments, the micron-sized particles comprising alumina make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition. In some embodiments, the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some

[0123] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria, a palladium salt, porous micron-sized particles comprising alumina, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles. In some embodiments, the micron- sized particles comprising alumina make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition, and wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some

[0124] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising porous micron-sized particles comprising ceria impregnated with palladium, porous micron-sized particles comprising alumina, and boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles. In some embodiments, the micron-sized particles comprising alumina make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition, and wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition. In some embodiments, the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the micron-sized particles comprising ceria make up about 60 wt% to about 95 wt% of the solids in the first washcoat composition. In some embodiments, the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm². [0125] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising about 85 wt% to about 90 wt% (such as about 88 wt%) porous micron-sized particles comprising ceria, a palladium salt, about 3 wt% to about 6 wt% (such as about 4.6 wt%) porous micron-sized particles comprising alumina, and about 5 wt% to about 10 wt% (such as about 7 wt%) boehmite particles, or comprising about 85 wt% to about 90 wt% (such as about 88 wt%) porous micron-sized particles comprising ceria impregnated with palladium, about 3 wt% to about 6 wt% (such as about 4.6 wt%) porous micron-sized particles comprising alumina, and about 5 wt% to about 10 wt% (such as about 7 wt%) boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising about 85 wt% to about 99 wt% (such as about 95 wt%) porous micron-sized particles comprising alumina, a platinum salt, and about 1 wt% to about 8 wt% (such as about 5 wt%) boehmite particles, or comprising about 85 wt% to about 99 wt% (such as about 95 wt%) porous micron-sized particles comprising alumina impregnated with platinum, and about 1 wt% to about 8 wt% (such as about 5 wt%)boehmite particles. In some embodiments, the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0126] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising about 85 wt% to about 90 wt% (such as about 88 wt%) porous micron-sized particles comprising ceria, a palladium salt, about 3 wt% to about 6 wt% (such as about 4.6 wt%) porous micron-sized particles comprising alumina, and about 5 wt% to about 10 wt% (such as about 7 wt%) boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising about 85 wt% to about 99 wt% (such as about 95 wt%) porous micron-sized particles comprising alumina, a platinum salt, and about 1 wt% to about 8 wt% (such as about 5 wt%) boehmite particles. In some embodiments, the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0127] In some embodiments, a method of making a catalyst comprises (1) coating a substrate with a first washcoat composition comprising about 85 wt% to about 90 wt% (such as about 88 wt%) porous micron-sized particles comprising ceria impregnated with palladium, about 3 wt% to about 6 wt% (such as about 4.6 wt%) porous micron-sized particles comprising alumina, and about 5 wt% to about 10 wt% (such as about 7 wt%) boehmite particles, wherein the boehmite particles have an average dispersed particle size of about 60 nm or less (such as about 10 nm to about 30 nm), and wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1; and (2) coating the substrate with a second washcoat composition comprising about 85 wt% to about 99 wt% (such as about 95 wt%) porous micron-sized particles comprising alumina impregnated with platinum, and about 1 wt% to about 8 wt% (such as about 5 wt%)boehmite particles. In some embodiments, the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1. In some embodiments, the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids. In some embodiments, the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids. In some embodiments, the porous micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer. In some embodiments, the substrate is about 0.5 cm to about 6 cm thick. In some embodiments, the substrate has a transverse profile of about 100 cm² to about 600 cm².

Exhaust Systems and Methods of Treating Exhaust

[0128] The catalysts described herein can be part of an exhaust treatment system, which can be used to treat exhaust gasses. An exhaust treatment system comprises the catalyst and a conduit for exhaust gas. The conduit fluidly connects the catalyst to an exhaust gas source, such as a stove, a furnace, a fireplace or a generator. In some embodiments, the exhaust gas source is indoors. The exhaust gas source burns a fuel (such as natural gas, a combustible hydrocarbon liquid, oil, kerosene, coal, or wood), thereby forming an exhaust gas. The exhaust gas can comprise carbon monoxide or hydrocarbons (such as methane or non-methane hydrocarbons). The exhaust gas can be treated by contacting the exhaust gas with the catalyst. The catalyst can oxidize the carbon monoxide or certain other exhaust gas components.

[0129] The catalysts described herein can oxidize carbon monoxide in exhaust gas with better performance than a single layer catalyst comprising micron-sized particles comprising alumina impregnated with platinum by wet-chemistry methods. For example, in some embodiments, the catalyst can oxidize a greater portion of the carbon monoxide in exhaust gas at temperatures lower than about 100 °C than a single layer catalyst comprising micron-sized particles comprising alumina impregnated with platinum by wet-chemistry methods. In some

embodiments, the catalyst can oxidize substantially all of the carbon monoxide in an exhaust gas at a temperature above about 130 °C with a lower platinum loading or platinum group metal loading than a single layer catalyst comprising micron-sized particles comprising alumina impregnated with platinum by wet-chemistry methods.

[0130] In some embodiments, the catalyst oxidizes substantially all of the carbon monoxide in an exhaust gas at a temperature above about 130 °C with a platinum group metal loading of about 0.85 g/1 or less (such as about 0.8 g/1 or less, about 0.75 g/1 or less, or about 0.7 g/1 or less). In some embodiments, the catalyst oxidizes substantially all of the carbon monoxide in an exhaust gas at a temperature above about 130 °C with a platinum group metal loading of about 0.6 g/1 to about 0.85 g/1 (such as about 0.6 g/1 to about 0.8 g/1, about 0.65 g/1 to about 0.75 g/1, about 0.65 g/1 to about 0.7 g/1, or about 0.67 g/1). [0131] In some embodiments, the catalyst oxidizes substantially all of the carbon monoxide in an exhaust gas at a temperature above about 130 °C with a platinum loading of about 0.85 g/1 or less (such as about 0.8 g/1 or less, about 0.75 g/1 or less, about 0.7 g/1 or less, about 0.65 g/1 or less, about 0.6 g/1 or less, about 0.55 g/1 or less, or about 0.5 g/1 or less). In some embodiments, the catalyst oxidizes substantially all of the carbon monoxide in an exhaust gas at a temperature above about 130 °C with a platinum loading of about 0.4 g/1 to about 0.85 g/1 (such as about 0. 4 g/1 to about 0.8 g/1, about 0.4 g/1 to about 0.75 g/1, about 0.4 g/1 to about 0.7 g/1, about 0.4 g/1 to about 0.65 g/1 about 0.4 g/1 to about 0.6 g/1, about 0.4 g/1 to about 0.55 g/1, about 0.4 g/1 to about 0.5 g/1, or about 0.45 g/1).

EXEMPLARY EMBODIMENTS

[0132] Embodiment 1. A catalyst comprising:

a substrate coated with a first washcoat layer and a second washcoat layer;

the first washcoat layer comprising porous micron-sized particles comprising ceria impregnated with palladium, and alumina derived from boehmite particles; and

the second washcoat layer comprising porous micron-sized particles comprising alumina impregnated with platinum, and alumina derived from boehmite particles.

[0133] Embodiment 2. The catalyst of embodiment 1, wherein the micron-sized particles comprising ceria in the first washcoat layer are impregnated with palladium by wet-chemistry methods.

[0134] Embodiment 3. The catalyst of embodiment 1 or 2, wherein the micron-sized particles comprising alumina in the second washcoat layer are impregnated with platinum by wet- chemistry methods.

[0135] Embodiment 4. The catalyst of any one of embodiments 1 -3, wherein the boehmite particles used to derive the alumina in the first washcoat layer have an average dispersed particle size of about 60 nm or less.

[0136] Embodiment 5. The catalyst of any one of embodiments 1 -4, wherein the boehmite particles used to derive the alumina in the first washcoat layer have a BET surface area of about 120 m²/g or more. [0137] Embodiment 6. The catalyst of any one of embodiments 1 -5, wherein the boehmite particles used to derive the alumina in the second washcoat layer have an average dispersed particle size of about 150 nm or more.

[0138] Embodiment 7. The catalyst of any one of embodiments 1 -6, wherein the boehmite particles used to derive the alumina in the second washcoat layer have a BET surface area of about 250 m²/g or less.

[0139] Embodiment 8. The catalyst of any one of embodiments 1 -7, wherein the micron-sized particles comprising alumina in the second washcoat layer are stabilized with lanthana.

[0140] Embodiment 9. The catalyst of any one of embodiments 1 -8, wherein the first washcoat layer further comprises porous micron-sized particles comprising alumina.

[0141] Embodiment 10. The catalyst of embodiment 9, wherein the porous micron-sized particles comprising alumina in the first washcoat layer are impregnated with palladium.

[0142] Embodiment 11. The catalyst of embodiment 10, wherein the porous micron-sized particles comprising alumina in the first washcoat layer are impregnated with palladium by wet- chemistry methods.

[0143] Embodiment 12. The catalyst of embodiment 9, wherein the porous micron-sized particles comprising alumina in the first washcoat layer are substantially free of palladium.

[0144] Embodiment 13. The catalyst of any one of embodiments 9-12, wherein the micron-sized particles comprising alumina are stabilized with lanthanaA

[0145] Embodiment 14. The catalyst of any one of embodiments 9-13, wherein the micron-sized particles comprising alumina in the first washcoat layer make up about 2 wt% to about 10 wt% of the solids in the first washcoat layer.

[0146] Embodiment 15. The catalyst of any one of embodiments 1-14, wherein the alumina derived from boehmite in the first washcoat layer makes up about 2 wt% to about 15 wt% of the solids in the first washcoat layer.

[0147] Embodiment 16. The catalyst of any one of embodiments 1-15, wherein the alumina derived from boehmite in the second washcoat layer makes up about 1 wt% to about 8 wt% of the solids in the second washcoat layer. [0148] Embodiment 17. The catalyst of any one of embodiments 1-16, wherein the first washcoat layer has a thickness of about 100 g/1 to about 300 g/1.

[0149] Embodiment 18. The catalyst of any one of embodiments 1-17, wherein the second washcoat layer has a thickness of about 40 g/1 to about 150 g/1.

[0150] Embodiment 19. The catalyst of any one of embodiments 1-18, wherein the first washcoat layer has a palladium loading of about 0.1 g/1 to about 0.5 g/1.

[0151] Embodiment 20. The catalyst of any one of embodiments 1-19, wherein the second washcoat layer has a platinum loading of about 0.2 g/1 to about 0.7 g/1.

[0152] Embodiment 21. The catalyst of any one of embodiments 1-20, wherein the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1.

[0153] Embodiment 22. The catalyst of any one of embodiments 1-21 , wherein the micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer.

[0154] Embodiment 23. The catalyst of any one of embodiments 1-22, wherein the micron-sized particles comprising alumina in the second washcoat layer make up about 85 wt% to about 99 wt% of the solids in the second washcoat layer.

[0155] Embodiment 24. The catalyst of any one of embodiments 1-23, wherein the substrate comprises cordierite.

[0156] Embodiment 25. The catalyst of any one of embodiments 1-24, wherein the substrate has a honeycomb structure.

[0157] Embodiment 26. The catalyst of any one of embodiments 1-25, wherein the substrate is about 0.5 cm to about 6 cm thick.

[0158] Embodiment 27. The catalyst of any one of embodiments 1-26, wherein the substrate has a transverse profile of about 100 cm² to about 600 cm².

[0159] Embodiment 28. An exhaust treatment system comprising a conduit for exhaust gas and the catalyst according to any one of embodiment 1-27.

[0160] Embodiment 29. The exhaust treatment system of embodiment 28, wherein the catalyst is fiuidly connected to an exhaust gas source. [0161] Embodiment 30. The exhaust treatment system of embodiment 29, wherein the exhaust gas source burns natural gas, a combustible hydrocarbon liquid, oil, kerosene, coal, or wood.

[0162] Embodiment 31. The exhaust treatment system of embodiment 29 or 30, wherein the exhaust gas source is a stove, a furnace, a fireplace, or a generator.

[0163] Embodiment 32. A method of treating an exhaust gas comprising contacting the exhaust gas with the catalyst according to any one of embodiments 1 -27.

[0164] Embodiment 33. A method of making a catalyst comprising:

i. coating a substrate with a first washcoat composition comprising:

porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles, or

porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles; and

ii. coating the substrate with a second washcoat composition comprising:

porous micron-sized particles comprising alumina, a platinum salt, and boehmite particles, or

porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles.

[0165] Embodiment 34. The method of embodiment 33, wherein the first washcoat composition comprises porous micron-sized particles comprising ceria, a palladium salt, and boehmite particles.

[0166] Embodiment 35. The method of embodiment 33, wherein the first washcoat composition comprises porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles.

[0167] Embodiment 36. The method of any one of embodiments 33-35, wherein the second washcoat composition comprises porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles.

[0168] Embodiment 37. The method of any one of embodiments 34-35, wherein the second washcoat composition comprises porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles. [0169] Embodiment 38. The method of any one of embodiments 33-37, further comprising drying the first washcoat composition after it has been coated onto the substrate.

[0170] Embodiment 39. The method of any one of embodiments 33-38, further comprising calcining the substrate after the first washcoat composition has been coated onto the substrate.

[0171] Embodiment 40. The method of any one of embodiments 33-39, further comprising drying the second washcoat composition after it has been coated onto the substrate.

[0172] Embodiment 41. The method of any one of embodiments 33-40, further comprising calcining the substrate after the second washcoat composition has been coated onto the substrate.

[0173] Embodiment 42. The method of any one of embodiments 33-41 , wherein the substrate is coated with the first washcoat composition prior to being coated with the second washcoat composition.

[0174] Embodiment 43. The method of any one of embodiments 33-42, wherein the boehmite particles in the first washcoat composition have an average dispersed particle size of about 60 nm or less.

[0175] Embodiment 44. The method of any one of embodiments 33-43, wherein the boehmite particles in the first washcoat composition have a BET surface area of about 120 m²/s or more.

[0176] Embodiment 45. The method of any one of embodiments 33-44, wherein the boehmite particles in the second washcoat layer has an average dispersed particle size of about 150 nm or more.

[0177] Embodiment 46. The method of any one of embodiments 33-45, wherein the boehmite particles in the second washcoat layer have a BET surface area of about 250 m²/g or less.

[0178] Embodiment 47. The method of any one of embodiments 33-46, wherein the micron- sized particles comprising alumina in the second washcoat composition are stabilized with lanthana.

[0179] Embodiment 48. The method of any one of embodiments 33-47, wherein the first washcoat composition further comprises porous micron-sized particles comprising alumina.

[0180] Embodiment 49. The method of embodiment 48, wherein the micron-sized particles comprising alumina in the first washcoat composition are stabilized with lanthana. [0181] Embodiment 50. The method of embodiment 48 or 49, wherein the micron-sized particles comprising alumina in the first washcoat composition make up about 2 wt% to about 10 wt% of the solids in the first washcoat composition.

[0182] Embodiment 51. The method of any one of embodiments 33-50, wherein the boehmite particles in the first washcoat composition make up about 2 wt% to about 15 wt% of the solids in the first washcoat composition.

[0183] Embodiment 52. The method of any one of embodiments 33-51 , wherein the boehmite particles in the second washcoat composition make up about 1 wt% to about 8 wt% of the solids in the second washcoat composition.

[0184] Embodiment 53. The method of any one of embodiments 33-52, wherein the first washcoat composition is coated onto the substrate at a thickness of about 100 g/1 to about 300 g/1 of solids.

[0185] Embodiment 54. The method of any one of embodiments 33-53, wherein the second washcoat composition is coated onto the substrate at a thickness of about 40 g/1 to about 150 g/1 of solids.

[0186] Embodiment 55. The method of any one of embodiments 33-54, wherein the first washcoat composition is coated onto the substrate to obtain a palladium loading of about 0.1 g/1 to about 0.5 g/1.

[0187] Embodiment 56. The method of any one of embodiments 33-55, wherein the second washcoat composition is coated onto the substrate to obtain a platinum loading of about 0.2 g/1 to about 0.7 g/1.

[0188] Embodiment 57. The method of any one of embodiments 33-56, wherein the micron- sized particles comprising ceria make up about 80 wt% to about 95 wt% of the solids in the first washcoat composition.

[0189] Embodiment 58. The method of any one of embodiments 33-57, wherein the micron- sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition.

[0190] Embodiment 59. The method of any one of embodiments 33-58, wherein the substrate comprises cordierite. [0191] Embodiment 60. The method of any one of embodiments 33-59, wherein the substrate has a honeycomb structure.

[0192] Embodiment 61. The method of any one of embodiments 33-60, wherein the substrate is about 1 cm to about 4 cm thick.

[0193] Embodiment 62. The catalyst of any one of embodiments 33-61 , wherein the substrate has a transverse profile of about 100 to about 600 cm².

[0194] Embodiment 63. The catalyst made according to the method of any one of embodiments 33-62.

EXAMPLE

[0195] A first catalyst (Catalyst A) was prepared as follows. A washcoat composition was formed by combining MI-386 particles (porous micron-sized alumina particles stabilized with lanthana), boehmite, and a platinum salt (chloroplatinic acid) in water. The washcoat composition was coated onto a substrate at a thickness of 100 g/1 of solids. The washcoat was dried and the coated substrate calcined. The resulting substrate was coated with a single washcoat layer with a platinum loading of 0.9 g/1.

[0196] A second catalyst (Catalyst B) was prepared as follows. A first washcoat composition was formed by combining 88 wt% HSA-20 particles (porous micron-sized ceria particles), palladium (II) nitrate, 4.6 wt% MI-368 particles, and 7 wt% DISPAL® 11N7-80 boehmite particles in water. The first washcoat composition was coated onto a substrate at a thickness of 220 g/1 of solids. The washcoat was dried and the coated substrate calcined. The resulting substrate was coated with a single washcoat layer with a palladium loading of 0.22 g/1. A second washcoat composition was formed by combining 95 wt% MI-386 particles, a platinum salt (chloroplatinic acid), and 5 wt% DISPAL® 1 1N7-80 boehmite particles in water. The washcoat composition was coated onto the substrate (which already includes the first washcoat layer) at a thickness of 65 g/1. The washcoat was dried and the coated substrate calcined. The resulting substrate was coated with two washcoat layers. The first (bottom) washcoat layer provided a palladium loading of 0.22 g/1, and the second (top) washcoat layer provided a platinum loading of 0.45 g/1. [0197] A third catalyst (Catalyst C) was prepared as follows. A first washcoat composition was formed by combining 89 wt% HSA-20 particles (porous micron-sized ceria particles), 11 wt% DISPERAL® P2 boehmite particles, and palladium (II) nitrate in water. The first washcoat composition was coated onto a substrate at a thickness of 241 g/1 of solids. The washcoat was dried and the coated substrate calcined. The resulting substrate was coated with a single washcoat layer with a palladium loading of 0.21 g/1. A second washcoat composition was formed by combining 95 wt% MI-386 particles, 5 wt% DISPAL® 1 1N7-80 boehmite particles, and a platinum salt (chloroplatinic acid) in water. The washcoat composition was coated onto the substrate (which already includes the first washcoat layer) at a thickness of 60 g/1. The washcoat was dried and the coated substrate calcined. The resulting substrate was coated with two washcoat layers. The first (bottom) washcoat layer provided a palladium loading of 0.21 g/1, and the second (top) washcoat layer provided a platinum loading of 0.46 g/1.

[0198] A synthetic exhaust gas (500 ppm CO, 2000 ppm CH₄, 5% C0₂, 5% 0₂, 5% H₂0, and the balance N₂) passed through the three catalysts (Catalyst A, Catalyst B, and Catalyst C) at a gas hourly space velocity (GHSV) of 50,000 h^"1 with increasing temperature. The amount of carbon monoxide exiting the catalysts was measured and plotted as against the temperature, as shown in FIG. 2. Catalyst A showed minimal catalysis of carbon monoxide below about 100 °C, with nearly complete catalysis of the carbon monoxide at about 125 °C. Catalyst B catalyzed the carbon monoxide in a near linear relationship with temperature between about 25 °C and about 105 °C, thereafter exhibiting a sharp increase in catalytic efficiency with increased temperature. Catalyst A catalyzed over 10% of the carbon monoxide at about 50 °C, over 20% of the carbon monoxide at about 90 °C, and nearly all of the carbon monoxide at about 125 °C. Catalyst C was more efficient than both Catalyst A and Catalyst B, and catalyzed over 10% of the carbon monoxide at about 30 °C, over 20% of the carbon monoxide at about 50 °C, over 30% of the carbon monoxide at about 90 °C, over 40% of the carbon monoxide at about 100 °C, over 50% of the carbon monoxide at about 105 °C, and substantially all of the carbon monoxide at about 1 15 °C.

[0199] The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto . It will be readily apparent to one skilled in the art that other various modifications can be made in the embodiments chosen for illustration without departing from the spirit and scope of the invention. Therefore, the description and examples should not be construed as limiting the scope of the invention.

Claims

CLAIMS What is claimed is:

1. A catalyst comprising:

a substrate coated with a first washcoat layer and a second washcoat layer;

2. The catalyst of claim 1, wherein the boehmite particles used to derive the alumina in the first washcoat layer have an average dispersed particle size of about 60 nm or less.

3. The catalyst of any one of claims 1 -2, wherein the boehmite particles used to derive the alumina in the first washcoat layer have a BET surface area of about 120 m²/g or more.

4. The catalyst of any one of claims 1 -3, wherein the boehmite particles used to derive the alumina in the second washcoat layer have an average dispersed particle size of about 150 nm or more.

5. The catalyst of any one of claims 1 -4, wherein the boehmite particles used to derive the alumina in the second washcoat layer have a BET surface area of about 250 m²/g or less.

6. The catalyst of any one of claims 1 -5, wherein the first washcoat layer further comprises porous micron-sized particles comprising alumina.

7. The catalyst of claim 6, wherein the porous micron-sized particles comprising alumina in the first washcoat layer are impregnated with palladium.

8. The catalyst of any one of claims 6-7, wherein the micron-sized particles comprising alumina in the first washcoat layer make up about 2 wt% to about 10 wt% of the solids in the first washcoat layer.

9. The catalyst of any one of claims 1 -5, wherein the alumina derived from boehmite in the second washcoat layer makes up about 1 wt% to about 8 wt% of the solids in the second washcoat layer.

10. The catalyst of any one of claims 1-10, wherein the first washcoat layer has a palladium loading of about 0.1 g/1 to about 0.5 g/1.

11. The catalyst of any one of claims 1-11 , wherein the second washcoat layer has a platinum loading of about 0.2 g/1 to about 0.7 g/1.

12. The catalyst of any one of claims 1-11 , wherein the catalyst has a platinum group metal loading of about 0.3 g/1 to about 1.2 g/1.

13. The catalyst of any one of claims 1-14, wherein the micron-sized particles comprising ceria in the first washcoat layer make up about 60 wt% to about 95 wt% of the solids in the first washcoat layer.

14. The catalyst of any one of claims 1-13, wherein the micron-sized particles comprising alumina in the second washcoat layer make up about 85 wt% to about 99 wt% of the solids in the second washcoat layer.

15. An exhaust treatment system comprising a conduit for exhaust gas and the catalyst according to any one of claim 1 -14.

16. A method of treating an exhaust gas comprising contacting the exhaust gas with the catalyst according to any one of claims 1 -14.

17. A method of making a catalyst according to claims 1-14 comprising:

i. coating a substrate with a first washcoat composition comprising:

ii. coating the substrate with a second washcoat composition comprising:

18. The method of claim 17, wherein the first washcoat composition comprises porous micron- sized particles comprising ceria impregnated with palladium, and boehmite particles.

19. The method of any one of claims 17-18, wherein the second washcoat composition comprises porous micron-sized particles comprising ceria impregnated with palladium, and boehmite particles.

20. The method of any one of claims 17-19, wherein the second washcoat composition comprises porous micron-sized particles comprising alumina impregnated with platinum, and boehmite particles.

21. The method of any one of claims 17-20, wherein the first washcoat composition further comprises porous micron-sized particles comprising alumina.

22. The method of any one of claims 17-21 , wherein the micron-sized particles comprising ceria make up about 80 wt% to about 95 wt% of the solids in the first washcoat composition.

23. The method of any one of claims 17-22, wherein the micron-sized particles comprising alumina make up about 85 wt% to about 99 wt% of the solids in the second washcoat composition.

24. The catalyst made according to the method of any one of claims 17-23.