Method and composition

Abstract

To provide a method for preparing a catalyst article preferable for treatment of exhaust from an internal combustion engine or a gas turbine, which is treatment of carbon monoxide and / or formaldehyde exhaust from the internal combustion engine or the gas turbine using natural gas as a fuel, for example.SOLUTION: The method according to the present invention includes the steps of: (a) preparing a washcoat composition by combining at least the following components: a support material comprising a mixed oxide, a mixture of oxides or a molecular sieve comprising (i) alumina and (ii) silica and / or zirconia; a metal oxide sol comprising at least one of titania, silica or zirconia; a liquid medium; (b) applying the washcoat composition to a substrate to form a washcoating; and (c) drying and / or calcining the washcoating. Furthermore, the method includes a step of impregnating the support material with a platinum group metal component.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for preparing a catalytic article for treating exhaust gas generated by a power generation device such as an engine or a turbine, particularly an engine and a turbine fueled by natural gas. The present invention further relates to a washcoat composition suitable for use in such a method.

Background Art

[0002] In normal operation, turbines and engines fueled by natural gas generate a significant amount of carbon dioxide (CO 2 2), water, carbon monoxide (CO), volatile organic compounds (VOCs) such as formaldehyde, and nitrogen oxides (NOx) as part of the combustion process.

[0003] Recent environmental regulations have emphasized the importance of reducing the levels of partially combusted fuel components from the exhaust of such turbines and engines. These regulated exhaust emissions include carbon monoxide (CO) and formaldehyde (CH 2 2O).

[0004] To treat the emissions from such engines, a catalytic converter can be used. The catalytic converter converts such emissions in the exhaust gas into less harmful substances before they are released into the atmosphere. The catalytic converter typically includes a suitable substrate coated with a catalytically active material.

[0005] In the production of the coated catalyst, a composition known as a "washcoat" is applied to a substrate (e.g., a ceramic monolith). The washcoat can take the form of a solution, slurry, or suspension of the catalytic material in a liquid medium. Once coated on the substrate, the washcoat typically undergoes a firing process to remove the liquid medium and fix the catalytically active material to the substrate.

[0006] Known catalysts suitable for catalyzing the oxidation of CO and formaldehyde typically use one or more platinum group metals (PGMs) supported on a suitable catalyst support. The catalyst support may be a high surface area refractory metal oxide such as alumina or silica. However, known oxidation catalysts may deactivate over time. Further, certain components present in the fuel or lubricating oil may cause catalyst poisoning. For example, in the operation of a two-stroke engine, sulfur in the exhaust stream derived from engine oil is a major cause of catalyst poisoning.

[0007] There is still a need for improved oxidation catalysts, particularly for the treatment of CO and formaldehyde emissions from engines and turbines fueled by natural gas. SUMMARY OF THE INVENTION

[0008] According to an aspect of the present disclosure, a method of preparing a catalyst article, comprising: (a) combining at least the following components: ● a carrier material comprising a mixed oxide, a mixture of oxides or a molecular sieve comprising (i) alumina and (ii) silica and / or zirconia, ● a metal oxide sol comprising at least one of titania, silica or zirconia, ● a liquid medium, to prepare a washcoat composition; (b) applying the washcoat composition to a substrate to form a washcoat; (c) drying and / or firing the washcoat, and further comprising impregnating the carrier material with a platinum group metal component. A method is provided.

[0009] According to a further aspect of the present disclosure, ● a carrier material comprising a mixed oxide, a mixture of oxides or a molecular sieve comprising (i) alumina and (ii) silica and / or zirconia, optionally impregnated with a platinum group metal component, ●A metal oxide sol containing at least one of titania, silica or zirconia, ●and a liquid medium, to provide a washcoat composition.

[0010] Advantageously, it has been found that a catalyst prepared according to the above method can provide improved CO and / or formaldehyde oxidation stability (i.e., maintained activity over time). Further, improved and / or equivalent oxidation activity can be achieved compared to known catalysts while using a smaller amount of PGM. Further, improved resistance to catalyst poisons, particularly improved sulfur resistance, can be achieved.

[0011] Furthermore, a catalyst prepared according to the methods described herein can find use in other stationary emission control applications, such as the treatment of exhaust gases from industrial processes or in indoor air treatment systems. In particular, a catalyst article prepared according to the method of the present invention can be useful for the decomposition of ozone (O 3 ) present in a gas stream.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0013] The present disclosure will now be further described. In the following sections, different aspects / embodiments of the present disclosure are defined in more detail. Each aspect / embodiment so defined can be combined with any other aspect / embodiment or aspects / embodiments, unless explicitly indicated otherwise. In particular, any feature shown as being preferred or advantageous can be combined with any other feature or features shown as being preferred or advantageous.

[0014] Furthermore, as used herein, the term "comprising" can be exchanged with the definitions "consisting essentially of" or "consisting of". The term "comprising" is intended to mean that the specified elements are essential, but that other elements can be added and still form a composition within the scope of the claim. The term "consisting essentially of" limits the scope of the claim to the specified materials or steps and those that do not materially affect the basic and novel characteristics of the claimed invention. The term "consisting of" closes the claim against including materials other than those recited, except for impurities normally associated therewith.

[0015] The washcoat composition can be prepared by combining the necessary components and any additives. The combination of components may be effected by mixing, for example, by stirring. Preferably, the components are mixed such that the washcoat composition is substantially homogeneous (e.g., uniform), i.e., the distribution of the components throughout the washcoat is substantially uniform.

[0016] The carrier material comprises a mixed oxide, a mixture of oxides or a molecular sieve containing (i) alumina and (ii) silica and / or zirconia. Preferably, the carrier material is a mixed oxide. As used herein, the term "mixed oxide" refers to a mixture of oxides in a single phase. For example, the mixed oxide material may be a silica-alumina mixed oxide or a zirconia-alumina mixed oxide. Alternatively, the carrier material may be an aluminosilicate molecular sieve (zeolite).

[0017] Preferably, the carrier material is a silica-alumina mixed oxide. The silica-alumina mixed oxide may have a silica content in the range of 1 to 40 wt%, 2 to 35 wt%, 5 to 35 wt% or 5 to 30 wt%. For example, the silica-alumina mixed oxide may have a silica content in the range of 2 to 10 wt%, for example about 5 wt%. Alternatively, the silica-alumina mixed oxide may have a silica content in the range of 25 to 40 wt%, for example about 30 wt%.

[0018] Generally, the carrier material used in the present invention is particulate. The carrier material may have a D90 particle size of ≤50 μm, ≤30 μm, ≤20 μm or ≤10 μm. The particles can be obtained by grinding.

[0019] As used herein, the term "D90 particle size" refers to the particle size distribution. The value of the D90 particle size corresponds to the following particle size value at which 90 volume% of the total particles in a particular sample are present. The D90 particle size can be determined using a laser diffraction method (for example, using a Malvern Mastersizer 2000).

[0020] The amount of carrier material present in the washcoat composition can be selected to provide a loading of carrier material in the final catalyst article of 0.5 to 4 g / in 3 , preferably 1 to 2 g / in 3 . This is within the ability of those skilled in the art.

[0021] As used herein, the term "loading" conventionally defines the amount of a component present in the catalyst layer on a substrate. The unit of loading is generally expressed in g / ft 3 or g / in 3 and is related to the volume of the substrate used.

[0022] The step of impregnating the carrier material with the platinum group metal component may be carried out before combining the carrier material with the other components of the washcoat (i.e., before step (a) of the method described herein). For example, the impregnation may be carried out by contacting the carrier material with an impregnation solution containing the platinum group metal component. The impregnated carrier material may be dried and / or calcined before combining it with the other components of the washcoat composition.

[0023] Alternatively, the carrier material may be impregnated with the platinum group metal component after step (a) and before step (b). For example, the washcoat composition prepared in step (a) may be blended with the impregnation solution before applying it onto the substrate in step (b).

[0024] Alternatively, after step (c) of the method, the carrier material may be impregnated with the PGM component, and the impregnation may be carried out by contacting the substrate with an impregnation solution containing the platinum group metal component. The contact between the washcoated substrate and the impregnation solution can be achieved by applying the impregnation solution onto the substrate (e.g., on top of the dried and / or calcined washcoat) to form a second coating. Thus, the method may further include (d) a step of applying an impregnation solution containing the platinum group metal component onto the substrate to form a second coating, and (e) a step of drying and / or calcining the second coating.

[0025] The impregnation solution may be an aqueous solution of the platinum group metal component.

[0026] The platinum group metal component may be a salt of platinum group metals (PGM). In particular, the platinum group metal component may be a nitrate of PGM, an acetate of PGM, or a carboxylate of PGM. PGM may be ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), or a mixture thereof. Preferably, PGM is platinum, palladium, or a mixture of platinum or palladium. More preferably, PGM is platinum. Suitable platinum group metal components include platinum nitrate or platinum acetate, such as tetraamine platinum acetate.

[0027] The amount of the platinum group metal component used is such that the final catalyst layer formed on the substrate contains a platinum group loading in the range of 1 - 100 g / ft 3 , for example, 4 - 90 g / ft 3 , 8 - 50 g / ft 3 , or 20 - 35 g / ft 3 and can be selected accordingly.

[0028] The above drying process may be carried out at a temperature below 120°C, for example, at a temperature of about 100°C. The firing process may be carried out at a temperature in the range of 550°C or less, preferably 450 - 550°C, for a period of 3 hours or less, preferably 30 minutes - 2 hours.

[0029] The metal oxide sol contains at least one of titania, silica, or zirconia. As used herein, the term "metal oxide sol" refers to a colloid containing particulate metal oxide having a BET surface area of at least 100 m 2 / g dispersed in a continuous liquid medium. Preferably, the metal oxide sol is a titania sol (i.e., a colloid containing particulate titania having a specific surface area of at least 100 m 2 / g dispersed in a continuous liquid medium).

[0030] The liquid medium of the metal oxide sol may be aqueous.

[0031] The metal oxide of the metal oxide sol has a BET surface area of ≧100 m 2 / g, ≥ 150 m 2 / g, ≥ 200 m 2 / g, ≥ 250 m 2 / g or ≥ 300 m 2 It may have a BET surface area of / g.

[0032] The metal oxide sol may be a titania sol having a BET surface area of titania of ≥ 250 m 2 / g or ≥ 300 m 2 / g.

[0033] The metal oxide sol may be acidic or basic. Preferably, the metal oxide sol is acidic. For example, the metal oxide sol may have a pH in the range of 0.5 to 5, such as 0.5 to 3 or 0.5 to 2.

[0034] The metal oxide particles of the sol may have a D50 particle size of ≤ 1 micron, such as ≤ 0.5 micron or ≤ 0.2 micron. The metal oxide particles of the sol may have a D90 particle size of ≤ 5 microns, such as ≤ 2 microns, ≤ 1 micron or ≤ 0.5 micron.

[0035] As used herein, the term "D50 particle size" refers to the particle size distribution. The value of the D50 particle size corresponds to the following particle size value at which 50 volume% of the total particles in a specific sample are present. The D50 particle size can be determined using the laser diffraction method (e.g., using a Malvern Mastersizer 2000).

[0036] The amount of the metal oxide sol used is selected such that the final catalyst layer formed on the substrate contains a metal oxide loading of 2.5 g / in 3 or less, such as ≤ 2 g / in 3 , ≤ 1 g / in 3 , ≤ 0.5 g / in 3 or ≤ 0.2 g / in 3 .

[0037] The washcoat composition further comprises a liquid medium in which other components are suspended or solvated. The liquid medium may be aqueous, for example, the liquid medium may be water. Preferably, the liquid medium consists essentially of water. That is, the liquid medium contains water, but may also contain trace amounts of non-aqueous (e.g., organic or inorganic) impurities. The water can be deionized water or demineralized water.

[0038] The washcoat composition can have a solids content of 50 wt% or less. "Solids content" means the proportion of solid material present in the composition based on the total weight of the washcoat composition. The solids content of the washcoat composition is preferably in the range of 20 to 40 wt%, more preferably in the range of 30 to 35 wt%.

[0039] The washcoat composition can have an acidic pH. For example, the pH of the washcoat can be < 7 or ≦ 5. For example, the washcoat composition can have a pH of about 3.

[0040] The washcoat composition can have a viscosity in the range of 100 to 1000 centipoise.

[0041] The washcoat composition may further comprise organic additives such as rheology modifiers, dispersants and / or other additives.

[0042] The relative amounts of the components used in the washcoat composition can be selected such that the washcoat has the desired solids content.

[0043] Preferred substrates include so-called honeycomb-shaped flow-through monoliths that have open ends and typically extend from an inlet face to an outlet face of the substrate, and thus have a high surface area to volume ratio and include a plurality of adjacent parallel channels. The catalyst composition is coated on the walls of the channels such that, in use, the exhaust gas contacts the catalyst as it flows through the channels.

[0044] The monolithic substrate may be an inert substrate. The substrate may be composed of a ceramic material or a metallic material. For example, the substrate may be made of or composed of cordierite (SiO 2 -Al 2 O 3 -MgO), silicon carbide (SiC), Fe-Cr-Al alloy, Ni-Cr-Al alloy, aluminum titanate, or a stainless steel alloy.

[0045] The shape, size, and cell density of the honeycomb substrate are typically selected to optimize the exposure of the catalytically active material in the catalytic article to the exhaust gas during use. For example, if the intended use of the catalytic article is the treatment of emissions from an internal combustion engine (e.g., a two-stroke reciprocating engine) fueled by natural gas, the substrate may have a cylindrical or substantially cylindrical shape with a diameter in the range of 20 to 40 inches. The cell density may be in the range of 100 to 400 cpsi (cells per square inch) or 200 to 400 cpsi, for example, about 300 cells per square inch.

[0046] Alternatively, if the intended use of the catalytic article is the treatment of emissions from a gas turbine, the substrate may have a square or rectangular cross-section. Typically, for such applications, a plurality of washcoated substrates are stacked in a grid pattern to fill a flue duct. Such a substrate may have a cross-sectional area of about 24×24 inches and a depth of about 3.5 inches. The cell density may be in the range of 100 to 400 cpsi, for example, 200 to 300 cpsi.

[0047] One way to apply a wash coating to a honeycomb substrate involves positioning the substrate so that the channels have a substantially vertical orientation, applying a wash coat composition to a first face (e.g., the upper face) of the substrate, and subjecting a second face (e.g., the lower face) on the opposite side of the substrate to at least a partial vacuum to effect movement of the wash coat composition through the channels. The monolithic substrate can be coated in a single dosage, and the wash coat can be applied to the substrate in a single step with the substrate remaining in a single orientation. Alternatively, the substrate can be coated in two injections. For example, in a first dosage, the monolithic substrate is in a first orientation with the first face at the top and the second face at the bottom. The coating is applied to the first face and the length portion of the substrate is coated. Thereafter, the substrate is inverted so that the second face is at the top. Next, the coating is applied to the second face to coat the portion of the substrate that was not coated by the first injection. WO 99 / 47260 describes a general method for coating a monolithic substrate.

[0048] Other ways to coat the substrate include dipping the substrate in a wash coat composition or passing the substrate through a curtain or waterfall of the wash coat composition. Compressed air can be used to blow the fluid into and through the substrate to ensure coating of the cells and to ensure that there are no or substantially no blocked cells.

[0049] If the method further includes steps (d) and (e) as defined above, the application of the impregnation solution to the substrate to form a second coating can be performed in a manner similar to the application of the wash coating in step (b).

[0050] The present disclosure further provides a catalyst article obtained by the above-described method, or using the above-described washcoat composition, or capable of being obtained. In particular, such a catalyst article includes a substrate having a layer of catalyst material coated thereon. The catalyst material is a carrier material impregnated with a PGM component, the carrier material including (i) alumina and (ii) a mixed oxide, a mixture of oxides or a molecular sieve including silica and / or zirconia, and a metal oxide having a BET surface area of at least 100 m 2 / g, at least 150 m 2 / g, at least 200 m 2 / g, at least 250 m 2 / g or at least 300 m 2 / g, the metal oxide including at least one of titania, silica or zirconia. Preferably, the carrier material is a silica-alumina mixed oxide and the metal oxide is titania.

[0051] The catalyst article obtainable by the above process can be used for the treatment of exhaust gases from an internal combustion engine (such as a diesel engine or an internal combustion engine fueled by natural gas or methanol) or a gas turbine. In particular, the catalyst article can be used to reduce formaldehyde and / or carbon monoxide emissions from an internal combustion engine fueled by natural gas or a turbine fueled by natural gas. In addition, the catalyst article may be used for the decomposition of ozone (O 3 ) present in the exhaust gas or air stream.

Examples

[0052] The present invention will be further described with reference to the following examples. These are illustrative and do not limit the present invention.

[0053] ● Comparative Example 1 Alumina powder was slurried in water and ground to a d50 < 10 microns. The slurry had a solids content of ≤ 50% and a pH of ≤ 7. The slurry was applied as a washcoat to a metal honeycomb monolith substrate of 200 cells per square inch (cpsi). The coated substrate was dried and then fired at a temperature of 525 °C. An impregnation solution was prepared using platinum tetraamine acetate. The impregnation solution was coated on the washcoated metal substrate and dried. Next, the impregnated coated substrate was fired at 525 °C. The resulting catalyst had a total PGM loading of 8.25 g ft -3 of Pt. The alumina loading was 1.6 g / in -3 .

[0054] ● Example 2 Alumina-silica (70% alumina, 30% silica) mixed oxide powder was slurried in water and ground to a d50 < 10 microns. The slurry had a solids content of less than 50% and a pH of less than 7. A titania sol having a surface area of ≥ 300 m 2 / g, a pH of about 1, D50 and D90 particle sizes of < 0.2 microns and < 0.5 microns respectively, and a TiO 2 content of about 20 wt% was added to the washcoat and mixed for 1 hour with a high shear mixer. The resulting slurry was then applied as a washcoat to a metal honeycomb monolith substrate of 200 cpsi and dried. An impregnation solution containing platinum nitrate in an acidic solution was prepared. The impregnation solution was applied to the washcoated metal substrate and dried. Next, the impregnated coated substrate was fired at 525 °C. The resulting catalyst had a total PGM loading of 8.25 g ft -3 of Pt. The alumina-silica loading was 1.6 g / in -3 and the titania loading was 0.178 g / in -3 .

[0055] ● Comparative Example 3 Alumina-silica (70% alumina, 30% silica) mixed oxide powder was slurried in water and ground to a d50 < 10 microns. The slurry had a solids content of less than 50% and a pH of less than 7. The resulting slurry was then applied as a washcoat to a 200 cpsi metallic honeycomb monolith substrate and dried. An impregnation solution containing platinum nitrate in an acidic solution was prepared. The impregnation solution was applied to the washcoated metallic substrate and dried. Next, the impregnated coating substrate was calcined at 525 °C. The resulting catalyst had a total PGM loading of 8.25 g ft-3 Pt. The alumina-silica loading was 0.8 g / in-3.

[0056] ● Example 4 Alumina-silica (70% alumina, 30% silica) mixed oxide powder was slurried in water and ground to a d50 < 10 microns. The slurry had a solids content of less than 50% and a pH of less than 7. ≧ 300 m 2 / g surface area, a pH of about 1, D50 and D90 particle sizes of < 0.2 microns and < 0.5 microns respectively, and a TiO 2 content of about 20 wt% was added to the washcoat and mixed for 1 hour with a high shear mixer. The resulting slurry was then applied as a washcoat to a 200 cpsi metallic honeycomb monolith substrate and dried. An impregnation solution containing platinum nitrate in an acidic solution was prepared. The impregnation solution was applied to the washcoated metallic substrate and dried. Next, the impregnated coating substrate was calcined at 525 °C. The resulting catalyst had a total PGM loading of 4 g ft-3 Pt. The alumina-silica loading was 1.6 g / in-3 and the titania loading was 0.178 g / in-3.

[0057] ● Carbon monoxide oxidation activity Core samples of the same volume (1.0 × 3.5 inches) were taken from the catalyst articles prepared in each of the above examples and tested in a synthetic catalytic activity test (SCAT) apparatus at a GHSV of 200,000 hr-1 using the following inlet gas mixture at the selected inlet temperature: 50 ppm of CO, 20 ppm of NO, 15 ppm of C1 propene, 15% O 2 2, 8% H 2 2O, 3% CO 2 and the balance N 2 2. The catalyst samples were tested both under fresh conditions and after hydrothermal sulfur aging (25 ppm of SO 2 2, 15% O 2 2, 8% H 2 2O, 3% CO 2 and the balance N 2 2, 24 hours at 250 °C).

[0058] The results for Comparative Example 1 and Example 2 are shown in Figure 1. Figure 1 compares the CO conversion achieved by the catalyst articles of Examples 1 and 2 at the selected inlet temperature.

[0059] The results for Comparative Example 3 and Example 4 are shown in Figures 2 and 3. Figure 2 compares the CO conversion achieved by the catalyst article of Comparative Example 3 at the selected inlet temperature. Figure 3 compares the CO conversion achieved by the catalyst article of Example 4 at the selected inlet temperature.

[0060] As demonstrated by the data shown in Figure 1, both catalyst articles achieve comparable CO oxidation rates under fresh conditions, but after sulfur aging, the CO oxidation activity of the catalyst article prepared in Example 2 is significantly improved compared to the catalyst article of Example 1.

[0061] As demonstrated by the data shown in Figures 2 and 3, under both fresh and aging conditions, the catalyst article of Example 4 provides comparable or improved CO oxidation rates compared to the catalyst article of Comparative Example 3, despite having a significantly reduced PGM loading.

[0062] Further aspects and embodiments of the present disclosure are set forth in the numbered clauses below.

[0063] Clause: 1. A method for preparing a catalyst article, comprising: (a) preparing a washcoat composition by combining at least the following components: ● a carrier material comprising a mixed oxide, a mixture of oxides or a molecular sieve containing (i) alumina and (ii) silica and / or zirconia; ● a metal oxide sol containing at least one of titania, silica or zirconia; ● a liquid medium; (b) applying the washcoat composition to a substrate to form a washcoat; (c) drying and / or firing the washcoat; and further comprising impregnating the carrier material with a platinum group metal component. A method. 2. The method according to clause 1, wherein step (a) comprises mixing the components together by stirring. 3. The method according to clause 1 or 2, wherein the carrier material comprises a mixed oxide. 4. The method according to clause 1 or 2, wherein the carrier material is a silica-alumina mixed oxide, a zirconia-alumina mixed oxide or an aluminosilicate molecular sieve. 5. The method according to any one of clauses 1 to 4, wherein the carrier material is a silica-alumina mixed oxide. 6. The method according to clause 5, wherein the silica-alumina mixed oxide has a silica content in the range of 1 to 40 wt%, 2 to 35 wt%, 5 to 35 wt% or 5 to 30 wt%. 7. The method according to any one of clauses 1 to 5, wherein the silica-alumina mixed oxide has a silica content in the range of 2 to 10 wt%. 8. The method according to clause 7, wherein the silica-alumina mixed oxide has a silica content of about 5 wt%. 9. The method according to any one of clauses 1 to 5, wherein the silica-alumina mixed oxide has a silica content in the range of 25 to 40 wt%. 10. The method as defined in clause 9, wherein the silica-alumina mixed oxide has a silica content of about 30% by weight. 11. The method as defined in any one of clauses 1 to 10, wherein the carrier material has a D90 particle size of ≦ 50 μm or ≦ 30 μm. 12. The amount of the carrier material used in step (a) is selected such that the prepared catalyst article contains a carrier material loading in the range of 0.5 to 4 g / in 3 , preferably 1 to 2 g / in 3 . The method as defined in any one of clauses 1 to 11. 13. Before step (a), the carrier material is impregnated with a PGM component by contacting the carrier material with an impregnating solution, and the impregnating solution contains the PGM component. The method as defined in any one of clauses 1 to 12. 14. After step (a) and before step (b), the carrier material is impregnated with a PGM component by blending the washcoat composition formed in step (a) with an impregnating solution containing the PGM component. The method as defined in any one of clauses 1 to 13. 15. After step (c), the carrier material is impregnated with a platinum group metal component by contacting the substrate with an impregnating solution, and the impregnating solution contains the platinum group metal component. The method as defined in any one of clauses 1 to 13. 16. After step (c), the carrier material is impregnated with a platinum group metal component, (d) applying an impregnating solution containing a PGM component to the substrate to form a second coating; (e) drying and / or firing the second coating. The method as defined in any one of clauses 1 to 13. 17. The method as defined in any one of clauses 1 to 16, wherein the platinum group metal component contains platinum, palladium, or a mixture of platinum and palladium. 18. The method as defined in clause 17, wherein the platinum group metal component contains platinum. 19. The method as defined in clause 18, wherein the platinum group metal component is platinum nitrate or platinum acetate. 20. The method defined in any one of clauses 13 to 16, or any one of clauses 17 to 19 when dependent on any one of clauses 13 to 16, where the impregnation solution is an aqueous solution of a platinum group metal component. 21. The method defined in any one of clauses 1 to 20, where the amount of platinum group metal used in the impregnation step is selected such that the prepared catalyst article contains a platinum group metal loading in the range of 1 to 100 g / ft 3 , 4 to 90 g / ft 3 , 8 to 50 g / ft 3 or 20 to 35 g / ft 3 . 22. The method defined in any one of clauses 1 to 21, where in step (c), the wash coating is dried at a temperature below 120°C. 23. The method defined in any one of clauses 1 to 22, where in step (c), the wash coating is calcined at a temperature in the range of 450 to 550°C. 24. The method defined in clause 16 or any one of clauses 17 to 23 when dependent on clause 16, where in step (e), the second coating is dried at a temperature below 120°C. 25. The method defined in clause 16 or any one of clauses 17 to 24 when dependent on clause 16, where in step (e), the second coating is calcined at a temperature in the range of 450 to 550°C. 26. The method defined in any one of clauses 1 to 25, where the metal oxide sol is a titania sol. 27. The method defined in any one of clauses 1 to 26, where the metal oxide of the metal oxide sol has a BET surface area of ≧100 m 2 / g, ≧150 m 2 / g, ≧200 m 2 / g, ≧250 m 2 / g or ≧300 m 2 / g. 28. The method defined in any one of clauses 1 to 27, where the metal oxide sol has a D50 particle size of ≦1 μm, ≦0.5 μm or ≦0.2 μm. 29. The method defined in any one of clauses 1 to 28, where the metal oxide sol has a D90 particle size of ≦5 μm, ≦2 μm, ≦1 μm or ≦0.5 μm. 30. The amount of the metal oxide sol used in step (a) is selected such that the prepared catalyst article has a metal oxide loading of ≦ 2.5 g / in 3 , ≦ 2 g / in 3 , ≦ 1 g / in 3 , ≦ 0.5 g / in 3 or ≦ 0.2 g / in 3 , a method according to any one of clauses 1 to 29. 31. A method according to any one of clauses 1 to 30, wherein the liquid medium is water. 32. A method according to any one of clauses 1 to 31, wherein the washcoat composition prepared in step (a) has a solids content of 50 wt% or less. 33. A method according to clause 32, wherein the washcoat composition prepared in step (a) has a solids content in the range of 20 - 40 wt% or 30 - 35 wt%. 34. A method according to any one of clauses 1 to 33, wherein the washcoat composition prepared in step (a) has a pH of < 7, ≦ 5 or about 3. 35. A method according to any one of clauses 1 to 34, wherein the washcoat composition prepared in step (a) has a viscosity in the range of 100 - 1000 centipoise. 36. A method according to any one of clauses 1 to 35, wherein the substrate is a flow-through monolith substrate. 37. A method according to clause 36, wherein the substrate has a substantially cylindrical shape and has a diameter in the range of 20 - 40 inches and a cell density in the range of 200 - 400 cpsi. 38. A method according to clause 36, wherein the substrate has a substantially square or rectangular cross-section. 39. ● A washcoat composition comprising a carrier material comprising (i) alumina and (ii) silica and / or zirconia, a mixture of oxides or a molecular sieve, ● A metal oxide sol comprising at least one of titania, silica or zirconia, ● And a liquid medium. 40. A washcoat composition according to clause 38, wherein the carrier material comprises a mixed oxide. 41. The washcoat composition as defined in clause 38 or 39, wherein the carrier material is a silica-alumina mixed oxide, a zirconia-alumina mixed oxide or an aluminosilicate molecular sieve. 42. The washcoat composition as defined in clause 40 or 41, wherein the carrier material is a silica-alumina mixed oxide. 43. The washcoat composition as defined in clause 42, wherein the silica-alumina mixed oxide has a silica content in the range of 1 to 40% by weight, 2 to 35% by weight, 5 to 35% by weight or 5 to 30% by weight. 44. The washcoat composition as defined in any one of clauses 38 to 42, wherein the silica-alumina mixed oxide has a silica content in the range of 2 to 10% by weight. 45. The washcoat composition as defined in clause 44, wherein the silica-alumina mixed oxide has a silica content of about 5% by weight. 46. The washcoat composition as defined in any one of clauses 38 to 42, wherein the silica-alumina mixed oxide has a silica content in the range of 25 to 40% by weight. 47. The washcoat composition as defined in clause 46, wherein the silica-alumina mixed oxide has a silica content of about 30% by weight. 48. The washcoat composition as defined in any one of clauses 38 to 47, wherein the carrier material has a D90 particle size of ≤ 50 μm or ≤ 30 μm. 49. The washcoat composition as defined in any one of clauses 38 to 48, wherein the carrier material is impregnated with a platinum group metal component. 50. The washcoat composition as defined in clause 49, wherein the platinum group metal component comprises platinum, palladium, or a mixture of platinum and palladium. 51. The washcoat composition as defined in clause 50, wherein the platinum group metal component comprises platinum. 52. The washcoat composition as defined in clause 51, wherein the platinum group metal component is platinum nitrate or platinum acetate. 53. The washcoat composition as defined in any one of clauses 38 to 52, wherein the metal oxide sol is a titania sol. 54. The metal oxide sol is ≥ 100 m2 / g, ≥ 150 m 2 / g, ≥ 200 m 2 / g, ≥ 250 m 2 / g or ≥ 300 m 2 A washcoat composition as defined in any one of clauses 38 to 53, having a BET surface area of / g. 55. A method as defined in any one of clauses 38 to 54, wherein the metal oxide sol has a D50 particle size of ≤ 1 μm, ≤ 0.5 μm or ≤ 0.2 μm. 56. A method as defined in any one of clauses 38 to 55, wherein the metal oxide sol has a D90 particle size of ≤ 5 μm, ≤ 2 μm, ≤ 1 μm or ≤ 0.5 μm. 57. A washcoat composition as defined in any one of clauses 38 to 56, wherein the liquid medium is water. 58. A washcoat composition as defined in any one of clauses 38 to 57, having a solids content of 50 wt% or less. 59. A washcoat composition as defined in clause 58, having a solids content in the range of 20 - 40 wt% or 30 - 35 wt%. 60. A washcoat composition as defined in any one of clauses 38 to 59, having a pH of < 7, ≤ 5 or about 3. 61. A washcoat composition as defined in any one of clauses 38 to 60, having a viscosity in the range of 100 - 1000 centipoise. 62. A washcoat composition as defined in any one of clauses 38 to 61, further comprising an organic additive.

Claims

1. 1. A method of preparing a catalyst article, comprising: (a) at least the following components: A support material comprising a mixed oxide, a mixture of oxides or a molecular sieve comprising (i) alumina and (ii) silica and / or zirconia; A metal oxide sol containing at least one of titania, silica, or zirconia; preparing a washcoat composition by combining a liquid medium; (b) applying the washcoat composition to a substrate to form a washcoat; (c) drying and / or baking the washcoating; The method further comprises the step of impregnating said support material with a platinum group metal component.

2. 2. The method of claim 1, wherein the support material is a silica-alumina mixed oxide, a zirconia-alumina mixed oxide or an aluminosilicate molecular sieve.

3. The process according to claim 1 or 2, wherein the support material is a silica-alumina mixed oxide.

4. 4. The method of claim 3, wherein the support material is a silica-alumina mixed oxide having a silica content in the range of 1 to 40 wt.%, 2 to 35 wt.%, 5 to 35 wt.%, or 5 to 30 wt.%.

5. The method according to any one of claims 1 to 4, wherein the support material has a D90 particle size of ≦50 μm or ≦30 μm.

6. 6. The method according to claim 1, wherein prior to step (a), the support material is impregnated with a PGM component by contacting the support material with an impregnation solution, the impregnation solution comprising the PGM component.

7. 6. The method of any one of claims 1 to 5, wherein the support material is impregnated with the PGM component after step (a) and before step (b) by blending the washcoat composition formed in step (a) with an impregnation solution comprising the PGM component.

8. After step (c), impregnating the support material with a platinum group metal component; (d) applying an impregnation solution containing the PGM component to the substrate to form a second coating; The method of any one of claims 1 to 5, further comprising: (e) drying and / or baking the second coating.

9. The method of any one of claims 1 to 8, wherein the platinum group metal component comprises platinum, palladium, or a mixture of platinum and palladium.

10. The method of any one of claims 1 to 9, wherein the platinum group metal component is platinum nitrate or platinum acetate.

11. The method according to any one of claims 1 to 10, wherein the metal oxide sol is a titania sol.

12. The metal oxide of the metal oxide sol is ≧100 m ２ / g, ≧150m ２ / g, ≧200m ２ / g, ≧250m ２ / g or ≧300m ２ The method according to any one of claims 1 to 11, wherein the SiO2 has a BET surface area of ​​0.1 to 0.5 g / g.

13. 13. The method of any one of claims 1 to 12, wherein the metal oxide sol has a D50 particle size of ≦1 μm, ≦0.5 μm or ≦0.2 μm.

14. a support material comprising a mixed oxide, a mixture of oxides or a molecular sieve comprising (i) alumina and (ii) silica and / or zirconia; A metal oxide sol containing at least one of titania, silica, or zirconia; A washcoat composition comprising: a liquid medium.

15. The washcoat composition of claim 14, wherein the support material is a silica-alumina mixed oxide and the metal oxide sol is a titania sol.

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