KR20140147658A - Multi-component filters for emissions control - Google Patents

Abstract

Catalyst articles, systems and methods for treating an exhaust gas stream are described. A catalytic article comprising a wall flow filter having a gas permeable wall, a hydrolysis catalyst, an optional soot oxidation catalyst, a selective catalytic reduction catalyst permeating the wall, an ammonia oxidation catalyst and an oxidation catalyst for oxidizing CO and hydrocarbons, do. Also provided is a method of treating an exhaust gas stream comprising ammonia precursors such as soot, urea, ammonia, NO _x , CO and hydrocarbons.

Description

[0001] MULTI-COMPONENT FILTERS FOR EMISSIONS CONTROL [0002]

The present invention relates to a catalytic article, an emission treatment system comprising a catalytic article, and a method for reducing contaminants in an exhaust gas stream. More particularly, the present invention relates to multi-component filters, systems, and methods for using them with lean-burn engines, including diesel engines and lean-burn gasoline engines.

The operation of lean-burn engines, such as diesel engines and lean-burn gasoline engines, provides users with excellent fuel economy and has very low gaseous hydrocarbon and carbon monoxide emissions due to operating at high air / fuel ratios under low fuel consumption conditions . In particular, diesel engines also provide significant advantages over gasoline engines in terms of their durability and their ability to generate high torque at low speeds.

Diesel engine exhaust gases include particulate emissions such as soot and gaseous emissions such as carbon monoxide, unburned or partially burned hydrocarbons and nitrogen oxides (collectively referred to as NO _x ), as well as condensed phases comprising so-called particulate or particulate matter It is a heterogeneous mixture containing substances (liquid and solid). Catalyst compositions often disposed on one or more monolithic substrates are located in engine exhaust systems to convert some or all of these exhaust components to harmless compounds. For example, the diesel exhaust system may contain at least one diesel oxidation catalyst, a soot filter, and a catalyst for the reduction of NO _x . These components are expensive and take up considerable space in the vehicle.

Therefore, there is a continuing need to improve the efficiency of the exhaust treatment system without adding the size and complexity of the system.

summary

An embodiment of the present invention relates to a catalytic article for removing emissions from a gas stream containing soot, ammonia, ammonia precursors NO _x , CO and hydrocarbons. The catalytic article includes a wall flow filter for capturing soot in a gas stream. The filter has an inlet end and an outlet end that define the overall length. The filter has a plurality of axially extending inlet channels and a gas permeable wall of constant thickness forming the outlet channels. Each inlet channel has an inlet wall, an open inlet end and a plugged outlet end, each outlet channel having an outlet wall, a plugged inlet end and an open outlet end. Each inlet channel has an adjacent outlet channel. The article includes an optional hydrolysis catalyst that promotes the hydrolysis of the ammonia precursor. The hydrolysis catalyst is coated on a portion of the inlet wall of the inlet channel extending from the inlet end. A selective catalytic reduction catalyst permeates the gas permeable wall to facilitate the conversion of NO _x to N _{2 in} the gas stream in the presence of excess oxygen. The ammonia oxidation catalyst coats the length of the outlet wall of the outlet channel to promote selective oxidation of ammonia in the gas stream to N ₂ . The oxidation catalyst is coated on a portion of the outlet wall of the outlet channel extending from the outlet end toward the inlet end to promote oxidation of CO and hydrocarbons to CO ₂ . In one or more embodiments, the wall flow type filter is a high efficiency filter.

In some embodiments, a hydrolysis catalyst is present and extends from the inlet end to about 50% of the wall-flow filter length so that the gas stream is first disposed to meet the hydrolysis catalyst. In some embodiments, a hydrolysis catalyst is present and extends from about 1/4 inch from the inlet end to a length in the range of about 10% of the wall flow filter length. In at least one embodiment, a hydrolysis catalyst is present and comprises titania.

In at least one embodiment, the selective catalytic reduction catalyst extends along the entire length of the wall flow filter. In some embodiments, the selective catalytic reduction catalyst loading is in the range of about 0.25 g / in ³ to about 2.5 g / in ³ . In one or more embodiments, the selective catalytic reduction catalyst comprises a metal promoted molecular sieve.

Some embodiments of the catalytic article also include a soot oxidation catalyst prior to the SCR catalyst. In at least one embodiment, the soot oxidation catalyst permeates the gas permeable wall. In some embodiments, the soot oxidation catalyst constitutes a layer that penetrates the inlet side of the gas permeable wall. According to some embodiments, the layer permeates the gas permeable wall to a depth of about 50% or less of the wall thickness. In a specific embodiment, the soot oxidation catalyst constitutes a layer on the inlet wall. The soot oxidation catalyst of at least one embodiment comprises zirconia stabilized cerium oxide.

In some embodiments, the ammonia oxidation catalyst extends to less than about 50% of the total length of the catalytic article. In some embodiments, the ammonia oxidation catalyst extends from the oxidation catalyst to no more than about 50% of the total length of the catalyst article.

In at least one embodiment, the oxidation catalyst extends a length of about 2 inches or less from the outlet end of the outlet channel. In some embodiments, the oxidation catalyst overlaps with a portion of the ammonia oxidation catalyst. In at least one embodiment, the oxidation catalyst does not substantially overlap with the ammonia oxidation catalyst. In some embodiments, the oxidation catalyst comprises a platinum group metal on a high surface area support.

A further embodiment of the present invention relates to a method of treating an exhaust stream comprising soot, urea, ammonia, NO _x , CO and hydrocarbons. The hydrolysis catalyst located at the inlet end of the inlet channel of the catalytic article promotes the hydrolysis of urea. The soot is filtered from the gas stream by passing the gas stream after the hydrolysis catalyst through a gas permeable wall in the catalyst article to form a filter cake on the walls of the inlet channel. Is promoted by a selective catalytic reduction catalyst permeating the gas permeable wall of the catalytic article so that ammonia and NO _x react to form N ₂ . Ammonia is oxidized in the gas stream exiting the gas permeable wall of the catalytic article by the acceleration of the ammonia oxidation catalyst coated on the outlet wall of the catalytic article. CO and hydrocarbons are oxidized by the acceleration of the oxidation catalyst coated on the outlet wall at the outlet end of the catalytic article to form carbon dioxide and water.

In some embodiments, the soot is oxidized by the acceleration of the soot oxidation catalyst prior to the selective catalytic reduction catalyst. In one or more embodiments, soot is oxidized after formation of the filter cake.

A further embodiment of the present invention relates to an engine and an emission treatment system comprising a catalytic article as described herein, which is located downstream of the engine and in communication with the engine. In some embodiments, the effluent treatment system also includes a diesel oxidation catalyst located downstream of the engine and upstream of the catalytic article and in communication with both. In at least one embodiment, the effluent treatment system also includes a reducing agent injector located upstream of the catalytic article.

1 shows a perspective view of a catalytic article according to one or more embodiments of the present invention;
Figure 2 shows a schematic cross-sectional view of a wall-flow monolith according to one or more embodiments of the present invention;
Figure 3 shows a schematic cross-sectional view of a catalyst article according to one or more embodiments of the present invention;
Figure 4 depicts a schematic cross-sectional view of a catalyst article according to one or more embodiments of the present invention;
5 shows a schematic diagram of an exhaust treatment system in accordance with one or more embodiments of the present invention;
Figure 6 depicts a schematic diagram of an exhaust treatment system in accordance with one or more embodiments of the present invention;
Figure 7 depicts a schematic diagram of an exhaust treatment system in accordance with one or more embodiments of the present invention;
Figure 8 shows a schematic view of an exhaust treatment system in accordance with one or more embodiments of the present invention.

Before describing certain exemplary embodiments of the present invention, it is to be understood that the invention is not limited to the details of construction or process steps described in the following description. The invention is capable of other embodiments and of being practiced or carried out in various ways.

The following terms have their respective meanings described below for the purposes of this application.

"Platinum group metal component" means a platinum group metal or one of their oxides. Platinum group metals include platinum, palladium, rhodium, ruthenium, osmium, and iridium.

"Washcoat" is used in the art to describe a thin, adhesive coating of catalytic or other materials applied to a refractory substrate, such as a honeycomb-through monolith substrate or filter substrate, that is sufficiently porous to allow the gas stream being treated to pass therethrough. It has meaning.

The term "washcoat " refers to a catalyst coating consisting of a powdered material on a substrate, the powdered material being obtained from a dried slurry of a liquid medium, typically an insoluble oxide or salt in an aqueous medium. The washcoat is distinguished from the impregnation of a catalytic material in solution of the soluble precursor applied to the substrate, for example by solution impregnation. The washcoat is also distinguished from the process of thin film growth by an oxide growth process or a sol-gel process.

As used herein, the terms "exhaust stream" and "engine exhaust stream" refer to emissions downstream of one or more other catalyst system components, including, but not limited to, engine emissions as well as diesel oxidation catalysts and / or soot filters.

By "communication" is meant that the component and / or conduit are coupled so that exhaust gas or other fluid can flow between the component and / or conduit.

"Downstream" means the location of an element in the exhaust stream in a path that is further from the engine than the preceding element. For example, when a diesel particulate filter is referred to as being downstream from a diesel oxidation catalyst, the exhaust gas from the engine at the exhaust line flows through the diesel oxidation catalyst before flowing through the diesel particulate filter. In other words, "upstream" means an element located closer to the engine than another element.

The term "decrease" means that the amount is decreased, and "decrease " means that the amount is decreased for some reason.

By "selective catalytic reduction catalyst" or "SCR catalyst" is meant a catalyst effective in promoting conversion of NO _x in the gas stream to nitrogen in the presence of excess oxygen. The term "SCR function" or "SCR reaction" means the chemical process represented by the stoichiometric reaction formula 1 herein. The SCR catalyst is effective to promote the reaction over the operating temperature range of the lean burn engine, e.g., from 150 캜 to about 500 캜 or from about 200 캜 to about 450 캜. Thus, the platinum group metals are excluded from the "SCR catalyst" because the material does not promote the SCR reaction at temperatures in excess of about 200-250 [deg.] C.

As is well understood by those skilled in the art, catalysts are substances that affect the rate of chemical reactions. When a catalyst is said to convert a species or react with a chemical species, etc., the catalyst promotes the reaction (e.g., catalyst) but is not consumed in the reaction. For example, SCR catalysts can be said to convert NO _x to nitrogen in the presence of excess oxygen. It will be understood by those skilled in the art that this means that the SCR catalyst promotes the conversion of NO _x to nitrogen in the presence of excess oxygen.

An embodiment of the present invention relates to a filter substrate having various functions for emission control. In order to obtain various functions of emission control, the order of the catalyst in which the gas flow is encountered is described. In one embodiment, the gas contacts the hydrolysis catalyst coated on the inlet channel walls at the inlet end of the substrate. That is, there is a region of the hydrolysis catalyst on the inlet wall in the plug region of the filter, possibly extending a short distance into the wall flow region. The SCR catalyst is disposed in the wall between the inlet plug and the outlet plug. The ammonia oxidation catalyst is disposed on the outlet channel wall upstream of the plug region and the CO / hydrocarbon oxidation catalyst is coated in the region on the outlet channel wall within the plug region. The exhaust stream containing soot, urea, ammonia, isocyanic acid (also known as ammonia precursor), water, NO _x , CO and hydrocarbons first meets the hydrolysis catalyst, where the decomposition of urea (and ammonia precursor) It then meets the filter wall, where the soot is filtered from the stream, where it meets an SCR catalyst where ammonia reacts with NO _x to form N ₂ , then undergoes an ammonia oxidation catalyst, where there is excess or residual ammonia Finally, a CO / hydrocarbon oxidation catalyst is encountered in which any residual CO or hydrocarbons are oxidized to carbon dioxide and water. During active regeneration, CO generated from partial oxidation of soot on the filter also reacts on CO / hydrocarbon oxidation catalysts. Embodiments of the variant can be referred to as 6-way catalysts.

In another embodiment, the order is the same as the addition of a soot oxidation catalyst disposed on the inlet channel walls or directly adjacent to the inlet channels. The soot oxidation catalyst will aid in the passive regeneration of the soot during normal operation and the soot oxidation catalyst generally should not react with the incidental ammonia to react with the SCR catalyst below it. Otherwise, the soot oxidation catalyst and the SCR catalyst may be present in the horny water or may be mixed together through the wall and spread over the wall to enable simultaneous oxidation of soot and selective reduction of NO _x . Embodiments of such variants can be referred to as 7-way catalysts.

One aspect of the present invention relates to catalysts. According to one or more embodiments, the catalyst may be disposed on a monolithic substrate with a washcoat layer. As used herein and in Heck, Ronald and Robert Farrauto, Catalytic Air Pollution Control, New York: Wiley-Interscience, 2002, pp. 18-19, the washcoat layer comprises a layer of material that is distinguished by the composition of the material disposed on the surface of the monolithic substrate or underlying washcoat layer. The catalyst may comprise at least one washcoat layer, and each washcoat layer may have a unique chemical catalytic function.

In order to provide one filter substrate with various emission control functions, it is desirable to regulate the order of the catalysts in which the gas flow is encountered. One or more embodiments of the present invention are directed to a catalyst article 100 for removing emissions from a gaseous stream containing soot ammonia, ammonia precursors, NO _x , CO, and hydrocarbons. 1-3, the catalyst article 100 includes a substrate 50, often referred to as a carrier or carrier substrate. In one or more embodiments, the substrate 50 is a wall flow type filter. The substrate 50 has an inlet end 54 and an outlet end 56 defining an overall length L. [ The substrate 50 also has a gas permeable wall 53 having a thickness T that defines a plurality of axially extending inlet channels 64 and outlet channels 66. Each inlet channel 64 has an outlet end 56 with an inlet wall 65, an open inlet end 54 and an outlet plug 60. Each outlet channel 66 has an outlet wall 67, an inlet end 54 with an inlet plug 58 and an open outlet end 56. Each inlet channel 64 has an adjacent outlet channel 66 that forms an opposite checkerboard pattern at the inlet end 54 and outlet end 56 as shown in FIG. The gas stream entering through the unplugged inlet end 54 of the inlet channel 64 is stopped by the outlet plug 60 and diffused into the outlet channel 66 through the gas permeable wall 53. The gas can not return back to the inlet channel 64 due to the pressure drop across the wall 53. In general, the inlet plug 58 prevents gas from entering the outlet channel 66 directly and may help prevent it from flowing from the outlet to the inlet across the wall. The substrate 50 is effective to remove at least a portion of the particulate material from the gaseous stream.

Referring to Figures 3 and 4, some embodiments of the present invention include an optional hydrolysis catalyst 110 that promotes hydrolysis of the ammonia precursor. The hydrolysis catalyst can be said to hydrolyze the ammonia precursor, but it will be understood by those skilled in the art that the hydrolysis catalyst does not actually hydrolyze the ammonia precursor, but rather promotes the hydrolysis reaction of the ammonia precursor. The hydrolysis catalyst 110 is often referred to as a urea hydrolysis catalyst. However, regardless of any particular theory of operation, it is understood by those skilled in the art that the urea hydrolysis catalyst catalyzes the hydrolysis of isocyanic acid, the pyrolysis product of urea. The hydrolysis catalyst 110 is coated on a portion of the inlet wall 65 extending from the inlet end 54 of the substrate 50. In one or more embodiments, the hydrolysis catalyst 110 is arranged such that the gas stream meets the hydrolysis catalyst 110 initially (i.e., before encountering another catalyst).

The length along which the hydrolysis catalyst 110 extends along the length L of the substrate 50 may vary depending on the requirements of the catalyst article 100 obtained. In some embodiments, the hydrolysis catalyst 110 extends from the inlet end 54 to about 50% of the length of the substrate 50. In one or more embodiments, the hydrolysis catalyst 110 extends the same length as the inlet plug 58 of the adjacent gas channel. In various embodiments, the hydrolysis catalyst 110 may range from about 5% to about 50% of the length of the substrate 50 from the inlet end 54, or from about 1/4 inch to about 50% of the length of the substrate 50, Or a length in the range of about 5% to about 10% of the length of the substrate 50, or a length of about 1/4 of an inch, or a length of more than about 1/4 of an inch of the length of the substrate 50, 60%, 50%, 40% or more of the length of the substrate 50, or more than 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% , 30%, 20%, or less than 10%. In one or more embodiments, the hydrolysis catalyst 110 extends from about 1/4 inch from the inlet end 54 of the substrate 50 to a length in the range of about 10% of the length L of the substrate.

The hydrolysis catalyst 110 has a particle size effective to ensure that substantially all of the hydrolysis catalyst 110 remains on the surface of the inlet wall 65. As used herein and in the appended claims, the term "substantially all of the hydrolysis catalyst remains on the surface" means that less than about 20% of the hydrolysis catalyst 110 penetrates the porous wall 53 of the substrate 50 .

The hydrolysis catalyst may be any suitable hydrolysis catalyst known to those skilled in the art. In some embodiments, the hydrolysis catalyst comprises at least one of titania, gamma-alumina, and transition metal oxide. Each of these materials may be stabilized or unstabilized. The stabilizer may be any suitable stabilizer including, but not limited to, ceria, zirconia, lanthana, titania, tungsten, and silica.

Substrate 50 includes a selective catalytic reduction catalyst 120 (SCR catalyst) permeable to gas permeable wall 53. The SCR catalyst 120 is effective to promote the conversion of NO _x to nitrogen in the gas stream in the presence of excess oxygen. The term "SCR function" or "SCR reaction" will be used herein to mean a chemical process represented by the following stoichiometric Reaction Scheme 1.

<Reaction Scheme 1>

4NO _x + 4 NH ₃ + (3-2x) O ₂ → 4 N ₂ + 6 H ₂ O

More generally, this will mean any chemical process in which NO _x and NH ₃ or other reducing agent are combined to produce preferably N ₂ . The term "SCR composition" means a material composition effective to catalyze the SCR function or to facilitate the conversion of NO _x . As used herein, the term "permeated " when used to describe the dispersion of the catalyst on a substrate means that the catalyst composition is dispersed through the walls of the substrate. Compositions penetrating walls are distinguished from compositions that coat the exterior of the walls and do not stay in the pores through the walls of the substrate. In some embodiments, the SCR composition has a soot oxidizing function.

The SCR catalyst extends along substantially the entire length of the wall flow filter to ensure that the entire exhaust stream is passed through the SCR catalyst 120 (i.e., to avoid bypassing the catalyst). The term "substantially full length" as used herein means that the SCR catalyst 120 extends at least about 95% of its overall length, and that some portion (s) Means that it is located at a certain place along the length of.

In some embodiments, the SCR component comprises a metal promoted molecular sieve. That is, a metal selected from one of VB, VIB, VIIB, VIIIB, IB or IIB of the periodic table is deposited on the outer surface of the molecular sieve or on an extra-framework site in its channel, cavity or cage There is a molecular sieve. The metal may be in any of several forms including, but not limited to, a zero valent metal atom or cluster, an isolated cation, a mononuclear or polynuclear oxyanion, or an extended metal oxide. In one or more embodiments, the metal comprises iron, copper, and mixtures or combinations thereof.

International Association of zeolite molecular sieves (International Zeolite Association, IZA), the database (Database of the zeolite structure issue of Zeolite Structures ). &Lt; RTI ID = 0.0 &gt; [0031] &lt; / RTI &gt; The framework structure includes, but is not limited to, those of the CHA, FAU, BEA, MFI, MOR type. Non-limiting examples of aluminosilicate zeolites having such a structure include charbazite, sporesite, zeolite Y, superstable zeolite Y, beta zeolite, mordenite, silicalite, zeolite X and ZSM-5.

In one or more embodiments, the SCR component comprises an aluminosilicate molecular sieve having a CHA crystal backbone type, a SAR greater than about 15, and a copper content greater than about 0.2 weight percent. In a more specific embodiment, the SAR is at least about 10 and the copper content is from about 0.2 wt% to about 5 wt%. The zeolite with CHA structure includes, but is not limited to, natural antimatter, SSZ-13, LZ-218, Linde D, Linde R, Phi, ZK-14 and ZYT-6. Other suitable zeolites are also described in U.S. Patent No. 7,601,662, entitled " Copper CHA Zeolite Catalyst ", the entire contents of which are incorporated herein by reference. In at least one embodiment, the SCR composition comprises copper antifouling.

A molecular sieve composition having a zeolite framework structure but containing other components, such as phosphorus, in its framework structure may be used in the SCR component according to embodiments of the present invention. Non-limiting examples of other molecular sieve compositions suitable as SCR components include silicoaluminophosphates SAPO-34, SAPO-37, SAPO-44. The synthesis of synthetic forms of SAPO-34 is described in U.S. Patent 7,264,789, which is incorporated herein by reference.

The selective catalytic reduction catalyst 120 may be present in any amount suitable to effectively promote the removal of NO _x from the gas stream without substantially adversely affecting the system back pressure. In various embodiments, the amount of SCR catalyst 120 supported is in the range of about 0.25 g / in ³ to about 2.5 g / in ³ , or in the range of about 0.38 g / in ³ to about 2.0 g / in ³ , in ³ to about 1.5 g / in ³ , or in the range of about 0.63 g / in ³ to about 1.25 g / in ³ .

Referring again to Figures 3 and 4, the catalytic article 100 includes an ammonia oxidation catalyst 130 on the outlet wall 67 of the outlet channel 66. The ammonia oxidation catalyst 130, also referred to as the ammonia oxidation composition, is effective in promoting the oxidation of ammonia in the gas stream. The term "NH ₃ oxidation function" will be used herein to mean a chemical process represented by the following reaction scheme 2.

<Reaction Scheme 2>

4 NH ₃ + 3 O ₂ → 2 N ₂ + 6 H ₂ O

More preferably, this would mean a process in which NH ₃ reacts with oxygen to produce NO, NO ₂ , N ₂ O or preferably N ₂ . The term "NH ₃ oxidation composition" or "ammonia oxidation catalyst" means a material composition effective to catalyze the NH ₃ oxidation function.

The ammonia oxidation catalyst 130 coats the entire length or a portion of the length of the outlet wall 67. It is not necessary to have an ammonia oxidation catalyst 130 coating that coats the entire length of the outlet wall 67 to effectively promote the oxidation of ammonia in the gas stream. When coating the entire length of the outlet wall 67, the back pressure in the system may increase to undesired levels. In some embodiments, the ammonia oxidation catalyst 130 extends to less than about 50% of the total length of the catalytic article. The ammonia oxidation catalyst 130, in some embodiments, extends from the oxidation catalyst 140 (described below) to less than about 50% of the total length of the catalyst article. In various embodiments, the ammonia oxidation catalyst 130 comprises about 5% to about 75%, or about 10% to about 65%, or about 15% to about 60%, or about 20% To about 55%, or from about 25% to about 50%. In various embodiments, the ammonia oxidation catalyst 130 extends from about 1/12 to about 1/4 of the length of the substrate 50.

The ammonia oxidation catalyst 130 may be any suitable catalyst known to those skilled in the art. According to one or more embodiments, the ammonia oxidation catalyst (130) is a zeolite or non-zeolite molecular sieves include, which International Zeolite Association (IZA) issued by the zeolite structure of the database (Database of Zeolite Structures . &Lt; / RTI &gt; The skeletal structure includes, but is not limited to, those of the CHA, FAU, BEA, MFI, and MOR types. In some embodiments, molecular sieves may be exchanged for metal components distributed on the outer surface of the molecular sieve, or in channels, cavities, or cages.

The ammonia oxidation catalyst has two components; SCR catalyst component and oxidation catalyst component. The two components are generally present in two layers with a bottom layer (i.e. the second layer where the gas stream meets) with an upper coating (i.e. the first layer where the gas stream meets) and an oxidizing catalyst component, which is the SCR catalyst component . However, it is also possible to provide a single-layer ammonia oxidation catalyst comprising a mixture of an SCR catalyst component and an oxidation catalyst component. In some embodiments, the oxidizable component layer contains a platinum group metal on alumina or other support directly over the substrate. In some embodiments, the ammonia oxidation catalyst comprises both an SCR catalyst and a platinum group metal containing catalyst, and substantially none can be absent. As used in this specification and the appended claims, the term "substantially absent " when referring to an ammonia oxidation catalyst means that the component in question is intentionally present in the composition. For example, where the composition is known to have a platinum group metal, the composition is substantially absent from the platinum group metal whether intentionally added or inherently present.

Using only platinum group metals may result in compositions having ammonia oxidation activity. However, this kind of composition is not selective for the production of molecular nitrogen and can produce undesirable products. In some embodiments, the ammonia oxidation catalyst has a selectivity for N ₂ greater than about 70% at 300 ° C. In various embodiments, the ammonia oxidation catalyst has a selectivity for N ₂ of greater than about 50%, 55%, 60%, 65%, 75%, 80%, 85% or 90% as measured at 300 ° C.

3 and 4, the catalytic article 100 includes an oxidation catalyst 140 coated on a portion of the outlet wall 67 of the outlet channel 66 of the substrate 50. The oxidation catalyst 140 is coated on a portion of the substrate extending from the outlet end 56 of the substrate 50 toward the inlet end. The oxidation catalyst 140 of some embodiments is effective to promote oxidation of carbon monoxide and hydrocarbons in the gas stream.

The length of the oxidation catalyst 140 may vary depending on the needs of the catalyst article 100. In various embodiments, the oxidation catalyst 140 may be about 3 inches, or about 2 inches, or about 1 inch, or about 1/2 inch, or about 1/4 inch, from the outlet end 56 of the outlet channel 67 Or less. In one or more embodiments, the oxidation catalyst 140 extends so that the length of the substrate 50 is approximately equal to the extended length of the outlet plug 60. This ensures that the gaseous stream diffusing through the porous wall 53 is in contact with the ammonia oxidation catalyst 130 prior to the oxidation catalyst 140.

In some embodiments, the oxidation catalyst 140 does not substantially overlap with the ammonia oxidation catalyst 130. As used herein and in the appended claims, the term "substantially non-overlapping" when referring to the oxidation catalyst 140 refers to about 10%, or less than about 5% of the oxidation catalyst 140, 130). In one or more embodiments, the oxidation catalyst 140 overlaps a portion of the ammonia oxidation catalyst 130.

Oxidation catalyst 140 may be any suitable oxidation catalyst known to those skilled in the art. In some embodiments, the oxidation catalyst 140 comprises a platinum group metal supported on a high surface area support (e.g., a refractory metal oxide). In one or more embodiments, the high surface area refractory metal oxide is alumina or stabilized alumina. The oxidation catalyst 140 may be a single region or multiple regions having respective regions that occupy different lengths of the substrate. In at least one embodiment, the oxidation catalyst comprises two regions, an inlet region and an outlet region.

Referring to FIG. 4, in some embodiments, the catalyst article 100 may include a soot oxidation catalyst 150 prior to the SCR catalyst 120. The soot oxidation catalyst 150 is a soot layer formed on the inlet wall 65 of the inlet channel 64 when the exhaust gas stream passes through the catalyst article 100 as the name implies, .

The soot oxidation catalyst 150 may be coated on the inlet wall 65 of the inlet channel 64 or may penetrate the inlet channel 64 side of the wall 53 of the substrate 53. In some embodiments, the soot oxidation catalyst 150 is coated on the inlet wall 65 of the inlet channel 64. When coated on the inlet wall 65, the soot oxidation catalyst 150 may extend over the entire length of the substrate or a partial length of the substrate. When the soot oxidation catalyst 150 extends over the entire length of the substrate, it forms a layer beneath the hydrolysis catalyst 110. The soot oxidation catalyst 150 extends to a partial length of the substrate, which may extend from the approximate end of the hydrolysis catalyst 110 to the outlet plug 60, or anywhere in between.

In some embodiments, the soot oxidation catalyst 150, which forms a layer that penetrates the porous wall 53, has a different composition than the SCR catalyst 120. When the soot oxidation catalyst 150 penetrates the wall 53 of the substrate 50 it may form a layer on the inlet side of the wall 53 or it may be intimately mixed with the SCR catalyst 120 , And SCR catalyst (120). In some embodiments, the soot oxidation catalyst 150 layer penetrates the inlet side of the gas permeable wall 53 to a depth of less than about 50% of the wall thickness T. [ In various embodiments, the soot oxidation catalyst 150 layer is formed on the inlet side of the wall 53 at about 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10% % Or less than 5%. In various embodiments, the soot oxidation catalyst 150 layer extends to a depth in the range of about 10% to about 40%, or about 20% to about 30%, of the wall thickness (T). In at least one embodiment, the soot oxidation catalyst 150 layer extends to a depth of about 25% of the wall thickness T. [

The soot oxidation catalyst 150 may be any suitable soot oxidation catalyst composition. Generally, the soot oxidation catalyst 150 is a highly selective material. Platinum group metals can oxidize soot, but these materials are also undesirable because they can also oxidize ammonia. Thus, in some embodiments, the soot oxidation catalyst 150 comprises less than about 40% platinum group metal, or less than about 30% platinum group metal, or less than about 20% platinum group metal, or less than about 10% platinum group metal do.

In at least one embodiment, the soot oxidation catalyst 150 is zirconia stabilized ceria. The soot oxidation catalyst may be a SCR catalyst having some soot oxidation properties, such as vanadia. In some embodiments, the soot oxidation catalyst 150 is a vanadia or stabilized titania or cerium / zirconium mixture or cerium phosphate or spinel supported on titania.

materials

Suitable substrates for use with embodiments of the present invention include wall flow filters. These filters generally have a plurality of microscopic, substantially parallel gas flow paths extending along the longitudinal axis of the substrate as shown in Figures 1 and 2 and described above. Typically, each path is blocked at one end of the substrate body and the other path is blocked at the opposite end-face. The path may have any shape, including, but not limited to, a rectangular, square, circular, oval, triangular, hexagonal, or other polygonal shape. The thickness of the wall can vary depending on the desired properties of the resulting catalytic article. Generally, when pore sizes are similar, larger wall thicknesses will have a greater impact on system backpressure. The wall thickness typically ranges from about 0.002 to about 0.1 inches.

Suitable wall-flow filter substrates may comprise ceramic-like materials such as cordierite, alpha-alumina, silicon carbide, silicon nitride, zirconia, mullite, ritira pyrochlore, alumina-silica-magnesia or zirconium silicate, or porous, refractory metals have. The wall flow type substrate may be formed of a ceramic filter composite material. Suitable wall-flow substrates are formed from cordierite and silicon carbide. The material is able to withstand the high temperatures encountered in the treatment of the environment, particularly the exhaust stream.

Wall flow filters for use with embodiments of the present invention may have various porosities and average pore sizes. In various embodiments, the wall flow filter has a porosity in the range of at least about 40%, or from about 40% to about 80%. Some embodiments of the wall flow filter have an average pore size in the range of at least 5 micrometers, or from about 5 micrometers to about 30 micrometers. In one or more embodiments, the substrate is a filter of high high filtration efficiency. A filter with a high filtration efficiency removes more than 85% of the soot particles on a mass basis.

Emission treatment system

One aspect of the present invention relates to an emission treatment system for treating exhaust gases. 5 shows an embodiment of the present invention wherein the catalyst article 100 described above is located downstream of the engine 10 and communicates with the engine. In one or more embodiments of the present invention, the effluent treatment system comprises an engine 10, and a catalytic article 100 as described above that is located downstream of and in communication with the engine 10. As used herein and in the appended claims, the term "predominantly comprised" means that additional components may be included, unless other catalysts are added. For example, FIG. 6 shows an emission treatment system consisting primarily of the engine 10 and the catalytic article 100 downstream as described above. A reducing agent injector 11 system is located therebetween and communicates with the exhaust stream between the engine 10 and the catalyst article 100. The inclusion of the reducing agent injector 11 does not add any other catalyst to the system other than just the reactants.

7 shows another embodiment of the present invention in which the diesel oxidation catalyst 12 is located downstream of the engine 10 and in communication therewith. The diesel oxidation catalyst 12 is located upstream and communicates with the catalyst article 100. Exhaust gas exiting the engine 10 passes through the diesel oxidation catalyst 12 and reaches the catalyst article 100 described above. In one or more embodiments, the effluent treatment system is predominantly comprised of a diesel oxidation catalyst that communicates with both downstream of the engine and upstream of the catalyst article as described herein.

Figure 8 shows an embodiment of the present invention. The exhaust gas from the engine 10 passes through the diesel oxidation catalyst 12 which is located downstream of the engine 10 and communicates with it. The exhaust gas exiting the diesel oxidation catalyst 12 is combined with the reducing agent from the reducing agent injector 11 located downstream of the diesel oxidation catalyst 12 and upstream of the catalytic article 100 described herein. The effluent passes through the catalyst article 100 before being discharged from the exhaust system. The reducing agent injector 11 may be configured to inject, for example, a hydrocarbon, an on-board fuel, a reducing agent, air, urea or ammonia. A heater, a burner or an ignition source may also be included in the reducing agent injector 11. In some embodiments, the reducing agent injector 11 includes a metering device 13 configured to regulate the amount of material injected into the exhaust gas stream upstream of the catalyst article 100.

Processing of the exhaust stream

A further embodiment of the present invention relates to a method of treating an exhaust gas stream comprising soot, urea, ammonia, NO _x , CO and hydrocarbons. 3 and 4, the hydrolysis of the urea is facilitated by the hydrolysis catalyst 110 located at the inlet end 54 of the inlet channel 64 of the catalyst article 100. The soot is filtered from the gas stream by passing the gas stream after the hydrolysis catalyst 110 to the gas permeable wall 53. Filtration of the gas stream results in the formation of a filter cake on the inlet wall 65 of the inlet channel 64. The NO _x reacts with ammonia in the presence and by the selective catalytic reduction catalyst 120 permeating the gas permeable wall 53 of the catalytic article 100 to form N ₂ . Ammonia in the gas stream exiting the gas permeable wall 53 is promoted and oxidized thereby in the presence of the ammonia oxidation catalyst 130 coated on the outlet wall 67. CO and hydrocarbons are promoted and oxidized thereby to form carbon dioxide and water in the presence of the oxidation catalyst 140 coated on the outlet wall 67 at the outlet end 56 of the catalytic article. In some embodiments, referring to FIG. 4, a portion of the soot is promoted and oxidized by the selective catalytic reduction catalyst 120 in the presence of the pre-soot oxidation catalyst 150. In some embodiments, soot is oxidized after formation of the filter cake.

While the present invention has been described with emphasis on preferred embodiments, it will be apparent to those skilled in the art that variations of the preferred apparatus and method may be used, and the present invention is intended to be practiced otherwise than as specifically described herein. Accordingly, the invention includes all modifications that are included within the spirit and scope of the invention as defined in the following claims.

Claims (26)

Permeable wall having an inlet end and an outlet end defining an overall length and a thickness defining a plurality of axially extending inlet channels and outlet channels, wherein each inlet channel has an inlet wall, an open inlet end, A wall flow type for trapping soot in a gas stream, the wall flow type having a plugged outlet end, each outlet channel having an outlet wall, a plugged inlet end and an open outlet end, wherein each inlet channel has an adjacent outlet channel. filter;
An optional hydrolysis catalyst that facilitates the hydrolysis of the ammonia precursor coated on a portion of the inlet wall of the inlet channel extending from the inlet end;
A selective catalytic reduction catalyst permeating the gas permeable wall which promotes the conversion of NO _x to N _{2 in} the gas stream in the presence of excess oxygen;
An ammonia oxidation catalyst coating the length of the outlet wall of the outlet channel to promote selective oxidation of ammonia to N _{2 in} the gas stream; And
CO and an oxidation catalyst coated on a part of the outlet wall of the outlet channel extending from the outlet end toward the inlet end, which promotes the oxidation of the hydrocarbon to CO ₂
And ammonia precursor NO _x , CO, and hydrocarbons, wherein the NO _x , CO, and hydrocarbons are substantially free of NO _x , CO, and hydrocarbons. The catalytic article of claim 1, wherein a hydrolysis catalyst is present and extends from the inlet end to about 50% of the wall flow filter length, wherein the gas stream is arranged to initially meet the hydrolysis catalyst. The catalytic article of claim 1 wherein the hydrolysis catalyst is present and extends from about 1/4 inch from the inlet end to a length in the range of about 10% of the wall flow filter length. The catalytic article of claim 1 wherein the hydrolysis catalyst is present and comprises titania. The catalytic article of claim 1, wherein the selective catalytic reduction catalyst extends along the entire length of the wall flow filter. The catalytic article of claim 1, wherein the selective catalytic reduction catalyst loading is in the range of about 0.25 g / in ³ to about 2.5 g / in ³ . The catalytic article of claim 1, wherein the selective catalytic reduction catalyst comprises a metal promoted molecular sieve. The catalytic article of claim 1, further comprising a soot oxidation catalyst prior to the SCR catalyst. The catalytic article of claim 8, wherein the soot oxidation catalyst is permeable to the gas permeable wall. 10. Catalyst article according to claim 9, wherein the soot oxidation catalyst constitutes a layer permeating the inlet side of the gas permeable wall. 11. Catalyst article according to claim 10, wherein the layer penetrates into the gas permeable wall to a depth of up to about 50% of the wall thickness. The catalytic article of claim 8, wherein the soot oxidation catalyst comprises a layer on the inlet wall. The catalytic article of claim 8, wherein the soot oxidation catalyst comprises zirconia-stabilized cerium oxide. The catalytic article of claim 1, wherein the ammonia oxidation catalyst extends to no more than about 50% of the total length of the catalyst article. The catalytic article of claim 1, wherein the ammonia oxidation catalyst extends from the oxidation catalyst to about 50% or less of the total length of the catalyst article. The catalytic article of claim 1, wherein the oxidation catalyst extends less than about two inches from the outlet end of the outlet channel. The catalytic article of claim 1, wherein the oxidation catalyst overlaps with a portion of the ammonia oxidation catalyst. The catalytic article of claim 1, wherein the oxidation catalyst is substantially non-overlapping with the ammonia oxidation catalyst. The catalytic article of claim 1, wherein the oxidation catalyst comprises a platinum group metal on a high surface area support. The catalytic article of claim 1, wherein the wall flow type filter is a high efficiency filter. Promoting the hydrolysis of urea using a hydrolysis catalyst located at the inlet end of the inlet channel of the catalytic article;
Filtering the soot from the gas stream by passing the gas stream after the hydrolysis catalyst through the gas permeable wall of the catalytic article to form a filter cake on the walls of the inlet channel;
Promoting the N ₂ formation reaction of ammonia and NO _x using a selective catalytic reduction catalyst permeating the gas permeable wall of the catalytic article;
Promoting the oxidation of ammonia in the gas stream exiting the gas permeable wall of the catalytic article using an ammonia oxidation catalyst coated on the outlet wall of the catalytic article;
Promoting carbon dioxide and water-forming oxidation of CO and hydrocarbons using an oxidation catalyst coated on the outlet wall at the outlet end of the catalytic article
Wherein the exhaust gas stream comprises soot, urea, ammonia, NO _x , CO and hydrocarbons. 23. The method of claim 21, further comprising promoting the oxidation of soot using a soot oxidation catalyst prior to the selective catalytic reduction catalyst. 22. The method of claim 21 wherein the soot is oxidized after formation of the filter cake. An exhaust treatment system comprising: an engine; and a catalytic article located downstream of the engine and in communication with the engine. 25. The emission treatment system of claim 24, further comprising a diesel oxidation catalyst located downstream of the engine and upstream of the catalytic article and in communication with both. 25. The emission treatment system of claim 24, further comprising a reducing agent injector upstream of the catalytic article.

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