JP2017530859A - Catalyst with improved hydrothermal stability - Google Patents

Abstract

A catalyst for treating exhaust gas emissions is disclosed. The catalyst comprises ceria-alumina particles having a ceria phase present in a composite mass percent ranging from about 20% to about 80% on an oxide basis, and an alkaline earth metal component supported on the ceria-alumina particles. CeO2 is hydrothermally stable after aging at 950 ° C. for 5 hours in N2 containing 2% O2 and 10% steam, and has an average crystallite size of less than 160 mm. It exists in the form of crystallites.

Description

TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst and a method of using the same. More particularly, the present invention relates to a catalyst resistant to thermal aging and a method of using the material. The exhaust gas purification catalyst can be used to treat an exhaust gas stream, particularly an exhaust gas stream originating from a lean burn engine.

BACKGROUND The operation of lean burn engines, such as diesel engines and lean burn gasoline engines, provides users with excellent fuel economy and for high air / fuel ratio operation under lean fuel conditions. Low emissions of carbon oxides. In addition, diesel engines offer significant advantages over gasoline (spark ignition) engines in terms of fuel consumption, durability, and their ability to generate high torque at low speeds.

However, diesel engines have more serious problems than their spark ignition counterparts in terms of emissions. This is because the exhaust gas of a diesel engine is a heterogeneous mixture and the emission problem is related to particulate matter (PM), nitric oxide (NO _x ), unburned hydrocarbons (HC), and carbon monoxide.

In order to meet exhaust emission standards, nitrogen oxide (NO _x ) emissions from lean burn engines must be reduced. Conventional three-way conversion (TWC) automotive catalysts are NO _x , carbon monoxide (CO) and hydrocarbon (HC) pollutants in the exhaust of engines operating at or near stoichiometric air-fuel conditions. Suitable for removing. The exact ratio of air to fuel that results in stoichiometric conditions varies with the relative proportions of carbon and hydrogen in the fuel. The air to fuel (A / F) ratio of 14.65: 1 (air mass to fuel mass) is the stoichiometric ratio corresponding to the combustion of hydrocarbon fuels such as gasoline having the average formula CH _1.88. is there. Thus, the symbol λ is used to represent the result of dividing a particular A / F ratio by a stoichiometric A / F ratio for a given fuel, where λ = 1 is a stoichiometric mixture and λ> 1 Is a lean fuel mixture and λ <1 is a fuel rich mixture.

Engines, particularly gasoline fuel engines to be used in passenger cars and the like, are designed to operate under lean conditions as a fuel economy measure. Such a futuristic engine is called a “lean combustion engine”. That is, the ratio of air to fuel in the combustion mixture supplied to such an engine is maintained above the stoichiometric ratio so that the resulting exhaust gas is “lean”, ie, the exhaust gas contains oxygen. The amount is relatively high. Although lean-burn engines which improves fuel economy, due to excessive oxygen in the exhaust, a conventional TWC catalyst has the disadvantage that effective non for reducing NO _x emissions from such engines. Attempts to overcome this problem included the use of NO _x traps. Such exhaust engines, lean (oxygen rich) occludes NO _x during operation, rich (fuel rich) is treated with a catalytic / NO _x absorbent to release the occluded NO _x during operation. During over-rich (or stoichiometric) operation, the catalyst components of the catalyst / NO _x adsorbent include NO _x (including NO _x released from the NO _x adsorbent) and HC, CO present in the exhaust. And / or promotes the reduction of NO _x to nitrogen by reaction with hydrogen.

In a reducing environment, a lean NO _x trap (LNT) activates the reaction by promoting hydrocarbon steam reforming and water gas shift (WGS) reactions to provide H ₂ as a reducing agent to remove NO _x. Make it. The water gas shift reaction is a chemical reaction in which carbon monoxide reacts with water vapor to generate carbon dioxide and hydrogen. The presence of ceria in the LNT catalyzes the WGS reaction, improves the resistance of the LNT to SO ₂ inactivation and stabilizes the PGM; ceria in the LNT also functions as a NO _x storage component.

NO _x storage materials containing barium (BaCO ₃ ) immobilized on ceria (CeO ₂ ) have been reported, and these NO _x materials showed improved thermal aging properties. However, ceria undergoes severe sintering during hot water aging at high temperatures. Sintering is not only to lower the low temperature _the NO _x storage capacity and WGS activity also results in the inclusion of BaCO ₃ and PGM by bulk CeO _2. Therefore, there is a need for a hydrothermally stable ceria-containing catalyst.

SUMMARY OF THE INVENTION An embodiment of the first aspect of the invention relates to a catalyst. In a first embodiment, a catalyst is supported on the ceria-alumina particles having ceria-alumina particles having a ceria phase present in a mass percent of particles ranging from about 20% to about 80% on an oxide basis. Wherein the CeO ₂ is hydrothermally stable after aging at 950 ° C. for 5 hours in N ₂ containing 2% O ₂ and 10% steam and less than 160% It exists in the form of crystallites having an average crystallite size.

  In the second embodiment, the catalyst of the first embodiment is improved, wherein the alkaline earth metal component includes a barium component.

  In the third embodiment, the catalyst of the second embodiment is improved, wherein the barium component is selected from the group consisting of barium oxide and barium carbonate.

  In the fourth embodiment, the catalysts of the first to third embodiments are improved, in which the ceria-alumina particles are a composite of ceria and alumina.

  In the fifth embodiment, the catalysts of the first to fourth embodiments are improved and selected from the group consisting of platinum, palladium, rhodium, iridium, and mixtures thereof supported on the ceria-alumina particles. Further comprising at least one platinum group metal.

  In a sixth embodiment, the catalyst of the fifth embodiment is improved, wherein the platinum group metal is selected from platinum, palladium, rhodium, and mixtures thereof.

  In a seventh embodiment, the catalysts of the second to sixth embodiments are improved, wherein the barium component is present in an amount ranging from about 0.5% to 50% by weight on an oxide basis.

  In an eighth embodiment, the catalysts of the second to seventh embodiments are improved, wherein the barium component is present in an amount ranging from about 5% to 30% by weight on an oxide basis.

In a ninth embodiment, the catalyst of the fourth embodiment is improved, wherein the complex of CeO ₂ and Al ₂ O ₃ is in an amount in the range of about 30% to 80% by weight on an oxide basis. Contains ceria.

In the tenth embodiment, the catalyst of the fourth embodiment is improved, wherein the complex of CeO ₂ and Al ₂ O ₃ is in an amount in the range of about 50 wt% to 80 wt% based on the oxide. Contains ceria.

  In the eleventh embodiment, the catalyst of the fifth or sixth embodiment is improved, in which the platinum group metal consists essentially of platinum and palladium.

  In the twelfth embodiment, the catalyst of the fifth or sixth embodiment is improved, in which the platinum group metal consists essentially of platinum.

In the thirteenth embodiment, the catalysts of the first to twelfth embodiments are improved. In this case, the catalyst is a three-way catalyst (TWC), a diesel oxidation catalyst (DOC), a gasoline particulate filter (GPF). ), Lean NO _x trap (LNT), integrated lean NO _x trap three way catalyst (LNT-TWC), or ammonia oxidation (AMOX).

  A second aspect of the present invention relates to a system. In a fourteenth embodiment, a system includes the catalyst of the first to thirteenth embodiments and a lean combustion engine upstream of the catalyst.

  In the fifteenth embodiment, the system of the twelfth embodiment is modified to further include a second catalyst and optionally a particulate filter.

In the sixteenth embodiment, the system of the thirteenth embodiment is modified, wherein the second catalyst is a three-way catalyst (TWC), a gasoline particulate filter (GPF), a selective catalytic reduction (SCR). , lean NO _x trap (LNT), ammonia oxidation (AMOX), SCR-on filter (SCRoF), and combinations thereof, and combinations thereof.

FIG. 1 is a perspective view of a honeycomb-type refractory substrate member that may include a washcoat composition that includes a catalyst according to one embodiment. 2 is a partial cross-sectional view taken along a plane that is enlarged with respect to FIG. 1 and parallel to the end face of the substrate of FIG. 1, showing an enlarged view of one of the gas flow paths shown in FIG. FIG. 3 is a graph of the crystallite size of CeO ₂ measured by XRD according to an example after aging at 950 ° C. for 5 hours at N ₂ containing 2% O ₂ and 10% steam. . FIG. 4 is a graph of the crystallite size of CeO ₂ measured by XRD according to an example after aging at 850 ° C. for 8 hours in air containing 10% steam.

DETAILED DESCRIPTION OF THE INVENTION Before describing some exemplary embodiments of the present invention, it is to be understood that the present invention is not limited to the details of construction or process steps set forth in the following description. . The invention is capable of other embodiments and of being practiced or carried out in various ways.

According to embodiments of the present invention, incorporating a barium component (eg, BaCO ₃ and / or BaO) into ceria-alumina (CeO ₂ / Al ₂ O ₃ ) has a tremendous stabilizing effect on CeO ₂ , Thus, the catalyst material provides improved hydrothermal stability, high NO _x trap capacity, and high NO _x conversion over the prior art.

In one or more embodiments, the catalyst comprises ceria-alumina particles having a ceria phase present at a weight percent of the composite ranging from about 20% to about 80% on an oxide basis, and supported on the ceria-alumina particles. Alkaline earth metal component. The average CeO ₂ crystallite size of fresh and aged samples obtained from XRD can be used as a measure of the hydrothermal stability of CeO ₂ . Thus, in one or more embodiments, CeO ₂ is hydrothermally stable after aging at 950 ° C. for 5 hours in N ₂ containing 2% O ₂ and 10% steam and an average of less than 160 kg It exists in the form of crystallites having a crystallite size.

  With respect to terms used in this disclosure, the following definitions are given.

  As used herein, the term “catalyst” or “catalytic material” or “catalytic material” refers to a material that promotes the reaction.

  As used herein, the terms “layer” and “layered” refer to structures supported on a surface, eg, a substrate. In one or more embodiments, the catalyst of the present invention is coated as a washcoat on a substrate or substrate member to form a layer on the substrate.

  As used herein, the term “washcoat” has its usual meaning in the art of thin adherent coatings of catalysts or other materials, which coatings pass through the gas stream being processed. Applies to carrier substrate materials, such as honeycomb type carrier members, that are sufficiently porous to enable. As is understood in the art, a washcoat is obtained from a dispersion of particles in a slurry, which is applied to a substrate, dried and fired to obtain a porous washcoat.

As used herein, the term “carrier” refers to an underlying high surface area material on which additional compounds or elements are supported. The carrier particles have pores larger than 20 及 び and a wide pore distribution. As defined herein, such metal oxide supports exclude molecular sieves, specifically zeolites. In certain embodiments, a high surface area refractory metal oxide support, such as “gamma”, which typically exhibits a BET surface area of greater than 60 square meters per gram (“m ² / g”), often up to about 200 m ² / g or more. An alumina support material, also referred to as “alumina” or “activated alumina” may be utilized. Such activated alumina is usually a mixture of gamma and delta phase alumina, but may also contain significant amounts of eta alumina phase, kappa alumina phase, and theta alumina phase. Refractory metal oxides other than activated alumina can be used as a support for at least some catalyst components in a given catalyst. For such applications, for example, bulk ceria, zirconia, alpha alumina, silica, titania, and other materials are known.

In one or more embodiments, the catalyst comprises ceria-alumina particles. Ceria-alumina particles range from about 20% to about 80% on the oxide basis (20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% , 70%, 75%, or 80%), with a ceria phase present at a weight percent of the catalyst. In one or more specific embodiments, the average CeO ₂ crystallite size of fresh and aged samples obtained from XRD can be used as a measure of the hydrothermal stability of CeO ₂ . Thus, in one or more embodiments, CeO ₂ is hydrothermally stable and less than 160 kg after aging at 950 ° C. for 5 hours in N ₂ containing 2% O ₂ and 10% steam. Of crystallites having an average crystallite size (including 160Å, 155Å, 150Å, 140Å, 130Å, 120Å, 110Å, 10.0Å, 90Å, 80Å, 70Å, 60Å, 50Å, 40Å, 30Å, 20Å, 10Å and 5Å) Exists in form. In certain embodiments, the ceria-alumina particles comprise a ceria phase that is present in an amount of about 30% to 80% by weight of the composite, based on oxide. In a very particular embodiment, the ceria-alumina particles comprise a ceria phase that is present in a weight percent of the composite in an amount of about 50-80% by weight based on the oxide.

In one or more embodiments, CeO ₂ is present in a crystallite form that is hydrothermally stable when aged at 950 ° C. and is resistant to growth to larger crystallites. As used herein, the term “resisting to growth” means that the crystallite grows to a size that is no larger than an average of 160 時 に upon aging. In certain embodiments, the CeO ₂ crystallite size measured by XRD is less than 160 後 after aging the catalyst article in N ₂ containing 2% O ₂ and 10% steam for 5 hours at 950 ° C. . According to one or more embodiments, the CeO ₂ crystallite size of the powder sample and the coated catalyst are different. The coated catalyst, other washcoat components may have a stabilizing effect on CeO _2. Thus, after aging at the same 950 ° C., the coated catalyst has a smaller CeO ₂ crystallite size than the powder.

  As used herein, the term “average crystallite size” refers to the average size as measured by XRD as described below.

The term “XRD” as used herein refers to X-ray diffraction crystallography, which is a method for determining the atomic and molecular structure of a crystal. In XRD, crystalline atoms diffract X-ray rays in many specific directions. By measuring the angle and intensity of these diffracted rays, a three-dimensional image of the electron density in the crystal can be generated. From this electron density, not only the position of atoms in the crystal, but also chemical bonds, their disturbances, and other information can be obtained. In particular, XRD can be used to estimate the crystallite size; as the crystallite size decreases, the peak broadens, so the peak width is inversely proportional to the crystallite size. In one or more embodiments, XRD is used to measure the average crystallite size of CeO ₂ particles.

The width of the XRD peak is interpreted as a combination of broadening effects related to both size and strain. The formula used to determine both is shown below. The first equation below is a Scherrer equation used to convert the full width at half maximum FWHM information to the crystallite size of a given phase. The second equation is used to calculate the strain in the crystal from the peak width information, and the sum of the peak width or width is the sum of these two effects, as shown in the third equation. Conceivable. Note that the increase in size and strain varies in various ways with respect to the Bragg angle θ. Scherer constants are described below.

The Scherrer constants are:
K: Shape constant (0.9 is used here)
L: Peak width (this is corrected for contributions from instrument optics through the use of NIST SRM 660b LaB6 Line Position & Line Shape Standard)
Θ: 1/2 of 2θ value of target reflection
λ: wavelength of radiation 1.5406 mm

As used herein, “crystallite size” is understood to be the length of the coherent scattering region in a direction orthogonal to the set of grating planes that cause reflection. For CeO _2, CeO ₂ <111> reflection is the strongest peak in X-ray diffraction pattern of CeO _2. The CeO ₂ <111> plane of atoms is a single body that intersects each of the crystal axes and is orthogonal to the diagonal line represented by the <111> vector. Therefore, the crystallite size of 312 cm calculated from the FWHM of CeO ₂ 111 reflection would be considered to be approximately 100 layers in the <111> plane of the atom.

Different directions and reflections in the crystal will result in different but near crystallite size values. Those values will only be accurate if the crystal is perfectly spherical. The Williamson Hall plot is used below to interpret the effect of size and strain by considering the total peak width as a linear equation, where the slope of the line represents the strain and the intercept is the size of the crystal .

  To determine the crystallite size, the FWHM value of the material is measured from the FWHM value of one reflection or the complete X-ray diffraction pattern. Conventionally, one reflection is adapted to determine the FWHM value of that reflection, the FWHM value is corrected for the contribution from the instrument, and the corrected FWHM value is converted to the crystallite size value using the Scherrer equation. Converted. This would be done by ignoring the effects of strain in the crystal. This method has been used primarily for questions regarding the crystallite size of noble metals that have only one useful reflection. It should be noted that when fitting peaks, it is desirable to have a clean reflection that does not overlap by reflections from other phases. This is rarely the case for the washcoat formulations of the present invention where the Rietveld process is currently used. The Rietveld method allows the adaptation of complex X-ray diffraction patterns using the known crystal structure of the existing phase. The crystal structure serves as a restraint or brake in the fitting process. Until the entire model matches the experimental data, the phase content, lattice parameters, and FWHM information will vary for each phase.

  In the following examples, the Rietveld method was used to match the experimental pattern of the new and aged samples. The crystallite size was calculated | required using the FWHM curve calculated | required about each phase in each sample. The strain effect was excluded.

As used herein, the term “alkaline earth metal” refers to elements including beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). One or more chemical elements defined in the periodic table. In one or more embodiments, an alkaline earth metal component is incorporated into the catalyst as a salt and / or sulfate and / or oxide (eg, BaCO ₃ , BaSO ₄ , and / or BaO). The “metal component” can be obtained. Note that during calcination, the barium component will be converted to barium carbonate and / or barium oxide. In one or more embodiments, the alkaline earth metal component includes a barium component. The alkaline earth metal component is in an amount in the range of about 0.5% to 50% by weight (0.5% by weight, 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight). %, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50% by weight) in the washcoat. . In certain embodiments, the alkaline earth metal component comprises a barium component, which is present in an amount ranging from about 0.5% to about 50% by weight on an oxide basis. In another particular embodiment, the alkaline earth metal component comprises a barium component, which is present in an amount ranging from about 5% to about 30% by weight based on the oxide.

In one or more embodiments, the CeO ₂ crystallite size of the aged sample obtained from XRD was used as a measure of the alkaline earth metal / Ce / Al hydrothermal stability.

In certain embodiments, when the ceria-alumina particles are impregnated with a barium precursor, particularly a water-soluble barium precursor salt (eg, barium acetate), a tremendous stabilization effect has been identified and calcined. Barium carbonate (BaCO ₃ ) and / or barium oxide (BaO) are obtained. As shown in FIG. 3, the CeO ₂ crystallizer of the BaCO ₃ / (CeO ₂ —Al ₂ O ₃ ) sample after aging at 950 ° C. for 5 hours in N ₂ containing 2% O ₂ and 10% steam. The lit size was in the range of about 75 mm to about 160 mm. This is significantly lower than the crystallite size (> 1000 Å) of the aged BaCO ₃ / CeO ₂ powder. Alternative BaCO ₃ was loaded onto 70% CeO ₂ / Al ₂ O ₃ powder to see if they could have the same effect. Referring to FIG. 4, after aging at 850 ° C. for 8 hours in air containing 10% steam, a sample filled with 15%, 10% and 5% by weight of barium component (calculated as barium oxide) is , CeO ₂ crystallite size much lower than BaCO ₃ / CeO ₂ . Overall, the barium component (eg, BaCO ₃ and / or BaO) appears to have an inherent stabilizing effect on the growth of Ba / Ce / Al based ceria crystallites. The stabilizing effect is, for example, a high beneficial potential for NO _x trap LNT catalyst. The increase in ceria surface area due to the smaller crystallite size will allow NO _x traps based on lower temperature ceria, improve WGS and improve PGM dispersion.

  Thus, according to one or more embodiments, ceria is destabilized in the Ba—Ce system and significantly stabilized in the Ba—Ce—Al system.

In one or more embodiments, without intending to be bound by theory, the increase in ceria surface area due to smaller crystallite size is based on higher BaCO ₃ due to better BaCO ₃ dispersion. Enables NO _x trap, enables more advanced CeO ₂ based NO _x trap at low temperature, enables improved NO _x reduction for more effective WGS, and for better PGM dispersion It is believed to enable improved NO oxidation and NO _x reduction. Therefore, the introduction of barium (BaCO ₃ and / or BaO) into ceria-aluminum (CeO ₂ / Al ₂ O ₃ ) has a tremendous stabilizing effect on CeO ₂ , and the catalyst material has a greater effect than in the prior art. Also provides improved hydrothermal stability, higher NO _x trap capacity, and higher NO _x conversion.

In one or more embodiments, the catalyst of the invention has improved NO _x during lean operation after aging at 950 ° C. for 5 hours in N ₂ containing 2% O ₂ and 10% steam. shows the trapping performance, during rich regeneration, exhibit improved _the NO _x reduction. This improvement is relative to conventional catalysts containing ceria in which Al ₂ O ₃ has not been introduced.

In one or more embodiments, the catalyst of the present invention, the three-way catalyst (TWC), a diesel oxidation catalyst (DOC), gasoline particulate filter (GPF), a lean NO _x trap (LNT), LNT-TWC integral Or as an ammonia oxidation catalyst (AMOx).

  In one or more embodiments, the catalyst further comprises at least one platinum group metal supported on barium (ceria-alumina) particles. As used herein, the term “platinum group metal” or “PGM” refers to one or more chemical elements defined in the periodic table of elements including platinum, palladium, rhodium, osmium, iridium, and ruthenium, And mixtures thereof. In one or more embodiments, the platinum group metal is selected from the group consisting of platinum, palladium, rhodium, iridium, and mixtures thereof. In certain embodiments, the platinum group metal is selected from platinum, palladium, rhodium, and mixtures thereof. Generally, there is no particular limitation as far as the total platinum group metal content of the catalyst is concerned.

  Usually, the catalyst of the present invention is disposed on a substrate. The substrate can be any of the materials typically used to prepare the catalyst and will typically include a ceramic or metal honeycomb structure. Any suitable substrate, such as a monolithic substrate of the type in which a fine, parallel gas channel passes through from the inlet or outlet surface of the substrate so that the flow path is in fluid communication (herein , Referred to as flow-through substrates). A flow path that is a substantially straight path from the inlet to the outlet is defined by a wall that is coated with the catalytic material as a washcoat, and the gas flowing through the flow path contacts the catalytic material. The flow path of the monolithic substrate is a thin-walled channel that can be any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, and the like.

  Such monolithic substrates may contain up to about 900 or more channels (or “cells”) per square inch of cross-section, although much less may be used. For example, the substrate may have from about 7 to 600 (“cpsi”) cells per square inch, more typically from about 100 to 400 (“cpsi”) cells. The cells may have a rectangular, square, circular, elliptical, triangular, hexagonal, or other polygonal cross section. The ceramic substrate may be made of any suitable refractory material, such as cordierite, cordierite-alumina, silicon nitride, or silicon carbide, or the substrate is composed of one or more metals or metal alloys. May be.

  The catalyst according to embodiments of the present invention may be applied to the substrate surface by any means known in the art. For example, the catalyst washcoat may be applied by spray coating, powder coating, or surface brushing or dipping in the catalyst composition.

  In one or more embodiments, the catalyst is disposed on the honeycomb substrate.

  When applied as a washcoat, the present invention can be more easily understood by referring to FIGS. 1 and 2 show a refractory substrate member 2 according to one embodiment of the present invention. Referring to FIG. 1, the refractory base member 2 has a cylindrical shape having a cylindrical outer surface 4, an upstream end surface 6, and a downstream end surface 8 that is the same as the end surface 6. The substrate member 2 has a plurality of fine and parallel gas flow paths 10 formed therein. As can be seen from FIG. 2, the flow path 10 is formed by a wall 12 and penetrates the substrate from the upstream end face 6 to the downstream end face 8, and the flow path 10 allows a fluid, for example a gas stream, to pass through the substrate. The gas passage 10 is not blocked so that it can flow in the vertical direction. A separate catalyst layer 14 in the art and sometimes referred to as a “washcoat” is deposited or coated on the wall 12 of the substrate member. In some embodiments, an additional catalyst layer 16 is coated on the catalyst layer 14. The second catalyst layer 16 can have the same composition as the catalyst layer 14, or the second catalyst layer 16 can include a separate catalyst composition.

As shown in FIG. 2, the base member includes a gap formed by the gas flow path 10, and the cross-sectional area of these passages 10 and the thickness of the wall 12 that defines the flow path depend on the type of the base member. It will be different. Similarly, the mass of washcoat applied to such a substrate will vary from case to case. Consequently, it is convenient to use mass units of the component per unit volume of substrate in describing the amount of washcoat or catalytic metal component or other compositional component. Accordingly, to mean the mass of a component per volume of substrate member, including the volume of voids in the substrate member, herein the unit of grams per cubic inch (“g / in ³ ”) and cubic Units of grams per foot (“g / ft ³ ”) are used.

In the second aspect of the invention, the catalyst of one or more embodiments may be used in an integrated exhaust treatment system that includes one or more additional components for the treatment of exhaust emissions. For example, the exhaust treatment system may include a lean combustion engine upstream of the catalyst of one or more embodiments, and may further include a second catalyst and optionally a particulate filter. In one or more embodiments, the second catalyst is a three way catalyst (TWC), gasoline particulate filter (GPF), selective catalytic reduction (SCR), lean NO _x trap (LNT), ammonia oxidation (AMOx). , SCR-on-filter (SCRoF), and combinations thereof, and combinations thereof. In one or more embodiments, the particulate filter may be selected from a gasoline particulate filter, a soot filter, or an SCRoF. Particulate filters can be catalyzed for specific functions. The catalyst can be placed upstream or downstream of the particulate filter.

  In one or more embodiments, the exhaust treatment system may include a lean combustion engine upstream of the catalyst of one or more embodiments, and may further include a TWC. In one or more embodiments, the waste treatment system may further include SCR / LNT.

  In certain embodiments, the particulate filter is a catalytic soot filter (CSF). The CSF can include a substrate coated with a washcoat layer containing one or more catalysts to burn trapped soot or to oxidize exhaust stream exhaust. In general, the soot combustion catalyst can be any known catalyst for soot combustion. For example, CSF can be one or more high surface area refractory oxides (eg, alumina, silica, silica alumina, zirconia, and zirconia alumina) to some degree of particulate matter for combustion of unburned hydrocarbons and And / or coated with an oxidation catalyst (eg, ceria-zirconia). In one or more embodiments, the soot combustion catalyst is an oxidation catalyst that includes one or more precious metal (PM) catalysts (platinum, palladium, and / or rhodium).

  In general, any filter substrate known in the art can be used, including, for example, honeycomb wall flow filters, wound or filled fiber filters, open cell foams, sintered metal filters, and the like. The filter is specifically illustrated. A wall flow substrate useful for carrying a CSF composition has a plurality of fine and substantially parallel gas flow paths extending along the longitudinal axis of the substrate. Usually, each flow path is blocked at one end of the base body, and another passage is blocked at the opposite end face. Such monolithic substrates may contain up to about 900 or more channels (or “cells”) per square inch of cross-section, although much less may be used. For example, the substrate may have from about 7 to 600 cells per square inch (“cpsi”), more typically from about 100 to 400 cells (“cpsi”). Porous wall flow filters used in embodiments of the present invention are optionally catalyzed, wherein the element walls have or contain one or more catalyst materials thereon, such CSF catalysts. The composition has been described above. The catalytic material can be present only on the inlet side of the element wall, only on the outlet side, both on the inlet side and on the outlet side, or the wall itself can consist of all or part of the catalytic material. In another embodiment, the invention includes the use of a combination of one or more washcoat layers of catalyst material and one or more washcoat layers of catalyst material on the inlet and / or outlet walls of the element. obtain.

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

EXAMPLES Example 1 the catalyst preparation CeO ₂ -Al ₂ O ₃ particles (1a to 5a) was impregnated with barium acetate solution, BaCO of BaCO ₃ content shown in Table 1 ₃ / _(CeO 2 _-Al 2 O Samples 1B to 5B having ₃ ) were obtained. The mixture was dried at 110 ° C. and calcined at 720 ° C. for 2 hours.

The CeO ₂ -Al ₂ O ₃ particles (4A) is impregnated with a barium acetate solution to obtain a 4C~4E with BaCO of BaCO ₃ content shown in Table 1 _{3 / (CeO 2 -Al 2 O} 3). The mixture was dried at 110 ° C. and calcined at 620 ° C. for 2 hours.

CeO ₂ particles (6A) were impregnated with a barium acetate solution to obtain 6B and 6C having BaCO ₃ / CeO ₂ having a BaCO ₃ content shown in Table 1. This mixture was dried at 110 ° C. and calcined at 600 ° C. for 2 hours.

Referring to FIG. 3, after aging at 950 ° C. for 5 hours in N ₂ containing 2% O ₂ and 10% vapor, BaO ₃ / (CeO ₂ —Al ₂ O ₃ ) samples 1B-5B CeO _{The 2} crystallite size was in the range of 79 to 158 cm.

Referring to FIG. 4, the CeO ₂ crystallite size of BaCO ₃ / (CeO ₂ —Al ₂ O ₃ ) Samples 4C-4E was 73 ° C. after aging at 850 ° C. for 8 hours in air containing 10% steam. It was in the range of ˜92 cm.

Table 1 shows the contents of 1A to 6A, and 1B to 6B, 6C, and 4C to 4E.

Example 2 XRD Measurement The CeO ₂ crystallite size of the sample of Example 1 was measured by XRD. The sample was ground using a mortar and pestle. Next, the obtained powder was returned to the flat table for analysis and packed. Bragg-Brentano geometry data was collected using a θ-θ panatical X'Pert Pro MPD X-ray diffractometer. Optical path: X-ray tube, 0.04 rad solar slit, 1/4 ° divergence slit, 15 mm beam mask, 1/2 ° anti-scatter slit, sample, 1/4 ° anti-scatter slit, 0.04 rad solar slit, Ni ⁰ It consisted of a filter and a PIXcel linear position sensitive detector with an effective length of 2.114 °. The Cu _kα line was used for analysis with a generator setting of 45 kV and 40 mA. X-ray diffraction data was collected from 10 ° to 90 ° 2θ using a step size of 0.0026 ° and a count time of 600 s per step. Phase identification was performed using Jade software. All numerical values were determined using the Rietveld method.

  Throughout this specification, references to “one embodiment,” “an embodiment,” “one or more embodiments,” or “embodiments” refer to particular features, structures, It means that a material or property is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one or more embodiments”, “in one embodiment”, “in one embodiment”, or “in an embodiment” in various places throughout this specification are not necessarily It does not mean the same embodiment. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. The order of description of the above methods should not be considered limiting, and these methods may use the operations described in any order or with omission or addition.

  It should be understood that the above description is illustrative and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. Accordingly, the scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims (15)

A catalyst comprising ceria-alumina particles having a ceria phase present in a mass percent of particles ranging from about 20% to about 80% on an oxide basis, and an alkaline earth metal component supported on the ceria-alumina particles. there are, of crystallites having an average crystallite size of less than hydrothermal is stable and 160Å after CeO ₂ is obtained by 5 hours aging at 950 ° C. in a N ₂ containing 2% O ₂ and 10% steam The catalyst present in the form.   The catalyst of claim 1, wherein the alkaline earth metal component comprises a barium component.   The catalyst according to claim 2, wherein the barium component is selected from the group consisting of barium oxide and barium carbonate.   The catalyst according to any one of claims 1 to 3, wherein the ceria-alumina particles are a composite of ceria and alumina.   5. The method according to claim 1, further comprising at least one platinum group metal selected from the group consisting of platinum, palladium, rhodium, iridium, and mixtures thereof supported on the ceria-alumina particles. The catalyst according to 1.   6. The catalyst of claim 5, wherein the platinum group metal is selected from platinum, palladium, rhodium, and mixtures thereof.   The barium component is present in an amount ranging from about 0.5% to 50% by weight on an oxide basis, and particularly the barium component is present in an amount ranging from about 5% to 30% by weight on an oxide basis. The catalyst according to claim 2. The complex of the CeO ₂ and _Al 2 _{O 3} contains ceria in an amount ranging from about 30 wt% to 80 wt% on an oxide basis, the catalyst of claim 4. The complex of the CeO ₂ and _Al 2 _{O 3} contains ceria in an amount ranging from about 50 wt% to 80 wt% on an oxide basis, the catalyst of claim 4.   The catalyst according to claim 5 or 6, wherein the platinum group metal consists essentially of platinum and palladium.   The catalyst according to claim 5 or 6, wherein the platinum group metal substantially consists of platinum. The catalyst is a three-way catalyst (TWC), a diesel oxidation catalyst (DOC), a gasoline particulate filter (GPF), a lean NO _x trap (LNT), an integrated lean NO _x trap three-way catalyst (LNT-TWC), Or a catalyst according to any one of claims 1 to 11, selected from ammonia oxidation (AMOX).   13. A system comprising the catalyst of any one of claims 1 to 12 and a lean burn engine upstream of the catalyst.   14. The system of claim 13, further comprising a second catalyst, and optionally a particulate filter. The second catalyst is a three-way catalyst (TWC), gasoline particulate filter (GPF), selective catalytic reduction (SCR), lean NO _x trap (LNT), ammonia oxidation (AMOX), SCR-on filter ( 15. The system of claim 14, selected from SCRoF), and combinations thereof.

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