CHA zeolite materials and related synthesis methods

Abstract

To provide a method for synthesizing a CHA-type zeolite exhibiting strong hydrothermal stability and catalytic performance while minimizing the structural defect density of the zeolite, a zeolite material, an effluent treatment system and an exhaust gas treatment method using the CHA-type zeolite.SOLUTION: The invention provides a method of synthesizing a zeolite having the CHA crystalline framework, the method including forming a reaction mixture comprising an alumina source comprising a zeolite having a FAU crystalline framework, a silica source, and an organic structure directing agent, the reaction mixture having a combined molar ratio of M / Si+R / Si higher than the molar ratio OH- / Si, where M is moles of alkali metal and R is moles of organic structure directing agent; and crystallizing the reaction mixture to form a product zeolite having the CHA crystalline framework, where the product zeolite has a mesopore surface area (MSA) of less than about 25 m2 / g.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure generally relates to the field of selective catalytic reduction catalysts and methods of preparing and using such catalysts to selectively reduce nitrogen oxides.

Background Art

[0002] Diesel engine emissions include particulate matter (PM), nitrogen oxides (NO x ), unburned hydrocarbons (HC), and carbon monoxide (CO). NO x is a term used to describe various species of nitrogen oxides, including, among others, nitric oxide (NO) and nitrogen dioxide (NO2). The two main components of exhaust particulate matter are the soluble organic fraction (SOF) and soot fraction. The SOF condenses in layers on top of the soot and generally originates from unburned diesel fuel and lubricating oil. The SOF can be present in diesel exhaust as a vapor or an aerosol (i.e., fine droplets of a liquid condensate) depending on the temperature of the exhaust gas. Soot is mainly composed of carbon particles. The HC content of the exhaust can vary depending on the engine type and operating parameters but typically includes various short-chain hydrocarbons such as methane, ethene, ethyne, propene.

[0003] NO x To treat NO

[0004] The catalyst used in the SCR process should ideally be able to maintain good catalytic activity under hydrothermal conditions over a wide temperature range, e.g., from 200°C to 600°C or higher. The SCR catalyst is generally exposed to high-temperature hydrothermal conditions, such as during the regeneration of a soot filter, which is a component of an exhaust gas treatment system used for particle removal.

[0005] Molecular sieves such as zeolites have been used in the SCR of nitrogen oxides with reducing agents such as ammonia, urea, or hydrocarbons in the presence of oxygen. Zeolites are crystalline materials with fairly uniform pore diameters in the range of about 3 to about 10 angstroms, depending on the type of zeolite and the type and amount of cations contained in the zeolite. Zeolites having 8-membered ring pore openings and double 6-ring secondary building units, especially those having a cage-like structure, are particularly suitable for use as SCR catalysts. A specific type of zeolite having these properties is chabazite (CHA), which is a small-pore zeolite having 8-membered ring pore openings (about 3.8 angstroms) accessible from three-dimensional porosity. The cage-like structure results from connecting four rings of double 6-ring building units. Molecular sieves having a CHA structure can be prepared, for example, according to the methods disclosed in U.S. Patent Nos. 4,544,538 and 6,709,644, which are hereby incorporated by reference.

[0006] Metal-promoted zeolite catalysts, often also referred to as ion-exchanged zeolite catalysts (e.g., iron-promoted and copper-promoted zeolite catalysts), are known for the selective catalytic reduction of nitrogen oxides by ammonia. Under severe hydrothermal conditions (e.g., as shown during the regeneration of soot filters at temperatures locally exceeding 700 °C), it has been found that the activity of many metal-promoted zeolites begins to decline. This decline is attributed to dealumination of the zeolite and the resulting loss of metal-containing active centers within the zeolite. In light-duty diesel (LDD) applications where SCR catalysts are often exposed to temperature fluctuations associated with the regeneration of soot filters, special requirements are imposed on the hydrothermal stability of the zeolite. Hydrothermal stability generally increases as the content of framework alumina decreases (i.e., as the silica-to-alumina molar ratio or SAR increases), but the latter also limits the amount of catalytically active Cu sites. Therefore, improving the hydrothermal stability of frameworks with lower SAR would present an effective strategy for improving LDD performance.

Brief Description of the Drawings

[0007] To provide an understanding of embodiments of the present invention, reference is made to the accompanying drawings, which are not necessarily drawn to scale, and in which reference numerals refer to components of exemplary embodiments of the present invention. The drawings are merely examples and are not to be construed as limiting the present invention.

Figure 1A

Figure 1B

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Summary of the Invention

[0008] The present invention provides a method for improving the hydrothermal stability of a product zeolite by synthesizing a zeolite having a CHA crystal framework that minimizes the structural defect density of the CHA zeolite. Thus, in various aspects, the present invention provides a method for synthesizing a CHA zeolite, a CHA zeolite product exhibiting strong hydrothermal stability and catalytic performance, and an exhaust gas treatment system and an exhaust gas treatment method using the CHA zeolite product.

[0009] In one aspect, the method comprises forming a reaction mixture comprising at least one alumina source (e.g., a zeolite having a FAU crystal framework) containing zeolite, at least one silica source containing an alkali metal silicate solution, and at least one organic structure-directing agent (e.g., a quaternary ammonium salt having a substituent selected from the group consisting of alkyl, aromatic, and combinations thereof), wherein the reaction mixture has a total molar ratio of M / Si + R / Si higher than the OH - / Si molar ratio, where M is the number of moles of alkali metal and R is the number of moles of organic structure-directing agent, and crystallizing the reaction mixture (advantageously, at a high temperature (e.g., about 100 °C to about 160 °C) and high pressure) to form a product zeolite having a CHA crystal framework, where the product zeolite has a mesopore surface area (MSA) of less than about 25 m 2 / g, and a method for synthesizing a CHA zeolite is provided. In certain embodiments, the zeolite having a FAU crystal framework can be zeolite Y. For example, zeolite Y can be Na +It is in a form and has a silica-to-alumina molar ratio (SAR) in the range of about 3 to about 6. In some embodiments, the alkali metal M can be sodium, and the alkali metal silicate solution can be sodium silicate. Examples of organic structure-directing agents include quaternary ammonium salts having an adamantyl, cyclohexyl, or benzyl substituent.

[0010] In certain embodiments, the reaction mixture can be characterized by various molar ratios such as at least about 0.4 M / Si molar ratio, less than about 0.12 R / Si molar ratio, less than about 0.7 OH - / Si molar ratio, and a total ratio of M / Si + R / Si greater than about 0.75.

[0011] In some embodiments, the method further comprises calcining the product zeolite having a CHA crystal framework to form a calcined zeolite in the H + form or the Na + form, and may further comprise ion-exchanging the product zeolite having a CHA crystal framework with a promoter metal (e.g., Fe or Cu) to form an ion-exchanged zeolite catalyst.

[0012] In another aspect, the present invention provides a zeolite material having a CHA crystal framework, wherein the zeolite material has a mesopore surface area (MSA) of less than about 25 m 2 / g and a zeolite surface area (ZSA) of at least about 400 m 2 / g. In various embodiments, the zeolite material is as follows: H + form of 27 less than about 20% extra-framework aluminum (EFAl) as determined by + Al NMR (or less than about 15% extra-framework aluminum (EFAl) as determined by 27 Al NMR in the H-1 is a peak at, where Y is 3609 CM -1 is a peak at), about 10 m 2 less than / g of MSA, at least about 450 m 2 / g of zeolite surface area (ZSA), and the H of the zeolite material + morphology was stirred / sonicated with a 40 wt% NH4F solution at 50 °C for 20 minutes and then dried and calcined at 450 °C for 6 hours, and may be further characterized by one or more of a normalized ZSA loss of less than about 60%.

[0013] In yet another aspect, the present invention provides a selective catalytic reduction (SCR) catalyst effective for the reduction of nitrogen oxides (NO x ), and the SCR catalyst comprises a zeolite material according to the present invention promoted with a metal selected from iron, copper, and combinations thereof. Exemplary ranges of promoter metal content are from about 1.0 wt% to about 10 wt% based on the total weight of the SCR catalyst. In certain embodiments, the SCR catalyst exhibits NO conversion of about 58% or more at 200 °C and about 76% or more at 600 °C in exhaust gas after a thermal aging treatment, where the thermal aging treatment is performed at 800 °C for 16 hours in the presence of 10 vol% steam and the balance air, and the exhaust gas has a volume-based space velocity of 80,000 h X per hour and contains a gas mixture of 500 ppm NO, 500 ppm NH -1 10% O 3、 5% H2O, and the balance N2 2、

[0014] In yet another aspect, the present invention provides a catalyst article effective for reducing nitrogen oxides (NO x ) from the exhaust gas of a lean burn engine, and the catalyst article comprises a substrate carrier having disposed thereon a selective catalytic reduction (SCR) catalyst according to the present invention. Examples of substrate carriers include honeycomb substrates optionally composed of metal or ceramic, such as flow-through substrates or wall-flow filters.

[0015] ​In a further aspect, the present invention provides an exhaust gas treatment system comprising a lean burn engine that generates an exhaust gas stream and a catalyst article according to the present invention disposed downstream of the lean burn engine and in fluid communication with the exhaust gas stream. The exhaust gas treatment system optionally further comprises one or more of the following: a diesel oxidation catalyst (DOC) disposed upstream of the catalyst article, a soot filter disposed upstream of the catalyst article, and an ammonia oxidation catalyst (AMOX) disposed downstream of the catalyst article.

[0016] In yet another aspect, the present invention provides a method for treating an exhaust gas stream from a lean burn engine, comprising contacting the exhaust gas stream with a catalyst article according to the present invention, whereby nitrogen oxides (NOx) in the exhaust gas stream are reduced.

[0017] The present disclosure includes, but is not limited to, the following embodiments.

[0018] Embodiment 1: A method for synthesizing a zeolite having a CHA crystal framework, comprising: i) forming a reaction mixture comprising at least one alumina source comprising zeolite, at least one silica source, and at least one organic structure directing agent, wherein the reaction mixture has a total molar ratio of M / Si + R / Si higher than the OH - / Si molar ratio, where M is the number of moles of alkali metal and R is the number of moles of organic structure directing agent; and ii) crystallizing the reaction mixture to form a product zeolite having a CHA crystal framework, wherein the product zeolite has a mesopore surface area (MSA) of less than about 25 m 2 / g.

[0019] Embodiment 2: The method according to Embodiment 1, wherein the zeolite of the alumina source has a FAU crystal framework.

[0020] Embodiment 3: The method according to Embodiment 1 or 2, wherein the zeolite having a FAU crystal framework is zeolite Y.

[0021] Embodiment 4: The method according to any one of Embodiments 1-3, wherein the zeolite Y is in the Na+ form and has a silica to alumina ratio (SAR) in the range of about 3 to about 6.

[0022] Embodiment 5: The method according to any one of Embodiments 1-4, wherein M is sodium and the alkali metal silicate solution is sodium silicate.

[0023] Embodiment 6: The reaction mixture is as follows: a. An M / Si molar ratio of at least about 0.4, b. An R / Si molar ratio of less than about 0.12, c. An OH - / Si molar ratio of less than about 0.7, and d. The method according to any one of Embodiments 1-5, characterized by one or more of a total ratio of M / Si + R / Si of greater than about 0.75.

[0024] Embodiment 7: The method according to any one of Embodiments 1-6, wherein the organic structure directing agent is a quaternary ammonium salt having a substituent selected from the group consisting of alkyl, aromatic, and combinations thereof.

[0025] Embodiment 8: The method according to any one of Embodiments 1-7, wherein the organic structure directing agent is a quaternary ammonium salt having an adamantyl, cyclohexyl, or benzyl substituent.

[0026] Embodiment 9: The method according to any one of Embodiments 1-8, wherein the crystallization step is carried out at a temperature of about 100°C to about 160°C.

[0027] Embodiment 10: The product zeolite having a CHA crystal framework is as follows: a. When determined by 27Al NMR in the H + form, less than about 20% extra-framework aluminum (EFAl), 27 b. An SAR in the range of about 10 to about 30, c. c. When determined by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, a surface silanol fraction (X / Y peak ratio) of less than about 0.04 (where X is the peak at 3742 cm -1 and Y is the peak at 3609 cm -1 ), D. Less than about 10 m 2 / g of MSA, and e. At least about 400 m 2 / g of zeolite surface area (ZSA), a method according to any one of embodiments 1-9, characterized by one or more of these.

[0028] Embodiment 11: A method according to any one of embodiments 1-10, further comprising calcining the product zeolite having a CHA crystal framework to form a calcined zeolite in the H + form or Na + form.

[0029] Embodiment 12: A method according to any one of embodiments 1-11, further comprising ion-exchanging the product zeolite having a CHA crystal framework with a promoter metal to form an ion-exchanged zeolite catalyst.

[0030] Embodiment 13: A method according to any one of embodiments 1-12, wherein the promoter metal is Fe or Cu.

[0031] Embodiment 14: A method according to any one of embodiments 1-13, wherein the silica source comprises an alkali metal silicate solution.

[0032] Embodiment 15: A method according to any one of embodiments 1-14, wherein crystallization of the reaction mixture is carried out at elevated temperature and autogenous pressure.

[0033] Embodiment 16: A method according to any one of embodiments 1-15, wherein the solids content of the reaction mixture is from about 5 to about 25 wt%.

[0034] Embodiment 17: A zeolite material having a CHA crystal framework, wherein the zeolite material has a surface area of about 25 m2 a mesopore surface area (MSA) of less than / g and a zeolite surface area (ZSA) of at least about 400 m 2 / g, and further, the zeolite material is as follows: a. 27 less than about 20% extra-framework aluminum (EFAl) as determined by Al NMR, b.less than about 0.04 surface silanol fraction (X / Y peak ratio) as determined by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy (where X is the peak at 3742 CM -1 and Y is the peak at 3609 CM -1 ), and C.one or more of a normalized ZSA loss of less than about 60% after treating the H + form of the zeolite material with a 40 wt% NH4F solution, a zeolite material.

[0035] Embodiment 18: The zeolite material according to any one of Embodiments 1 to 17, having a SAR in the range of about 10 to about 30.

[0036] Embodiment 19: The zeolite material according to any one of Embodiments 1 to 18, having a SAR in the range of about 16 to about 22.

[0037] Embodiment 20: The zeolite material according to any one of Embodiments 1 to 19, having a SAR in the range of about 18 to about 20.

[0038] Embodiment 21: The zeolite material according to any one of Embodiments 1 to 20, having less than 15% extra-framework aluminum (EFAl) as determined by Al NMR in the H + form. 27 of

[0039] Embodiment 22: The zeolite material according to any one of Embodiments 1 to 21, having an MSA of less than about 10 m 2 / g.

[0040] Embodiment 23: Nitrogen oxides (NO x) A selective catalytic reduction (SCR) catalyst effective for reduction, wherein the SCR catalyst comprises a zeolite material according to any of embodiments 1 to 22 promoted with a metal selected from iron, copper, and combinations thereof.

[0041] Embodiment 24: The SCR catalyst according to any of embodiments 1 to 23, wherein the promoter metal is present in an amount of about 1.0 wt% to about 10 wt% based on the total weight of the SCR catalyst.

[0042] Example 25: The SCR catalyst shows NO conversion of about 58% or more at 200 °C and about 76% or more at 600 °C in the exhaust gas after the thermal aging treatment. X The thermal aging treatment is carried out at 800 °C for 16 hours in the presence of 10% by volume of steam and the rest air, and the exhaust gas has a volume-based space velocity of 80,000 h -1 per hour and contains a gas mixture of 500 ppm of NO, 500 ppm of NH 3、 10% of O 2、 5% of H2O, and the rest N2. The SCR catalyst according to any of embodiments 1 to 24.

[0043] Embodiment 26: The SCR catalyst shows at least about 5% higher NO conversion than a comparative metal-promoted CHA zeolite material having the same metal loading at one or both of the exhaust gas temperatures of 200 °C and 600 °C in the exhaust gas after the thermal aging treatment. x The comparative metal-promoted CHA zeolite material is defined as a zeolite material prepared using a reaction mixture that does not meet one or more of the following criteria: an M / Si molar ratio of at least about 0.4, an R / Si molar ratio of less than about 0.12, an OH - / Si molar ratio of less than about 0.7, and a total ratio of M / Si + R / Si of more than about 0.75. The thermal aging treatment is carried out at 800 °C for 16 hours in the presence of 10% by volume of steam and the rest air, and the exhaust gas has a volume-based space velocity of 80,000 h -1 per hour and contains a gas mixture of 500 ppm of NO, 500 ppm of NH 3、 10% of O 2、An SCR catalyst according to any one of Embodiments 1 to 25, comprising a gas mixture of 5% H2O and the balance N2.

[0044] Embodiment 27: After thermal aging treatment, the SCR catalyst exhibits at least about 5% higher NO conversion in the exhaust gas at one or both of exhaust gas temperatures of 200 °C and 600 °C than a comparative metal-promoted CHA zeolite material having the same metal loading, where the comparative metal-promoted CHA zeolite material meets the following criteria: H x form of + When determined by Al NMR, less than about 20% extraframework aluminum (EFAl), SAR in the range of about 10 to about 30, when determined by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, a surface silanol fraction (X / Y peak ratio) of less than about 0.04 (where X is the peak at 3742 cm 27 and Y is the peak at 3609 cm -1 ), MSA of less than about 25 m -1 / g, a zeolite surface area (ZSA) of at least about 400 m 2 / g, or a zeolite material that does not meet one or more of a normalized ZSA loss of less than about 60% after treating the H 2 form of the zeolite material with a 40 wt% NH4F solution, where the thermal aging treatment is carried out at 800 °C for 16 hours in the presence of 10 vol% steam and the balance air, and the exhaust gas has a volume-based space velocity of 80,000 h + per hour under pseudo-steady-state conditions, with 500 ppm NO, 500 ppm NH -1 3, 10% O 3、 2, and 5% H2O, with the balance N2 in the gas mixture. An SCR catalyst according to any one of Embodiments 1 to 26. 2、 5% H2O and the balance N2 in the gas mixture. An SCR catalyst according to any one of Embodiments 1 to 26.

[0045] Embodiment 28: A catalytic article effective for reducing nitrogen oxides (NO x ) from the exhaust gas of a lean burn engine, the catalytic article comprising a substrate carrier having disposed thereon a selective catalytic reduction (SCR) catalyst according to any one of Embodiments 1 to 27.

[0046] Embodiment 29: The catalyst article according to any one of Embodiments 1 to 28, wherein the substrate carrier is a honeycomb substrate optionally composed of metal or ceramic.

[0047] Embodiment 30: The catalyst article according to any one of Embodiments 1 to 29, wherein the honeycomb substrate carrier is a flow-through substrate or a wall-flow filter.

[0048] Embodiment 31: An exhaust gas treatment system, comprising: a lean burn engine that generates an exhaust gas flow, and a catalyst article according to any one of Embodiments 1 to 30, disposed downstream of the lean burn engine and in fluid communication with the exhaust gas flow.

[0049] Embodiment 32: The following: a. A diesel oxidation catalyst (DOC) disposed upstream of the catalyst article, b. A soot filter disposed upstream of the catalyst article, and c. The exhaust gas treatment system according to any one of Embodiments 1 to 31, further comprising one or more of an ammonia oxidation catalyst (AMOX) disposed downstream of the catalyst article.

[0050] Embodiment 33: A method for treating an exhaust gas flow from a lean burn engine, the method comprising contacting the exhaust gas flow with a catalyst article according to any one of Embodiments 1 to 32, whereby nitrogen oxides (NOx) in the exhaust gas flow are reduced.

[0051] These and other features, aspects, and advantages of the present disclosure will become apparent from the following detailed description together with the accompanying drawings described briefly below. The present invention includes any combination of two, three, four, or more of the above-described embodiments, as well as any combination of two, three, four, or more features or elements described in the present disclosure, regardless of whether such features or elements are explicitly combined in a particular embodiment herein. In the present disclosure, it is intended to be read as a whole that separable features or elements of the disclosed invention should be considered combinable in any of its various aspects and embodiments, unless the context clearly indicates otherwise. Other aspects and advantages of the present invention will become apparent below.

Best Mode for Carrying Out the Invention

[0052] Before describing some exemplary embodiments of the present invention, it should be understood that the present invention is not limited to the details of the configurations or process steps described in the following description. The present invention can have other embodiments and can be implemented or executed in various ways. Although the invention herein is described with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It will be apparent to those skilled in the art that various modifications and changes can be made to the methods and apparatuses of the present invention without departing from the spirit and scope of the present disclosure. Therefore, the present invention is intended to include modifications and changes within the scope of the appended claims and their equivalents.

[0053] Regarding the terms used in this disclosure, the following definitions are provided.

[0054] Throughout this specification, references to "one embodiment", "a particular embodiment", "one or more embodiments", or "an embodiment" mean that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases "in one or more embodiments", "in a particular embodiment", "in one embodiment", or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. The articles "a" and "an" are used herein to refer to one or more than one (i.e., at least one) of the grammatical object of the article.

[0055] Any ranges recited herein are inclusive. The term "about" as used throughout this specification represents small variations and is used for illustrative purposes. For example, the term "about" can refer to ±5% or less, such as ±2% or less, ±1% or less, ±0.5% or less, ±0.2% or less, ±0.1% or less, or ±0.05% or less. All numerical values, whether or not explicitly indicated, are modified by the term "about". Of course, the value modified by the term "about" includes the specific value. For example, "about 5.0" should include 5.0.

[0056] The term "catalyst" or "catalyst material" or "catalytic material" refers to a material that promotes a reaction.

[0057] As used herein, the term "catalyst article" refers to an element used to promote a desired reaction. For example, a catalyst article can include a substrate, such as a honeycomb substrate, having a washcoat containing a catalyst species, such as a catalyst composition.

[0058] The term "washcoat" has its ordinary meaning in the art of thin adherent coatings of catalytic or other materials applied to a carrier substrate material that is porous enough to permit passage of the gas stream being treated, such as a honeycomb-type carrier member. As understood in the art, a washcoat is obtained from a dispersion of particles in a slurry, which is applied to the substrate, dried, and calcined to provide a porous washcoat.

[0059] As used herein, the term "flow" broadly refers to any combination of flowing gases that may contain particulate matter of a solid or liquid nature. The terms "gas flow" or "exhaust gas flow" mean a flow of gaseous components such as engine exhaust, which may contain entrained non-gaseous constituents such as droplets, solid particulates, etc. Engine exhaust gas flow typically includes combustion products, incomplete combustion products, nitrogen oxides, combustible and / or carbonaceous particulate matter (soot), and unreacted oxygen and nitrogen.

[0060] As used herein, "BET surface area" has its ordinary meaning as related to the Brunauer, Emmett, Teller method for determining surface area by N2 adsorption. Pore diameter and pore volume can be determined using BET-type N2 adsorption or desorption experiments.

[0061] "Support" in a catalytic material or catalytic washcoat refers to a material that receives a catalyst (including, for example, a noble metal, stabilizer, promoter, binder, etc.) by precipitation, association, dispersion, impregnation, or other suitable methods.

[0062] As used herein, the term "selective catalytic reduction" (SCR) refers to a catalytic process for reducing nitrogen oxides to dinitrogen (N2) using a nitrogen-containing reducing agent. As used herein, the term "nitrogen oxides" or "NO x " refers to nitrogen oxides. The SCR process typically uses the catalytic reduction of nitrogen oxides with ammonia to form nitrogen and water according to the following reaction. 4NO + 4NH3 + O2 → 4N 2+ 6H2O (standard SCR reaction) 2NO2 + 4NH3 → 3N2 + 6H2O (slow SCR reaction) NO + NO2 + 2NH3 → 2N2 + 3H2O (fast SCR reaction)

[0063] As used herein, the term "zeolite" refers to a specific example of a molecular sieve containing silicon and aluminum atoms. Zeolites are crystalline materials having a fairly uniform pore diameter in the range of about 3 to 10 angstroms, depending on the type of zeolite, as well as the type and amount of cations contained in the zeolite lattice.

[0064] In a more specific embodiment, reference to the "aluminosilicate zeolite" framework type is limited to molecular sieves that do not contain phosphorus or other metals substituted into the framework. However, for clarity, as used herein, "aluminosilicate zeolite" excludes aluminophosphate materials such as SAPO, ALPO, and MeAPO materials, and the broader term "zeolite" is intended to include aluminosilicates and aluminophosphates.

[0065] Molecular sieves of the zeolite CHA - framework type are also referred to herein as "CHA zeolites" and have the approximate formula: (Ca, Na2, K2, Mg)Al2Si4O 12It contains a zeolite group having 6H2O (for example, calcium aluminum silicate hydrate). Three synthetic forms of molecular sieves of the zeolite CHA-framework type are described in "Zeolite Molecular Sieves," by D.W. Breck, published in 1973 by John Wiley & Sons, which is incorporated by reference. The three synthetic forms reported by Breck are Zeolite K-G described in J. Chem. Soc., p. 2822 (1956), Barrer et al, which is incorporated by reference, Zeolite D described in British Patent No. 868,846 (1961), and Zeolite R described in U.S. Patent No. 3,030,181. The synthesis of SSZ-13, another synthetic form of the zeolite CHA framework type, is described in U.S. Patent No. 4,544,538, which is incorporated by reference.

[0066] As used herein, the term "promoted" refers to a metal constituent ("promoter metal") that is intentionally added to the molecular sieve material as opposed to inherent impurities in the molecular sieve. Thus, a promoter is intentionally added to improve the activity of a catalyst as compared to a catalyst that does not have the intentionally added promoter. In order to promote the selective catalytic reduction of nitrogen oxides in the presence of ammonia, in one or more embodiments, a suitable metal(s) is independently exchanged into the molecular sieve.

[0067] In some embodiments, the disclosed zeolites are promoted with promoter metals selected from the group consisting of alkali metals, alkaline earth metals, Group IIIB, Group IVB, Group VB, Group VIB, Group VIIB, Group VIIIB, Group IB, and Group IIB transition metals, Group IIIA elements, Group IVA elements, lanthanides, actinides, and combinations thereof. In some embodiments, further, promoter metals that can be used to prepare the promoted zeolites of the disclosed catalyst compositions include, but are not limited to, copper (Cu), cobalt (Co), nickel (Ni), lanthanum (La), manganese (Mn), iron (Fe), vanadium (V), silver (Ag), cerium (Ce), neodymium (Nd), praseodymium (Pr), titanium (Ti), chromium (Cr), zinc (Zn), tin (Sn), niobium (Nb), molybdenum (Mo), hafnium (Hf), yttrium (Y), tungsten (W), and combinations thereof. In one or more embodiments, the promoter metal content calculated as an oxide is independently in the range of about 0.01 wt% to about 15 wt%, about 0.5 wt% to about 12 wt%, or about 1.0 wt% to about 10 wt% based on the total weight of the corresponding calcined zeolite (including the promoter metal), and is reported on a volatile-free basis. In some embodiments, the promoter metal is copper or iron.

[0068] The promoter metal can be exchanged onto the zeolite by a liquid-phase exchange process, where soluble metal ions exchange with protons or ammonium or sodium ions associated with the zeolite. The exchange can also be carried out by a solid-state process, where solid particles of the promoter metal oxide or metal salt are mixed with the zeolite powder and treated under certain temperatures and gas environments that may or may not contain vapor. The exchange process can also be achieved via an in-situ process during slurry preparation, where fine metal oxide particles are suspended in the zeolite slurry under conditions suitable for solid-liquid interaction.

[0069] In one aspect, the present invention provides a method for forming a CHA zeolite material with improved hydrothermal stability. Hydrothermal stability generally increases with a decrease in framework alumina content (increase in SAR), but the latter also limits the amount of catalytic activity promoter metal (e.g., Cu) sites. Surprisingly, it has been discovered that CHA zeolites with relatively low SAR can be prepared using a FAU zeolite starting material by a method that significantly improves hydrothermal stability by minimizing surface and internal structural defects in the product CHA zeolite.

[0070] The method of the present invention involves forming a reaction mixture comprising at least one alumina source (typically a zeolite having a FAU crystal framework), at least one silica source (such as a source containing an alkali metal silicate solution and / or colloidal silica), at least one organic structure-directing agent, and optionally a secondary alkali metal cation source for increasing the alkali metal content of the reaction mixture. The reaction mixture is typically provided under alkaline aqueous conditions. In certain embodiments, the total molar ratio of alkali metal to Si (M / Si, where M is the number of moles of alkali metal) and the molar ratio of organic structure-directing agent to Si (R / Si, where R is the number of moles of organic structure-directing agent) are greater than the molar ratio of hydroxide ion to Si (OH - / Si). In other words, the total molar ratio of M / Si + R / Si is greater than the molar ratio of OH - / Si. For the bulk reaction mixture, the SAR typically ranges from about 25 to about 35.

[0071] In certain embodiments, the total ratio of M / Si + R / Si is greater than about 0.75, or greater than about 0.80, or greater than about 0.82, or greater than about 0.85, and exemplary ranges are from about 0.75 to about 0.95, or from about 0.80 to about 0.95, or from about 0.85 to about 0.95.

[0072] In some embodiments, OH -The M / Si molar ratio is less than about 0.7, or less than about 0.65, or less than about 0.6, or less than about 0.55, and exemplary ranges are from about 0.3 to about 0.7 or from about 0.4 to about 0.65.

[0073] In certain embodiments, the individual M / Si molar ratio is at least about 0.4, or at least about 0.5, or at least about 0.6, or at least about 0.7, or at least about 0.8, and exemplary ranges are from about 0.4 to about 1.2, or from about 0.6 to about 1.0, or from about 0.7 to about 0.9. The alkali metal can be, for example, lithium, sodium, potassium, rubidium, cesium, or francium. In certain embodiments, the alkali metal is sodium or potassium.

[0074] In certain embodiments, the individual R / Si molar ratio is less than about 0.12, or less than about 0.11, or less than about 0.10, or less than about 0.08, or less than about 0.06, and exemplary ranges are from about 0.04 to about 0.12, or from about 0.06 to about 0.10.

[0075] The reaction mixture can also be characterized by a molar ratio of water to Si (H2O / Si), which is typically in the range of about 12 to about 40.

[0076] The alkali metal silicate solution used in the reaction mixture can provide all of the alkali metal content necessary to achieve the above ratios. However, the alkali metal content of the reaction mixture is optionally supplemented with a secondary alkali metal cation source including alkali metal sulfates (e.g., Na2SO4), alkali metal acetates (e.g., sodium acetate), and alkali metal bromides (e.g., sodium bromide). Optionally, in certain embodiments, the alkali metal silicate solution can be supplemented or replaced with other silica sources such as colloidal silica, fumed silica, tetraethyl orthosilicate (TEOS), and combinations thereof.

[0077] The zeolites used as the alumina source can be diverse and will include various zeolite materials known in the art, particularly various aluminosilicate zeolites. In certain embodiments, zeolites having a FAU crystal structure are used, which are formed by a 12-ring structure and have channels of about 7.4 Å. Examples of such zeolites include faujasite, zeolite X, zeolite Y, LZ-210, and SAPO-37. Such zeolites are characterized by a three-dimensional pore structure with pores running perpendicular to each other in the x, y, and z planes and having secondary building units 4, 6, and 6-6. An example of the SAR range of bulk FAU zeolite materials is from about 3 to about 6, and typically, the unit cell size ranges from 24.35 to 24.65 as determined by XRD. Zeolite Y is particularly useful in certain embodiments of the present invention. FAU zeolites are typically used in an alkali metal form such as Na + form. In one particular embodiment, the FAU zeolite is in the sodium form and contains from about 2.5 wt% to 13 wt% Na2O.

[0078] A typical organic structure-directing agent for this synthesis is adamantyltrimethylammonium hydroxide, although other amines and / or quaternary ammonium salts can be substituted or added. Examples include quaternary ammonium cations having substituents selected from the group consisting of alkyl, adamantyl, cyclohexyl, aromatic, and combinations thereof. Further examples of organic structure-directing agents include cyclohexyltrimethylammonium, benzyltrimethylammonium, and dimethylpiperidinium hydroxide.

[0079] Hydroxide ions are the only necessary mineralizing agent required in the reaction mixture, and the amount of hydroxide required to achieve the above ratios can be provided from the alkali metal silicate solution alone and, to a lesser extent, from the organic structure-directing agent source. Optionally, the hydroxide ion content can be supplemented with an additional source of hydroxide ions such as NaOH or KOH.

[0080] The reaction mixture can be characterized in terms of the solids content expressed as the weight percentage of silica (SiO2) and alumina (Al2O3). The solids content can vary, and exemplary ranges are from about 5% to about 25%, or from about 8% to about 20%.

[0081] The reaction mixture is heated in a pressure vessel while stirring to obtain the desired CHA crystalline product. Typical reaction temperatures are in the range of about 100 °C to about 160 °C, for example, about 120 °C to about 160 °C, at the corresponding autogenous pressure. Typical reaction times are between about 30 hours and about 3 days. Optionally, the product can be centrifuged. Organic additives can be used to assist in the handling and isolation of the solid product. Spray drying is an optional step in the processing of the product.

[0082] In certain embodiments, zeolites having the MOR crystal framework are formed as intermediate products or as by-products. The MOR phase can contain an organic template.

[0083] The solid zeolite product is heat-treated or calcined in air or nitrogen. Typical calcination temperatures are about 400 °C to about 850 °C (e.g., about 500 °C to about 700 °C) over a period of 1 to 10 hours. Following the initial calcination, the CHA zeolite product is mainly in the alkali metal form (e.g., Na + form). Optionally, single or multiple ammonia ion exchanges can be used to obtain the NH4 + form of the zeolite, which can optionally be further calcined to form the H + form.

[0084] In certain embodiments, the CHA zeolite is further ion-exchanged with a promoter metal to form a metal-promoted zeolite catalyst. For example, copper or iron can be ion-exchanged to form Cu-chabazite or Fe-chabazite. When copper acetate is used, the copper concentration of the liquid copper solution used in the copper ion exchange is, in certain embodiments, in the range of about 0.01 to about 0.4 moles, more specifically in the range of about 0.05 to about 0.3 moles.

[0085] In some embodiments, the CHA zeolite crystals obtained from crystallization can be about 80% to about 99% crystals or about 90% to about 97% crystals.

[0086] The CHA zeolite product is characterized by a relatively low mesopore surface area (MSA) combined with a zeolite surface area (ZSA) that provides good catalytic performance. In some embodiments, the MSA of the CHA zeolite product is less than about 25 m 2 / g or less than about 10 m 2 / g (e.g., about 5 to about 25 m 2 / g). The ZSA of the CHA zeolite product is typically at least about 400 m 2 / g, or at least about 450 m 2 / g, or at least about 500 m 2 / g, and an exemplary ZSA range is about 400 to about 600 m 2 / g or about 450 to about 600 m 2 / g. The pore volume and surface area characteristics can be determined by nitrogen adsorption (BET surface area method). The surface areas of the mesopores and zeolites (micropores) were determined by N2 adsorption porosimetry using a Micromeritics TriStar 3000 series instrument according to the ISO9277 method. The samples were degassed for a total of 6 hours using a Micromeritics SmartPrep degasser (heated to 300 °C for 2 hours under a dry nitrogen flow and then held at 300 °C for 4 hours). The nitrogen BET surface area was determined using five partial pressure points from 0.08 to 0.20. The surface areas of the zeolite and matrix were determined using the same five partial pressure points and calculated using the Harkins and Jura t-plot. Pores with diameters greater than 20 Å are considered to contribute to the surface area of the matrix.

[0087] The CHA zeolite product can also be used to exchange the H of the zeolite material with a 40 wt% NH4F solution at 50 °C +After processing the morphology, stirring and sonicating (35 kHz, 90 W) at 350 rpm for 20 minutes, and then drying and firing at 450 °C for 6 hours, relatively low normalized ZSA losses after treatment with an NH4F solution, such as less than about 60% (or less than about 50%), can also be characteristic. The calculation formula for the normalized ZSA loss is presented in the examples.

[0088] Using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, at 3742 cm -1 (Peak X), the integrated intensity of the peak centered around it is compared with the integrated intensity of the peak at 3609 cm -1 (Peak Y). It is estimated that the CHA zeolite product typically exhibits relatively few surface silanols compared to bridged silanols (Bronsted sites). The DRIFT measurements were performed on a Thermo Nicolet equipped with an MCT detector and a Harrick environmental chamber equipped with a ZnSe window. The sample was ground into a fine powder using a mortar and pestle and filled into a sample cup. The sample powder was first dehydrated at 400 °C for 1 hour while flowing Ar at a flow rate of 40 ml / min, and then cooled to 30 °C. The spectrum of the sample was acquired, and KBr was used as a reference. In certain embodiments, the surface silanol fraction (X / Y peak ratio) of the CHA zeolite product is less than about 0.04 or less than about 0.03.

[0089] The CHA zeolite product obtained from the method of the present invention typically has an average crystal size in the range of up to about 3 μm, or about 200 nm to about 3 μm, or about 500 nm to about 2 μm, or about 800 nm to about 1.5 μm. The average crystal size can be measured, for example, using microscopy methods such as scanning electron microscopy (SEM).

[0090] The CHA zeolite product can also 27 be characterized by the amount of extra-framework aluminum (EFAl) in the H + form, determined as a percentage of the total aluminum detected by 27Al NMR. The H + form of the zeolite is Na +The morphology is obtained by ammonium exchange with NH4NO3 followed by calcination at 450 °C (for 6 hours). In certain embodiments, the CHA zeolite product has an EFAl of less than about 20% or less than about 18%, for example, from about 5% to about 18% (or from about 5% to about 15%). All NMR experiments were performed on an Agilent DD2 600 MHz (14.1) spectrometer. The aluminum-27 NMR spectra were measured at a spinning speed of 15 - 20 kHz using a 3.2 mm magic angle spinning assembly. One-dimensional NMR spectra were acquired using a non-selective pi / 12 pulse. Typically, 4 - 16k scans were acquired with a relaxation delay of 1 - 5 s. A 1.0 M Al(NO3)3 solution was used to calibrate the rf field and was used as a reference. The NMR spectra were processed using ACD / Labs® to output intensities and were fitted using Origin Pro®. The percentage of extra-framework aluminum (EFAl) is defined as the integrated peak intensity in the frequency range of 20 to -30 ppm in the NMR spectrum. Prior to measurement, the zeolite was hydrated for 48 hours before measurement in a desiccator containing a saturated solution of the NH4NO3 solution.

[0091] The CHA zeolite product can also be characterized by an SAR range. In certain embodiments, the CHA zeolite product has an SAR of from about 10 to about 30, for example, from about 14 to about 20.

[0092] In certain embodiments, the metal-promoted CHA zeolite materials of the present invention can be characterized by SCR activity at various temperatures. For example, certain embodiments of a copper-promoted CHA zeolite material exhibit NO X conversion of about 58% or more at 200 °C and about 76% or more at 600 °C after a thermal aging treatment, where the thermal aging treatment is performed at 800 °C for 16 hours in the presence of 10 vol% steam and the remainder air. NO x conversion rates were measured under pseudo-steady state conditions with a temperature gradient of 0.5 °C / min from 200 °C to 600 °C, at a volume-based space velocity of 80,000 h -1 -1 and in the presence of 500 ppm NO, 500 ppm NH 3、 3, and 10% O2、 NO of the exhaust gas containing a gas mixture of 5% H2O and the balance N2 x refers to conversion.

[0093] In certain embodiments, the metal-promoted CHA zeolite material of the present invention may be characterized by SCR activity after a thermal aging treatment (the same treatment described in the previous paragraph), where the NO x conversion rate of the metal-promoted CHA zeolite material of the present invention is at least about 5% or at least about 10% higher than that of a comparative metal-promoted CHA zeolite material having the same metal loading at one or both of exhaust gas temperatures of 200 °C and 600 °C, and the comparative zeolite is prepared using a comparative process (e.g., any of Comparative Zeolites A - C) as described in the examples. For example, the comparative metal-promoted CHA zeolite material is a zeolite material made using a reaction mixture that does not meet one or more of the following criteria: an M / Si molar ratio of at least about 0.4, an R / Si molar ratio of less than about 0.12, an OH - / Si molar ratio of less than about 0.7, or a total ratio of M / Si + R / Si of greater than about 0.75. Alternatively, the comparative metal-promoted CHA zeolite material is a zeolite that does not meet the criteria provided herein for the CHA zeolite material of the present invention in one or more of the following properties: extra-framework aluminum (EFAl), SAR, surface silanol fraction (X / Y peak ratio), MSA, ZSA, or the normalized ZSA loss after treatment of the H + form of the zeolite material with a 40 wt% NH4F solution. Similar to the previous paragraph, the NO x conversion rate is at a temperature gradient of 0.5 °C / min from 200 °C to 600 °C, has a volume-based space velocity of 80,000 h -1 per hour under pseudo-steady state conditions, and has 500 ppm NO, 500 ppm NH 3、 10% O 2、 NO of the exhaust gas containing a gas mixture of 5% H2O and the balance N2 x refers to conversion.

[0094] substrate In one or more embodiments, the metal-promoted CHA zeolite catalyst composition of the present invention is disposed on a substrate. As used herein, the term "substrate" refers to a monolith material on which the catalyst material is typically placed in the form of a washcoat. A washcoat is formed by preparing a slurry containing a catalyst with a specific solids content (e.g., 30 wt% to 90 wt%) in a liquid, then coating this onto the substrate and drying to provide a washcoat layer. The washcoat containing the metal-promoted molecular sieve of the present invention may optionally include a binder selected from silica, alumina, titania, zirconia, ceria, or combinations thereof. The loading of the binder is typically about 0.1 to 10 wt% based on the weight of the washcoat.

[0095] In one or more embodiments, the substrate is selected from one or more of a flow-through honeycomb monolith or a particulate filter, and the catalyst material(s) is applied to the substrate as a washcoat.

[0096] Figures 1A and 1B illustrate an exemplary substrate 2 in the form of a flow-through substrate coated with a catalyst composition as described herein. Referring to FIG. 1A, the exemplary substrate 2 has a cylindrical shape and a cylindrical outer surface 4, an upstream end face 6, and a corresponding downstream end face 8 that is identical to the end face 6. The substrate 2 has a plurality of fine and parallel gas flow paths 10 formed therein. As seen in FIG. 1B, the flow paths 10 are formed by walls 12 and extend through the carrier 2 from the upstream end face 6 to the downstream end face 8, and the passages 10 are not blocked so as to allow a fluid, e.g., a gas flow, to flow longitudinally through the carrier 2 via its gas flow paths 10. As more readily seen in FIG. 1B, the walls 12 are sized and configured such that the gas flow paths 10 have a substantially regular polygonal shape. As shown, the catalyst composition can be applied, if desired, in a plurality of separate layers. In the illustrated embodiment, the catalyst composition consists of both a separate bottom layer 14 adhered to the wall 12 of the carrier member and a second separate top layer 16 coated on top of the bottom layer 14. The present invention can be implemented using one or more (e.g., 2, 3, or 4) catalyst layers and is not limited to the two-layer embodiment illustrated in FIG. 1B.

[0097] In one or more embodiments, the substrate is a ceramic or metal having a honeycomb structure. Any suitable substrate can be used, such as a monolithic substrate of the type having fine and parallel gas flow paths extending from the inlet or outlet face of the substrate so that the passages are open and fluid can flow therethrough. The passages, which are essentially straight paths from the fluid inlet to the fluid outlet, are defined by walls on which the catalyst material is coated as a washcoat so that the gas flowing through the passages contacts the catalyst material. The flow paths of the monolithic substrate are thin-walled channels, which can have any suitable cross-sectional shape and size, such as trapezoidal, rectangular, square, sinusoidal, hexagonal, elliptical, circular, etc. Such a structure can include from about 60 to about 900 or more gas inlet openings (i.e., cells) per square inch of cross-section.

[0098] The ceramic substrate can be made from any suitable refractory material, such as cordierite, cordierite-α-alumina, silicon nitride, zircon mullite, spodumene, alumina-silica-magnesia, zircon silicate, sillimanite, magnesium silicate, zircon, petalite, α-alumina, aluminosilicate, etc. The substrate useful for the catalyst of the embodiments of the present invention can also be essentially metallic and can be composed of one or more metals or metal alloys. The metal substrate can include any metal substrate, such as those having openings or "punch-outs" in the channel walls. The metal substrate can be used in various shapes such as pellets, corrugated sheets, or monolithic forms. Specific examples of the metal substrate include heat-resistant base metal alloys, especially alloys in which iron is a substantial or major constituent. Such alloys can contain one or more of nickel, chromium, and aluminum, and the total of these metals is advantageously, in any case, at least about 15% by weight of the alloy based on the weight of the substrate, for example, about 10-25% by weight of chromium, about 1-8% by weight of aluminum, and about 0-20% by weight of nickel.

[0099] In one or more embodiments where the substrate is a particulate filter, the particulate filter can be selected from a gasoline particulate filter or a soot filter. As used herein, the terms "particulate filter" or "soot filter" refer to filters designed to remove particulate matter from an exhaust gas stream such as soot. Particulate filters include, but are not limited to, honeycomb wall flow filters, partial filtration filters, wire mesh filters, wound fiber filters, sintered metal filters, and foam filters. In certain embodiments, the particulate filter is a catalyzed soot filter (CSF). The catalyzed CSF includes, for example, a substrate coated with the catalyst composition of the present invention.

[0100] A wall flow substrate useful for supporting the catalyst material of one or more embodiments has a plurality of fine, substantially parallel gas flow paths extending along the longitudinal axis of the substrate. Typically, each passage is blocked at one end of the substrate body and alternative passages are blocked at the opposite end face. Such a monolithic substrate can include up to about 900 or more flow paths (or "cells") per square inch of cross-section, although far fewer numbers can be used. For example, the substrate can have from about 7 to 600, more typically from about 100 to 400 cells per square inch ("cpsi"). The porous wall flow filter used in embodiments of the present invention can be catalyzed such that the walls of the element have or contain a platinum group metal thereon. The catalyst material can be present on only the inlet side of the substrate wall, only the outlet side, both the inlet and outlet sides, or the wall itself can be entirely or partially composed of the catalyst material. In another embodiment, the present invention can include the use of one or more catalyst layers and combinations of one or more catalyst layers on the inlet and / or outlet walls of the substrate.

[0101] As seen in FIG. 2, an exemplary substrate has a plurality of passages 52. The passages are surrounded tubularly by an inner wall 53 of the filter substrate. The substrate has an inlet end 54 and an outlet end 56. The passages are alternately blocked at the inlet end by an inlet plug 58 and at the outlet end by an outlet plug 60 to form a checkerboard pattern at the inlet 54 and outlet 56. The gas flow 62 enters through an unblocked channel inlet 64, is stopped by the outlet plug 60, and diffuses through the (porous) channel wall 53 to the outlet side 66. The gas cannot return through the inlet side of the wall due to the inlet plug 58. The porous wall flow filter used in the present invention can be catalyzed such that the walls of the substrate have one or more catalyst materials thereon.

[0102] Exhaust gas treatment system A further aspect of the present invention relates to an exhaust gas treatment system. In one or more embodiments, the exhaust gas treatment system includes an engine, particularly a lean burn engine such as a diesel engine or a lean burn gasoline engine, and the catalyst composition of the present invention downstream of the engine.

[0103] One exemplary emissions treatment system is illustrated in FIG. 3, which shows a schematic of emissions treatment system 20. As shown, the emissions treatment system can include a plurality of catalyst components in series downstream of an engine 22, such as a lean burn gasoline engine. At least one of the catalyst components will be an SCR catalyst of the present invention as described herein. The catalyst compositions of the present invention can be combined with a number of additional catalyst materials and placed at various positions relative to the additional catalyst materials. FIG. 3 illustrates five catalyst components 24, 26, 28, 30, 32 in series, although the total number of catalyst components can vary and the five components are merely an example.

[0104] Without limitation, Table 1 presents various exhaust gas treatment system configurations of one or more embodiments. Note that each catalyst is connected to the next via an exhaust duct such that the engine is upstream of catalyst A, which is upstream of catalyst B, which is upstream of catalyst C, which is upstream of catalyst D, which is upstream of catalyst E (if present). References to components A - E in the table can be cross - referenced with the same symbols in FIG. 3.

[0105] The DOC catalyst described in Table 1 can be any catalyst conventionally used to reduce carbon monoxide (CO) and hydrocarbon (HC) pollutants in an engine's exhaust gas and will typically include a platinum group metal (PGM) supported on a refractory metal oxide support (e.g., alumina).

[0106] The LNT catalyst described in Table 1 can be any catalyst conventionally used as a NO x trap and will typically include a base metal oxide (such as BaO, MgO, CeO2, etc.) and a platinum group metal (e.g., Pt and Rh) for oxidation and reduction of NO by the catalyst, and an NO x adsorbent composition.

[0107] References to DPF in the table refer to a diesel particulate filter, which typically consists of a wall flow filter adapted to filter particulate matter in the exhaust gas.

[0108] References to SCR in the table refer to an SCR catalyst that may include the SCR catalyst composition of the present invention. References to SCRoF (or SCR on filter) refer to a particulate or soot filter (e.g., a wall flow filter) that may include the SCR catalyst composition of the present invention. If both SCR and SCRoF are present, one or both may include the SCR catalyst of the present invention, or one of the catalysts may include a conventional SCR catalyst. The exhaust treatment system may optionally include an injector disposed upstream of the SCR catalyst and adapted to inject ammonia or an ammonia precursor (e.g., urea) into the exhaust stream.

[0109] References to AMOx in the table refer to an ammonia oxidation catalyst provided downstream of the catalyst of one or more embodiments of the present invention and capable of removing any leaked ammonia from the exhaust gas treatment system. In certain embodiments, the AMOx catalyst may include a PGM component. In one or more embodiments, the AMOx catalyst may include a bottom coat having PGM and a top coat having an SCR function.

[0110] As will be recognized by those skilled in the art, in the configurations listed in Table 1, any one or more of components A, B, C, D, or E may be disposed on a particulate filter such as a wall flow filter or on a flow-through honeycomb substrate. In one or more embodiments, the engine exhaust system includes one or more catalyst compositions attached at a location near the engine (a direct connection location, CC), and additional catalyst compositions are located under the vehicle body (an underfloor location, UF).

[0111]

Table 1

[0112] Method for treating engine exhaust Another aspect of the present invention relates to a method for treating the exhaust gas stream of an engine, particularly a lean burn engine. The method may include placing a catalyst according to one or more embodiments of the present invention downstream of the engine and flowing the exhaust gas stream of the engine over the catalyst. In one or more embodiments, the method further includes placing additional catalyst components downstream of the engine as described above.

[0113] Hereinafter, the present invention will be described with reference to the following examples. Before describing some exemplary embodiments of the present invention, it should be understood that the present invention is not limited to the details of the configurations or process steps described in the following description. The present invention is capable of other embodiments and can be implemented or carried out in various ways.

[0114] Experiment A series of CHA zeolites were synthesized using the process of the present invention and comparative processes. The gel compositions and crystallization conditions leading to the zeolite materials of the comparative (A - C) and the present invention (D - F) are summarized in Table 2, and the properties of the resulting products are presented in Table 3. Trimethyladamantylammonium hydroxide (TMAdaOH) was used as the organic structure - directing agent (OSDA) for CHA.

[0115] For the crystallization of the zeolites of Comparative A - C, NaOH was used as the mineralizing agent and the sole source of Na in the gel, and aluminum isopropoxide and colloidal silica (40 wt% SiO2) functioned as the Si and Al sources, respectively. + For the crystallization of the zeolites of D - F of the present invention, sodium silicate solution (SiO2 / Na2O = 2.6, 37% solids content) and Na - FAU (SiO2 / Al2O3 = 5.1) were used as the Si and Al sources, respectively. The Na content of the gel was supplemented with Na2SO4 to achieve the desired Na / Si ratio. Further, H2SO4 was used to neutralize the excess OH

[0116] to obtain the desired OH / Si ratio. For the sodium silicate solution, Na + and OH - and for the sodium silicate solution, Na + and OH- Assuming a 1:1 ratio with OH - / SiO2 ratio was calculated.

[0117] It should be noted that the examples of the present invention have significantly higher Na / Si and OH / Si ratios than the comparative examples. In all cases, crystallization was carried out at autogenous pressure in a 2 L stirred autoclave.

[0118] The product was isolated by filtration, dried, and calcined (540 °C, 6 h) to obtain the Na + form, which was characterized by XRD and N2-physical adsorption.

[0119] After calcination, single or multiple NH4 + exchanges were carried out until the Na2O content reached <500 ppm. The NH4 + form was calcined (450 °C, 6 h) to obtain the H + form, which was subjected to solid-state 27 Al-NMR, FTIR measurements, and NH4F treatment (details below). Copper filling (by in-situ solid-state exchange) was also carried out on the H + form of the zeolite.

[0120]

Table 2

[0121] All crystallizations yielded products with >90% crystallinity of the primary phase and a corresponding high micropore surface area (>500 m 2 / g). For Comparative Examples A - C, the gel silica to alumina ratio (SAR) is similar to the product SAR, following a >90% silica yield (based on complete aluminum conversion). In the examples of the present invention, the silica yield varies from 35 - 54% and is consistent with a large difference between the gel and product SAR. Furthermore, the product SAR of Examples D - F increases as the OH / Si ratio of the gel decreases.

[0122] In addition to compositional differences, the sets of comparative examples and examples of the present invention also show important structural differences. First, the MSA of products A - C is in the range of 34 - 50 m 2 / g, while products D - F exhibit a mesopore surface area (MSA) of < 18 m 2 / g. Furthermore, the H + form of products D - F contains 30 - 50% less extra-framework aluminum than the corresponding products A - C with similar SAR. Dealumination typically occurs in the as-prepared state and during the calcination of the NH4 + form, and the tendency to retain framework Al during these high-temperature treatments may also be related to hydrothermal stability.

[0123]

Table 3

[0124] The DRIFT spectra of samples A and D are shown in Figure 4, and the spectra are scaled to the peak at 3609 cm -1 . The absolute intensity of the spectra depends on the packing density and particle size, but the relative abundance of surface silanols compared to bridged silanols (Bronsted sites) can be estimated by comparing the intensity of the peak at 3742 cm -1 (peak X) to the intensity at 3609 cm -1 (peak Y). Since products A and D have very similar SAR, the lower the X / Y peak ratio of D, the lower the density of surface silanols. Similarly, the X / Y peak ratio of the examples of the present invention is substantially lower than that observed from comparative examples with similar SAR.

[0125] The NH4F treatment that selectively etches the grain boundaries of zeolite materials, which are interfaces between mutually grown crystallites and other defect-rich regions, was originally developed by Qin et al. [Qin et.al, Angew.Chem.Int.Ed. 2016 55, 19049] as a means of imparting mesoporosity. In this specification, this treatment is used as a means of quantifying the defect density by measuring the relative rate of etching. In this treatment, 10 g of zeolite (H + form) is dispersed in a 40 wt% NH4F solution with stirring and sonication at 50 °C for 20 minutes. The resulting product is isolated by filtration and washed with excess water. After drying and calcination (450 °C, 6 h), the product was characterized by N2 physisorption and XRD. The relative disappearance rate of the zeolite material may be related to the mass-normalized loss of microporosity (zeolite surface area or ZSA), as defined below, where ZSA is the zeolite surface area and M represents the mass. This quantity is presented in Table 4 along with the N2 physisorption characteristics of the selected materials before and after NH4F treatment.

[0126] [Number]

[0127] [Table 4]

[0128] The material (F) of the present invention exhibits a significantly lower normalized ZSA loss compared to the comparative materials (B and C). Furthermore, within each set of materials, the etching rate increases with decreasing SAR. The results showed that the defect density depends on the SAR but is generally higher for the comparative materials. Therefore, the zeolite materials of the present invention demonstrate that minimizing the structural defects on the surface and inside of the zeolite leads to a substantial improvement in hydrothermal stability.

[0129] To prepare an SCR catalyst from the aforementioned materials, H +Cu ions were introduced into the morphological zeolite to achieve a CuO loading of 5.7 - 6.3 wt%. A catalyst coating containing Cu-CHA, zirconium oxide, and pseudoboehmite (PB-250) binder was deposited by a washcoat process onto a porous ceramic monolith having a cell density of 400 cpsi and a wall thickness of 6 mils. The coated monolith was dried at 110 °C and calcined at about 550 °C for 1 hour. The coating process provided a catalyst loading of 2.1 g / inch 3 and 5% of which was zirconium oxide and 5% was an aluminum oxide binder. In the presence of 10% H2O / air, the coated monolith was hydrothermally aged at 800 °C for 16 hours. NO X conversion (Figure 5) was measured in a laboratory reactor at a volumetric-based space velocity of 80,000 h 3、 per hour of gas under pseudo-steady state conditions in a gas mixture of 500 ppm NO, 500 ppm NH 2、 10% O -1 5% H2O, and the balance N2 with a temperature gradient of 0.5 °C / min from 200 °C to 600 °C. For materials with similar SARs, the materials of the present invention have improved performance in low temperature (200 °C) NO conversion. This advantage is greatest at SAR11 and tends to decrease with increasing SAR (for CHA-based catalysts).

[0130] At SAR 11 and 6.3% CuO, catalyst D of the present invention shows a 53% (absolute) advantage over comparative catalyst A. In the SAR 14 - 16 range, catalyst E shows an 8 - 30% (based on CuO content) advantage over material B. Finally, in the upper part of the SAR range (18 - 19), catalyst F shows a 12% significance over catalyst C. In combination with the results of the above property studies, a relationship can be observed between the defect density of the zeolite and the hydrothermal stability of the resulting catalyst. In conclusion, differences in the synthesis route can be used to minimize the defect density and result in improved hydrothermal stability.

[0131] The solids content and the silica source were varied, but the details of all other experiments were made the same as in the examples of catalyst F of the original invention, and the experimental procedure of catalyst F of the present invention was repeated. Table 5 below compares the original catalyst F of the present invention with two examples of the same general composition having different solids contents and / or silica sources. As shown in the table, varying the silica source and the solids content did not prevent the formation of zeolites having the desired ranges of ZSA and MSA. The characteristics of the other gels and the crystallization conditions are as in entry F of Table 2.

[0132]

Table 5

[0133] It will be readily apparent to those skilled in the relevant art that suitable modifications and adaptations to the compositions, methods, and uses described herein can be made without departing from the scope of any embodiment or aspects thereof. The compositions and methods provided are exemplary and are not intended to limit the scope of the claimed embodiments. All of the various embodiments, aspects, and options disclosed herein can be combined in any variation. The scope of the compositions, formulations, methods, and processes described herein includes all actual or potential combinations of all of the embodiments, aspects, options, examples, and preferences of this specification. All patents and publications cited herein are incorporated herein by reference for their specific teachings as described, unless a specific incorporation of other descriptions is provided.

Claims

1. A method for synthesizing a zeolite material having a CHA crystal framework, comprising: i) forming a reaction mixture comprising at least one alumina source comprising zeolite, at least one silica source, and at least one organic structure-directing agent, wherein the reaction mixture has a total molar ratio of M / Si + R / Si higher than the OH － / Si molar ratio, where M is the number of moles of alkali metal and R is the number of moles of organic structure-directing agent; ii) crystallizing the reaction mixture to form a product zeolite having the CHA crystal framework, wherein the product zeolite has a mesopore surface area (MSA) of less than 25 m ２ / g, and forming; and ion-exchanging the product zeolite having the CHA crystal framework with a promoter metal to form an ion-exchanged zeolite catalyst, and the zeolite material having a CHA crystal framework is defined as a zeolite material prepared using a predetermined reaction mixture, the predetermined reaction mixture satisfies one or more of the following criteria: an M / Si molar ratio of at least 0.4; an R / Si molar ratio of less than 0.12; an OH− / Si molar ratio of less than 0.7; and a total ratio of M / Si + R / Si of greater than 0.75, and the crystallization in step ii) is carried out at a) 100 °C to 160 °C, or b) at a high temperature and autogenous pressure, a method.

2. The method according to claim 1, wherein the zeolite of the alumina source has a FAU crystal framework.

3. The method according to claim 2, wherein the zeolite having a FAU crystal framework is zeolite Y.

4. The method according to claim 3, wherein the zeolite Y is in the Na+ form and has a silica-to-alumina ratio (SAR) in the range of 3 to 6.

5. The method according to claim 1, wherein M is sodium and the silica source comprises an alkali metal silicate solution, and the alkali metal silicate solution is sodium silicate.

6. The method according to claim 1, wherein the organic structure-directing agent is a quaternary ammonium salt having a substituent selected from the group consisting of alkyl, aromatic, and combinations thereof.

7. The method according to claim 1, wherein the organic structure-directing agent is a quaternary ammonium salt having an adamantyl, cyclohexyl, or benzyl substituent.

8. The product zeolite having the CHA crystal framework is as follows: a. H ＋ In the form of ２７ When determined by Al NMR, less than 20% of the extra-framework aluminum (EFAl), b. an SAR in the range of 10 to 30, c. When determined by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, a surface silanol fraction (X / Y peak ratio) of less than 0.04 (where X is the peak at 3742 cm －１ and Y is the peak at 3609 cm －１ ). d. 10 m ２ MSA less than / g, and e. At least 400 m ２ / g of the zeolite surface area (ZSA), one or more of which are characterized, the method according to claim 1.

9. Firing the product zeolite having the CHA crystal framework to form a fired zeolite in the H ＋ form or the Na ＋ form, the method according to claim 1, further comprising.

10. The method according to claim 1, wherein the promoter metal is Fe or Cu.

11. The method according to claim 1, wherein the silica source comprises an alkali metal silicate solution.

12. The method according to claim 1, wherein the solids content of the reaction mixture is 5 to 25% by weight.

13. A zeolite material having a CHA crystal framework, wherein the zeolite material has a mesopore surface area (MSA) of less than 25 m ２ / g and a zeolite surface area (ZSA) of at least 400 m ２ / g, and further, the zeolite material is as follows: a. ２７ When determined by Al NMR, less than 20% of extra-framework aluminum (EFAl), b. When determined by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, a surface silanol fraction (X / Y peak ratio) of less than 0.04 (where X is the peak at 3742 cm －１ and Y is the peak at 3609 cm －１ ), and c. The H ＋ form of the zeolite material is characterized by one or more of less than 60% of the normalized ZSA loss after treatment with a 40 wt% NH ４ F solution, and The zeolite material having a CHA crystal framework is defined as a zeolite material prepared using a predetermined reaction mixture, the predetermined reaction mixture satisfies the following criteria: At least a molar ratio of M / Si of 0.4; a molar ratio of R / Si of less than 0.12; a molar ratio of OH− / Si of less than 0.7; and a total ratio of M / Si + R / Si of more than 0.75, and the normalized ZSA loss is given by the following equation 【Number 1】 where M represents mass and ZSA is the zeolite surface area A zeolite material defined by

14. The zeolite material according to claim 13, having an SAR in the range of 10 to 30.

15. The zeolite material according to claim 13, having an SAR in the range of 16 to 22.

16. The zeolite material according to claim 13, having an SAR in the range of 18 to 20.

17. H ＋ in the form of ２７ The zeolite material according to claim 13, having less than 15% extra-framework aluminum (EFAl) as determined by Al NMR.

18. A zeolite material according to claim 13, having an MSA of less than 10 m ２ / g.

19. A selective catalytic reduction (SCR) catalyst effective for reducing nitrogen oxides (NO ｘ ), which comprises the zeolite material according to claim 13, promoted with a promoter metal selected from iron, copper, and combinations thereof.

20. The SCR catalyst according to claim 19, wherein the promoter metal is present in an amount of 1.0 wt% to 10 wt% based on the total weight of the SCR catalyst.

21. The SCR catalyst shows NO conversion of 58% or more at 200 °C and 76% or more at 600 °C in exhaust gas after the heat aging treatment, the heat aging treatment is carried out at 800 °C for 16 hours in the presence of 10% by volume of steam and the rest being air, and the exhaust gas has a volume-based space velocity of 80,000 h Ｘ per hour under quasi-steady state conditions and contains a gas mixture of 500 ppm of NO, 500 ppm of NH －１ 10% of O ３、 5% of H ２、 O, and the rest being N ２ The SCR catalyst according to claim 19. ２ ​

22. A catalytic article effective for reducing nitrogen oxides (NO ｘ ) from the exhaust gas of a lean combustion engine, the catalytic article comprising a substrate carrier having disposed thereon the selective catalytic reduction (SCR) catalyst according to claim 19.

23. The catalyst article according to claim 22, wherein the substrate carrier is a honeycomb substrate optionally composed of metal or ceramic.

24. The catalyst article according to claim 23, wherein the honeycomb substrate is a flow-through substrate or a wall-flow filter.

25. An exhaust gas treatment system comprising: A lean burn engine that generates an exhaust gas flow, and The catalyst article according to claim 22, disposed downstream of the lean burn engine and in fluid communication with the exhaust gas flow.

26. The following: a. A diesel oxidation catalyst (DOC) disposed upstream of the catalyst article, b. A soot filter disposed upstream of the catalyst article, and c. The exhaust gas treatment system according to claim 25, further comprising one or more of an ammonia oxidation catalyst (AMOX) disposed downstream of the catalyst article.

27. A method for treating an exhaust gas flow from a lean burn engine, comprising: Contacting the exhaust gas flow with the catalyst article according to claim 22 so as to reduce nitrogen oxides (NOx) in the exhaust gas flow.

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