Method for forming catalyst article

Abstract

The present disclosure relates to a process for forming a catalyst article, the process comprising: (a) forming a slurry having a solids content of at most 50% by weight by mixing together at least the following components at a temperature in the range of 10 DEG C to 35 DEG C: a crystalline molecular sieve in the form of H + or NH4 +, an insoluble active metal precursor, and an aqueous solvent; (b) coating a substrate with the slurry formed in step (a); and (c) calcining the coated substrate formed in step (b) to form a catalyst layer on the substrate. The present disclosure further relates to a catalyst article, in particular a catalyst article suitable for selective catalytic reduction of nitrogen oxides, and to an exhaust system.

Description

[0001] This application is a divisional application of the application with application date of May 26, 2021, application number 202180032350.4, and invention name “Method for forming catalyst products”. Technical Field

[0002] The present invention relates to a method for forming a catalyst article. In particular, the present invention relates to a method for forming a catalyst article suitable for the selective catalytic reduction of nitrogen oxides (NOx) in exhaust gases. Background Art

[0003] Numerous catalytic converters are manufactured annually to treat emissions from mobile and stationary sources. Catalytic converters for motor vehicles typically comprise an extruded ceramic monolith provided with channels for the exhaust gases to flow through. The channels of the monolith may be coated with a catalytically active material. Alternatively, the extruded monolith itself may be formed from the catalytically active material (referred to as a "fully active extrudate" or "extruded catalyst").

[0004] In the production of coated catalysts, a composition called a "washcoat" is applied to a substrate (e.g., a ceramic monolith). The washcoat typically comprises a liquid and a catalytically active material. The washcoat can take the form of a solution, slurry, or suspension of the catalytic material in a solvent. Once applied to the substrate, the washcoat typically undergoes a calcination step to remove the solvent and fix the catalytically active material to the substrate.

[0005] The substrate for a catalytic converter typically comprises a unitary structure in the form of a honeycomb structure having uniformly sized, parallel channels extending from a first end to a second end. Typically, the channels are open at the first and second ends—a so-called "flow-through" configuration. Alternatively, the channels at the first, upstream end may be plugged, for example, with a suitable ceramic cement, and the unplugged channels at the first, upstream end may be plugged at the second, downstream end to form a so-called wall-flow filter.

[0006] Nitrogen oxides (NO) are reduced by ammonia selective catalytic reduction (NH3-SCR) x ) is considered to be a novel NOx removal agent for exhaust gases emitted from stationary sources as well as mobile engines (primarily diesel engines) of vehicles such as cars, trucks, locomotives and ships. x The most practical and efficient technology.

[0007] Known SCR (selective catalytic reduction) catalysts include molecular sieves. Available molecular sieves include crystalline or quasi-crystalline materials, which can be, for example, aluminosilicates (zeolites) or silicoaluminophosphates (SAPOs). Such molecular sieves are composed of repeated SiO4, AlO4 and optionally PO4 tetrahedral units, which are connected together in the form of rings to form a framework with regular intracrystalline cavities and molecular-sized channels. The specific arrangement of tetrahedral units (ring members) produces the framework of the molecular sieve, and by convention, the International Zeolite Association (IZA) assigns a unique three-letter code (e.g., "CHA") to each unique framework. Examples of molecular sieve frameworks of known SCR catalysts include framework type codes CHA (chabazite), BEA (β), MOR (mordenite), AEI, MFI, and LTA.

[0008] Molecular sieves (e.g., zeolites) can also be classified based on pore size, e.g., the maximum number of tetrahedral atoms present in the framework of the molecular sieve. As defined herein, "small pore" molecular sieves such as CHA contain a maximum ring size of eight tetrahedral atoms, while "medium pore" molecular sieves such as MFI contain a maximum ring size of ten tetrahedral atoms; and "large pore" molecular sieves such as BEA contain a maximum ring size of twelve tetrahedral atoms. Small pore molecular sieves and medium pore molecular sieves, especially small pore molecular sieves, are preferred for use in SCR catalysts because they can, for example, provide improved SCR performance and / or improved hydrocarbon tolerance.

[0009] The molecular sieve catalyst can be metal-promoted. Examples of metal-promoted molecular sieve catalysts include iron-promoted molecular sieves, copper-promoted molecular sieves, and palladium-promoted molecular sieves, wherein the metal can be loaded into the molecular sieve. In metal-loaded molecular sieves, the loaded metal is a type of "extra-framework metal," i.e., a metal that resides within the molecular sieve and / or on at least a portion of the molecular sieve surface, and does not include atoms that constitute the molecular sieve framework. For example, it is known that iron-loaded zeolites and copper-loaded zeolites promote SCR reactions.

[0010] In the literature, several methods for preparing metal-loaded molecular sieves, particularly metal-loaded zeolites, have been mentioned. The direct synthesis of metal-loaded zeolites is a complicated process and depends on synthesis conditions (see M. Moliner, ISRN Materials Science [ISRN Materials Science], 2012, article number 789525). An alternative is to use a commercial zeolite support, and subsequently, by for example wet impregnation, wet ion exchange or solid-state ion exchange, zeolite is subjected to post-synthesis treatment to add metal.

[0011] Known wet ion exchange methods for adding metals to molecular sieves (e.g., zeolites) typically employ soluble metal salts, such as metal acetates, metal sulfates, or metal chlorides, as active metal precursors, wherein the active metal precursors react with the molecular sieve in an aqueous solution. To accelerate ion exchange, such methods typically require a heating step, wherein the mixture may be heated to a temperature in the range of 70°C to 80°C for up to several hours. In addition, additional processing steps (e.g., filtration, evaporation, spray drying, etc.) may be required before the resulting metal-loaded molecular sieve can be used in a carrier coating composition to form a catalyst product. Furthermore, it has been found that when certain metal acetates (e.g., copper acetate) are employed to prepare metal-loaded molecular sieves (e.g., metal-loaded zeolites) for use as SCR catalysts, any residual metal acetate remaining after calcination may have a poisonous effect on the ammonia slip catalyst (ASC) used downstream or proximal to the SCR catalyst.

[0012] The present invention provides an improved process for preparing washcoated catalyst articles that utilize metal-supported crystalline molecular sieves as the catalytically active material.

[0013] According to a first aspect of the present disclosure, there is provided a method for forming a catalyst article, the method comprising:

[0014] (a) forming a slurry by mixing together at least the following components:

[0015] (i) H + or NH4 + in the form of crystalline molecular sieves;

[0016] (ii) insoluble active metal precursors;

[0017] (iii) aqueous solvent;

[0018] wherein the solids content of the slurry is up to 50 wt %, and wherein step (a) is carried out at a temperature in the range of 10°C to 35°C;

[0019] (b) coating a substrate with the slurry formed in step (a); and

[0020] (c) calcining the coated substrate formed in step (b) to form a catalyst layer on the substrate.

[0021] Advantageously, it has been found that the heat used to calcine the coated substrate can be used to facilitate metal loading onto the molecular sieve. Thus, the need for any heating step during the wet ion exchange or wet impregnation process, as well as the need for expensive, high-temperature resistant equipment, can be avoided. Furthermore, the long reaction times typical of wet ion exchange or wet impregnation processes and / or energy- and labor-intensive processes such as spray drying can be avoided. Thus, the method according to the first aspect can be more energy-efficient and economical.

[0022] Furthermore, it has been found that the slurry prepared in step (a) of the method according to the first aspect can be used directly as a washcoat composition without any further processing steps.

[0023] Furthermore, the use of insoluble metal species (such as metal carbonates) as active metal precursors can result in fewer hazardous substances being generated during calcination than when metal acetates are used as active metal precursors. Thus, the use of insoluble active metal precursors can provide health and safety benefits.

[0024] Furthermore, it has been found that catalysts prepared by the method according to the first aspect can provide SCR activity at least comparable to that of catalysts comprising metal-supported molecular sieves (e.g., metal-supported zeolites) (prepared by wet ion exchange or wet impregnation). Additionally, it has been found that poisoning of associated ammonia slip catalysts can be mitigated compared to catalysts comprising metal-supported molecular sieves that have been prepared using metal acetates as active metal precursors.

[0025] According to a second aspect of the present disclosure, there is provided a catalyst article obtainable or obtainable according to the method of the first aspect.

[0026] According to a third aspect of the present disclosure, there is provided an exhaust system comprising: a source of nitrogenous reductant and an injector for injecting the nitrogenous reductant into the flowing exhaust gas, wherein the injector is disposed upstream of the catalyst article according to the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The NO reduction achieved by the catalyst article prepared according to the first aspect of the present disclosure is shown in FIG. x Graph of conversion and N2O selectivity compared to catalyst preparations prepared by prior art methods.

[0028] Figure 2 The NO conversion achieved by the catalyst prepared according to the first aspect of the present disclosure is shown in FIG. x Graph of conversion and N2O selectivity. DETAILED DESCRIPTION

[0029] The present disclosure will now be further described. In the following paragraphs, different aspects / embodiments of the present disclosure are defined in more detail. Unless otherwise expressly stated, each aspect / embodiment so defined may be combined with any other aspect / embodiment or multiple aspects / embodiments. Specifically, any feature indicated as preferred or advantageous may be combined with any other feature or features indicated as preferred or advantageous.

[0030] Additionally, as used herein, the term "comprising" may be replaced with the definition of "consisting essentially of" or "consisting of." The term "comprising" is intended to indicate that the recited elements are essential, but other elements may be added and still form a construction within the scope of the claim. The term "consisting essentially of" limits the scope of the claim to the specified materials or steps and those that do not materially affect the basic and novel characteristics of the claimed invention. The term "consisting of" limits the claim to not including materials other than those recited, except for impurities normally associated therewith.

[0031] Crystalline molecular sieves are typically composed of aluminum, silicon and / or phosphorus.Crystalline molecular sieves generally have a three-dimensional arrangement (eg, a framework) of repeating SiO4, AlO4, and optionally PO4 tetrahedral units connected by shared oxygen atoms.

[0032] The term "H" for molecular sieves + The term "form" refers to a molecular sieve having an anionic framework wherein the charge of the framework is determined by protons (i.e., H + cations) in reverse equilibrium.

[0033] The term NH4 about molecular sieves + The form refers to a molecular sieve having an anionic framework wherein the charge of the framework is provided by ammonium cations (i.e., NH4 + cations) in reverse equilibrium.

[0034] When the crystalline molecular sieve has an aluminosilicate framework, then the molecular sieve is preferably a zeolite.

[0035] The molecular sieve may be a small pore molecular sieve (ie, having a maximum ring size of eight tetrahedral atoms) or a medium pore molecular sieve (ie, having a maximum ring size of ten tetrahedral atoms).

[0036] In the case where the crystalline molecular sieve is a small pore molecular sieve, the small pore molecular sieve can be selected from the group of framework types consisting of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, KFI, LEV, LTA, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SFW, SIV, THO, TSC, UEI, UFI, VNI, YUG and ZON and mixtures and / or intergrowths thereof. Preferably, the small pore molecular sieve has a framework type selected from the group of framework types consisting of AEI, AFT, AFX, CHA, DDR, ERI, KFI, LEV, LTA, SFW and RHO. More preferably, the small pore crystalline molecular sieve has a framework type that is AEI, AFX, CHA, LTA, ERI or AEI-CHA intergrowth.

[0037] In the case where the crystalline molecular sieve is a mesoporous molecular sieve, the mesoporous molecular sieve can be selected from the group of framework types consisting of AEL, AFO, AHT, BOF, BOZ, CGF, CGS, CHI, DAC, EUO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS, MRE, MTT, MVY, MWW, NAB, NAT, NES, OBW, PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, -SVR, SZR, TER, TON, TUN, UOS, VSV, WEI and WEN and mixtures and / or intergrowths thereof. Preferably, the mesoporous crystalline molecular sieve is a group of framework types consisting of FER, MEL, MFI, STI and STT.

[0038] Preferably, the crystalline molecular sieve is a small pore molecular sieve having the framework type CHA, AEI, AFX, LTA or ERI.

[0039] Wherein the crystalline molecular sieve is a zeolite, the zeolite may have a silica to alumina ratio (SAR) of 5 to 200, preferably 5 to 100, more preferably 10 to 80. For example, the zeolite may have a silica to alumina ratio (SAR) of 5 to 30.

[0040] Where the crystalline molecular sieve is a SAPO, the silicon content of the SAPO may range from 5 wt% to 30 wt%, preferably from 8 wt% to 16 wt%, based on the total weight of the molecular sieve.

[0041] The crystalline molecular sieve is preferably a powdered crystalline molecular sieve (i.e., in the form of particles), wherein the particles comprise individual crystals, aggregates of crystals, or a combination of both. As measured by scanning electron microscopy (SEM), the average crystal size of the crystalline molecular sieve may be ≥0.5 μm, preferably between about 0.5 μm and about 15 μm, such as about 0.5 μm to 10 μm, about 0.5 μm to about 5 μm, about 1 μm to about 5 μm, or about 2 μm to about 5 μm.

[0042] The D90 particle size of the powdered crystalline molecular sieve is preferably less than 10 μm. For example, the powdered crystalline molecular sieve can have a D90 particle size in the range of 2 μm to 9 μm, preferably 3 μm to 8 μm. As used herein, the term "D90 particle size" refers to a particle size distribution. The value of the D90 particle size corresponds to the particle size value at which 90% (by volume) of the total particles in a particular sample are located. The D90 particle size can be determined using a laser diffraction method (e.g., using a Malvern Mastersizer 2000).

[0043] If desired, the molecular sieve may be subjected to a particle size reduction treatment such as jet milling, wet milling or steam assisted jet milling prior to forming the slurry in step (a) of the process of the first aspect.

[0044] The components to be mixed together in step (a) of the first aspect may comprise two or more + or NH4 + Thus, the resulting catalyst layer formed in step (c) may comprise two or more different types of metal-supported molecular sieves.

[0045] As used herein, " active metal precursor " refers to a metal species capable of supplying a framework extrametallic metal to a crystalline molecular sieve. As used herein, the term "framework extrametallic metal" refers to a metal that resides in the molecular sieve (i.e., in a microporous structure, an ion exchange position or a non-ion exchange position) and / or at least a portion of the molecular sieve surface (e.g., in the form of ions or oxides), and does not include the metal atoms of the tetrahedral units that constitute the molecular sieve framework. It should be understood that additional metal species may be present in the slurry formed in step (a), and these metal species themselves will not participate in the metal loading.

[0046] "Insoluble active metal precursor" means an active metal precursor that is insoluble in water. Specifically, the water solubility of the insoluble active metal precursor may be less than 1 g / 100 ml, for example, less than 0.1 g / 100 ml or less than 0.01 g / 100 ml. Water solubility is a measure of the amount of a material that will dissolve in a certain volume of water to form a saturated solution at a specified temperature and pressure. As used herein, the term "water solubility" with respect to an insoluble active metal precursor means the amount of the insoluble active metal precursor (in grams) that will dissolve in 100 milliliters of water at a temperature of 20° C. and a pressure of 1 atmosphere (g / 100 ml).

[0047] Suitable insoluble active metal precursors include certain metal salts. Specifically, the insoluble active metal precursor can be a metal carbonate, a metal hydroxide, or a metal oxalate.

[0048] The insoluble active metal precursor preferably comprises a metal salt that undergoes thermal decomposition by pyrolysis at temperatures below 500°C.

[0049] The insoluble active metal precursor may comprise a salt of a transition metal, a salt of a noble metal, or a salt of a rare earth metal. For example, the insoluble active metal precursor may comprise one or more insoluble copper salts, manganese salts, nickel salts, cobalt salts, iron salts, palladium salts, platinum salts, cerium salts, yttrium salts, niobium salts, lanthanum salts, zinc salts, calcium salts, magnesium salts, or any mixture of two or more thereof.

[0050] Specifically, the insoluble active metal precursor is selected from the group consisting of copper carbonate, manganese carbonate, nickel carbonate, cobalt carbonate, iron carbonate, palladium carbonate, platinum carbonate, cerium carbonate, yttrium carbonate, niobium carbonate, lanthanum carbonate, zinc carbonate, zirconium carbonate, calcium carbonate, magnesium carbonate, copper hydroxide, manganese hydroxide, nickel hydroxide, cobalt hydroxide, iron hydroxide, palladium hydroxide, platinum hydroxide, cerium hydroxide, yttrium hydroxide, niobium hydroxide, lanthanum hydroxide, zinc hydroxide, zirconium hydroxide, calcium hydroxide, magnesium hydroxide, copper oxalate, calcium oxalate, iron oxalate, manganese oxalate, cobalt oxalate, cerium oxalate, yttrium oxalate, zinc oxalate, and any mixture of two or more thereof.

[0051] Preferably, the insoluble active metal precursor may comprise one or more of the following: copper (II) carbonate, copper (II) hydroxide, and copper oxalate. More preferably, the insoluble active metal precursor comprises copper (II) carbonate. In one example, the insoluble active metal precursor may comprise a mixture of copper (II) carbonate and cerium carbonate.

[0052] In addition to the insoluble active metal precursor, the components to be mixed in step (a) may also include a soluble (i.e., water-soluble) active metal precursor. Suitable soluble active metal precursors may include soluble metal salts, such as metal acetates or metal nitrates, or mixtures of any two or more thereof. In one example, the insoluble active metal precursor may include copper carbonate, and the soluble active metal precursor may include cerium acetate.

[0053] The relative amounts of molecular sieve and insoluble active metal precursor employed in step (a) will depend on the targeted metal loading of the molecular sieve and the amount of any soluble active metal precursor employed. The metal loading of the metal-loaded molecular sieve present in the catalyst layer produced in step (c) may be from ≥0.1 wt% to ≤10 wt%, preferably ≥0.1 wt% and ≤7 wt%, more preferably ≥0.1 wt% and ≤5 wt%.

[0054] In particular, where the crystalline molecular sieve is a zeolite, the relative amounts of the molecular sieve, the insoluble active metal precursor and any soluble active metal precursor employed in step (a) may be selected to provide a metal to alumina ratio in the metal-loaded zeolite in the range of 0.2 to 0.5, preferably 0.3 to 0.5.

[0055] As used herein, the term "aqueous solvent" refers to an aqueous liquid medium (i.e., a water-containing liquid medium) and does not necessarily mean that any component is dissolved therein. For example, the aqueous solvent can be an aqueous liquid medium in which components (i) and (ii) become dispersed during step (a). However, the skilled person will understand that partial or complete dissolution of some components in the aqueous solvent may occur. For example, the rheology modifier that may be optionally employed in step (a) may itself be dissolved in the aqueous solvent. Preferably, the aqueous solvent consists essentially of water. That is, the aqueous solvent comprises water, but may also contain trace amounts of non-aqueous (e.g., organic or inorganic) impurities. The water may be deionized water or demineralized water.

[0056] The solids content of the slurry formed in step (a) is at most 50% by weight. "Solids content" means the proportion of solid material present in the slurry based on the total weight of the slurry. The solids content of the slurry is preferably in the range of 30% to 50% by weight, more preferably in the range of 30% to 48% by weight.

[0057] The components to be mixed together in step (a) may also include a binder component, a rheology modifier and / or other additives.

[0058] In particular, the components to be mixed together in step (a) may also include a binder component, which is selected from alumina, alumina precursors (such as boehmite and / or bayerite), aluminum hydroxide, TiO2, SiO2, ZrO2, CeZrO2, SnO2, aluminum phosphate, non-zeolitic aluminosilicates, silica-alumina, clay or mixtures thereof.

[0059] The binder may be present in the slurry in an amount ranging from 5 wt% to 15 wt%, preferably from 8 wt% to 12.5 wt%, such as from 10 wt% to 12.5 wt%, based on the total weight of the slurry.

[0060] The components to be mixed together in step (a) may also include a rheology modifier. The rheology modifier may be selected from polysaccharides, starches, celluloses, alginates or mixtures thereof. The rheology modifier may be present in the slurry in an amount of up to 0.4 wt %, preferably ≤ 0.2 wt %.

[0061] Optionally, the components to be mixed together in step (a) may also include organic additives, such as pore formers, surfactants and / or dispersants as processing aids.

[0062] In some embodiments, the components to be mixed together in step (a) may also include additional catalytically active materials (such as materials active for catalyzing ammonia slip), for example, where it is desired that the catalyst article be multifunctional (i.e., perform more than a catalytic function).

[0063] The relative amount of each component adopted in step (a) can be selected so that the slurry has the required solid content, and the catalyst layer formed in step (c) is made to comprise the metal-loaded molecular sieve of desired ratio after removing solvent and any organic matter. This is completely within the capabilities of technicians. Preferably, the relative amount of each component adopted in step (a) is selected so that the catalyst layer formed in step (c) comprises the metal-loaded molecular sieve of 85 wt % to 92 wt % and the binding agent of 8 wt % to 15 wt %.

[0064] In step (a), a slurry is formed by mixing the components together. Preferably, the slurry is substantially uniform (e.g., homogeneous), i.e., the distribution of the components throughout the slurry is substantially uniform. The components may be mixed by any suitable method. Preferably, the components are mixed by stirring.

[0065] Optionally, the pH of the slurry can be adjusted by adding an acid or base. Advantageously, it has been found that changes in the pH of the slurry have little effect on the performance of the SCR catalyst prepared according to the method of the first aspect. This is in contrast to some prior art methods in which the pH of the washcoat composition is known to affect the performance of the final catalyst.

[0066] Step (a) may be carried out at ambient temperature. Preferably, step (a) is carried out at a temperature in the range of 10°C to 30°C, preferably in the range of 18°C ​​to 28°C.

[0067] A particular advantage of the present invention is that the slurry formed in step (a) can be used directly as a washcoat composition.Thus, the slurry formed in step (a) can be used directly in step (b) without the need for any further processing steps.

[0068] In step (b), the slurry formed in step (a) can be applied to the substrate by carrier coating techniques well known in the art. One such method involves positioning the monolith substrate so that the channel has a substantially vertical orientation, applying a carrier coating to a first side of the substrate (e.g., above), and subjecting the opposite second side of the substrate (e.g., below) to at least partial vacuum to enable movement of the carrier coating through the channel. The monolith substrate can be coated in a single dose, wherein the carrier coating can be applied to the substrate in a single step, wherein the substrate is maintained in a single orientation. Alternatively, the substrate can be coated in two doses. For example, in a first dose, the monolith substrate is in a first orientation, wherein the first side is uppermost and the second side is lowermost. A coating is applied to the first side and coats a portion of the length of the substrate. The substrate is then inverted so that the second side is uppermost. A coating is then applied to the second side to coat the portion of the substrate that is not coated by the first dose. WO 99 / 47260 describes a general method for coating a monolith substrate.

[0069] The coating should be applied to the substrate in an amount sufficient to provide the desired washcoat loading. Preferably, the coating is applied in an amount sufficient to provide a washcoat loading of 0.5 g / in 3 Up to 5g / in 3 In the range of 1.5 g / in 3 Up to 3.5g / in 3 A range of washcoat loadings are applied.

[0070] The substrate is preferably a honeycomb monolith substrate. Honeycomb monoliths are well known in the art. "Honeycomb monolith substrates" as defined herein include metal and ceramic flow-through monoliths having a plurality of channels or cells extending longitudinally along the length of the substrate structure and wherein the channels are open at both ends; and metal and ceramic filters, including ceramic wall-flow filters having a plurality of channels or cells extending longitudinally along the length of the substrate structure and wherein the channels that are open at a first end of the substrate are blocked at the opposite end and the channels that are open at the opposite end are blocked at the first end, arranged such that each other adjacent cell has an open end (or blocked end) at the first end of the wall-flow filter and a blocked end (or open end) at its opposite end so that when the ends of the wall-flow filter are viewed, it resembles a checkerboard of open and blocked channels. The fluid communication between the open channels at the first end of the wall-flow filter and the open channels at its opposite end is via the porous wall structure of the wall-flow filter.

[0071] Alternatively, the substrate may be a plate-type substrate.

[0072] The substrate may be an inert substrate. The substrate may be composed of a ceramic material or a metal material. For example, the substrate may be made of or composed of cordierite (SiO2-Al2O3-MgO), silicon carbide (SiC), Fe-Cr-Al alloy, Ni-Cr-Al alloy, aluminum titanate, or a stainless steel alloy.

[0073] Where it is desired that the catalyst article be multifunctional (i.e., that it simultaneously performs more than a catalytic function), the substrate may already be catalytically active before being coated with the slurry formed in step (a) of the first aspect. For example, the substrate may be a fully active extrudate. Alternatively, the substrate may already include a first washcoat. In this example, the slurry formed in step (a) may be applied as a second washcoat on top of the first layer, and / or where the first washcoat does not cover the entire length of the substrate, the slurry formed in step (a) may be applied as an adjacent or overlapping washcoat. For example, where the present invention provides an SCR catalyst, the slurry may be applied on top of an ASC catalyst or at a location to be used upstream thereof.

[0074] In principle, the substrate may have any shape or size. However, the shape and size of the substrate are generally selected to optimize the exposure of the catalytically active material in the catalyst article to the exhaust gas in use.

[0075] Step (b) may be carried out at ambient temperature. Preferably, step (b) is carried out at a temperature in the range of 10°C to 35°C, preferably in the range of 10°C to 30°C, more preferably in the range of 18°C ​​to 28°C.

[0076] Most preferably, both steps (a) and (b) are carried out at a temperature in the range of 10°C to 35°C, such as in the range of 10°C to 30°C or 18°C ​​to 28°C.

[0077] Prior to calcining in step (c), the coated substrate formed in step (b) may undergo a drying process.Thus, the method of the first aspect may further comprise drying the coated substrate formed in step (b) before performing step (c).

[0078] Drying of the coated substrate can be performed at a temperature below 120° C. For example, drying of the coated substrate can be performed at a temperature of about 100° C. Drying can be performed statically (e.g., using a batch oven) or continuously (e.g., using a belt furnace).

[0079] In step (c) of the first aspect, the (optionally dried) coated substrate formed in step (b) undergoes calcination to form a catalyst layer on the substrate comprising the metal-supported molecular sieve. The term "calcination" refers to a heat treatment step. Calcination results in the fixation of the catalytically active material to the substrate and the removal of any remaining solvent and any residual organic components, such as organics derived from the decomposition of the active metal precursor or from organic additives contained in the slurry formed in step (a).

[0080] Without wishing to be bound by theory, it is believed that at least some metal loading of the molecular sieve occurs during calcination of the coated substrate.For example, solid state ion exchange may occur during calcination.

[0081] Calcination of the coated substrate can be performed by techniques well known in the art. Specifically, calcination can be performed statically (eg, using a batch oven) or continuously (eg, using a belt furnace).

[0082] Preferably, the calcining step (c) is carried out at a temperature of at most 550°C, preferably in the range of 450°C to 550°C.

[0083] Preferably, the coated substrate is calcined for up to 3 hours, preferably 30 minutes to 2 hours.

[0084] The calcining performed in step (c) may comprise multiple heat treatment steps, for example, the coated substrate may be subjected to a first heat treatment at a first temperature and then to a second heat treatment at a second temperature.

[0085] Drying and calcining can optionally be combined in a continuous process in which the coated substrate is conveyed on a belt furnace through multiple heating zones, each zone being set to a different temperature.

[0086] The catalyst article according to the second aspect of the present disclosure can be used to treat combustion exhaust streams. Specifically, the catalyst article can be used to treat exhaust gases derived from combustion processes, such as those from internal combustion engines (whether mobile or stationary), gas turbines, or power plants (such as coal-fired or oil-fired power plants). A preferred application of the catalyst article of the present disclosure is in motor vehicle exhaust systems. Specifically, the catalyst article can be used as an SCR catalyst.

[0087] In some embodiments, for example, where it is desired that the catalyst article be multifunctional (i.e., it simultaneously performs more functions than catalytic function), after step (b), the method of the first aspect may include the step of applying an additional washcoat composition to the substrate. The additional washcoat composition may be applied directly on top of the coating applied in step (b) or at a location proximal thereto. Such a step may be performed before or after step (c).

[0088] The catalyst article may be part of an exhaust gas treatment system, wherein the catalyst article is disposed downstream of a source of a nitrogenous reductant.

[0089] Example

[0090] The present invention will now be further described with reference to the following examples, which are intended to illustrate but not to limit the present invention.

[0091] · Comparative Example

[0092] Granular SSZ-13 (CHA) zeolite was combined with water to form a slurry having a solids content of 37 wt%, and the particle size of the zeolite was then reduced to a D90 of 7 μm using a bead mill.

[0093] Copper acetate was added to the slurry and the resulting mixture was heated to 70°C for 4 hours.After cooling to room temperature, a sample of the slurry was taken for ICP analysis which confirmed that greater than 84% copper uptake had occurred.

[0094] To replace water lost by evaporation during heating, additional water was added to the slurry so that the solids content was adjusted back to 37 wt%. Tetraethylammonium hydroxide (TEAOH) was then added to complex any free copper ions remaining in the supernatant.

[0095] The binder component (a water soluble boehmite-dispersant commercially available from Sasol) was then added to the slurry which was then stirred under continuous high shear conditions until it was homogenized.

[0096] To make the slurry suitable for washcoat, the rheology of the slurry was adjusted by adding a cellulose rheology modifier. The pH of the slurry was adjusted to 3.8 by adding a base.

[0097] The final slurry carrier was then coated onto a square unit ceramic flow-through substrate using a vacuum deposition carrier coating technique (as described in WO 99 / 47260). The coated substrate was then dried to complete dryness using a dynamic inline dryer. The dried coated substrate was then calcined in a dynamic inline calciner at 500° C. for at least 30 minutes to form a catalyst layer on the substrate.

[0098] The quantitative proportions of the starting materials were chosen such that the catalyst layer contained 87.5% by weight of copper-loaded zeolite and 12.5% ​​by weight of alumina.

[0099] · Example 1

[0100] Granular SSZ-13 (CHA) zeolite was combined with water to form a slurry at 37% solids, and the particle size of the zeolite was reduced to a D90 of 7 μm using a bead mill.

[0101] Copper carbonate was added to the slurry and the resulting mixture was stirred under high shear conditions for a minimum of 20 minutes.The amount of copper carbonate was selected to give an equivalent weight % of copper in the final slurry as provided in the comparative example.

[0102] The binder component (a water soluble boehmite-dispersant commercially available from Sasol) was then added to the slurry which was then stirred under continuous high shear conditions until it was homogenized.

[0103] To make the slurry suitable for washcoat, the rheology of the slurry was adjusted by adding a cellulosic rheology modifier.The pH of the slurry was adjusted to about 3.8 by adding a base.

[0104] The final slurry support was then coated onto a substrate having the same shape and size as employed in the Comparative Example in the same manner as described with respect to the Comparative Example. The coated substrate was then dried and calcined in the same manner as described in the Comparative Example.

[0105] The quantitative proportions of the starting materials were chosen such that the final catalyst layer contained 87.5% by weight of copper and zeolite and 12.5% ​​by weight of alumina.

[0106] · Example 2

[0107] Example 1 was repeated except that the pH of the slurry was adjusted to 4.

[0108] · Example 3

[0109] Example 1 was repeated except that the pH of the slurry was adjusted to 7.

[0110] · Catalyst testing

[0111] Core samples of equal volume were extracted from the catalyst articles prepared in each of the comparative examples and Examples 1 to 3 and tested in a synthetic catalytic activity test (SCAT) apparatus using the following feed gas mixture at the selected feed gas temperature: 500 ppm NO, 750 ppm NH3, 10% H2O, 5% O2, 350 ppm CO, balance N2, at a flow rate of 31.6 L / min. The catalyst samples were tested in fresh condition and after hydrothermal aging (800°C for 16 hours in 10% water).

[0112] The results are shown in Figure 1 and Figure 2 middle.

[0113] Figure 1 The NOx conversion and N2O selectivity achieved by the catalyst articles of Example 1 and the Comparative Example at selected inlet temperatures were compared.

[0114] Figure 2 The NOx conversion and N2O selectivity achieved by the catalyst articles of Examples 1 to 3 at selected inlet temperatures are compared.

[0115] like Figure 1 The data presented indicate that the catalyst article of Example 1 achieved comparable NOx conversion and similar or slightly improved N2O selectivity compared to the Comparative Example.

[0116] Advantageously, the preparation of Example 1 requires fewer processing steps and reduced water and energy consumption compared to the overall preparation of the Comparative Example.

[0117] like Figure 2 The data presented indicate that variations in the pH of the slurry used for washcoating have little effect on the performance of the final catalyst article.

[0118] Other aspects and embodiments of the present disclosure are set forth in the following numbered clauses:

[0119] Clause 1. A method for forming a catalyst article, the method comprising:

[0120] (a) forming a slurry by mixing together at least the following components:

[0121] (i) H + or NH4 + in the form of crystalline molecular sieves;

[0122] (ii) insoluble active metal precursors;

[0123] (iii) aqueous solvent;

[0124] wherein the solids content of the slurry is up to 50 wt %, and wherein step (a) is carried out at a temperature in the range of 10°C to 35°C;

[0125] (b) coating a substrate with the slurry formed in step (a); and

[0126] (c) calcining the coated substrate formed in step (b) to form a catalyst layer on the substrate.

[0127] Clause 2. The method according to clause 1, wherein the components to be mixed together in step (a) further comprise: (iv) a binder component and / or (v) a rheology modifier.

[0128] Clause 3. A method for forming a catalyst article, the method comprising:

[0129] (a) Form a slurry by mixing together the following components:

[0130] (i) H + or NH4 + in the form of crystalline molecular sieves;

[0131] (ii) insoluble active metal precursors;

[0132] (iii) aqueous solvent;

[0133] (iv) a binder component;

[0134] (v) optional rheology modifier;

[0135] wherein the solids content of the slurry is up to 50 wt %, and wherein step (a) is carried out at a temperature in the range of 10°C to 35°C;

[0136] (b) coating a substrate with the slurry formed in step (a); and

[0137] (c) calcining the coated substrate formed in step (b) to form a catalyst layer on the substrate.

[0138] Clause 4. A method for forming a catalyst article, the method comprising:

[0139] (a) Form a slurry by mixing together the following components:

[0140] (i) H + or NH4 + in the form of crystalline molecular sieves;

[0141] (ii) insoluble active metal precursors;

[0142] (iii) aqueous solvent;

[0143] (iv) a binder component;

[0144] (v) optional rheology modifier;

[0145] wherein the solids content of the slurry is up to 50 wt %, and wherein step (a) is carried out at a temperature in the range of 10°C to 35°C;

[0146] (b) coating a substrate with the slurry formed in step (a);

[0147] (b i ) optionally drying the coated substrate formed in step (b);

[0148] (c) calcining the i ) to form a catalyst layer on the substrate.

[0149] Item 5. A method according to Item 2, 3 or 4, wherein the binder component is selected from alumina, an alumina precursor, aluminum hydroxide, TiO2, SiO2, ZrO2, CeZrO2, SnO2, aluminum phosphate, non-zeolitic aluminosilicate, silica-alumina, clay or a mixture thereof.

[0150] Clause 6. The method of Clause 5, wherein the binder component is an alumina precursor selected from boehmite and bayerite.

[0151] Clause 7. The method according to any one of clauses 2 to 6, wherein the rheology modifier is selected from polysaccharides, starches, celluloses, alginates or mixtures thereof.

[0152] Item 8. A method according to any preceding item, wherein the relative quantitative proportions of the components used in step (a) are selected so that the catalyst layer formed in step (c) contains 85 wt% to 92 wt% of the metal-loaded molecular sieve and 8 wt% to 15 wt% of the binder.

[0153] Clause 9. The method of any preceding clause, wherein the crystalline molecular sieve is a small pore molecular sieve or a medium pore molecular sieve.

[0154] Clause 10. The method of any preceding clause, wherein the crystalline molecular sieve is a small pore molecular sieve.

[0155] Clause 11. The method of clause 10, wherein the small pore molecular sieve has a framework type selected from the group consisting of AEI, AFT, AFX, CHA, DDR, ERI, KFI, LEV, LTA, SFW, and RHO.

[0156] Clause 12. The method of any preceding clause, wherein the crystalline molecular sieve is a small pore zeolite having a framework type selected from CHA, AEI or AFX, LTA or ERI.

[0157] Clause 13. The method of Clause 9, wherein the crystalline molecular sieve is a medium pore size molecular sieve.

[0158] Clause 14. The method of Clause 13, wherein the mesoporous molecular sieve has a framework type selected from the group consisting of FER, MEL, MFI, STI, and STT.

[0159] Clause 15. The method of any preceding clause, wherein the crystalline molecular sieve is a zeolite.

[0160] Clause 16. The method of Clause 15, wherein the zeolite has a silica to alumina ratio (SAR) of 5 to 200, 5 to 100, 10 to 80, or 5 to 30.

[0161] Clause 17. The method of any preceding clause, wherein the crystalline molecular sieve is in particulate form and has a D90 particle size of less than 10 μm.

[0162] Clause 18. The process of Clause 17, wherein the crystalline molecular sieve has a D90 particle size in the range of 2 μm to 9 μm, or in the range of 2 μm to 8 μm.

[0163] Clause 19. A method according to any preceding clause, wherein component (i) comprises two or more H + or NH4 + The form of crystalline molecular sieve.

[0164] Clause 20. The method of any preceding clause, wherein the insoluble active metal precursor has a water solubility of less than 1 g / 100 ml, less than 0.1 g / 100 ml, or less than 0.01 g / 100 ml.

[0165] Clause 21. The method according to any preceding clause, wherein the insoluble active metal precursor is selected from metal carbonates, metal hydroxides, metal oxalates, or a mixture of any two or more thereof.

[0166] Clause 22. The method of any preceding clause, wherein the insoluble active metal precursor comprises a copper salt, a manganese salt, a nickel salt, a cobalt salt, an iron salt, a palladium salt, a platinum salt, a cerium salt, a yttrium salt, a niobium salt, a lanthanum salt, a zinc salt, a calcium salt, a magnesium salt, or any mixture of two or more thereof.

[0167] Clause 23. A method according to any preceding clause, wherein the insoluble active metal precursor is selected from the group consisting of copper carbonate, manganese carbonate, nickel carbonate, cobalt carbonate, iron carbonate, palladium carbonate, platinum carbonate, cerium carbonate, yttrium carbonate, niobium carbonate, lanthanum carbonate, zinc carbonate, zirconium carbonate, calcium carbonate, magnesium carbonate, copper hydroxide, manganese hydroxide, nickel hydroxide, cobalt hydroxide, iron hydroxide, palladium hydroxide, platinum hydroxide, cerium hydroxide, yttrium hydroxide, niobium hydroxide, lanthanum hydroxide, zinc hydroxide, zirconium hydroxide, calcium hydroxide, magnesium hydroxide, copper oxalate, calcium oxalate, iron oxalate, manganese oxalate, cobalt oxalate, cerium oxalate, yttrium oxalate, zinc oxalate, and any mixture of two or more thereof.

[0168] Clause 24. The method of any preceding clause, wherein the insoluble active metal precursor comprises one or more of copper (II) carbonate, copper (II) hydroxide, and copper oxalate.

[0169] Clause 25. The method of any preceding clause, wherein the insoluble active metal precursor comprises copper (II) carbonate.

[0170] Clause 26. The method of any preceding clause, wherein the insoluble active metal precursor comprises a mixture of copper (II) carbonate and cerium carbonate.

[0171] Clause 27. The method of any preceding clause, wherein the insoluble active metal precursor comprises one or more metal salts that undergo thermal decomposition by pyrolysis at a temperature below 500°C.

[0172] Clause 28. The method of any preceding clause, wherein in step (a), the components to be mixed together further comprise: (vi) a soluble active metal precursor.

[0173] Clause 29. The method of any preceding clause, wherein the aqueous solvent consists essentially of water.

[0174] Clause 30. The method of any preceding clause, wherein the aqueous solvent is water.

[0175] Clause 31. The method of any preceding clause, wherein the solids content of the slurry formed in step (a) is in the range of 30 wt% to 50 wt%, or in the range of 30 wt% to 48 wt%.

[0176] Clause 32. The method of any preceding clause, wherein in step (a), the components are mixed together by stirring.

[0177] Clause 33. The method of any preceding clause, wherein step (a) is performed at ambient temperature.

[0178] Clause 34. The process according to any preceding clause, wherein step (a) is carried out at a temperature in the range of 10°C to 30°C, preferably 18°C ​​to 28°C.

[0179] Clause 35. The method of any preceding clause, wherein the substrate is a honeycomb monolithic substrate.

[0180] Clause 36. The method of Clause 35, wherein the honeycomb monolith substrate is a flow-through monolith.

[0181] Clause 37. The method of Clause 35, wherein the honeycomb monolith substrate is a wall flow filter.

[0182] Clause 38. The method of any preceding clause, wherein step (b) is performed at ambient temperature.

[0183] Clause 39. The process according to any preceding clause, wherein step (b) is carried out at a temperature in the range of 10°C to 35°C, or in the range of 10°C to 30°C, or in the range of 18°C ​​to 28°C.

[0184] Clause 40. The process according to any preceding clause, wherein step (b) is carried out at a temperature in the range of 10°C to 35°C, or in the range of 10°C to 30°C, or in the range of 18°C ​​to 28°C.

[0185] Clause 41. The method of any preceding clause, further comprising drying the coated substrate formed in step (b) prior to step (c).

[0186] Clause 42. The process according to any preceding clause, wherein step (c) is carried out at a temperature of at most 550°C, preferably at a temperature in the range of 450°C to 550°C.

[0187] Clause 43. The method according to any preceding clause, wherein in step (c), calcination is carried out for a period of up to 3 hours, preferably 30 minutes to 2 hours.

[0188] Clause 44. The method of any preceding clause, wherein the catalyst layer formed in step (c) comprises a metal-supported molecular sieve.

[0189] Clause 45. The method of any preceding clause, wherein the catalyst layer formed in step (c) comprises a metal-supported molecular sieve that is catalytically active for SCR.

[0190] Clause 46. The method of any preceding clause, wherein at least some metal loading of the molecular sieve occurs during step (c).

[0191] Clause 47. A catalyst article obtained or obtainable by a process according to any preceding clause.

[0192] Clause 48. The catalyst article of Clause 47, configured as a flow-through honeycomb monolith or a wall-flow filter.

[0193] Clause 49. The catalyst article of Clause 47 or 48, which is catalytically active for SCR.

[0194] Clause 50. An exhaust system comprising: a source of a nitrogenous reductant and an injector for injecting the nitrogenous reductant into a flowing exhaust gas, wherein the injector is positioned upstream of the catalyst article according to Clause 49.

Claims

1. A method for forming a catalyst article, the method comprising: (a) forming a slurry by mixing together at least the following components: (i) H + or NH4 + A crystalline molecular sieve in the form of a small pore zeolite having a CHA framework type; (ii) a water-insoluble active metal precursor, wherein the water-insoluble active metal precursor is copper (II) carbonate; (iii) an aqueous solvent, wherein the aqueous solvent is water; wherein the solids content of the slurry is up to 50 wt %, and wherein step (a) is carried out at a temperature in the range of 10°C to 35°C; (b) coating a substrate with the slurry formed in step (a); as well as (c) calcining the coated substrate formed in step (b) to form a catalyst layer on the substrate.

2. The method according to claim 1, wherein the components to be mixed together in step (a) further comprise: (iv) a binder component and / or (v) a rheology modifier.

3. The method of claim 2, wherein the binder component is selected from alumina, alumina precursors, aluminum hydroxide, TiO2, SiO2, ZrO2, CeZrO2, SnO2, aluminum phosphate, non-zeolitic aluminosilicates, silica-alumina, clay, or mixtures thereof.

4. The method according to claim 2 or 3, wherein the rheology modifier is selected from polysaccharides, starch, cellulose, alginates or mixtures thereof.

5. A method according to any preceding claim, wherein the solids content of the slurry formed in step (a) is in the range of 30 wt% to 50 wt%, or in the range of 30 wt% to 48 wt%.

6. A process according to any preceding claim, wherein step (a) is carried out at a temperature in the range of 10°C to 30°C, preferably in the range of 18°C ​​to 28°C.

7. The process according to any preceding claim, wherein step (b) is carried out at a temperature in the range of 10°C to 35°C, preferably in the range of 10°C to 30°C, more preferably in the range of 18°C ​​to 28°C.

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