Method for forming a catalyst article

Abstract

The present disclosure provides a method for producing a composition comprising: (a) at least the following components: H + or NH4 + (b) forming a slurry having a solids content of up to 50 wt. % by mixing together a crystalline molecular sieve in the form of a crystalline molecular sieve, an insoluble active metal precursor, and an aqueous solvent at a temperature ranging from 10 to 35° C.; (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 catalyst articles, particularly catalyst articles and exhaust systems suitable for use in the selective catalytic reduction of nitrogen oxides.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a method of forming a catalytic article, and in particular to a method of forming a catalytic article suitable for use in the selective catalytic reduction of nitrogen oxide (NOx) in exhaust gases. [Background technology]

[0002] Large numbers of catalytic converters are manufactured each year for use in treating emissions from mobile and stationary power sources. Catalytic converters for use in motor vehicles typically comprise an extruded ceramic monolith provided with channels for the throughflow of exhaust gases. The monolith channels may be coated with a catalytically active material. Alternatively, the extruded monolith itself may be formed of the catalytically active material (referred to as a "fully active extrudate" or "extruded catalyst").

[0003] In producing coated catalysts, a composition known as 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 may take the form of a solution, slurry, or suspension of the catalytic material in a solvent. Once coated on the substrate, the washcoat typically undergoes a calcination step to remove the solvent and fix the catalytically active material to the substrate.

[0004] Substrates for use in catalytic converters typically comprise a monolithic structure in the form of a honeycomb having uniformly sized parallel channels extending from a first end to a second end of the molding. Typically, the channels are open at both the first and second ends, a so-called "flow-through" structure. Alternatively, the channels at the first, upstream end can be plugged with a suitable ceramic cement, and the unplugged channels at the first, upstream end can also be plugged at the second, downstream end to form a so-called wall-flow filter.

[0005] Nitrogen oxides (NO) by ammonia (NH3-SCR) x Selective catalytic reduction of NO from exhaust gases emitted by stationary and mobile engines, primarily diesel engines, for vehicles such as automobiles, trucks, locomotives, and marine vehicles. x This is considered to be the most practical and efficient technique for reducing

[0006] Known selective catalytic reduction (SCR) catalysts include molecular sieves. Useful molecular sieves include crystalline or paracrystalline materials that can be, for example, aluminosilicates (zeolites) or silicoaluminophosphates (SAPOs). Such molecular sieves are constructed, for example, from repeating SiO, AlO, and optionally PO tetrahedral units linked in rings to form a framework with regular intracrystalline cavities and channels of molecular dimensions. The specific arrangement of tetrahedral units (ring members) gives rise to the molecular sieve framework, and by convention, each unique framework is assigned a unique three-letter code (e.g., "CHA") by the International Zeolite Association (IZA). Examples of molecular sieve frameworks that are known SCR catalysts include framework type codes CHA (chabazite), BEA (beta), MOR (mordenite), AEI, MFI, and LTA.

[0007] Molecular sieves (e.g., zeolites) can also be classified by pore size, e.g., the maximum number of tetrahedral atoms present in the molecular sieve framework. As defined herein, "small pore" molecular sieves, such as CHA, contain a maximum ring size of 8 tetrahedral atoms, while medium pore molecular sieves, e.g., MFI, contain a maximum ring size of 10 tetrahedral atoms, and large pore molecular sieves, such as BEA, contain a maximum ring size of 12 tetrahedral atoms. Small pore and medium pore molecular sieves, particularly small pore molecular sieves, are preferred for use in SCR catalysts because they may, for example, provide improved SCR performance and / or improved hydrocarbon tolerance.

[0008] The molecular sieve catalyst may be metal-promoted. Examples of metal-promoted molecular sieve catalysts include iron-, copper-, and palladium-promoted molecular sieves, where the metal may be supported within the molecular sieve. In metal-supported molecular sieves, the supported metal is of the "extraframework metal" variety, i.e., a metal present within and / or on at least a portion of the molecular sieve surface, but not among the atoms that make up the molecular sieve framework. For example, iron- and copper-supported zeolites are known to promote SCR reactions.

[0009] Several methods for preparing metal-loaded molecular sieves, especially metal-loaded zeolites, have been described in the literature. Direct synthesis of metal-loaded zeolites is a complex process and depends on synthesis conditions (see M. Moliner, ISRN Materials Science, 2012, Article ID 789525). An alternative is to use commercially available zeolite supports and then load the metals by post-synthesis treatment of the zeolite, such as wet impregnation, wet ion exchange, or solid ion exchange.

[0010] Known wet ion exchange methods for loading metals onto molecular sieves (e.g., zeolites) typically use soluble metal salts, such as metal acetates, sulfates, or chlorides, as active metal precursors, which react with the molecular sieves in aqueous solution. To accelerate the ion exchange, such processes typically require a heating step, in which the mixture may be heated to temperatures ranging from 70 to 80°C for up to several hours. Furthermore, 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 washcoat composition to form a catalyst article. Furthermore, when certain metal acetates (e.g., copper acetate) are used to prepare metal-loaded molecular sieves (e.g., metal-loaded zeolites) used as SCR catalysts, it has been found that any residual metal acetate remaining after calcination can have a poisoning effect on ammonia slip catalysts (ASCs) used downstream or near the SCR catalyst.

[0011] The present invention provides an improved process for the preparation of washcoated catalyst articles using metal-supported crystalline molecular sieves as the catalytically active material.

[0012] According to a first aspect of the present disclosure, there is provided a method of forming a catalyst article, the method comprising: (a) containing at least the following components: (i)H + or NH4 + a crystalline molecular sieve in the form of (ii) an insoluble active metal precursor; (iii) an aqueous solvent, by mixing together to form a slurry, forming a slurry, the slurry having a solids content of up to 50% by weight, and step (a) being carried out at a temperature in the range of 10 to 35°C; (b) coating a substrate with the slurry formed in step (a); (c) calcining the coated substrate formed in step (b) to form a catalyst layer on the substrate.

[0013] Advantageously, it has been found that the heat used to calcinate the coated substrate can be used to promote metal loading on the molecular sieve. This can avoid the need for any heating steps during the wet ion exchange or impregnation process, and the need for expensive high-temperature resistant equipment. Furthermore, the long reaction periods and / or energy- and labor-intensive processes, such as spray drying, that are typical of wet ion exchange or impregnation processes can be avoided. This can make the method according to the first aspect more efficient and economical.

[0014] 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 the need for any further process steps.

[0015] Furthermore, the use of insoluble metal species such as metal carbonates as active metal precursors may result in the generation of fewer hazardous species during calcination compared to when metal acetates are used as the active metal precursors. Thus, the use of insoluble active metal precursors may provide health and safety benefits.

[0016] Additionally, it has been found that catalysts prepared via the process according to the first aspect can provide SCR activity at least equivalent to that of catalysts comprising metal-loaded molecular sieves (e.g., metal-loaded zeolites) prepared via wet ion exchange or impregnation. Moreover, it has also been found that the associated ammonia slip catalyst poisoning can be reduced compared to catalysts comprising metal-loaded molecular sieves prepared using metal acetate salts as active metal precursors.

[0017] According to a second aspect of the present disclosure, there is provided a catalyst article obtained or obtainable by the method of the first aspect.

[0018] According to a third aspect of the present disclosure, there is provided an exhaust system comprising a nitrogen-based reductant source and an injector for injecting the nitrogen-based reductant into flowing exhaust gas, the injector being disposed upstream from a catalyst article according to the second aspect. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a graph showing NOx conversion and N2O selectivity achieved by a catalyst article prepared according to a first embodiment of the present disclosure compared to a catalyst article prepared via a prior art method. [Figure 2] 1 is a graph showing NOx conversion and N2O selectivity achieved with a catalyst prepared according to a first embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present disclosure will now be further described. In the following sections, different aspects / embodiments of the present disclosure are defined in more detail. Each aspect / embodiment so defined can be combined with any other aspect / embodiment or aspects / embodiments, unless expressly indicated otherwise. In particular, any feature indicated as being preferred or advantageous can be combined with any other feature or features indicated as being preferred or advantageous.

[0021] Additionally, as used herein, the term "comprising" is interchangeable with the definitions "consisting essentially of" or "consisting of." The term "comprising" is intended to mean that the specified elements are essential, although other elements may be added and still form a structure within the scope of the claim. The term "consisting essentially of" limits the scope of the claim to the specified materials or steps and those that do not materially affect the basic and novel characteristics of the claimed invention. The term "consisting of" closes the claim to the inclusion of materials other than those recited, except for impurities ordinarily associated therewith.

[0022] Crystalline molecular sieves are typically composed of aluminum, silicon, and / or phosphorus. Crystalline molecular sieves generally have a three-dimensional arrangement (e.g., framework) of repeating SiO, AlO, and optionally PO tetrahedral units bonded by shared oxygen atoms.

[0023] In relation to molecular sieves, "H + The term "morphology" refers to the structure in which the backbone charge is a proton (i.e., H + It refers to a molecular sieve with an anionic framework balanced by cations.

[0024] In relation to molecular sieves, the term NH4 + The structure is such that the backbone charge is an ammonium cation (NH4 + It refers to a molecular sieve with an anionic framework balanced by cations.

[0025] When the crystalline molecular sieve has an aluminosilicate framework, the molecular sieve is preferably a zeolite.

[0026] The molecular sieve can be a small pore molecular sieve (ie, having a maximum ring size of 8 tetrahedral atoms) or a medium pore molecular sieve (ie, having a maximum ring size of 10 tetrahedral atoms).

[0027] When the crystalline molecular sieve is a small pore molecular sieve, the small pore molecular sieve may be selected from the framework type group 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 framework type group 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 an AEI-CHA intergrowth.

[0028] When the crystalline molecular sieve is a medium pore molecular sieve, the medium pore molecular sieve may be selected from the framework type group 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 medium pore crystalline molecular sieve is selected from the framework type group consisting of FER, MEL, MFI, STI, and STT.

[0029] Preferably, the crystalline molecular sieve is a small pore molecular sieve having framework type CHA, AEI, AFX, LTA, or ERI.

[0030] When 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, and more preferably 10 to 80. For example, the silica-to-alumina ratio (SAR) of the zeolite may be 5 to 30.

[0031] When the crystalline molecular sieve is SAPO, the SAPO may have a silicon content in the range of 5 to 30 wt. %, preferably 8 to 16 wt. % (based on the total weight of the molecular sieve).

[0032] The crystalline molecular sieve is preferably a powdered crystalline molecular sieve (i.e., in particulate form), where the particles comprise individual crystals, aggregates of crystals, or a combination thereof. The crystalline molecular sieve may have an average crystal size of 0.5 μm or more, preferably about 0.5 to about 15 μm, e.g., about 0.5 to 10 μm, about 0.5 to about 5 μm, about 1 to about 5 μm, or about 2 to about 5 μm, as measured by scanning electron microscopy (SEM).

[0033] The powdered crystalline molecular sieve preferably has a D90 particle size of less than 10 μm. For example, the powdered crystalline molecular sieve may have a D90 particle size in the range of 2 to 9 μm, preferably 3 to 8 μm. As used herein, the term "D90 particle size" refers to particle size distribution. The D90 particle size value corresponds to the particle size value below which 90% by volume of the total particles in a particular sample are present. The D90 particle size can be determined using laser diffraction methods (e.g., using a Malvern Mastersizer 2000).

[0034] If desired, prior to forming the slurry in step (a) of the method of the first embodiment, the molecular sieve may be subjected to a particle size reduction treatment such as jet milling, wet milling, or steam-assisted jet milling.

[0035] The components mixed together in step (a) of the first embodiment are + or NH4 + Thus, the resulting catalyst layer formed in step (c) may contain two or more different types of metal-supported molecular sieves.

[0036] As used herein, "active metal precursor" refers to a metal species capable of providing extra-framework metal to a crystalline molecular sieve. As used herein, the term "extra-framework metal" refers to a metal that is present within the molecular sieve (i.e., within micropores at either ion-exchange or non-ion-exchange locations) and / or on at least a portion of the molecular sieve surface (e.g., in the form of ions or oxides) and does not comprise the tetrahedral metal atoms that form the framework of the molecular sieve. It will be understood that additional metal species may be present in the slurry formed in step (a) that are not themselves involved in metal loading.

[0037] By "insoluble active metal precursor" is meant an active metal precursor that is insoluble in water. In particular, the insoluble active metal precursor may have a water solubility of less than 1 g / 100 ml, e.g., less than 0.1 g / 100 ml, or less than 0.01 g / 100 ml. Water solubility is a measure of the amount of material that will dissolve in a specific volume of water at a given temperature and pressure to form a saturated solution. As used herein, in reference to an insoluble active metal precursor, the term "water solubility" refers to the amount (in grams) of insoluble active metal precursor that will dissolve in 100 milliliters of water (g / 100 ml) at a temperature of 20° C. and 1 atmosphere of pressure.

[0038] Suitable insoluble active metal precursors include certain metal salts. In particular, the insoluble active metal precursor may be a metal carbonate, metal hydroxide, or metal oxalate.

[0039] The insoluble active metal precursors preferably comprise metal salts that are pyrolyzed by pyrolysis at temperatures below 500°C.

[0040] The insoluble active metal precursor may comprise a salt of a transition metal, a noble metal, or a rare earth metal, for example, the insoluble active metal precursor may comprise a salt of one or more of copper, manganese, nickel, cobalt, iron, palladium, platinum, cerium, yttrium, niobium, lanthanum, zinc, calcium, magnesium, or any mixture of two or more thereof.

[0041] In particular, the insoluble active metal precursor may be 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.

[0042] Preferably, the insoluble active metal precursor may include one or more of copper (II) carbonate, copper (II) hydroxide, and copper oxalate. More preferably, the insoluble active metal precursor includes copper (II) carbonate. In one example, the insoluble active metal precursor may include a mixture of copper (II) carbonate and cerium carbonate.

[0043] In addition to the insoluble active metal precursor, the components mixed in step (a) may further 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 a mixture 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.

[0044] The relative amounts of molecular sieve and insoluble active metal precursor used in step (a) depend on the target metal loading of the molecular sieve and the amount of any soluble active metal precursor used. The metal-loaded molecular sieve present in the catalyst layer produced in step (c) can have a metal loading of 0.1% to 10% by weight, preferably 0.1% to 7% by weight, and more preferably 0.1% to 5% by weight.

[0045] In particular, when the crystalline molecular sieve is a zeolite, the relative amounts of molecular sieve, insoluble active metal precursor, and optional soluble active metal precursor used 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.

[0046] As used herein, the term "aqueous solvent" refers to an aqueous liquid medium (i.e., a water-containing liquid medium) and does not necessarily indicate that any components are dissolved therein. For example, the aqueous solvent may be the water-containing liquid medium in which components (i) and (ii) are dispersed during step (a). However, it will be understood by those skilled in the art that partial or complete dissolution of some components in the aqueous solvent may occur. For example, a rheology modifier that may be optionally used in step (a) may itself be soluble in the aqueous solvent. Preferably, the aqueous solvent consists essentially of water. That is, the aqueous solvent contains 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.

[0047] The slurry formed in step (a) has a solids content of up to 50% by weight. "Solids content" refers to the percentage 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.

[0048] The ingredients mixed together in step (a) may further include a binder component, a rheology modifier, and / or other additives.

[0049] In particular, the components mixed together in step (a) may further comprise a binder component selected from alumina, alumina precursors (such as boehmite and / or bayerite), aluminum hydroxide, TiO, SiO, ZrO, CeZrO, SnO, aluminophosphates, non-zeolitic aluminosilicates, silica-aluminas, clays, or mixtures thereof.

[0050] The binder may be present in the slurry in an amount ranging from 5 to 15% by weight, preferably from 8 to 12.5% ​​by weight, for example from 10 to 12.5% ​​by weight, based on the total weight of the slurry.

[0051] The ingredients mixed together in step (a) may further comprise 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% by weight, preferably 0.2% by weight or less.

[0052] Optionally, the components mixed together in step (a) may further comprise organic additives, such as pore formers, surfactants, and / or dispersants as processing aids.

[0053] In some embodiments, the components mixed together in step (a) may further include additional catalytically active materials (such as materials active in the catalytic action of ammonia slip), for example, where it is desired that the catalyst article be multifunctional (i.e., perform more than just a catalytic function).

[0054] The relative amounts of each component used in step (a) can be selected so that the slurry has the required solids content and, after removal of the solvent and any organics, the catalyst layer formed in step (c) contains the desired proportion of metal-loaded molecular sieve. This is within the ability of one skilled in the art. Preferably, the relative amounts of each component used in step (a) are selected so that the catalyst layer formed in step (c) contains 85-92 wt.% metal-loaded molecular sieve and 8-15 wt.% binder.

[0055] In step (a), a slurry is formed by mixing the components together. Preferably, the slurry is substantially uniform (e.g., homogeneous), i.e., the components are substantially evenly distributed in the slurry. The components may be mixed by any suitable method. Preferably, the components are mixed by stirring.

[0056] Optionally, the pH of the slurry can be adjusted by the addition of an acid or base. Advantageously, variability in the pH of the slurry has been found to have little effect on the performance of SCR catalysts 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.

[0057] Step (a) may be carried out at ambient temperature. Preferably, step (a) is carried out at a temperature in the range of 10 to 30°C, preferably 18 to 28°C.

[0058] A particular advantage of the present invention is that the slurry formed in step (a) can be used directly as a washcoat composition, and therefore the slurry formed in step (a) can be used directly in step (b) without any additional process steps.

[0059] In step (b), the slurry formed in step (a) can be coated onto a substrate by washcoating techniques well known in the art. One such method involves positioning a monolith substrate so that the channels have a substantially vertical orientation, applying a washcoat to a first side (e.g., the top side) of the substrate, and subjecting an opposite second side (e.g., the bottom side) of the substrate to at least a partial vacuum to achieve movement of the washcoat through the channels. The monolith substrate can be coated in a single dose, and the washcoat can be applied to the substrate in a single step while the substrate remains in a single orientation. Alternatively, the substrate can be coated in two infusions. For example, in the first infusion, the monolith substrate is in a first orientation with the first side at the top and the second side at the bottom. A coating is applied to the first side, coating the length of the substrate. The substrate is then inverted so that the second side is at the top. A coating is then applied to the second side to coat the portions of the substrate not coated by the first infusion. WO 99 / 47260 describes a general method for coating monolithic substrates.

[0060] The coating should be applied to the substrate in an amount sufficient to provide the desired washcoat loading. Preferably, the coating is applied at a rate of 0.5 to 5 g / in. 3 in the range of 1.5 to 3.5 g / in 3 The washcoat is applied in an amount sufficient to provide a washcoat loading in the range of 0.1 to 1000 ppm.

[0061] The substrate is preferably a honeycomb monolith substrate. Honeycomb monoliths are well known in the art. As defined herein, "honeycomb monolith substrates" include metal and ceramic flow-through monoliths having a plurality of channels or cells extending longitudinally along the length of the substrate structure, the channels being open at both ends. Metal and ceramic filters include ceramic wall-flow filters having a plurality of channels or cells extending longitudinally along the length of the substrate structure, where the channels at a first end of the substrate that are open are blocked at the opposite end, and the channels that are open at the opposite end are blocked at the first end, with all other adjacent cells having an open end (or blocked end) at the first end of the wall-flow filter and a blocked end (or open end) at the opposite end, such that when the end of the wall-flow filter is viewed, it resembles a chessboard of open and blocked channels. Fluid communication between the open channels at the first end of the wall-flow filter and the open channels at the opposite end is through the porous wall structure of the wall-flow filter.

[0062] Alternatively, the substrate can be a plate-shaped substrate.

[0063] The substrate may be an asymmetric substrate. The substrate may be made of a ceramic material or a metal material. For example, the substrate may be made of or comprised of cordierite (SiO-AlO-MgO), silicon carbide (SiC), an Fe-Cr-Al alloy, an Ni-Cr-Al alloy, an aluminum titanate, or a stainless steel alloy.

[0064] If the catalyst article is desired to be multifunctional (i.e., to perform more than one catalytic function simultaneously), the substrate may already have catalytic activity before being coated with the slurry formed in step (a) of the first embodiment. For example, the substrate may be an all-active extrudate. Alternatively, the substrate may already include a first washcoat layer. In this example, the slurry formed in step (a) may be coated as a second washcoat layer on top of the first washcoat layer, and / or may be coated as an adjacent or overlapping washcoat layer if the first washcoat layer does not cover the entire length of the substrate. For example, if the present invention provides an SCR catalyst, the slurry may be coated at a location that will be on or upstream of an ASC catalyst during use.

[0065] In principle, the substrate can be of any shape or size, however, the shape and size of the substrate is typically selected to optimize exposure of the catalytically active material in the catalyst article to exhaust gases during use.

[0066] Step (b) may be carried out at ambient temperature. Preferably, step (b) is carried out at a temperature in the range of 10 to 35°C, preferably 10 to 30°C, more preferably 18 to 28°C.

[0067] Most preferably, both steps (a) and (b) are carried out at a temperature in the range of 10 to 35°C, such as in the range of 10 to 30°C or 18 to 28°C.

[0068] The coated substrate formed in step (b) may undergo a drying process prior to firing in step (c). Thus, the method of the first aspect may further comprise drying the coated substrate formed in step (b) prior to carrying out step (c).

[0069] Drying of the coated substrate can be carried out at a temperature of less than 120° C. For example, drying of the coated substrate can be carried out at a temperature of about 100° C. Drying can be carried out statically (e.g., using a batch oven) or continuously (e.g., using a belt furnace).

[0070] In step (c) of the first embodiment, the (optionally dried) coated substrate formed in step (b) is subjected to calcination to form a catalyst layer on the substrate comprising the metal-loaded molecular sieve. The terms "calcining" or "calcination" refer to a heat treatment step. Calcination fixes the catalytically active material to the substrate and causes the removal of any remaining solvent and any residual organic components, such as decomposition of the active metal precursor or organics derived from organic additives contained in the slurry formed in step (a).

[0071] Without wishing to be bound by any theory, it is believed that at least a portion of the metal loading of the molecular sieve occurs during calcination of the coated substrate. For example, solid-state ion exchange may occur during calcination.

[0072] Calcination of the coated substrate can be carried out via techniques well known in the art. In particular, calcination can be carried out statically (e.g., using a batch oven) or continuously (e.g., using a belt furnace).

[0073] Preferably, the calcination step (c) is carried out at a temperature up to 550°C, preferably in the range of 450 to 550°C.

[0074] Preferably, the coated substrate is baked for up to 3 hours, preferably 30 minutes to 2 hours.

[0075] The calcination carried out in step (c) may include multiple heat treatment steps, for example, the coated substrate may be subjected to a first heat treatment at a first temperature and then a second heat treatment at a second temperature.

[0076] Drying and firing 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 set at a different temperature.

[0077] The catalytic article according to the second aspect of the present disclosure may be used to treat combustion exhaust gas streams. That is, the catalytic article may be used to treat exhaust gases from combustion processes, such as internal combustion engines (either mobile or stationary), gas turbines, or power plants (e.g., coal- or oil-fired power plants). A preferred application of the catalytic article of the present disclosure is in the exhaust systems of automotive vehicles. In particular, the catalytic article may be used as an SCR catalyst.

[0078] In some embodiments, for example, if the catalytic article is desired to be multifunctional (i.e., to perform more than just a catalytic function simultaneously), the method of the first aspect may include, after step (b), coating an additional washcoat composition onto the substrate. The additional washcoat composition may be applied directly on top of or adjacent to the coating applied in step (b). Such a step may be performed either before or after step (c).

[0079] The catalytic article can be part of an exhaust gas treatment system, the catalytic article being disposed downstream of a nitrogenous reductant source. [Example]

[0080] The present invention will now be further described with reference to the following examples, which are intended to be illustrative and not limiting.

[0081] Comparison example Particulate SSZ-13 (CHA) zeolite was combined with water to form a slurry with a solids content of 37 wt %, and then bead milling was used to reduce the particle size of the zeolite to a D90 of 7 μm.

[0082] Copper acetate was added to the slurry and the resulting mixture was heated for 4 hours to 70° C. 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.

[0083] Additional water was added to the slurry to replace the water lost to evaporation during heating and adjust the solids content back to 37 wt %. Tetraethylammonium hydroxide (TEAOH) was then added to complex any free copper ions remaining in the supernatant.

[0084] A binder component (water soluble boehmite - Dispersal available from Sasol) was then added to the slurry, which was then stirred under continuous high shear conditions until it was homogenized.

[0085] The rheology of the slurry was adjusted by the addition of a cellulose rheology modifier so that the slurry was suitable for washcoating. The pH of the slurry was adjusted to 3.8 by the addition of a base.

[0086] The final slurry was then washcoated onto a square-cell ceramic flow-through substrate using a vacuum deposition washcoating technique (as described in WO 99 / 47260). The coated substrate was then dried, and drying was completed using a dynamic line dryer. The dried coated substrate was then calcined in a dynamic line calciner at 500°C for at least 30 minutes to form a catalyst layer on the substrate.

[0087] The quantitative proportions of the starting materials were chosen so that the catalyst layer contained 87.5 wt. % copper-loaded zeolite and 12.5 wt. % alumina.

[0088] Example 1 Particulate SSZ-13 (CHA) zeolite was combined with water to form a slurry with a solids content of 37 wt %, and bead milling was used to reduce the particle size of the zeolite to a D90 of 7 μm.

[0089] 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 achieve an equivalent weight percent of copper in the final slurry as provided in the comparative examples.

[0090] A binder component (water soluble boehmite - Dispersal available from Sasol) was then added to the slurry, which was then stirred under continuous high shear conditions until it was homogenized.

[0091] The rheology of the slurry was adjusted by the addition of a cellulose rheology modifier so that the slurry was suitable for washcoating. The pH of the slurry was adjusted to about 3.8 by the addition of a base.

[0092] The final slurry was then washcoated onto a substrate having the same shape and dimensions as that used in the comparative example in the same manner as described in connection with the comparative example, and the coated substrate was then dried and fired in the same manner as that described in the comparative example.

[0093] The quantitative proportions of the starting materials were chosen so that the final catalyst layer contained 87.5 wt. % copper and zeolite, and 12.5 wt. % alumina.

[0094] Example 2 Example 1 was repeated except that the pH of the slurry was adjusted to 4.

[0095] Example 3 Example 1 was repeated except that the pH of the slurry was adjusted to 7.

[0096] Catalyst testing Identical volume core samples were taken from the catalyst articles prepared in each of the Comparative Example and Examples 1-3 and tested in a synthetic catalytic activity test (SCAT) apparatus using the following inlet gas mixture at a flow rate of 31.6 L / min and selected inlet temperatures: 500 ppm NO, 750 ppm NH, 10% HO, 5% O, 350 ppm CO, balance N. Catalyst samples were tested both fresh and after hydrothermal aging (16 hours in 10% water at 800°C).

[0097] The results are shown in Figures 1 and 2.

[0098] FIG. 1 compares the NOx conversion and N2O selectivity achieved by the catalyst articles of Example 1 and the Comparative Example at selected inlet temperatures.

[0099] FIG. 2 compares the NOx conversion and N2O selectivity achieved by the catalyst articles of Examples 1-3 at selected inlet temperatures.

[0100] As demonstrated by the data shown in Figure 1, the catalyst article of Example 1 achieves comparable NOx conversion and similar or slightly improved N2O selectivity compared to the Comparative Example.

[0101] Advantageously, the preparation of Example 1 required fewer process steps and reduced water and energy consumption compared to the preparation of the Comparative Examples overall.

[0102] As demonstrated by the data shown in Figure 2, varying the pH of the slurry for washcoating has little effect on the performance of the final catalyst article.

[0103] Further aspects and embodiments of the present disclosure are described in the following numbered clauses.

[0104] Clause 1. A method of forming a catalyst article, comprising: (a) containing at least the following components: (i)H +or NH4 + a crystalline molecular sieve in the form of (ii) an insoluble active metal precursor; (iii) an aqueous solvent, by mixing together to form a slurry, forming a slurry, the slurry having a solids content of up to 50% by weight, and step (a) being carried out at a temperature in the range of 10 to 35°C; (b) coating a substrate with the slurry formed in step (a); (c) calcining the coated substrate formed in step (b) to form a catalyst layer on the substrate.

[0105] Clause 2. The method defined in clause 1, wherein in step (a), the components mixed together further comprise (iv) a binder component and / or (v) a rheology modifier.

[0106] Clause 3. A method of forming a catalyst article, comprising: (a) the following components: (i)H + or NH4 + a crystalline molecular sieve in the form of (ii) an insoluble active metal precursor; (iii) an aqueous solvent; (iv) a binder component; and (v) an optional rheology modifier, by mixing together to form a slurry; forming a slurry, the slurry having a solids content of up to 50% by weight, and step (a) being carried out at a temperature in the range of 10 to 35°C; (b) coating a substrate with the slurry formed in step (a); (c) calcining the coated substrate formed in step (b) to form a catalyst layer on the substrate.

[0107] Clause 4. A method of forming a catalyst article, comprising: (a) the following components: (i)H +or NH4 + a crystalline molecular sieve in the form of (ii) an insoluble active metal precursor; (iii) an aqueous solvent; (iv) a binder component; and (v) an optional rheology modifier, by mixing together to form a slurry; forming a slurry, the slurry having a solids content of up to 50% by weight, and step (a) being carried out at a temperature in the range of 10 to 35°C; (b) coating a substrate with the slurry formed in step (a); (b i ) optionally drying the coated substrate formed in step (b); and (c) Step (b) or (b i and calcining the coated substrate formed in step (a) to form a catalyst layer on the substrate.

[0108] Clause 5. The method of clauses 2, 3, or 4, wherein the binder component is selected from alumina, an alumina precursor, aluminum hydroxide, TiO2, SiO2, ZrO2, CeZrO2, SnO2, an aluminophosphate, a non-zeolitic aluminosilicate, a silica-alumina, a clay, or a mixture thereof.

[0109] Clause 6. The method defined in clause 5, wherein the binder component is an alumina precursor selected from boehmite and bayerite.

[0110] Clause 7. The method of any one of clauses 2 to 6, wherein the rheology modifier is selected from polysaccharides, starches, celluloses, alginates, or mixtures thereof.

[0111] Clause 8. The method defined in any one of clauses 1 to 7, 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 to 92 wt. % metal-loaded molecular sieve and 8 to 15 wt. % binder.

[0112] Clause 9. The process defined in any one of clauses 1 to 8, wherein the crystalline molecular sieve is a small pore or medium pore molecular sieve.

[0113] Clause 10. The method of any one of clauses 1 to 9, wherein the crystalline molecular sieve is a small pore molecular sieve.

[0114] Clause 11. The process defined in clause 10, wherein the small pore molecular sieve has a framework type selected from AEI, AFT, AFX, CHA, DDR, ERI, KFI, LEV, LTA, SFW, and RHO.

[0115] Clause 12. The process defined in any one of clauses 1 to 11, wherein the crystalline molecular sieve is a small pore zeolite having a framework type selected from CHA, AEI or AFX, LTA, or ERI.

[0116] Clause 13. The method defined in clause 9, wherein the crystalline molecular sieve is a medium pore molecular sieve.

[0117] Clause 14. The method defined in clause 13, wherein the medium pore molecular sieve has a framework type selected from FER, MEL, MFI, STI, and STT.

[0118] Clause 15. The method of any one of clauses 1 to 14, wherein the crystalline molecular sieve is a zeolite.

[0119] Clause 16. The method defined in clause 15, wherein the zeolite has a silica-alumina ratio (SAR) of 5 to 200, 5 to 100, 10 to 80, or 5 to 30.

[0120] Clause 17. The method of any one of clauses 1 to 16, wherein the crystalline molecular sieve is in particulate form and has a D90 particle size of less than 10 μm.

[0121] Clause 18. The method defined in clause 17, wherein the crystalline molecular sieve has a D90 particle size in the range of 2 to 9 μm, or in the range of 2 to 8 μm.

[0122] Clause 19. Component (i) is H + or NH4 + 19. The process of any one of clauses 1 to 18, comprising two or more crystalline molecular sieves in the form

[0123] Clause 20. The method of any one of clauses 1 to 19, 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.

[0124] Clause 21. The method of any one of clauses 1 to 20, wherein the insoluble active metal precursor is selected from a metal carbonate, a metal hydroxide, a metal oxalate, or a mixture of any two or more thereof.

[0125] Clause 22. The method of any one of clauses 1 to 21, wherein the insoluble active metal precursor comprises a salt of copper, manganese, nickel, cobalt, iron, palladium, platinum, cerium, yttrium, niobium, lanthanum, zinc, calcium, magnesium, or any mixture of two or more thereof.

[0126] Clause 23. The method of any one of clauses 1 to 22, 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.

[0127] Clause 24. The method of any one of clauses 1 to 23, wherein the insoluble active metal precursor comprises one or more of copper(II) carbonate, copper(II) hydroxide, and copper oxalate.

[0128] Clause 25. The method of any one of clauses 1 to 24, wherein the insoluble active metal precursor comprises copper(II) carbonate.

[0129] Clause 26. The method of any one of clauses 1 to 25, wherein the insoluble active metal precursor comprises a mixture of copper(II) carbonate and cerium carbonate.

[0130] Clause 27. Insoluble active metal precursors, 500 ℃ 27. A process as defined in any one of clauses 1 to 26, comprising pyrolyzing one or more metal salts by pyrolysis at a temperature below 27°C.

[0131] Clause 28. The method defined in any one of clauses 1 to 27, wherein the components mixed together in step (a) further comprise (vi) a soluble active metal precursor.

[0132] Clause 29. The method defined in any one of clauses 1 to 28, wherein the aqueous solvent consists essentially of water.

[0133] Clause 30. A method as defined in any one of clauses 1 to 29, wherein the aqueous solvent is water.

[0134] Clause 31. The method of any one of clauses 1 to 30, wherein the slurry formed in step (a) has a solids content in the range of 30 to 50% by weight or in the range of 30 to 48% by weight.

[0135] Clause 32. The method of any one of clauses 1 to 31, wherein in step (a), the ingredients are mixed together by stirring.

[0136] Clause 33. The method of any one of clauses 1 to 32, wherein step (a) is carried out at ambient temperature.

[0137] Clause 34. The method according to any one of clauses 1 to 33, wherein step (a) is carried out at a temperature in the range of 10 to 30°C, preferably in the range of 18 to 28°C.

[0138] Clause 35. The method defined in any one of clauses 1 to 34, wherein the substrate is a honeycomb monolith substrate.

[0139] Clause 36. The method defined in clause 35, wherein the honeycomb monolith substrate is a flow-through monolith.

[0140] Clause 37. The method defined in clause 35, wherein the honeycomb monolith substrate is a wall-flow filter.

[0141] Clause 38. The method of any one of clauses 1 to 37, wherein step (b) is carried out at ambient temperature.

[0142] Clause 39. The method of any one of clauses 1 to 38, wherein step (b) is carried out at a temperature in the range of 10 to 35°C, or in the range of 10 to 30°C, or in the range of 18 to 28°C.

[0143] Clause 40. The method of any one of clauses 1 to 39, wherein step (b) is carried out at a temperature in the range of 10 to 35°C, or in the range of 10 to 30°C, or in the range of 18 to 28°C.

[0144] Clause 41. The method defined in any one of clauses 1 to 40, wherein the method further comprises drying the coated substrate formed in step (b) prior to step (c).

[0145] Clause 42. The method of any one of clauses 1 to 41, wherein step (c) is carried out at a temperature of up to 550°C, preferably at a temperature in the range of 450 to 550°C.

[0146] Clause 43. The method according to any one of clauses 1 to 42, wherein in step (c), the calcination is carried out for a period of up to 3 hours, preferably from 30 minutes to 2 hours.

[0147] Clause 44. The method defined in any one of clauses 1 to 43, wherein the catalyst layer formed in step (c) comprises a metal-supported molecular sieve.

[0148] Clause 45. The method of any one of clauses 1 to 44, wherein the catalyst layer formed in step (c) comprises a metal-supported molecular sieve that is catalytically active for SCR.

[0149] Clause 46. The method of any one of clauses 1 to 45, wherein during step (c) at least a partial metal loading of the molecular sieve occurs.

[0150] Article 47. Catalytic articles obtained or obtainable by the methods specified in any one of Articles 1 to 46.

[0151] Clause 48. A catalytic article as defined in clause 47 configured as a flow-through honeycomb monolith or wall-flow filter.

[0152] Clause 49. A catalytic article as defined in clause 47 or 48 which is catalytically active for SCR.

[0153] Clause 50. An exhaust system comprising a source of nitrogen-based reductant and an injector for injecting the nitrogen-based reductant into flowing exhaust gas, the injector being disposed upstream from a catalytic article as defined in Clause 49.

Claims

1. 1. A method of forming a catalyst article, comprising: (a) at least the following components: (i) H ＋ or NH ４ ＋ a crystalline molecular sieve in the form of (ii) a water-insoluble active metal precursor; and (iii) an aqueous solvent, by mixing together to form a slurry, forming a slurry, said slurry having a solids content of up to 50% by weight, and step (a) being carried out at a temperature in the range of 10 to 35°C; (b) coating a substrate with the slurry formed in step (a); (c) calcining the coated substrate formed in step (b) to form a catalyst layer on the substrate; The method wherein the crystalline molecular sieve is a small pore zeolite having a framework type that is CHA, the water-insoluble active metal precursor is copper (II) carbonate, and the aqueous solvent is water.

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

3. The binder component is selected from the group consisting of alumina, alumina precursor, aluminum hydroxide, and TiO ２ , SiO ２ , ZrO ２ , CeZrO ２ , SnO ２ 3. The method of claim 2, wherein the zeolitic aluminosilicates are selected from the group consisting of aluminophosphates, non-zeolitic aluminosilicates, silica-aluminas, clays, or mixtures thereof.

4. 4. The method of claim 2 or 3, wherein the rheology modifier is selected from polysaccharides.

5. 5. The method of any one of claims 1 to 4, wherein the slurry formed in step (a) has a solids content in the range of 30 to 50 wt%.

6. 6. The method of any one of claims 1 to 5, wherein step (a) is carried out at a temperature in the range of 10 to 30°C.

7. 7. The method of any one of claims 1 to 6, wherein step (b) is carried out at a temperature in the range of 10 to 35°C.

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