Catalytic articles for filtering particulate matter and uses thereof - Patents.com

Abstract

A catalytic article and its use in an exhaust system for an internal combustion engine are disclosed. The catalytic article includes a substrate that is a wall-flow filter, a first catalytic composition, and a second catalytic composition. The first and second catalytic compositions each independently include an oxygen storage component (OSC) derived from a CeZr mixed oxide sol having a D90 of less than 1.3 microns and a particulate inorganic oxide having a D90 of 1 to 20 microns.

Description

[Technical field]

[0001] SUMMARY The present disclosure relates to catalytic articles for treating exhaust gas emissions from gasoline engines. [Background technology]

[0002] Spark ignition engines use spark ignition to create the combustion of a hydrocarbon and air mixture. In contrast, compression ignition engines create the combustion of hydrocarbons by injecting them into compressed air. Spark ignition engines can be fueled by gasoline fuel, gasoline fuel blended with oxygenates including methanol and / or ethanol, liquid petroleum gas, or compressed natural gas. Spark ignition engines can be stoichiometrically operated or lean burn operated engines.

[0003] Three-way catalysts (TWCs) typically contain one or more platinum group metals, particularly those selected from the group consisting of platinum, palladium, and rhodium. TWCs are intended to simultaneously catalyze the following three reactions: (i) the oxidation of carbon monoxide to carbon dioxide, (ii) the oxidation of unburned hydrocarbons to carbon dioxide and water, and (iii) the reduction of nitrogen oxides to nitrogen and oxygen.

[0004] These three reactions occur most efficiently when the TWC receives exhaust gases from an engine operating at or near the stoichiometric point. As is well known in the art, carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NO ) are emitted when gasoline fuel is burned in a spark-ignited (e.g., spark-ignited) internal combustion engine. x The amount of oxidizing gas (NO x and O2) and reducing gases (HC and CO) are substantially matched in concentration. The air-fuel ratio that produces this stoichiometrically balanced exhaust gas composition is typically given as 14.7:1.

[0005] Theoretically, in a stoichiometrically balanced exhaust gas composition, O2, NO x The engine must be able to completely convert CO, CO, and HC to CO2, H2O, and N2 (and residual O2), which is the role of the TWC. Ideally, therefore, the engine should be operated in such a way that the air-fuel ratio of the combustion mixture produces a stoichiometrically balanced exhaust gas composition.

[0006] A way to define the compositional balance between oxidizing and reducing gases in the exhaust gas is the lambda (λ) value of the exhaust gas, which can be defined as the actual engine air-fuel ratio divided by the stoichiometric engine air-fuel ratio. A lambda (λ) value of 1 represents a stoichiometrically balanced (or stoichiometric) exhaust gas composition, while a lambda value >1 represents an excess of O2 and NO x where lambda represents excess HC and CO and the composition is described as "lean" and where lambda is <1, where excess HC and CO are represented and the composition is described as "rich". It is also common in the art to refer to the air / fuel ratio at which an engine operates as "stoichiometric", "lean" or "rich" depending on the exhaust gas composition which gives rise to the air / fuel ratio: thus, the air / fuel ratio in a stoichiometrically operating gasoline engine or a lean-burn gasoline engine.

[0007] NO using TWC x It should be appreciated that the reduction of CO to N2 is less efficient when the exhaust gas composition is lean of stoichiometry. Similarly, the TWC is less capable of oxidizing CO and HC when the exhaust gas composition is rich. Thus, the challenge is to keep the composition of the exhaust gas entering the TWC as close to stoichiometric as possible.

[0008] Naturally, when the engine is at steady state, it is relatively easy to ensure that the air-fuel ratio is stoichiometric. However, when the engine is used to propel a vehicle, the amount of fuel required varies temporarily depending on the load demand placed on the engine by the driver. This makes it particularly difficult to control the air-fuel ratio so that a stoichiometric exhaust gas is produced for a three-way conversion. In practice, the air-fuel ratio is controlled by an engine control unit that receives information about the exhaust gas composition from an exhaust gas oxygen (EGO) (or lambda) sensor, a so-called closed-loop feedback system. A characteristic of such a system is that the air-fuel ratio oscillates (or perturbs) between a slightly rich stoichiometric (or control set) point and slightly lean, due to the time lag associated with adjusting the air-fuel ratio. This perturbation is characterized by the amplitude and response frequency (Hz) of the air-fuel ratio.

[0009] The active components in a typical TWC include one or both of platinum and palladium in combination with rhodium supported on a high surface area oxide, or even palladium alone (no rhodium), and an oxygen storage component.

[0010] When the exhaust gas composition is slightly richer than the set point, a small amount of oxygen is needed to consume unreacted CO and HC, i.e., to make the reaction more stoichiometric. Conversely, when the exhaust gas becomes slightly lean, excess oxygen needs to be consumed. This has been achieved by the development of oxygen storage components (OSCs) that release or absorb oxygen during perturbations. The most commonly used oxygen storage components in modern TWCs are cerium oxide (CeO2) or mixed oxides or composite oxides containing cerium, such as CeZr mixed oxide or CeZr mixed oxide composite oxide.

[0011] Carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NO x ) (all of which can be treated with TWC catalysts), particulate matter (PM) emissions must be considered.

[0012] Environmental PM is classified by most authors into the following categories based on its aerodynamic diameter (the aerodynamic diameter is the diameter of 1 g / cm of the particle with the same settling velocity in the air as the particle being measured): 3 (ii) fine particles (PM-2.5), which have a diameter of less than 2.5 μm; (iii) ultrafine particles, which have a diameter of less than 0.1 μm (or 100 nm); and (iv) nanoparticles, which are characterized by a diameter of less than 50 nm.

[0013] Since the mid-1990s, the particle size distribution of particulate matter emitted from internal combustion engines has received increasing attention due to the possible adverse health effects of fine and ultrafine particles. The concentration of PM-10 particulate matter in ambient air is regulated by US law. A new additional ambient air quality standard of PM-2.5 was introduced in the US in 1997 as a result of health studies that showed a strong correlation between human mortality and concentrations of fine particles smaller than 2.5 μm.

[0014] Attention is now shifting to nanoparticles, as they are understood to penetrate deeper into the human lungs than larger sized particulate matter and, as a result, are considered to be more harmful than larger particles, as extrapolated from research findings on particulate matter in the 2.5-10.0 μm range.

[0015] The size distribution of diesel particulate matter has a well-established bimodal character corresponding to particle nucleation and agglomeration mechanisms. Diesel PM is composed of many small particles that retain very little mass. Nearly all diesel particulate matter is significantly below 1 μm in size; it includes a mixture of fine particles (i.e., falling under the 1997 US legislation), ultrafine particles, and nanoparticles.

[0016] It is understood that diesel particulate filters such as ceramic wall flow monoliths can function with a combination of depth and surface filtration, where the depth filtration capacity becomes saturated and the particulate layer begins to cover the filter surface, resulting in a filter cake with higher soot loading. Depth filtration is characterized by a slightly lower filtration efficiency and lower pressure drop than cake filtration.

[0017] PM produced by spark ignition engines has a very high proportion of ultrafine, with negligible accumulation and coarse modes compared to that produced by diesel (compression ignition) engines, which presents a challenge to removing it from the exhaust gas of a spark ignition engine to prevent emission to the atmosphere. In particular, because the majority of PM from spark ignition engines is relatively small compared to the size distribution of diesel PM, it is practically not possible to use filter substrates that promote cake filtration of spark ignition PM surface types, because the relatively small average pore size of the required filter substrate would create impractically high backpressures in the system.

[0018] Furthermore, conventional wall-flow filters designed to trap diesel PM cannot be used to facilitate surface-type filtration of PM from spark-ignition engines to meet relevant emission standards, because there is generally less PM in spark-ignition exhaust gas (and therefore less chance of soot cake formation), and spark-ignition exhaust gas temperatures are generally higher, which can result in faster removal of PM by oxidation, thus preventing increased PM removal by cake filtration. Deep filtration of spark-ignition PM in conventional diesel wall-flow filters is also difficult because the PM is significantly smaller than the pore size of the filter media. Thus, under normal operation, uncoated conventional diesel wall-flow filters have lower filtration efficiency when used with spark-ignition engines than with compression-ignition engines.

[0019] European emission regulations (Euro 6) from 1 September 2014 require the control of the number of particles emitted by both diesel and gasoline (spark ignition) passenger cars. For gasoline EU light vehicles, the permissible limits are: 1000mg / km of carbon monoxide; 60mg / km of nitrogen oxides (NO x ); 100mg / km total hydrocarbons (of which ≤68mg / km is non-methane hydrocarbons); and 4.5mg / km particulate matter (for direct injection engines only). Euro 6 includes a standard limit of 6.0×10 PM per km. 11 However, original equipment manufacturers are expected to continue to operate at 6×10 12 km -1 In practical terms, the legislated range for particulate matter is between 23 nm and 3 μm.

[0020] In the United States, on March 22, 2012, the California Air Resources Board (CARB) adopted new emissions standards for "LEV III" passenger cars, light trucks, and medium-duty vehicles, beginning with model years 2017 and after, that include a 3 mg / mile emissions limit, with the possibility of later implementation of 1 mg / mile, provided various interim reviews deem it feasible.

[0021] The new Euro 6 emissions standards present some challenging design problems for meeting gasoline emissions standards. In particular, the design must be able to reduce PM gasoline (spark ignition) emissions and simultaneously reduce nitrogen oxides (NO x The challenge is how to design a filter, or an exhaust system including a filter, to meet emission standards for non-PM pollutants such as one or more of PM, carbon monoxide (CO), and unburned hydrocarbons (HC).

[0022] There have been some recent efforts to combine TWCs with filters to meet Euro 6 emission standards.

[0023] WO2014125296 discloses a spark ignition engine including an exhaust system for a spark ignition internal combustion engine of a vehicle. The exhaust system includes a filter for filtering particulate matter from exhaust gas emitted from the spark ignition internal combustion engine of the vehicle coated with a three-way catalytic washcoat. The washcoat includes a platinum group metal and a plurality of solid particles, the plurality of solid particles including at least one base metal oxide and at least one oxygen storage component that is a mixed oxide or complex oxide including cerium. The mixed oxide or complex oxide including cerium and / or at least one base metal oxide has a median particle size (D50) of less than 1 μm.

[0024] US Patent Application Publication No. 20090193796 discloses an emission treatment system downstream of a gasoline direct injection engine for treating exhaust gases including hydrocarbons, carbon monoxide, nitrogen oxides, and particulate matter, the emission treatment system including a catalyzed particulate trap including a TWC catalyst coated on or within the particulate trap. In the description and examples provided, the catalyst coating (also referred to as layered or layered catalyst composite) is prepared from a slurry mixture of a solution of a desired precious metal compound and at least one support material (such as a finely divided high surface area, refractory metal oxide). The slurry mixture is ground, for example, in a ball mill or other similar device, resulting in substantially all solids having a particle size less than about 20 μm, i.e., a mean diameter [known as "D50"] between about 0.1-15 μm. In the examples, the grinding by milling of alumina was performed such that 90% of the particles [known as "D90"] have a particle size between 8-10 μm. Comminution of the ceria-zirconia composite was carried out by milling to a D90 particle size of <5 μm.

[0025] In GB 2514875, the inventors investigated the use of a washcoat composition comprising milled Ce / Zr mixed oxide for use in three-way catalysts for coating filters such as those disclosed in US 20090193796 for low backpressure applications. Here, milling the Ce / Zr mixed oxide reduced backpressure with a reduction in the D50 of the cerium / zirconium mixed oxide, but at the same time reduced CO and NO emissions. x It was found that the three-way catalyst activity was significantly reduced with respect to emissions.

[0026] It is therefore an object to provide an improved TWC catalyzed filter that overcomes the shortcomings of the prior art, or at least to provide a commercially viable alternative thereto, and more particularly to provide a catalytic article that allows for the treatment of exhaust gases to address the emission of fine sub-23 nm particulate matter.

[0027] The present inventors have found that they can address the problem of reduced three-way catalyst activity observed in GB Patent No. 2514875. They have also found that by carefully selecting the particle size of the cerium / zirconium mixed oxide component and the inorganic oxide material, such as alumina, the backpressure can be reduced to desirable levels.

[0028] The benefits of this discovery are evident in addressing the health risks associated with ultrafine soot particles mentioned above, recently referenced and discussed at length in the International Journal of Environmental Research and Public Health (Int. J. Environ. Res. Public Health, 2018, Vol. 15, p. 304). Indeed, the global acceptance of ultrafine particles and their impact on cardiopulmonary and central nervous system health issues is driving increased legislation and regulation worldwide for automotive applications. Beyond today's emission limits, legislators are looking to further improve air quality, and one area to consider is particulate matter, currently measured as PN or particulate matter number in the Euro 6d standard.

[0029] Currently, the measurement requirement for PN is for particles 23 nm and above. One obvious aspect to consider in tightening the legislation as measurement accuracy improves is to consider particle sizes below 23 nm. The described invention therefore helps to solve the technical challenges of the expected tightening of particulate matter emission laws beyond Euro 6d and provide the desired health benefit of reducing ultrafine particles in the air. Summary of the Invention

[0030] One aspect of the present disclosure relates to a catalyst article for treating exhaust gas from a spark ignition internal combustion engine, the catalyst article comprising: a substrate that is a wall-flow filter having an inlet end, an outlet end and an axial length L therebetween; a plurality of inlet channels extending from the inlet end; and a plurality of outlet channels extending from the outlet end, the plurality of inlet channels comprising a first catalyst composition extending from the inlet end or the outlet end over at least 50% of L; and the plurality of outlet channels comprising a second catalyst composition extending from the outlet end or the inlet end over at least 50% of L; the first and second catalyst compositions overlap over up to 80% of L; and the first and second catalyst compositions each independently comprise an oxygen storage component (OSC) derived from a CeZr mixed oxide sol having a D90 of less than 1.3 microns; and a particulate inorganic oxide having a D90 of 1 to 20 microns.

[0031] Another aspect of the present disclosure relates to an exhaust gas treatment system including a catalytic article as described herein in fluid communication with an exhaust manifold of a spark ignition engine.

[0032] Another aspect of the present disclosure relates to a method for treating exhaust gas emitted from a spark ignition internal combustion engine, comprising contacting the exhaust gas with a catalytic article described herein.

[0033] Another aspect of the present disclosure relates to the use of the catalytic article of the present invention in an exhaust gas treatment system to reduce emissions of particles less than 23 nm. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a schematic diagram of one embodiment of a wall-flow filter as described herein. [Diagram 2] FIG. 2 is a schematic diagram of another embodiment of a wall-flow filter as described herein. [Diagram 3] 1 shows simulated WLTC engine bench data for particulate emissions, specifically 10-23 nm emissions, and in particular 10-23 nm particulate counts, for an exemplary catalyst article (# / km). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] One aspect of the present disclosure relates to a catalyst article for treating exhaust gas from a spark ignition internal combustion engine, the catalyst article comprising: a substrate that is a wall-flow filter having an inlet end, an outlet end and an axial length L therebetween; a plurality of inlet channels extending from the inlet end; and a plurality of outlet channels extending from the outlet end, the plurality of inlet channels comprising a first catalyst composition extending from the inlet end or the outlet end over at least 50% of L; and the plurality of outlet channels comprising a second catalyst composition extending from the outlet end or the inlet end over at least 50% of L; the first and second catalyst compositions overlap over up to 80% of L; and the first and second catalyst compositions each independently comprise an oxygen storage component (OSC) derived from a CeZr mixed oxide sol having a D90 of less than 1.3 microns; and a particulate inorganic oxide having a D90 of 1 to 20 microns.

[0036] In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined can be combined with any other aspect or aspects, 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.

[0037] The catalyst article comprises a substrate that is a wall-flow filter having an inlet end, an outlet end and an axial length L therebetween, a plurality of inlet channels extending from the inlet end and a plurality of outlet channels extending from the outlet end. Wall-flow filters are well known in the art and typically comprise a ceramic porous filter structure having a plurality of inlet channels and a plurality of outlet channels, each of which is defined in part by a ceramic wall of the porous structure, and each of which is separated from an outlet channel by a ceramic wall of the porous structure.

[0038] Typical lengths are 2 to 12 inches (5.1 to 30.5 cm) long, preferably 3 to 6 inches (7.6 to 15.2 cm) long. The cross section is preferably circular, and may typically have a filter diameter of 4.66 and 5.66 inches (11.8 cm and 14.4 cm). However, the cross section may also be dictated by the space on the vehicle where the filter needs to be secured.

[0039] The substrate may be a ceramic, such as silicon carbide, cordierite, aluminum nitride, silicon nitride, aluminum titanate, alumina, mullite, such as acicular mullite (see, for example, WO 01 / 16050), pollucite, cermets such as Al2O3 / Fe, or a composite material comprising any two or more segments thereof. In embodiments in which the catalytic article of the present invention comprises a ceramic substrate, the ceramic substrate may be made of any suitable refractory material, such as alumina, silica, titania, ceria, zirconia, magnesia, zeolites, silicon nitride, silicon carbide, zirconium silicate, magnesium silicate, aluminosilicates and metalloaluminosilicates (such as cordierite and spodumene), or mixtures or mixed oxides of any two or more thereof. Cordierite, magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0040] Substrates suitable for use in the present invention typically have a porosity of >40% or >50%, with porosities of 45-75%, such as 50-65% or 55-60% being advantageously used. Porosity is a measure of the proportion of void space within the substrate and is related to backpressure within an exhaust system. In general, the lower the porosity, the higher the backpressure.

[0041] Substrates suitable for use in the present invention typically have an average pore size of surface pores of from 8 to 45 μm, for example from 8 to 25 μm, 10 to 20 μm, or 10 to 15 μm. Pore size is well known to those skilled in the art and suitable measurement techniques will be known to those skilled in the art.

[0042] Each of the first and second catalyst compositions independently comprises an oxygen storage component (OSC) derived from a CeZr mixed oxide sol having a D90 of less than 1.3 microns and a particulate inorganic oxide having a D90 of 1 to 20 microns.

[0043] Particle size distribution can be characterized by measurements of D10, D50, and D90. In each case, the numbers indicate the percentage amount of particles smaller than the stated value. In other words, a D90 of 100 microns means that 90% of the particles are smaller than 100 microns in diameter. Knowing the D10 and D90 allows one to define the range of particles in a particle distribution. Characterizing the particle size of a sample by D10 and D90 values ​​generally defines the width of the particle size distribution. The closer these values ​​are, the narrower the particle size distribution.

[0044] The particle size measurements required to obtain the D10, D50 and D90 values ​​of the CeZr mixed oxide sol and / or particulate inorganic oxide can be obtained by laser diffraction particle size analysis using a Malvern Mastersizer 2000, which is a volume-based technique (i.e., D50 and D90 are the D V 50 and D V90 (also referred to as D(v,0.50) and D(v,0.90)), a mathematical Mie theory model is applied to determine the particle size distribution. Laser diffraction systems work by determining the diameter of the particles based on a spherical approximation. For particle size measurement by laser diffraction particle size analysis, diluted samples were prepared by sonication in surfactant-free distilled water at 35 watts for 30 seconds.

[0045] In some embodiments, the D90 of the CeZr mixed oxide sol can be less than 1.2 microns, or less than 1.1 microns, or less than 1.0 microns, or less than 900 nm, or less than 800 nm, or less than 700 nm, or less than 600 nm, or less than 500 nm, or less than 400 nm, or less than 300 nm.

[0046] In some other embodiments, the D90 of the CeZr mixed oxide sol can be 1.2 microns to 1.3 microns, or 1.1 microns to 1.2 microns, or 1.0 microns to 1.1 microns, or 900 nm to 1.0 microns, or 800 nm to 900 nm, or 700 nm to 800 nm, or 600 nm to 700 nm, or 500 nm to 600 nm, or 400 nm to 500 nm, or 300 nm to 400 nm, or 200 nm to 300 nm, or 100 nm to 200 nm.

[0047] The CeZr mixed oxide sol may have a D50 of 100 nm to 700 nm, preferably 200 nm to 600 nm, more preferably 300 nm to 400 nm.

[0048] Particle size can also be characterized by obtaining the Z-average particle size of a sample. The Z-average is the intensity-weighted average hydrodynamic size of an ensemble collection of particles measured by dynamic light scattering (DLS). The Z-average is derived from a cumulant analysis of the measured correlation curve, where a single particle size is assumed and a single exponential fit is applied to the autocorrelation function. The particle size measurements required to obtain the Z-average particle size of CeZr mixed oxide sols and / or particulate inorganic oxides can be obtained by dynamic light scattering particle size analysis using a Malvern Zetasizer Nano. All tests are performed in dilute aqueous media, and the harmonic mean hydrodynamic diameter of a sphere of equivalent diffusivity is determined by cumulant analysis of the time dependence of light scattered by randomly moving particles according to the Stokes-Einstein equation.

[0049] The Z-average particle size of the CeZr mixed oxide sol is preferably 150 nm to 350 nm, more preferably 230 to 310 nm.

[0050] The CeZr mixed oxide sol comprises CeZr mixed oxide (CeZr mixed oxide particles or CeZr mixed oxide nanoparticles) dispersed in an aqueous medium. The CeZr mixed oxide comprises ceria and zirconia. Although nominally described as "ceria" or "cerium dioxide" and "zirconia" or "zirconium oxide", it will be understood by those skilled in the art that the actual oxide anions present may comprise oxide anions or hydroxide anions, or mixtures thereof, such as hydrated oxide phases (e.g., oxyhydroxides).

[0051] Preferably, the concentration of the CeZr mixed oxide in the CeZr mixed oxide sol ranges from 10 to about 50 weight percent ("wt %), more preferably from 15 to about 45 wt %, and most preferably from 20 to about 40 wt %, based on the weight of the CeZr mixed oxide sol.

[0052] The CeZr mixed oxide present in the CeZr mixed oxide sol may preferably contain ceria in an amount of about 5 to about 60 wt %, more preferably about 10 to about 50 wt %, and most preferably about 30 to about 40 wt %, based on the total weight of the CeZr mixed oxide.

[0053] The CeZr mixed oxide present in the sol may preferably contain zirconia in an amount of about 10 to about 75 wt %, more preferably about 30 to about 70 wt %, and most preferably about 50 to about 65 wt %, based on the total weight of the CeZr mixed oxide.

[0054] In one embodiment, the CeZr mixed oxide sol has a weight ratio of ZrO2 to CeO2 of about 2:1.

[0055] The CeZr mixed oxide present in the sol may contain rare earth oxides other than ceria. The rare earth oxides in the CeZr mixed oxide are selected from the group consisting of oxides of dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), yttrium (Y), and mixtures thereof. The CeZr mixed oxide preferably contains an oxide of La, Nd, Pr, or Y, or a mixture thereof, more preferably an oxide of La or Nd, or a mixture thereof.

[0056] The amount of rare earth oxide in the CeZr mixed oxide in the CeZr mixed oxide sol may be preferably about 1 to about 25% by weight, more preferably about 2 to about 20% by weight, and most preferably about 5 to about 15% by weight, based on the total weight of the CeZr mixed oxide.

[0057] The CeZr mixed oxide present in the CeZr mixed oxide sol may contain a transition metal oxide. The transition metal present in the CeZr mixed oxide is preferably selected from the group consisting of titanium (Ti), hafnium (Hf), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), and mixtures thereof. More preferably, the transition metal is selected from the group consisting of Ti, Hf, and mixtures thereof. Most preferably, the transition metal is Hf.

[0058] The CeZr mixed oxide sol suitable for the present invention can be prepared by known techniques, see, for example, WO 2020161459, US 10,570,063, US 9,820,917, US 9,820,917, CN1371867A, H. He, Integrated Ferroelectrics, 161:1, 36-44, JJ Gulicovski, SK Milonjic, and K. Meszaros Szecsenyi, "Synthesis and Characterization of Stable Aqueous Ceria Sols, Materials and Manufacturing Processes", Vol. 24:10-11, 2009, pp. 1080-1085.

[0059] The particulate inorganic oxide used in the present invention is preferably an oxide of an element of group 2, group 3, group 4, group 5, group 13, and group 14. The particulate inorganic oxide is preferably selected from the group consisting of alumina, magnesia, lanthana, silica, neodymium, praseodymium, yttrium oxide, titania, niobia, tantalum oxide, molybdenum oxide, tungsten oxide, and mixed oxides or composite oxides thereof. More preferably, the particulate inorganic oxide is selected from the group consisting of alumina, magnesia, silica, lanthanum, neodymium, praseodymium, yttrium oxide, and mixed oxides or composite oxides thereof. Particularly preferably, the particulate inorganic oxide is alumina, lanthanum / alumina composite oxide, or magnesia / alumina composite oxide. One particularly preferred particulate inorganic oxide is lanthanum / alumina composite oxide.

[0060] Preferably, the particulate inorganic oxide has a particle size of at least 80 mm. 2 / g, more preferably at least 150m 2 / g, and most preferably at least 200m 2 / g surface area.

[0061] Generally, the particulate inorganic oxide has a D90 of 1 to 20 microns. Preferably, the particulate inorganic oxide has a D90 of 5 to 20 microns. More preferably, the particulate inorganic oxide has a D90 of 5 to 15 microns.

[0062] The first and second catalyst compositions are preferably both TWC compositions. TWC compositions are well known in the art and the specific components can be readily selected by those skilled in the art. TWCs typically include one or more platinum group metals (PGMs) provided on a high surface area support (i.e., inorganic oxide) along with an oxygen storage component (OSC). TWC compositions are generally provided in a washcoat on a substrate.

[0063] Preferably, the first and / or second catalyst composition has a weight ratio of OSC (mixed oxide derived from CeZr mixed oxide sol) to particulate OSC to particulate inorganic oxide of 10:1 to 1:10, preferably 3:1 to 1:3. Preferably, the loading of OSC in each composition is 0.5 to 4 g / in 3 , preferably 1 to 3 g / in 3 It is.

[0064] Preferably, the first and / or second catalyst composition further comprises a platinum group metal (PGM) component, preferably selected from the group consisting of platinum, palladium, rhodium, and mixtures thereof.

[0065] When a PGM component is present in the first and / or second catalyst compositions, the PGM component is preferably supported on a particulate inorganic oxide.

[0066] The first and / or second catalyst composition may comprise from 1 to 100 g / ft of PGM components. 3 , preferably 5 to 80 g / ft 3 More preferably, the PGM content is 10 to 50 g / ft 3 It could be.

[0067] The first and / or second catalyst composition may further comprise an alkali or alkaline earth metal component. Preferably, the first and / or second catalyst composition comprises barium or strontium. Preferably, the barium or strontium, if present, is present in an amount of 0.1-15 wt%, more preferably 3-10 wt%, based on the total weight of the first and / or second catalyst composition. Preferably, the barium is present as a BaCO3 composite material. Such materials can be impregnated by any method known in the art, for example, incipient wetness impregnation or spray drying.

[0068] The catalyst article of the present invention may include other components known to those skilled in the art. For example, the first and / or second catalyst composition may further include at least one binder and / or at least one surfactant. When a binder is present, a dispersible alumina binder is preferred.

[0069] Preferably, the first and second catalyst compositions are substantially the same. They may have the same composition but different loadings. Preferably, the first and second catalyst compositions are the same to reduce manufacturing complexity.

[0070] The first and second catalyst compositions may be coated onto a substrate by a washcoating process. A washcoat slurry is prepared containing the CeZr mixed oxide sol, particulate inorganic oxides, and other components such as PGMs, if used, and a suitable solvent, preferably water. Additional components such as binders, stabilizers, or promoters may also be incorporated. The slurry preferably contains from about 10% to about 70% by weight solid material, more preferably from about 20% to about 50% by weight solid material.

[0071] A number of techniques can be used to coat the substrate with the washcoat slurry.

[0072] In one method of washcoating, the substrate may then be dipped into the washcoat slurry one or more times to deposit a desired loading of the composition on the substrate, or the slurry may be coated onto the substrate. Depending on the particle size and viscosity of the washcoat slurry, the washcoat slurry may at least partially penetrate the pores of the substrate during coating.

[0073] When coating with techniques such as Johnson Matthey's Precision Coating Process described in WO 1999 / 47260, which relies on vacuum or pressure drawing of the washcoat onto the substrate, it is possible to apply the coating to the inlet end of the outlet channel and the outlet end of the inlet channel. This technique not only provides the washcoat within the pores of the substrate, but also draws the material through to provide a coating on the wall opposite where the substrate was applied.

[0074] After the substrate is coated with the first and second compositions, the coated substrate is preferably dried and then calcined by heating at an elevated temperature to form a catalyst article. Preferably, the calcination is at 400-600° C. for about 1-8 hours.

[0075] According to the invention, the plurality of inlet channels of the catalyst article comprises a first catalyst composition extending from the inlet or outlet end over at least 50% of L, and the plurality of outlet channels comprises a second catalyst composition extending from the outlet or inlet end over at least 50% of L. The first and second catalyst compositions overlap by up to 80% of L. The first and second catalyst compositions preferably overlap by up to 20% of L, more preferably by up to 10% of L. One of the first and second compositions may provide a complete coating of the plurality of inlet or outlet channels.

[0076] If the overlap is at most 20%, the first catalyst composition may be provided on the inlet channel extending a distance of at least 50% and at most 70% (of L) from the inlet end, while the second catalyst composition may be provided on the outlet channel extending a distance of at least 50% and at most 70% from the outlet end. Since the overlap is at most 20%, if the first catalyst composition is, for example, 70%, the second catalyst composition may extend by 50%.

[0077] Preferably, the first and / or second catalyst composition is provided directly on the substrate.

[0078] The location of the first and second compositions on the substrate will depend on the coating technique used. The first and second compositions coated on the substrate may be in-wall, on-wall, or a combination of in-wall and on-wall. Preferably, at least a portion of the coating is provided on the wall.

[0079] In one embodiment, the inlet and / or outlet channels of the wall-flow filter have a wedge-shaped profile on the walls, with the thickest end of the wedge at the plug end of the channel, and the washcoat also resides in the wall. This arrangement differs from Applicant's WO 2017 / 056067, which discloses a catalytic wall-flow filter that includes a three-way catalytic washcoat arranged on the walls in a "wedge" shape when the wall-flow filter is viewed in longitudinal cross section. That is, the thickness of the wall coating tapers from the thickest end at the open channel end of the wall-flow filter.

[0080] When coating by vacuum infiltration as disclosed in WO 1999 / 47260, conditions are used that "pull" the particles in the washcoat from the side of the wall of the wall-flow filter structure such that the washcoat composition is first contacted through the porous filter wall, causing some of them to rest on the opposite (second) wall of the wall.

[0081] Another aspect of the present disclosure is an exhaust gas treatment system including a catalytic article as described herein in fluid communication with an exhaust manifold of a spark ignition engine.

[0082] Optionally, the exhaust system may include additional components. For example, in an exhaust system particularly applicable to lean-burn engines, a NOx trap may be placed upstream of the described catalytic article. NOx traps, also known as NOx absorption catalysts (NACs), are known, for example, from US Pat. No. 5,473,887, and are designed to adsorb nitrogen oxides (NOx) from lean (oxygen-rich) exhaust gases (lambda>1) during operation in a lean operating mode, and to desorb NOx when the oxygen concentration in the exhaust gas decreases (stoichiometric or rich operating modes). The desorbed NOx may be reduced to N2 with a suitable reducing agent, for example gasoline fuel, promoted by catalytic components such as rhodium or ceria in the NAC itself or located downstream of the NAC.

[0083] After leaving the catalyst article described herein as desired, the exhaust gas stream can then be optionally conveyed through a suitable exhaust pipe to a downstream NOx trap to adsorb any remaining NOx emission pollutants in the exhaust gas stream. From the NOx trap through a further exhaust pipe, an SCR catalyst can be positioned receiving the outlet of the NOx trap to treat further emissions with a selective catalytic reduction catalyst that uses ammonia as a reductant to reduce nitrogen oxides to form nitrogen and water. From the SCR catalyst, the exhaust pipe can be directed to a tailpipe and out of the system.

[0084] Another aspect of the present disclosure is a method of treating exhaust gas emitted from a spark ignition internal combustion engine, the method comprising contacting the exhaust gas with a catalytic article described herein. Preferably, the engine is a lean-burn gasoline engine. Additionally, the present disclosure can include a vehicle, such as a passenger car, comprising an engine as described herein.

[0085] Another aspect of the present disclosure is the use of the catalytic article described herein in an exhaust gas treatment system to reduce emissions of particles less than 23 nm, particularly to reduce emissions of particles between 10 and 23 nm. Preferably, the use of the catalytic article reduces the number of emissions of particles less than 23 nm by at least 20 percent, more preferably by at least 30 percent, and even more preferably by at least 40 percent.

[0086] Another aspect of the present disclosure is a method for treating exhaust gas emitted from a spark ignition internal combustion engine, comprising contacting the exhaust gas with a catalytic article described herein, the method for reducing emissions of particles less than 23 nm, particularly for reducing emissions of particles between 10 and 23 nm.

[0087] Another aspect of the present disclosure is the use of the catalytic articles described herein in exhaust gas treatment systems to reduce emissions of particles less than 23 nm, particularly to reduce emissions of particles between 10 and 23 nm.

[0088] The term "washcoat" is well known in the art and typically refers to an adherent coating that is applied to a substrate during the preparation of a catalyst.

[0089] As used herein, the acronym "PGM" refers to "platinum group metals." The term "platinum group metals" generally refers to metals selected from the group consisting of Ru, Rh, Pd, Os, Ir, and Pt, preferably metals selected from the group consisting of Ru, Rh, Pd, Ir, and Pt. Generally, the term "PGM" preferably refers to metals selected from the group consisting of Rh, Pt, and Pd.

[0090] As used herein, the term "mixed oxide" generally refers to a mixture of oxides in a single phase, as is conventionally known in the art. As used herein, the term "complex oxide" generally refers to a composition of oxides having two or more phases, as is conventionally known in the art.

[0091] As used herein, the term "loading" is defined as g / ft on a metal weight basis unless other units are provided. 3 Refers to the measurement in units of .

[0092] The invention will now be described with reference to the following non-limiting drawings.

[0093] FIG 1 illustrates one embodiment of the present invention. FIG 1 shows a cross-section of a wall-flow filter 1 made from a porous cordierite substrate. Wall-flow filter 1 has a length L extending between an inlet end 5 and an outlet end 10. Wall-flow filter 1 comprises a plurality of inlet channels 15 and a plurality of outlet channels 20 (only one shown). The plurality of inlet channels 15 and outlet channels 20 are plugged at their respective ends with plugs 21.

[0094] The inner surface 25 of the inlet channel 15 is coated with a wall-on coating 30 comprising a first catalyst composition. The coating 30 extends at least 50% of L from the inlet end 5 and has a substantially uniform thickness along the length of the channel.

[0095] The inner surface 35 of the outlet channel 20 is coated with a wall-on coating 40 comprising a second catalyst composition. The coating 40 extends at least 50% of L from the outlet end 10 and has a substantially uniform thickness along the length of the channel.

[0096] The overlap area 45 between coatings 30 and 40 is less than or equal to 20% of L.

[0097] In use, exhaust gas flow 50 (indicated by arrows) passes through the walls of the wall-flow filter 1 into the inlet channels 15 and out the outlet channels 20 .

[0098] Figure 2 illustrates another embodiment of the present invention. Figure 2 shows a cross-section of a wall-flow filter 1 made from a porous cordierite substrate. Wall-flow filter 1 has a length L extending between an inlet end 5 and an outlet end 10. Wall-flow filter 1 comprises a plurality of inlet channels 15 and a plurality of outlet channels 20 (only one shown). The plurality of inlet channels 15 and outlet channels 20 are plugged at their respective ends with plugs 21.

[0099] The inner surface 25 of the inlet channel 15 is coated with a wall-on coating 30 comprising a first catalyst composition. Additionally, the first catalyst composition is present within the wall structure of the inlet channel 15. The coating 30 extends at least 50% of L from the outlet end 10. The coating 30 is wedge-shaped, with a thicker amount at the outlet end 10. The coating 30 is applied according to the methods of WO 1999 / 47260.

[0100] The inner surface 35 of the outlet channel 20 is coated with a wall-on coating 40 comprising a second catalyst composition. Additionally, the second catalyst composition is present within the wall structure of the outlet channel 20. The coating 40 extends at least 50% of L from the inlet end 5. The coating 40 is wedge-shaped, with a thicker amount at the inlet end 5. The coating 40 is applied according to the methods of WO 1999 / 47260.

[0101] The overlap area 45 between coatings 30 and 40 is less than or equal to 20% of L.

[0102] In use, exhaust gas flow 50 (indicated by arrows) passes through the walls of the wall-flow filter 1 into the inlet channels 15 and out the outlet channels 20 .

[0103] The invention will now be described with reference to the following non-limiting examples.

[0104] material All materials are commercially available and were obtained from known sources unless otherwise stated.

[0105] Example 1 1.2 g / in derived from CeZr mixed oxide sol with a ZrO2 to CeO2 weight ratio of approximately 2:1 and a D90 of <1 μm 3 CeZr mixed oxide (OSC) and 0.4 g / in with a D90 of 12 μm 3 La-stabilized alumina component, 1.6 g / in 3 The three-way catalyst washcoat was prepared with a PGM loading of 22 g / ft 3 (Pt:Pd:Rh, 0:20:2).

[0106] The finished washcoat slurry was adjusted to an appropriate final washcoat solids content of approximately 24% for coating onto GPF substrates using Johnson Matthey's precision coating process described in WO 1999 / 47260. The substrate used was a commercially available cordierite GPF substrate with a nominal porosity of 63% and an average pore size of 17.5 μm, a diameter of 4.66 inches, a length of 6 inches, 300 cells / sq. inch, and a channel wall thickness of 8 thousandths of an inch. The coatings were applied from each end of the substrate, with each application covering 58% of the length of the total substrate length to give a fully coated final product with no uncoated areas (16% overlap). The amount of washcoat slurry applied to the inlet and outlet channels was the same. The coated substrate was then dried and calcined by conventional methods known in the art. The product profile is shown in Figure 2.

[0107] Example 2 Example 2 was prepared in the same manner as Example 1, except that the La-stabilized alumina component further had a D90 of 5 μm.

[0108] Comparative Example 3 The reference coated GPF was prepared by applying the latest TWC coating developed for GPF substrates. The washcoat loading was 1.2 g / in 3 of OSC component (CeZr mixed oxide particles, not derived from sol), 0.4 g / in 3 La-stabilized alumina component, and 22 g / ft 3 PGM loading of 1.6 g / in 3 (Pt:Pd:Rh, 0:20:2). In contrast to Examples 1 and 2, here the D90 of both the OSC and La-stabilized alumina components is about 7 μm.

[0109] Uncoated 220 / 6 reference GPF For further comparison with the present invention, an uncoated GPF reference was used. This is a commercially available GPF substrate with a 6×10 11The use of such a bare filter in an aftertreatment system with the Euro 6PN limit of 1000 nm can be considered. The same catalyst diameter and length, and therefore catalyst volume, were selected as in Examples 1-3, 4.66 inches in diameter and 6 inches in length. However, to achieve the required filtration efficiency, such bare filters require a lower nominal porosity and average pore size. Because this can cause an undesirable increase in back pressure, the cells and wall thickness per square inch are typically thinner than substrates designed to be coated with a washcoat. The uncoated reference GPF had 220 cells per square inch and a wall thickness of 6 thousandths of an inch.

[0110] Filtration performance evaluation The above samples were evaluated for particulate matter emissions, specifically emissions between 10 and 23 nm. The evaluation was carried out in a simulated WLTC run on an engine bench equipped with a 2.0L gasoline direct injection engine. Particles were measured using a Combustion DMS500 particle analyzer.

[0111] The results are shown in Figure 3 and were an average of three WLTC tests completed for each Example. The results show the advantages of Examples 1 and 2 compared to uncoated low porosity 220 / 6GPF and Comparative Example 3. In particular, Example 1 offers significant improved advantages over currently available alternatives.

[0112] Table 1 below shows the additional backpressure reduction benefit of Examples 1 and 2 versus Comparative Example 3.

[0113] [Table 1]

Claims

1. 1. A catalytic article for treating exhaust gas from a spark ignition internal combustion engine, comprising: a substrate that is a wall-flow filter having an inlet end, an outlet end and an axial length L therebetween; a plurality of inlet channels extending from the inlet end; and a plurality of outlet channels extending from the outlet end; the plurality of inlet channels comprises a first catalyst composition extending from the inlet end or the outlet end across at least 50% of the L, the plurality of outlet channels comprises a second catalyst composition extending from the outlet end or the inlet end across at least 50% of the L, the first and second catalyst compositions overlap up to 80% of the L; A catalytic article, wherein the first and second catalytic compositions each independently comprise an oxygen storage component (OSC) derived from a CeZr mixed oxide sol having a D90 of less than 1.3 microns, and a particulate inorganic oxide having a D90 of 1 to 20 microns.

2. 10. The catalytic article of claim 1, wherein the CeZr mixed oxide sol has a D90 of less than 1.0 microns.

3. 10. The catalyst article of claim 1, wherein the first and second catalyst compositions overlap by up to 20% of the L.

4. 10. The catalyst article of claim 1, wherein the first and second catalyst compositions overlap by a maximum of 10% of the L.

5. The CeZr mixed oxide sol has a ratio of about 2:1 ZrO ２ vs. CeO ２ 10. The catalyst article of claim 1 having a weight ratio of:

6. 2. The catalytic article of claim 1, wherein said particulate inorganic oxide is selected from the group consisting of alumina, magnesia, silica, lanthanum, neodymium, praseodymium, yttrium oxide, and mixed or composite oxides thereof.

7. 10. The catalytic article of claim 1, wherein the first and / or second catalytic composition further comprises a platinum group metal (PGM) component.

8. The catalytic article of claim 7, wherein the platinum group metal (PGM) component is selected from the group consisting of platinum, palladium, rhodium, and mixtures thereof.

9. The catalytic article of claim 1 , wherein the first and / or second catalytic composition further comprises an alkali or alkaline earth metal component.

10. The catalytic article of claim 1 , wherein the first and second catalytic compositions are the same.

11. 10. The catalyst article of claim 1, wherein the first and / or second catalyst composition has a weight ratio of the OSC to the particulate inorganic oxide of 3:

1.

12. The catalytic article of claim 1 , wherein the first and / or second catalytic composition is provided directly on the substrate.

13. 10. An exhaust gas treatment system comprising the catalytic article of claim 1 in fluid communication with an exhaust manifold of a spark ignition engine.

14. 13. A method for treating exhaust gas emitted from a spark ignition internal combustion engine, comprising contacting said exhaust gas with the catalytic article of claim 1.

15. 13. Use of the catalytic article of claim 1 in an exhaust gas treatment system for reducing emissions of particles less than 23 nm.

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