Method for producing an exhaust gas catalyst to suppress the aging of platinum group metal (PGM) particles

Abstract

A method for producing an exhaust gas catalyst (30) for suppressing the aging of platinum group metal (PGM) particles (16), the method comprising: the deposition of PGM particles (16) onto a support (18); the reduction of a functional group on a surface of the PGM particles (16), whereby the PGM particles (16) do not become reactive during a subsequent selective growth process; and the selective growth of a barrier layer (24) on the support (18) around the PGM particles (16), wherein selective growth is carried out by atomic layer deposition (ALD), and wherein a total number of ALD cycles is 5 to 10.

Description

TECHNICAL AREA

[0001] The present disclosure relates generally to exhaust catalysts, more specifically to catalysts that suppress aging. BACKGROUND

[0002] Vehicles with internal combustion (ICU) incorporate an exhaust aftertreatment system to treat the engine's exhaust gases. The configuration of the treatment system depends in part on whether the engine is a diesel engine (which typically operates with lean combustion and contains high concentrations of oxygen in the exhaust gases under all operating conditions) or a stoichiometric spark-ignition engine (which operates at a near-stoichiometric air / fuel ratio). The exhaust aftertreatment system for the diesel engine includes a diesel oxidation catalyst (DOC), which can oxidize carbon monoxide (CO) and hydrocarbons (HC). The exhaust aftertreatment system for the stoichiometric spark-ignition engine includes a three-way catalytic converter (TWC), which operates on the principle of non-selective catalytic reduction of NOₓ. x works through CO and HC. SUMMARY

[0003] An exhaust catalyst includes a catalyst. The catalyst contains a support, platinum group metal (PGM) particles dispersed on the support, and a barrier layer formed on the substrate. The barrier layer is positioned between a first set of PGM particles and a second set of PGM particles to suppress the aging of the PGM particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Features of examples of the present disclosure will become apparent by reference to the following detailed description and the drawings, in which the same reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features with a previously described function may or may not be described in conjunction with other drawings in which they appear.

[0005] Fig. Figure 1 is a schematic representation illustrating the two mechanisms for the growth or sintering of the PGM particles;

[0006] Fig. 2A is a semi-schematic top view of an example of a catalyst disclosed herein;

[0007] Fig. 2B is a semi-schematic cross-sectional view along line 2B-2B of the in Fig. 2A catalyst shown;

[0008] Fig. Figure 3 is a semi-schematic cross-sectional view representing an example of the catalyst disclosed herein, formed by selective atomic layer deposition (ALD);

[0009] Fig. 4A is a perspective, partially cutaway view of an example of an exhaust gas catalyst;

[0010] Fig. 4B is an enlarged view of part of Fig. 4A;

[0011] Fig. 5A is a diagram showing the distribution of palladium (i.e., the ratio of the number of metal atoms on the surface to the total number of metal atoms, shown as a percentage) for a baseline example (BL) and examples that have undergone a different number of atomic layer deposition (#ALD) cycles;

[0012] Fig. Figure 5B is a diagram of the distribution of palladium (shown as a percentage) for a baseline example (BL), an example with a barrier layer formed from 5 ALD cycles (5 ALD), and an example incorporating a barrier layer from 10 ALD cycles (10 ALD) after exposure to an aging process; and

[0013] Fig. Figure 6 is a diagram of the ignition temperature (in °C) during the conversion of carbon monoxide (CO) and C3H6 (propene, also known as propylene) for a baseline example (BL) and an example with a barrier layer formed from 5 ALD cycles (Pd / Al2O3 + 5ALD). DETAILED DESCRIPTION

[0014] DOCs and TWCs often contain a support loaded with a platinum group metal (PGM) as the active catalytic / catalyst material. When the exhaust gas temperature from the vehicle engine rises (e.g., to temperatures of 150 °C to approximately 1000 °C), the PGM loaded on the support can undergo particle growth (i.e., sintering). Fig. Figure 1 shows two mechanisms for PGM particle growth during vehicle operation. The mechanisms involve atomic and / or PGM crystallite migration. The first mechanism involves PGM migration via a vapor phase, with 12characterized, and the second mechanism involves PGM migration via surface diffusion, with 14 characterized. In the first mechanism, a mobile species (not shown) that is on the carrier 18 loaded PGM particles 16 is released through the vapor phase 12 migrate and with other metal particles 20 in the vapor phase 12 forming larger PGM particles 16’ agglomerate. In the second mechanism, a mobile species (not shown) can be formed by the PGM particles. 16 is released along a surface 18a of the carrier 18 diffuse, and with other metal particles 22 on the surface 18a forming larger PGM particles 16’ agglomerate.

[0015] An increase in the size of the PGM particles 16’This leads to poor PGM utilization and undesirable aging of the catalyst material. More precisely, the increased particle size reduces the PGM distribution, which is the ratio of the number of PGM surface atoms in the catalyst to the total number of PGM atoms in the catalyst. A reduced PGM distribution is directly related to a decrease in the active metallic surface area (as a result of particle growth) and thus indicates a loss of active reaction sites on the catalyst. This loss of active reaction sites leads to poor PGM utilization and indicates that the catalyst has been undesirably aged or deactivated.

[0016] It has been shown that after 100,000 to 150,000 miles in a typical turbocharged water heater (TWC), approximately 1% of the propellant mineral oils (PGMs) remain catalytically active (i.e., 99% of the PGMs have been consumed). One approach to counteract the effects of sintering is to use a sufficiently high PGM loading to compensate for the deactivation of the catalyst. However, this increases the cost of the TWC.

[0017] The catalysts disclosed herein suppress aging by physically separating the PGM particles. 16 through a carrier 18 The barrier layer formed is achieved through the physical separation of the PGM particles. 16The barrier layer blocks vapor-phase migration and surface diffusion. This slows down or prevents PGM particle growth / sintering, and more active PGM sites are retained over time, resulting in slower catalyst aging compared to catalysts without a barrier layer. Furthermore, reducing or preventing sintering also prevents drift in the catalyst's operating temperature over time.

[0018] Referring to Fig. 2A and Fig. 2B is an example of the catalyst 10 depicted. More precisely, it is in Fig. 2A A top view of the catalyst 10 depicted, and in Fig. 2B a cross-sectional view of the catalyst 10 .

[0019] The catalyst 10 includes the carrier 18 The carrier 18can have a porous metal oxide structure. The porous metal oxide structure can be formed from Al₂O₃, CeO₂, ZrO₂, CeO₂-ZrO₂, SiO₂, TiO₂, MgO, ZnO, BaO, K₂O, Na₂O, CaO, or combinations thereof. The porous metal oxide structure can be in the form of a powder, spheres, or in another suitable configuration. The support 18 It can contain several small pores. More pores increase the surface area, allowing for many PGM particles. 16 to fit into a small volume. In one example, the pore volume of the support is 18 between approximately 0.5 ml / g and approximately 2 ml / g.

[0020] The catalyst 10 also contains PGM particles 16 , which are on the carrier 18 are distributed. By "distributed across" we mean that the PGM particles are 16 on the surface 18a of the carrier 18 They can be bound, and also within the pores (not shown) in the carrier 18 may be present.

[0021] Any incident or occurrence of PGM particles 16 on the surface 18a The carrier is referred to here as a set of PGM particles. Although several sets are shown, four of the sets are described in the Fig. 2A and Fig. 2B with 16A , 16B , 16C , 16D designated. While the sentences 16A , 16B , 16C and 16D They are depicted as if they were made from a single PGM particle. 16 to exist, it is self-evident that the sentences 16A , 16B , 16C and 16D each consisting of a single PGM particle or of several agglomerated PGM particles 16 can exist. For example, every sentence 16A , 16B , 16C , 16D a small cluster of particles 16 include, whereby the particles 16They can be of similar size, or they can have a particle size distribution. For another example, each set 16A , 16B , 16C , 16D an individual particle 16 include each of which is distinct from every other individual particle 16 through the barrier layer 24 is separated.

[0022] The PGM particles 16 are made from active, catalytic material and can consist of palladium (Pd), platinum (Pt), rhodium (Rh), ruthenium (Ru), osmium (Os), iridium (Ir), or various combinations thereof (e.g., Pd and Pt, Pt and Rh, Pd and Rh, Pd, Pt and Rh, Pt and Ir, Pd and Os, or any other combination). The PGM particles 16 lie in the catalyst 10 in an amount of approximately 0.1 wt.% to approximately 10 wt.% of the catalyst 10 before.

[0023] The catalyst 10 also includes the barrier layer 24, which are located on at least one of the surfaces 18a of the carrier 18 was formed (e.g., in the area where no PGM particles were present). 16 (exist). As in Fig. Shown in 2B, the barrier layer separates 24 spatially each PGM particle set 16A , 16B , 16C , 16D from any other PGM particle set 16A , 16B , 16C and 16D The barrier layer 24 It essentially forms on the surface 18a of the carrier 18 a wall between the PGM catalyst particle sets 16A , 16B , 16C and 16D , and prevents the particles 16 at the agglomeration, either through the vapor phase 12 or surface diffusion 22 The barrier layer 24 does not extend to any of the PGM particles 16 , and thus the PGM particles can 16are directly exposed to exhaust fumes during vehicle operation. As in Fig. As shown in 2A, the barrier layer 24 a continuous layer around each of the PGM particle sets 16A , 16B , 16C and 16D be.

[0024] The barrier layer 24 can consist of any of Al2O3, CeO2, ZrO2, CeO2-ZrO2, SiO2, TiO2, MgO, ZnO, BaO, K2O, Na2O, CaO, or combinations thereof. In one example, the carrier 18 made of CeO2 / Al2O3, and the barrier layer 24 made from Al2O3.

[0025] To prevent particle migration 16 to prevent this, the barrier layer 24 a height 24h , which ranges from about 0.05X to about 10X, where X is a dimension of at least one of the PGM particle sets 16A , 16B , 16C and 16D In one example, the dimension of at least one of the PGM particle sets corresponds to 16A ,16B , 16C and 16D a diameter or width of a single particle 16 or an agglomeration / cluster of particles 16 In another example, the dimension of at least one of the PGM particle sets corresponds to 16A , 16B , 16C and 16D the height of a single particle 16 or an agglomeration / cluster of particles 16 . The height 24h the barrier layer 24 can be chosen so that the barrier layer 24 large enough to prevent or suppress migration, and short enough so that the barrier layer 24 not the neighboring PGM particles 16 covers and prevents the exhaust gas from reaching the PGM particles 16 not obstructed. For example, if the particle size is in the range of approximately 3 nm to approximately 5 nm, the height 24hthe barrier layer lies in the range of approximately 0.15 nm (0.05 × 3) to approximately 50 nm (10 × 5).

[0026] The barrier layer 24 also forms gaps 26A , 26B , 26C , 26D , each with a respective PGM particle set 16A , 16B , 16C , 16D are occupied. The height of the gap 26A , 26B , 26C , 26D corresponds to the height 24h the barrier layer 24 , while at least one other dimension (e.g. length, width, diameter, or the like) of the spaces between 26A , 26B , 26C , 26D depending on the size of the respective PGM particle sets 16A , 16B , 16C , 16D depends. In one example, the dimensions (apart from the height) of the gaps 26A , 26B , 26C , 26Da size range of up to about 100 nm, and can be larger particles 16 or to accommodate particle agglomerations / clusters. In another example, the dimensions (apart from the height) of the spaces between have 26A , 26B , 26C , 26D a size on the order of about 3 nm to about 5 nm.

[0027] The barrier layer 24 blocks the surface diffusion of the PGM particles 16 Furthermore, the barrier layer suppresses 24 PGM growth via vapor phase migration. Each mobile species of PGM particles 16 , which are via the vapor phase 12 migrate, can form on the side walls 28 the barrier layer 24 deposit (as particles) 16’’ These PGM particles 16’’ remain catalytically active.

[0028] The catalyst 10 can be achieved by applying the PGM particles 16 on the carrier 18, Removal or passivation of a functional group on the surface of the PGM particles 16 , and selective growth of the barrier layer 24 on the carrier 18 , to remove the PGM particles 16 , are formed.

[0029] In an example of catalyst formation 10 , can the carrier 18 Pre-sintering can be carried out at a temperature in the range of approximately 900 °C to approximately 1000 °C. Pre-sintering can improve the surface area of ​​the substrate. 18 before the formation of the barrier layer 24 Reduce. Reduction of the surface area of ​​the carrier. 18 This means that a smaller surface area 18a for the growth of the barrier layer 24 can be available (and thus a smaller barrier layer) 24 A smaller barrier layer 24 reduces the weight increase of the final catalyst 10 .

[0030] The PGM particles 16 can be applied to the substrate using a dry impregnation process 18 to be applied. During the impregnation of the PGM particles. 16A PGM precursor solution is used on the support. The PGM precursor solution can be an aqueous solution containing water and a PGM precursor. Any number of PGM-containing coordination complexes can be used as the PGM precursor. Some exemplary PGM precursors include chloroplatinic acid (CPA), tetraammineplatinum chloride (or nitrate or hydroxide), platinum nitrate, platinum acetate, dinitrodiamine platinum, palladium nitrate, palladium acetate, bis(acetylacetonato)palladium, rhodium nitrate, rhodium acetate, etc. PGM precursors of ruthenium, osmium, and / or iridium can also be used. Examples of the PGM precursor solution include a platinum nitrate solution, a platinum acetate solution, a palladium nitrate solution, a palladium acetate solution, a rhodium nitrate solution, a rhodium acetate solution, or combinations thereof. The combinations can be used to create mixtures of different types of PGM particles. 16to form (e.g. a mixture of platinum and palladium particles).

[0031] The concentration of the precursor solution depends on the desired loading of the PGM particles. 16 on the carrier 18 and in the catalyst 10 from. For example, 10 g of total catalyst corresponds to 10 With 1.5% platinum, 0.15 g of platinum (i.e., 1.5% of 10 g) is used. The mass ratio of pure platinum to platinum precursor can be used to determine how much of the platinum precursor should be used to achieve the desired platinum mass for the catalyst. 10 to obtain the aqueous solution. The total amount of water added to prepare the aqueous solution depends on the volume of water required to achieve an initial moisture content. This solution can be added to 9.85 g of dried support (i.e., 10 g total – 0.15 g platinum = g support).

[0032] The PGM pre-stage solution becomes the carrier 18added until all pores of the carrier 18 are filled with the solution. In some cases, no additional solution is added beyond the amount required to fill the pores (i.e., up to the initial moisture level).

[0033] The impregnated carrier 18 It is then dried and calcined to convert the PGM precursor into PGM particles. 16 to convert it. In one example, air drying is carried out for a period of approximately 12 to 24 hours, followed by calcination at a temperature of approximately 550 °C for approximately 2 hours. This process decomposes the PGM precursor and forms the PGM particles. 16 , both within the pores of the carrier 18 and at least some places on the surface 18a of the carrier 18 .

[0034] The PGM particles 16 They are then subjected to a process that removes the particles. 16During the subsequent formation of the barrier layer (i.e., a selective growth process), it becomes non-reactive. In one example, this process reduces functional groups on the surface of the PGM particles. 16 , so that the PGM particles 16 during the subsequent formation of the barrier layer, functional OH (hydroxyl) groups must react, for example, in both atomic layer deposition (ALD) and molecular layer deposition (MLD). If the OH groups are removed by the PGM particles... 16 Once removed, the reactions that occur during ALD or MLD affect the PGM particle. 16 not. The reduction process can be used to remove the PGM particles. 16 to prepare for any subsequent formation of a barrier layer that uses OH groups for the reaction.

[0035] This reduction process affects the exposed surface. 18aof the carrier 18 not adversely affecting (i.e., the functional group(s)) on the surface 18a (remain reactive). The procedure can also reduce the exposure of PGM particles. 16 on (and in) the carrier 18 Exposure to a reducing environment at temperatures up to 400 °C for a period ranging from approximately 0.5 hours to approximately 10 hours is possible. The reducing environment can be hydrogen gas, carbon monoxide (CO) gas, or a mixture of argon and hydrogen or CO gas. In one example, functional hydroxyl (OH) groups are found on the surface of the PGM particles. 16 reduced by the formation of water, which evaporates as a result of the high temperature.

[0036] The barrier layer 24 can then be applied to the exposed sections of the surface 18a of the carrier 18 are formed. The barrier layer 24can be formed via atomic layer deposition (ALD), molecular layer deposition (MLD), or any other selective deposition process that uses OH groups for the reaction.

[0037] Each of these processes is self-limiting because it encompasses the sequential chemical reactions with specific functional groups that occur on the surface. Since the PGM particles 16 The PGM particles are treated to reduce or otherwise remove the reactive functional groups used in the ALD or MLD procedures. 16 no barrier layer 24 educated.

[0038] During the ALD and MLD processes, the barrier layer material can grow wherever a functional OH group is present. The ALD and MLD cycles can be observed on the PGM particles. 16Introduce reactive functional OH groups. The reduction procedure described so far can be performed after each ALD or MLD cycle and before the next ALD or MLD cycle to remove the PGM particles. 16 to purify by removing the OH groups. It is obvious that the temperature used during the reduction process is not high enough to remove the OH groups from the barrier layer. 24 to remove. In this example, the ALD or MLD cycle and the reduction process are repeated to remove the barrier layer. 24 to remove the PGM particles 16 to form, but not on the PGM particles.

[0039] Furthermore, it has been shown that controlling the barrier height 24a is desirable. Firstly, if the height 24h the barrier layer 24 much larger than the particles 16 (e.g., > 10X, as described above), then the exhaust gas can contain the PGM particles. 16They cannot make contact and catalysis will not work. Secondly, if the barrier layer 24 has grown much taller than the neighboring PGM particles 16 , then the chemicals used during the additional cycles of ALD or MLD react with OH groups above the PGM particles 16 (e.g. on the now exposed sides of the barrier layer) 24 This causes the barrier layer to... 24 grows inwards and the particles 16 covered or encapsulated. As such, the number of ALD or MLD cycles can be controlled to achieve the desired height. 24h for the barrier layer 24 to achieve this. For example, when forming the barrier layer. 24 If ALD is used, then fewer than 20 ALD cycles may be required. For example, 5 to 10 ALD cycles may be needed to form the barrier layer. 24 be used.

[0040] Both the ALD and the MLD form a conformal (or continuous) layer on the exposed surface. 18a These processes precisely control the thickness of each layer formed. For example, one ALD cycle forms a conformal layer with a thickness of approximately 1.1 angstroms.

[0041] Fig. Figure 3 shows an exemplary barrier layer formed using the ALD method. 24 In this example, the barrier layer formed consists of... 24 consisting of several Al2O3 layers 1 , 2 , 3 , 4 and the carrier 18 consists of CeO2 / Al2O3. The PGM particles 16 were already formed and on the surface 18a reduced.

[0042] The starting components for the ALD process to form the Al2O3 layers can include trimethylaluminum and water. The overall reaction is represented as reaction (1), and the half-reactions are represented as reactions (2) and (3): 2Al(CH3)3 + 3H2O → Al2O3 + 6CH4 (1) Al(CH3) 3(g) + :Al-OH (s) → :Al-O-Al(CH3) 2(s) + CH4 (2) 2H2O (g) + :O-Al(CH3) 2(s) → :Al-O-Al(OH) 2(s) + 2CH 4. (3)

[0043] The reaction during the ALD process is based on the presence of -OH bonds on the surface of the support. 18In the ALD process, a monolayer is deposited per cycle. Over many cycles, alternating layers of oxygen and aluminum are formed, resulting in a hydroxylated Al₂O₃ surface. As mentioned above, the ALD process is a self-limiting reaction process at the surface. For example, in the first half of the cycle, Al(CH₃)₃ reacts with -OH groups on the support. 18 and forms Al-(CH)2 at the exposed sections of the surface 18a Then water is introduced, which reacts with Al-(CH)₂ to form Al-OH again. This completes one cycle, resulting in the formation of a layer of Al₂O₃. The process is repeated to form multiple layers of Al₂O₃ and complete the barrier layer. 24 to form. As in Fig. Figure 3 illustrates how the aluminium oxide layers formed by the ALD process are deposited. 1 , 2 , 3 , 4 selectively on the substrate surface 18aand no aluminum oxide layers are formed by the ALD process 1 , 2 , 3 , 4 formed, which the PGM particles 16 coating. The reason for this is the presence of -OH groups, initially on the surface. 18a , and subsequently on each layer, and the absence of -OH groups on the PGM particle 16 .

[0044] To complete the selective ALD process (or MLD process or any other selective growth process that uses OH groups), the PGM particles must 16 The particles must be retained in the metallic state (not as metal oxide) to avoid -OH groups or other species that could initiate the growth of a barrier layer. In one example, this is achieved by integrating the reduction process between ALD cycles. Alternatively, the number of cycles performed can be limited to prevent growth over the PGM particles. 16to avoid.

[0045] The methods disclosed herein can also be used to control the operating temperature of the catalyst. 10 and that of an exhaust gas catalyst, in which the catalyst 10 is used to maintain it over time.

[0046] The catalyst 10 It can be applied to a monolithic substrate and used in an exhaust catalyst. An example of an exhaust catalyst is in Fig. 4A is shown and an example of the monolithic substrate is in Fig. 4A and Fig. 4B is shown.

[0047] The exhaust catalyst 30 The monolithic substrate includes 32 The monolithic substrate 32It can be manufactured from a ceramic compound or a metal alloy that can withstand high temperatures (e.g., 100 °C or higher). Synthetic cordierite is a ceramic magnesium aluminosilicate material suitable for use as a monolithic substrate. 32 suitable. A ferritic iron-chromium-aluminum alloy is an example of a metal alloy suitable for use as a monolithic substrate. 32 suitable. The monolithic substrate 32 has a honeycomb-shaped or other three-dimensional structure.

[0048] An enlarged partial view of part of the monolithic substrate. 32 is in Fig. 4B shows the monolithic substrate. 32 includes a multitude of parallel flow channels 34 , in order to ensure a sufficiently large contact area between the exhaust gas 35 and the catalyst 10 (the one in the coating 36(included) to create without the formation of excessive pressure losses.

[0049] The coating 36 includes the catalyst disclosed herein 10 In some cases, the coating 36 It may also contain a binder material (e.g., sol-binder or similar). The coating 36 can be applied to the monolithic substrate 32 applied as a back coating or using a similar process.

[0050] With reference to Fig. 4A is the monolithic substrate 32 in the exhaust catalyst 30 from a mat 38 surrounded, which in turn are surrounded by insulation 40 is surrounded. The upper and lower shells 42 , 44 (shaped from metal) can be placed between the mat 38 and the insulation 40 be positioned. An insulating cover. 46 can be above the upper shell 42and the insulation placed above it 40 be positioned, and provide shielding 48 can be adjacent to the lower shell 44 and the insulation 40 be positioned.

[0051] The exhaust catalyst 30 This could be a diesel oxidation catalyst used in a diesel engine. The diesel oxidation catalyst is a two-way exhaust catalyst that removes hydrocarbons and CO by oxidizing them to water and CO2. The diesel oxidation catalyst can also reduce NO during the cold start phase. x -have storage capacity. In such diesel engines, the reduction of NO can be achieved. x The process involves the conversion of water and N2 in a separate unit and may include the injection of urea into the exhaust gas. In one example, the ignition temperature of carbon monoxide (CO) (measured at T) is 50, or the temperature at which 50% of the CO is converted) of the diesel oxidation catalyst 226 °C or less and the ignition temperature of hydrocarbons (measured at T 50 , or the temperature at which a conversion of 50% of the C3H6 is achieved) of the diesel oxidation catalyst 253 °C or less.

[0052] The exhaust catalyst 30 It could also be a three-way catalytic converter (TWC), which is used in stoichiometric spark-ignition engines. The TWC is a three-way exhaust catalyst that reduces NOx to N2 and oxidizes HC and CO to water and CO2.

[0053] Examples are given here to further illustrate the present disclosure. It is understood that these examples are provided for illustrative purposes and should not be interpreted as limiting the scope of the present disclosure. EXAMPLE 1

[0054] This example was carried out to test the effect of different numbers of ALD cycles on the palladium distribution.

[0055] All samples contain an aluminum oxide support loaded with palladium particles via a dry impregnation process. During this process, an aqueous solution of palladium nitrite was added to the aluminum oxide powder until the pores of the aluminum oxide powder were filled. No excess solution was added. The impregnated powders were air-dried overnight and then calcined in air at 550 °C for 2 hours to decompose the palladium precursor and form the palladium particles.

[0056] The baseline sample consisted of the aluminum oxide support loaded with palladium particles. The baseline sample was not subjected to any of the ALD cycles.

[0057] The other samples were subjected to OH reduction and various ALD cycles to form an aluminum oxide barrier layer on the exposed surfaces of the aluminum oxide support. One sample was subjected to reduction and 5 ALD cycles (referred to as the 5-ALD cycle sample), another sample was subjected to reduction and 10 ALD cycles (referred to as the 10-ALD cycle sample), and yet another sample was subjected to reduction and 20 ALD cycles (referred to as the 20-ALD cycle sample). The reduction and ALD conditions were as follows: the respective samples (i.e.,The aluminum oxide support (loaded with the palladium particles) was reduced for 1 hour in 3% H₂ at 250 °C and 5 Torr; the samples were then cooled to 180 °C and 5 Torr before alternating gas-phase pulses of trimethylaluminum (TMA) and H₂O were passed over the samples; the gases were passed over them until the reaction, based on mass spectroscopic values, was complete.

[0058] The palladium distribution (i.e., the ratio of the number of surface Pd atoms to the total number of Pd atoms) was determined for each sample by chemisorption. Chemisorption measured the adsorption of a molecule (such as CO or H₂) onto the PGM metal. This measurement, along with the total mass of PGM in the sample, allows for the determination of, for example, the amount of PGM present on the surface. Generally, the higher the distribution, the higher the PGM efficiency during catalyst operation.

[0059] The results of the palladium distribution are in Fig. Figure 5A illustrates this. As shown, the baseline sample (labeled “BL”, no barrier layer) had a palladium distribution of approximately 36%, while the 5- and 10-ALD cycle samples (labeled “5 ALD” and “10 ALD” respectively) had palladium distributions of approximately 31% and 29%. The 5- and 10-ALD cycle samples exhibit a palladium distribution similar to that of the baseline sample, indicating that the ALD aluminum oxide (i.e., the barrier layer) grew selectively on the aluminum oxide support rather than on the palladium particles.

[0060] The palladium distribution of the 20-ALD cycle sample (labeled “20 ALD”) was significantly reduced compared to the baseline sample (to approximately 17%), indicating the beginning of the formation of ALD aluminum oxide on the palladium particles or a coating of the palladium particles.

[0061] Based on these results, fewer than 20 ALD cycles can be used to form the barrier layer disclosed herein to obtain a suitable PGM distribution. The 5- and 10-ALD cycle samples contained an aluminum oxide barrier layer of approximately 10 wt% to approximately 20 wt%. Alternatively, the reduction process could be repeated between ALD cycles. EXAMPLE 2

[0062] The baseline sample and the 5- and 10-ALD cycle samples from Example 1 were subjected to an aging process. The aging process involved exposing the samples to 950 °C for 2 hours in air with the addition of 10% water.

[0063] The palladium distribution was determined for each aged sample using chemisorption. Generally, the higher the distribution, the higher the PGM efficiency during catalyst operation.

[0064] The results of the palladium distribution for the aged samples are in Fig. 5B. As shown, the baseline sample (BL, no ALD aluminum oxide barrier layer) had a palladium distribution of approximately 6%, which was significantly reduced compared to the palladium distribution of the unaged (or fresh) baseline sample (see BL in Fig. 5A). This reduction in the palladium distribution indicates that the palladium particles underwent sintering and particle growth, and that fewer palladium atoms are available at the surface. Also as shown, each of the aged 5- and 10-ALD cycle samples (labeled “5 ALD” and “10 ALD,” respectively) had a palladium distribution of approximately 14%. The palladium content of the aged 5- and 10-ALD cycle samples was twice that of the aged baseline sample. This means that the aluminum oxide barrier layers formed from 5- and 10-ALD cycles suppressed the migration of palladium particles and individual palladium atoms. EXAMPLE 3

[0065] A baseline sample containing palladium loaded onto an aluminum oxide support and no exposure to an ALD process was prepared in the same manner as described in Example 1. The palladium loading was 0.63 wt%.

[0066] A 5-ALD sample, comprising palladium loaded onto an aluminum oxide support and an aluminum oxide barrier layer formed by 5-ALD cycles, was prepared in the same manner as described in Example 1. The palladium loading was 0.57 wt%.

[0067] The baseline sample and the 5-ALD cycle samples were subjected to an aging process in which they were exposed to air at a temperature of 950 °C for 2 hours with the addition of 10% water.

[0068] The baseline sample and 5-ALD cycle samples were then exposed to exhaust gas (containing 5000 ppm CO, 500 ppm hydrocarbons (e.g., C3H6 and C3H8), 1% O2, 5% H2O, balance N2) at an inlet temperature that was increased at a rate of 2 °C per minute. The space velocity (SV) was 1,500,000 cm³ / s. 3 g catalyst –1 h –1 , where space velocity refers to the quotient of the incoming volume flow rate of the reactants divided by the reactor volume (or the volume of the catalyst bed) in one unit of time.

[0069] The ignition temperatures of the baseline sample and the 5-ALD cycle samples for CO and for C3H6 were determined. The ignition temperatures were measured at T 50 This is measured at the temperature at which 50% of the CO or C3H6 conversion is achieved. The lower the temperature, the higher the conversion rate. 50 The more, the better.

[0070] The results are shown below. Fig. 6 and shown in Table 1. As shown, the catalyst disclosed herein (including the barrier layer formed from 5 ALD cycles, designated as “Pd / Al2O3 + 5 ALD”) exhibits lower CO and HC ignition temperatures than the baseline sample without a barrier layer. Table I. CO and C3H6 Ignition temperature (T50) Baseline-Probe (BL) 5 ALD cycle sample (Pd / Al2O3 + 5 ALD) ΔT CO 242 °C 226 °C 16 °C C3H6 280 °C 253 °C 27 °C

[0071] The reduction in ignition temperatures (ΔT in the range of approximately 16 °C to approximately 30 °C) of the sample with the barrier layer is advantageous, partly because the catalyst exhibits CO and HC oxidation activity at lower temperatures. It is also expected that this will lead to significantly lower PGM loadings for the same performance, resulting in a cost reduction for the precious metals used in the catalyst.

[0072] It is understood that the ranges provided here include the specified range and any value or subrange within that range. For example, a range of approximately 900 °C to approximately 1000 °C should be interpreted to include not only the explicitly stated limits of approximately 900 °C to approximately 1000 °C, but also individual values ​​such as 925 °C, 980 °C, etc., and subranges such as approximately 915 °C to approximately 975 °C, etc. Furthermore, when "approximately" is used to describe a value, it should be understood to include minor variations of the specified value (up to + / - 10%).

[0073] References in the description to "an example," "another example," "example," etc., mean that a specific element (e.g., feature, structure, and / or property) described in connection with the example is included in at least one example described here and may or may not be present in other examples. Furthermore, it is understood that the described elements for each example can be combined in any suitable way across the various examples, unless the context clearly dictates otherwise.

[0074] When describing and claiming the examples revealed here, the singular forms “ein”, “eine” and “der / die / das” imply plural references, unless the context clearly dictates otherwise.

[0075] Although several examples have been described in detail, it goes without saying that the disclosed examples can be modified. Therefore, the foregoing description should be considered non-restrictive.

Claims

[1] Exhaust catalyst, comprising: a catalyst, comprising: a carrier; Platinum group metal (PGM) particles dispersed on the support; and a barrier layer formed on the substrate, the barrier layer arranged between a first set of PGM particles and a second set of PGM particles to suppress the aging of the PGM particles. [2] Exhaust catalyst according to claim 1, wherein: The carrier and the barrier layer are selected independently from a group consisting of Al2O3, CeO2, ZrO2, CeO2-ZrO2, SiO2, TiO2, MgO, ZnO, BaO, K2O, Na2O, CaO, or combinations thereof; and The PGM particles are selected from the group consisting of palladium, platinum, rhodium, ruthenium, osmium, iridium, and combinations thereof. [3] Exhaust catalyst according to claim 1, wherein: the first set of PGM particles is located in a first space and the second set of PGM particles is located in a second space, and wherein each of the first and second spaces has at least one dimension up to about 100 nm; and the barrier layer has a height in the range of about 0.05X to about 10X, where X is a dimension of at least one of the first and second sets of PGM particles. [4] Exhaust catalyst according to claim 1, wherein the barrier layer does not extend to any of the PGM particles. [5] Exhaust catalyst according to claim 1, wherein the barrier layer is a continuous coating formed around each of the first and second sets of PGM particles. [6] Method for suppressing the aging of platinum group metal (PGM) particles in an exhaust gas catalyst, the method comprising: the application of PGM particles to a carrier; the reduction of a functional group on a surface of the PGM particles, thereby rendering the PGM particles unreactive during a subsequent selective growth process; and the selective growth of a barrier layer on the substrate around the PGM particles. [7] Method according to claim 6, wherein selective growth is carried out by atomic layer deposition (ALD) or molecular layer deposition (MLD). [8] Method according to claim 6, wherein selective growth is carried out by ALD, and wherein the total number of ALD cycles is less than 20. [9] The method of claim 6, further comprising: i) performing an ALD or MLD cycle; ii) the reduction of another functional group on the surface of the PGM particles, thereby rendering the PGM particle non-reactive during a subsequent ALD or MLD cycle; and iii) the repetition of i and ii. [10] Method according to claim 6, wherein: the reduction of the functional group on the surface of the PGM particles is achieved by exposing the PGM particles to a reducing environment at a temperature up to 400 °C, and the reducing atmosphere contains hydrogen gas, carbon monoxide gas, a mixture of argon gas and carbon monoxide gas, or a mixture of argon gas and hydrogen gas.