Catalyst and method for suppressing the ageing of platinum group metal (PGM) particles in a catalyst

Abstract

Catalyst (40) comprising: a catalyst element (10') comprising: a carrier oxide layer (24); and Platinum group metal particles (16) partially embedded in the carrier oxide layer (24) such that a portion (16B) of each platinum group metal particle (16) is surrounded by the carrier oxide layer (24) and another portion (16A) of each platinum group metal particle (16) remains exposed; characterized in that the catalyst element (10') further includes a space (32) separating the support oxide layer (24) from the portion (16B) of each platinum group metal particle (16) surrounded by the support oxide layer (24).

Description

TECHNICAL FIELD

[0001] The present disclosure generally relates to a catalyst according to the preamble of claim 1 and to a process according to the preamble of claim 3, as known in its nature essentially from US Pat. No. 8,513,158 B2. Substantially comparable catalysts are disclosed in WO 2006 / 137 579 A1 and WO 2010 / 102 930 A1. BACKGROUND

[0002] Vehicles with an internal combustion engine (ICE) include an exhaust treatment 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 with a near-stoichiometric air-fuel (A / F) ratio). The treatment system for the diesel engine includes a diesel oxidation catalyst (DOC) capable of oxidizing carbon monoxide (CO) and hydrocarbons (HC). The exhaust treatment system for the stoichiometric spark-ignition engine includes a three-way catalyst (TWC) that operates on the principle of non-selective catalytic reduction of NO x works through CO and HC.

[0003] The invention is based on the object of providing an ageing-resistant catalyst and a process for its production. SUMMARY

[0004] This object is achieved with a catalyst having the features of claim 1 and with a method having the features of claim 3. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Features of examples of the present disclosure will become apparent by reference to the following detailed description and the drawings, in which like reference numerals correspond to similar, though perhaps not identical, components. For brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear. Fig. Figure 1 is a schematic illustration showing the two mechanisms for PGM particle growth or sintering; Fig. 2A to 2C are schematic cross-sectional views together illustrating an example of a method for forming a catalyst element not according to the present invention; Fig. 3A to 3D are schematic cross-sectional views which together illustrate a method according to the invention for forming another example of a catalyst element disclosed herein; Fig. 4A is a perspective, partially cutaway view of an exemplary catalyst; and Fig. Figure 4B is an enlarged view of a section of Fig. 4A. DETAILED DESCRIPTION

[0006] Diesel oxidation catalysts and three-way catalysts often incorporate a carrier loaded with a platinum group metal (PGM) as the active catalytic / catalyst element material. As the exhaust gas temperature from the vehicle engine increases (e.g., to temperatures of 150°C to approximately 1000°C), the PGM loaded on the carrier can undergo particle growth (i.e., sintering). Fig. Figure 1 illustrates two mechanisms for PGM particle growth during vehicle operation. The mechanisms involve atomic and / or crystalline PGM migration. The first mechanism involves PGM migration via a vapor phase, designated 12, and the second mechanism involves PGM migration via surface diffusion, designated 14. In the first mechanism, a mobile species (not shown) emitted from the PGM particles 16 is loaded onto the carrier 18, can pass through the vapor phase 12, and agglomerate with other metal particles 20 in the vapor phase 12 to form larger PGM particles 16'. In the second mechanism, a mobile species (not shown) released from the PGM particles 16 can diffuse along the surface 18a of the support 18 and agglomerate with other metal particles 22 on the surface 18a to form larger PGM particles 16'.

[0007] An increase in the size of the PGM particles 16' leads to poor PGM utilization and undesirable aging of the catalyst material. More specifically, the increased particle size reduces the PGM dispersion, which is a ratio of the number of surface PGM atoms in the catalyst element to the total number of PGM carbon atoms in the catalyst element. Reduced PGM dispersion is directly related to a decrease in the active metal area (as a result of particle growth) and thus indicates a loss of active catalyst element reaction sites. The loss of active catalyst element reaction sites leads to poor PGM utilization efficiency and indicates that the catalyst element has undergone undesirable aging or deactivation.

[0008] It has been shown that approximately 1% by weight of the PGM in a typical three-way catalyst remains catalytically active (i.e., 99% of the PGM is wasted) after 100,000 to 150,000 miles of driving. One approach to counteracting the effects of sintering is to use a PGM loading high enough to offset catalyst element deactivation. However, this increases the cost of the three-way catalyst.

[0009] The catalyst elements disclosed herein suppress aging by physically separating the PGM particles 16 with a modified support (referred to herein as support oxide layer 24, shown in Fig. 2B, Fig. 2C, Fig. 3C and Fig. 3D). The support oxide layer 24 partially embeds the particles 16 such that a portion of each particle 16 is surrounded by the support oxide layer 24 and such that another portion of each particle 16 remains exposed (for subsequent exposure and interaction with exhaust gases). In some examples, the portion of the particles 16 surrounded by the support oxide layer 24 is also anchored to the support oxide layer 24. In other examples, the portion of the particles 16 surrounded by the support oxide layer 24 is not attached to the support oxide layer 24, but is held within the support oxide layer 24. In any of the examples, the particles 16 are substantially immobilized within the support oxide layer 24 and are not allowed to undergo surface diffusion 14 (i.e., agglomeration and sintering).

[0010] As mentioned above, the PGM particles 16 may evaporate at high temperatures (e.g., when exposed to exhaust gases). Some of the examples disclosed herein include a gap between the portion of each particle 16 and the surrounding support oxide layer 24. This gap exposes the maximum surface area of the particle 16 for contact with exhaust gases. This gap also exposes an interior surface of the support oxide layer 24, thus providing a physical barrier that can trap PGM vapors (through condensation of the PGM vapor on the interior surface / wall). The mobile species in the trapped vapor agglomerate to form new PGM nanoparticles within the gap. The newly formed PGM nanoparticles may be smaller than the PGM particles 16 and may provide additional active PGM sites for catalysis.

[0011] The configuration of the catalyst element disclosed herein slows or prevents the growth / sintering of the PGM particles and maintains multiple active PGM sites over time, thus causing the catalyst element to age more slowly than catalyst elements without the support oxide layer. Furthermore, by reducing or preventing sintering, the operating temperature of the catalyst element is prevented from increasing over time.

[0012] Two approaches have been developed to form catalyst elements. One approach is described in Fig. 2A to 2C, and another approach is shown in Fig. 3A to 3D.

[0013] In Fig. 2A to 2C, the non-inventive example is section 16B (see Fig. 2B and Fig. 2C) the particle 16, which is surrounded by the carrier oxide layer 24, is also anchored to the carrier oxide layer 24.

[0014] This exemplary method begins with a sacrificial layer 26. The sacrificial layer 26 may be made of a material that can be easily removed without adversely affecting the particles 16 or the carrier oxide layer 24, which may be in contact with the sacrificial layer 26. Examples of the sacrificial layer 26 include a high surface area carbon, graphite, graphene, graphene nanoplatelets, a carbonaceous polymer, and carbon black. Examples of carbonaceous polymers include polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), poly(3,4-ethylenedioxythiophene)polystyrenesulfonate (PEDOT:PSS), polypyrrole (PPy), poly(p-phenylenevinylene) (PPV or polyphenylenevinylene), and polyethylene oxide (PEO or polyoxyethylene (POE)).

[0015] The sacrificial layer 26 provides a surface upon which the catalyst element 10 is formed and thus may have any suitable configuration to serve this purpose. The sacrificial layer 26 may have any shape, as long as the PGM particles 16 are removably attached to the surface 26a and the distance between adjacent particles 16 is equal to or greater than the average diameter of the particles 16. In one example, the sacrificial layer 26 has a substantially planar surface and has a thickness sufficient to support the PGM particles 16 deposited thereon. As an example, the thickness of the sacrificial layer 26 may range from about 1 nanometer (nm) to about 3 microns (µm).

[0016] As in Fig. 2A, a plurality of PGM particles 16 are deposited on a surface 26a of the sacrificial layer 26. The PGM particles 16 are formed of active catalytic material, and may be 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), or other precious metals used in catalysts. The PGM particles 16 are present in the catalyst element 10 in an amount ranging from about 0.1 wt.% to about 10 wt.% of the catalyst element 10.

[0017] While each particle 16 is illustrated as a single PGM particle 16, it is understood that the particles 16 may each consist of multiple PGM particles 16 agglomerated together. For example, each of the Fig. 2A may include a small cluster of particles 16, wherein the particles 16 are similarly sized or have a particle size distribution. In another example, each of the particles 16 shown in Fig. 2A may include an individual particle 16 that is isolated from every other individual particle 16 by a space 28. The distance of the space 28 may be at least the average diameter of the particles 16.

[0018] The plurality of PGM particles 16 can be deposited on a surface 26a of the sacrificial layer 26 by a deposition method, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), or molecular layer deposition (MLD). When CVD or PVD is used to form the PGM particles 16, the deposition time can be relatively short. When these techniques are performed for longer deposition times, continuous sheets can form. As such, the deposition time can be controlled to ensure the formation of PGM particles with nano- or micro-sized particles (e.g., from approximately 1 nm to about 3 µm). Furthermore, it should be understood that ALD and MLD require OH (hydroxyl) functional groups (at the surface 26a) or oxygen (e.g., from O2 plasma) to react.

[0019] The deposition process utilizes a PGM solution. The PGM solution may be an aqueous solution containing a PGM precursor dissolved or dispersed in water. Examples of other suitable PGM solutions include a platinum nitrate solution, a platinum(II) chloride solution, a platinum acetate solution, a platinum palladium nitrate solution, a palladium acetate solution, a rhodium nitrate solution, a rhodium acetate solution, or combinations thereof. PGM precursor solutions of ruthenium, osmium, and / or iridium may also be used. The sacrificial layer 26 is immersed in or mixed with the PGM solution and then dried in air. The PGM particles 16 are deposited on the surface 26a of the sacrificial layer 26.

[0020] Platinum nanoparticles (~1 nm in diameter) can be used as a precursor in the CVD process using (trimethyl)methylcyclopentadienylplatinum(IV). In this example, the sacrificial layer 26 is placed in a reaction chamber into which the evaporated precursor (mixed with a carrier gas, such as O2) is introduced. The precursor diffuses or is carried onto the surface of the sacrificial layer 26 and absorbed thereon, where it decomposes to form platinum PGM nanoparticles.

[0021] Examples of other precursors suitable for the formation of PGM particles via CVD, ALD or MLD include platinum(II) acetylacetonate, platinum(II) hexafluoroacetylacetonate, (trimethyl)cyclopentadienylplatinum(IV), (trimethyl)pentamethylcyclopentadienylplatinum(IV), tris(dibenzylideneacetone)platinum(0), allyl(cyclopentadienyl)palladium(II), bis(2,2,6,6-tetramethyl-3,5-heptanedionato)palladium(II), palladium(II) hexafluoroacetylacetonate, bis(cyclopentadienyl)ruthenium(II), bis(ethylcyclopentadienyl)ruthenium(II), bis(pentamethylcyclopentadienyl)ruthenium(II), triruthenium dodecacarbonyl and combinations thereof.

[0022] As in Fig. 2B, a carrier oxide layer 24 is deposited on the PGM particles 16 and on the sacrificial layer 26. Since a portion 16A of each of the PGM particles 16 is in contact with the sacrificial layer 26, this portion 16A is not in contact with the carrier oxide layer 24. Another portion 16B of each of the PGM particles 16 is in direct contact with the carrier oxide layer 24 in this example. As shown in Fig. 2B, the carrier oxide layer 24 is also formed directly on the exposed surface 26a of the sacrificial layer 26.

[0023] The support oxide layer 24 may be any of the metal oxide materials (e.g., ceramic) commonly used in catalysts. Examples of suitable metal oxides include Al2O3, CeO2, ZrO2, CeO2-ZrO2, SiO2, TiO2, MgO, ZnO, BaO, K2O, Na2O, CaO, and combinations thereof.

[0024] The support oxide layer 24 can be formed using any suitable method that deposits the metal oxide conformally onto the portion 16B of the PGM particles 16 and onto the exposed surface 26a of the sacrificial layer 26. Examples of suitable deposition methods include wet chemistry, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), or molecular layer deposition (MLD). As mentioned above, in some cases, ALD and MLD require OH (hydroxyl) functional groups to react, and therefore, these techniques can be used when the surfaces of the PGM particles 16 and the sacrificial layer 26 contain OH groups.

[0025] Since the carrier oxide layer 24 serves to partially embed the particles 16 (e.g., around the portion 16B), the formed carrier oxide layer 24 should conformally coat the particles 16 and be at least as thick as the PGM particles 16, which have a thickness / diameter in the range of about 3 nm to about 5 nm, or as small as 1 nm and down to a few micrometers (e.g., 3 µm).

[0026] As in Fig. 2C, the sacrificial layer 26 is removed to form the catalyst element 10. The removal of the sacrificial layer 26 can be performed mechanically (e.g., by grinding), or chemically (e.g., by exposure to a chemical etchant), or by means of a plasma, or by heating. The removal method used is selective toward the sacrificial layer 26 (i.e., does not adversely affect the PGM particles 16 or the support oxide layer 24) and thus depends on the materials used. In one example of chemical removal, perchloric acid can be used to remove a sacrificial oxide layer, such as ZnO, CuO, etc., but will not adversely affect the support oxide layer 24 (e.g., Al2O3). In one example where a plasma is used, the sacrificial layer 26 can be etched away by exposure to an oxidizer plasma, such as a plasma.In yet another example, if the sacrificial layer 26 is carbon, heating to a temperature above 200°C in air or oxygen converts the carbon to CO2. In other examples, heating may exceed 400°C.

[0027] As a result of the selective removal of the sacrificial layer 26, the portion 16A of each PGM particle 16 is exposed. For this exemplary catalyst element 10, "exposed" means that the support oxide layer 24 is not in contact with or surrounding the portion 16A. The portion 16A is not covered, and thus can be contacted by exhaust gases, which can react with it.

[0028] In the catalyst element 10, which is Fig. As shown in Figure 2C, portion 16B of the PGM particles 16 is in direct contact with and surrounded by the carrier oxide layer 24, while portion 16A of the PGM particles 16 is exposed. The particles 16 are anchored / attached to the carrier oxide layer 24 and thus are unable to migrate when exposed to high temperatures.

[0029] With reference now to Fig. 3A to 3D illustrate a method according to the present invention for forming a catalyst element 10'. In this example, the portion 16B of the particles 16 surrounded by the support oxide layer 24 is not attached to the support oxide layer 24, but is held within the support oxide layer 24.

[0030] This exemplary method also begins with the sacrificial layer 26, and that PGM particles 26 are deposited on the sacrificial layer 26, as in Fig. 3A. The previously described materials for the sacrificial layer 26 and the PGM particles 16 can be used in this example. Furthermore, the PGM particles 26 can be deposited using any of the previously described methods.

[0031] As in Fig. 3B, another sacrificial layer 30 (also referred to herein as a second sacrificial layer) is deposited on the PGM particles 16 and on the sacrificial layer 26. Since the portion 16A of each of the PGM particles 16 is in contact with the sacrificial layer 26, this portion 16A is not in contact with the sacrificial layer 30. However, the portion 16B of each of the PGM particles 16 in this example is in direct contact with the other / second sacrificial layer 30. As in Fig. 3B, the other / second sacrificial layer 30 is also formed directly on the exposed surface 26a of the sacrificial layer 26.

[0032] The other / second sacrificial layer 30 may be made of a material that can be easily removed without adversely affecting the particles 16 or the carrier oxide layer 24 that may be in contact with the sacrificial layer 30. Examples of the other / second sacrificial layer 30 include high surface area carbon, graphite, carbon black, and any of the carbonaceous polymers described herein for the sacrificial layer 26. Other materials that may be used for the other / second sacrificial layer 30 include polymers such as polyacrylonitrile (PAN).

[0033] The other / second sacrificial layer 30 can be formed using any suitable method that conformally deposits the metal oxide on the sacrificial layer 30, on the portion 16B of the PGM particles 16, and on the exposed surface 26a of the sacrificial layer 26. Examples of suitable deposition methods include wet chemistry, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), or molecular layer deposition (MLD). If the PGM particles 16 and the sacrificial layer 26 have surface OH groups, ALD or MLD can be used.

[0034] The other / second sacrificial layer 30 forms a gap 32 between the portion 16B of the PGM particles 16 and oxide layer 24, as in Fig. 3D. As such, the thickness of the other / second sacrificial layer 30 should be large enough to create a space into which the exhaust gas can flow, yet small enough that the particulates 16 are retained by the surrounding carrier oxide layer 24. The thickness of the other / second sacrificial layer 30 is less than half the diameter of the PGM particles 16. In one example, the thickness of the other / second sacrificial layer 30 is in the range of 1 / 10 1 / 2 the particle diameter.

[0035] As in Fig. 3C, the oxide layer 24 is deposited on the other / second sacrificial layer 30, and thus also on (but not in direct contact with) the PGM particles 16 and the sacrificial layer 26. The previously described materials for the carrier oxide layer 24 can be used in this example. Furthermore, the carrier oxide layer 24 can be deposited using the previously described method. However, if ALD or MLD are to be used, the surface of the other / second sacrificial layer 30 must contain OH groups.

[0036] Since the carrier oxide layer 24 serves to partially embed the particles 16 (e.g., to surround the portion 16B and the adjacent gap 32), the formed carrier oxide layer 24 should conformally coat the particles 16 and be at least as thick as the PGM particles 16.

[0037] As in Fig. As shown in Figure 3d, the sacrificial layer 26 and the other / second sacrificial layer 30 are removed to form the catalyst element 10', which includes the gap 32 between the support oxide layer 24 and the particles 16. The removal of the sacrificial layer 26 and the other / second sacrificial layer 30 can be performed simultaneously or sequentially. The selective removal technique depends on the material of each of the sacrificial layer 26 and the other / second sacrificial layer 30. Any of the previously described selective removal techniques can be used.

[0038] As a result of the selective removal of the sacrificial layer 26 and the other / second sacrificial layer 30, the portion 16A of each PGM particle 16 is exposed, and the gap 32 is created. In this example, the catalyst element 10', the exposed portion 16A is not in contact with or surrounded by the carrier oxide layer 24, and the exposed portion 16B is not in contact with the carrier oxide layer 24 (due to the gap 32), but is surrounded by it. The carrier oxide layer 24 keeps the particles 16 within the gap 32 (thus preventing migration), while the gap 32 increases the surface area of the particles 16 that can be exposed to exhaust gas (thereby improving catalysis).

[0039] When comparing the two approaches used in Fig. 2A-2C and 3A-3D, it can be seen that the inventive approach has an additional step and can expose a maximum surface area of PGM particles 16 while the PGM particles 16 are still immobilized.

[0040] The method(s) disclosed herein can be used to suppress the aging of the PGM particles 16 in a catalyst. For example, the catalyst element 10, 10' is formed as previously described, and then the catalyst element 10, 10' is incorporated into the catalyst. For incorporation into the catalyst, the catalyst element 10, 10' can be applied to a monolithic substrate and used in the catalyst. An example of the catalyst is described in Fig. 4A, and an example of the monolithic substrate is shown in Fig. 4A and Fig. 4B.

[0041] The catalyst 40 includes the monolithic substrate 42. The monolithic substrate 42 may be formed from a ceramic or metal alloy capable of withstanding high temperatures (e.g., 100°C or higher). Synthetic cordierite is a magnesium aluminum silicate ceramic material suitable for use as the monolithic substrate 42. A ferritic iron-chromium-aluminum alloy is an example of a metal alloy suitable for use as the monolithic substrate 42. The monolithic substrate 42 has a honeycomb or other three-dimensional structure.

[0042] An enlarged view of a portion of the monolithic substrate 42 is shown in Fig. 4B. The monolithic substrate 42 includes a large number of parallel flow channels 44 to allow sufficient contact area between the exhaust gas 46 and the catalyst element 10, 10' (contained in coating 48) without creating excessive pressure losses.

[0043] The coating 48 includes the catalyst element 10, 10' disclosed herein. In some cases, the coating 48 may also include a binder material (e.g., a sol binder or the like). The coating 48 may be applied to the monolithic substrate 42 by wash coating or some other similar method.

[0044] With further reference to Fig.4A, the monolithic substrate 42 in the catalyst 40 (with the coating 48 thereon) is surrounded by a mat 50, which in turn is surrounded by insulation 52. Upper and lower shells 54, 56 (made of metal) can be positioned between the mat 50 and the insulation 52. An insulating cover 58 can be positioned over the upper shell 54 and the insulation 52 thereon, and a shield 60 can be positioned adjacent to the lower shell 56 and the insulation 52 thereon.

[0045] The catalyst 40 may be a diesel oxidation catalyst used in a diesel engine. The diesel oxidation catalyst is a two-way catalyst that removes hydrocarbons and CO by oxidizing them to water and CO2, respectively. The diesel oxidation catalyst may also remove NO x -storage capacity during the cold start period of the vehicle. In such diesel engines, the reduction of NO xto water and N2 in a separate unit and may include the injection of urea into the exhaust gases.

[0046] The catalyst 40 may also be a three-way catalyst used in a stoichiometric spark-ignition engine. The three-way catalyst is a three-way catalyst that reduces NOx to N2 and oxidizes HC and CO to water and CO2, respectively.

[0047] It should be understood that the ranges provided herein include the stated range and any value or range of portions within the stated range. For example, a range of about 3 nm to about 5 nm should be interpreted to include not only the explicitly stated limits of about 3 nm to about 5 nm, but also individual values, such as 3.2 nm, 4 nm, etc., and ranges of portions, such as from about 3.5 nm to about 4.6 nm, etc. Furthermore, when "about" is used to describe a value, it should be understood to include minor variations of the stated value (up to + / - 10%).

[0048] Reference in the specification to "an example," "another example," "example," etc., means that a particular element (e.g., feature, structure, and / or property) described in connection with the example is included in at least one example described herein and may or may not be present in other examples. Furthermore, it is understood that the described elements for each example may be combined in any suitable manner in the various examples, unless the context clearly dictates otherwise.

[0049] In describing and claiming the examples disclosed herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

Claims

[1] Catalyst (40) comprising: a catalyst element (10') comprising: a carrier oxide layer (24); and Platinum group metal particles (16) partially embedded in the carrier oxide layer (24) such that a portion (16B) of each platinum group metal particle (16) is surrounded by the carrier oxide layer (24) and another portion (16A) of each platinum group metal particle (16) remains exposed; characterized by , that the catalyst element (10') further includes a space (32) separating the support oxide layer (24) from the portion (16B) of each platinum group metal particle (16) surrounded by the support oxide layer (24). [2] The catalyst of claim 1, wherein the support oxide layer (24) is selected from the group consisting of Al2O3, CeO2, ZrO2, CeO2-ZrO2, SiO2, TiO2, MgO, ZnO, BaO, K2O, Na2O, CaO, and combinations thereof. [3] A method for suppressing the aging of platinum group metal particles (16) in a catalyst (40), the method comprising: depositing the platinum group metal particles (16) on a sacrificial layer (26); applying a carrier oxide layer (24) on the platinum group metal particles (16) and on the sacrificial layer (26), whereby a portion (16B) of each of the platinum group metal particles (16) is surrounded by the carrier oxide layer (24) to partially embed the platinum group metal particles (16); and removing the sacrificial layer (26), thereby exposing a different portion (16A) of each of the platinum group metal particles (16); characterized by , that the method further comprises depositing a second sacrificial layer (30) in direct contact with the platinum group metal particles (16) and the sacrificial layer (26) prior to depositing the carrier oxide layer (24) on the platinum group metal particles (16) and on the sacrificial layer (26); the carrier oxide layer (24) is in direct contact with the second sacrificial layer (30); and the method further comprises removing the second sacrificial layer (30), thereby creating a gap (32) between the carrier oxide layer (24) and the portion (16B) of the platinum group metal particles (16). [4] The method of claim 3, wherein: the sacrificial layer (26) is selected from the group consisting of high surface area carbon, graphite, graphene, graphene nanoplatelets, a carbonaceous polymer and carbon black; and the carrier oxide layer (24) is selected from the group consisting of Al2O3, CeO2, ZrO2, CeO2-ZrO2, SiO2, TiO2, MgO, ZnO, BaO, K2O, Na2O, CaO and combinations thereof. [5] The method of claim 3, wherein the second sacrificial layer (30) is selected from the group consisting of high surface area carbon, graphite, carbon black, carbonaceous polymers, and polyacrylonitrile. [6] The method of claim 3, wherein: the deposition of the platinum group metal particles (16) on the sacrificial layer (26) is carried out by a deposition process, chemical vapor deposition, physical vapor deposition, atomic layer deposition or molecular layer deposition; the deposition of the carrier oxide layer (24) on the platinum group metal particles (16) and on the sacrificial layer (26) is carried out by wet chemistry, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD) or molecular layer deposition (MLD); and the removal of the sacrificial layer (26) is carried out by mechanical etching, chemical etching, plasma etching or heating.

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