Method for producing single-atom catalysts by electrochemical deposition on a substrate or a layer of conductive oxides

Abstract

The invention relates to a method for manufacturing catalytic devices or catalytic supports comprising the creation of substrates or layers of conductive oxides and the deposition or fixing of catalyst atoms on the substrates or layers of conductive oxides by the electrochemical deposition method. The method is particularly suitable for honeycombs and monoliths of catalytic converters. The method makes it possible to fix single catalyst atoms on oxides and thus provide stable single-atom catalysts. This method thus makes it possible to obtain catalytic converters or catalytic devices or catalytic supports comprising single catalyst atoms fixed on the oxides, and more particularly on oxygen vacancies. The use of this method will make it possible to reduce the use of rare metals in the manufacture of catalytic converters and various catalytic supports, while improving their performance under certain conditions such as operation at low temperatures.

Description

[0001] Description

[0002] Title of the invention: Method for manufacturing single-atom catalysts by electrochemical deposition on a substrate or layer of conductive oxides.

[0003] The invention relates to a method for manufacturing catalytic devices, catalytic supports, or similar elements, based on the prior preparation of conductive oxide substrates or layers, followed by the electrochemical deposition of catalyst atoms onto their surface. This method is particularly well-suited to the production of honeycomb-type structures, especially those used in catalytic converters.

[0004] This approach allows for the direct application of catalysts consisting of single, firmly anchored atoms to oxides. The method promotes their fixation in specific sites within the crystal structure, such as oxygen vacancies, thereby enhancing the stability and efficiency of the resulting catalysts.

[0005] This process makes it possible to reduce the amount of rare metals needed to manufacture catalytic devices, while improving their performance under certain conditions, particularly when operating at low temperatures.

[0006] Technical field:

[0007] The present invention falls within the field of catalysis. In chemistry, catalysis refers to the acceleration or modification of reaction kinetics through the use of a catalyst. Sometimes, catalysis also promotes selectivity, directing the reaction in a preferred direction.

[0008] Catalysis is a technique used in many fields, including chemical manufacturing, oil refining, catalytic converters for internal combustion engine vehicles, the pharmaceutical industry, hydrogen production, fuel cells, polymer production and the food industry.

[0009] Although it is possible to apply the present invention to all fields of catalysis application, we will focus more on using the manufacturing process of the present invention to manufacture catalytic converters for internal combustion engine vehicles. The same manufacturing process used to manufacture catalytic converters can be applied to manufacture catalytic devices or supports for various fields and industries. Prior art:

[0010] Catalytic converters (Figure 1) are devices used in the exhaust systems of internal combustion engine vehicles to minimize pollutant emissions. They transform toxic gases produced by fuel combustion—such as carbon monoxide (CO) and nitrogen oxides (NOx). X ) and hydrocarbons – into less harmful substances such as carbon dioxide (CO2), nitrogen (N2) and water vapor (H2O). This process occurs via catalytic oxidation and reduction.

[0011] Installed in vehicle exhaust systems since the 1970s, catalytic converters are crucial for meeting environmental standards and reducing the impact of vehicle emissions on air quality. They are an essential component of automotive pollution reduction systems.

[0012] A catalytic converter primarily consists of a honeycomb-shaped ceramic (Figure 2) or metallic (Figure 3) monolith coated with catalysts such as platinum (Pt), palladium (Pd), and rhodium (Rh). When exhaust gases pass over this coated surface, the catalysts facilitate chemical reactions that break down pollutants.

[0013] In Figures 2 and 3, elements (1) represent internal surfaces of honeycombs, and elements (2) represent sometimes internal surfaces of honeycombs.

[0014] Catalytic converters come in two main forms: metallic and ceramic, each with its own distinct advantages and disadvantages. Ceramic converters, typically made from a robust ceramic, are valued for their affordability. However, their fragility can lead to cracking under physical shock or extreme temperature fluctuations. On the other hand, metallic converters, made from thin sheets of metal alloys often containing elements like nickel and chromium, offer greater resistance to physical shock. They also heat up and cool down more quickly, which is beneficial during cold starts. However, these advantages come at a relatively higher cost.

[0015] For both forms of catalytic converters, the internal surface of the honeycomb structure is covered by a "Washcoat" primarily intended to increase the contact area of ​​the catalytic converter.

[0016] The washcoat is a thin layer (generally 20 to 100 micrometers thick) deposited on the internal surfaces of honeycombs (Figure 4). The materials used in this thin layer are highly porous and have an irregular, rough surface. These characteristics allow the washcoat to create microporosity and crevices on the honeycomb surface. In Figure 4, (1) represents an internal honeycomb surface, (2) represents a washcoat, and (3) represents catalyst nanoparticles.

[0017] The microporosity of the Washcoat increases the contact area between the honeycomb and the air (exhaust gas), thus allowing gas molecules to come into contact more frequently with the precious metal catalysts (platinum, palladium, rhodium and others) deposited on the surface of the Washcoat.

[0018] Applying a washcoat significantly increases the contact area between the catalytic converter and the air. For example, the specific surface area of ​​cordierite, from which ceramic honeycombs are made, is generally less than 1 m². 2 / g while this surface area can exceed 100 m 2 / g with alumina (Al2O3) Washcoats [[1],[2]].

[0019] In addition to the application of a washcoat, the honeycomb design is generally optimized to maximize (within certain constraints) the contact area, thus allowing greater exposure of the exhaust gases to the coated surfaces of the catalysts. The cell density (number of cells per square inch) and wall thickness are optimized for peak performance with the catalytic converters.

[0020] It is worth noting that the washcoat does not only increase the contact surface area. This coating also plays a role in improving catalyst dispersion by allowing for better distribution across the entire substrate surface. The washcoat also protects the system against physical and chemical degradation, acting as a shield against high temperatures and corrosive compounds present in exhaust gases.

[0021] Its oxygen storage capacity is also vital. This capacity helps regulate oxygen levels in the exhaust gases, storing oxygen when there is an excess and releasing it when there is a deficiency. This regulation is essential for maintaining optimal conditions for the oxidation of hydrocarbons and carbon monoxide, as well as for the reduction of nitrogen oxides, across a wide range of operating conditions.

[0022] Finally, the thermal stability of the Washcoat ensures that the catalytic converter operates efficiently even under extreme temperatures, contributing to the long-term durability and reliability of the system.

[0023] Below is a description of the main materials used in the washcoats of catalytic converters:

[0024] 1. Alumina (Aluminum oxide, Al2O3)

[0025] Alumina is the most commonly used base material for washcoats due to its large specific surface area and thermal stability. It serves as a support material that maximizes the exposure of the catalytic materials to the exhaust gases.

[0026] 2. Ceria (Cerium oxide, CeO2)

[0027] Ceria is added to washcoats because of its oxygen-binding capacity, which is crucial for maintaining the efficiency of the catalytic process under varying oxygen conditions in the exhaust gas stream. It aids in the oxidation of hydrocarbons and carbon monoxide, as well as the reduction of nitrogen oxides.

[0028] 3. Silica (Silicon dioxide, SiO2)

[0029] • Silica is sometimes used in conjunction with alumina to improve the physical and chemical properties of Washcoat.

[0030] 4. Zirconia (Zirconium oxide, ZrO2)

[0031] • Zirconia is often used alongside ceria for its oxygen storage capabilities and resistance to high temperatures. It can also improve the washcoat contact surface.

[0032] Other materials can be used in the Washcoats of catalytic converters to improve their performance, namely titanium dioxide (TiO2), vanadium pentoxide (V2O5), lanthanum oxide (La2O3) and various zeolites.

[0033] Regarding the manufacturing process of catalytic converters, it should be noted that several methods currently exist in the state of the art in science and industry. To simplify, a standard manufacturing process for catalytic converters generally includes the following steps (NB: other processes different from the one described below exist):

[0034] 1. Honeycomb construction

[0035] Ceramic Converters:

[0036] • Composition of Materials: Mainly composed of cordierite, chemically represented by 2MgO-2Al2O3-5SiO2. This material is chosen for its exceptional thermal stability and low thermal expansion.

[0037] • Extrusion Process: Cordierite powder is mixed with water and additives to create a malleable paste. This paste is extruded through a die to form a honeycomb structure. The channel density and wall thickness are controlled to ensure converter performance.

[0038] • Drying and Firing: The formed substrate is dried to remove moisture, then fired at high temperature (typically above 1400°C) to induce sintering, which solidifies the structure and gives it strength. Metal Converters:

[0039] • Materials used: Metal converters are generally made from sheets of stainless steel or other alloys. Stainless steel typically contains iron (Fe), chromium (Cr), and nickel (Ni), providing resistance to high temperatures and corrosion.

[0040] • Forming and Assembly of Sheets for Metal Honeycomb Structures: Steel sheets are cut, shaped by bending, rolling or stamping, then corrugated to improve their rigidity and contact surface. These sheets are then stacked and alternated to build the honeycomb structure, before being assembled by welding or brazing.

[0041] 2. Washcoat Application

[0042] Applying the washcoat to the internal surfaces of the honeycomb structure, whether ceramic or metallic, is a crucial step in the manufacturing of catalytic converters. Here is an overview of this phase:

[0043] • Washcoat Preparation: Washcoat is generally composed of metal oxides such as alumina (Al2O3), zirconia (ZrO2), and ceria (CeO2). They are prepared as a slurry, a liquid suspension, by mixing the oxide powders with water, solvents, and binders.

[0044] Washcoat Application: Application can be done in different ways, often by dipping, the honeycomb is immersed in the Washcoat slurry, allowing the pores and surface of the substrate to become impregnated with the solution.

[0045] • Removal of excess and drying: After application, excess slurry must be removed, often by draining or using compressed air, to prevent pooling and ensure a uniform layer. The substrate is then dried, usually in ovens or drying chambers, to evaporate the solvents and fix the washcoat.

[0046] • Baking: Once dry, the Washcoat is baked at high temperatures (for example, between 500°C and 800°C). This step, called calcination, is important because it physically transforms the Washcoat into a porous and adherent layer, while completely eliminating organic binders and solidifying the structure.

[0047] 3. Catalyst Loading

[0048] • Preparation of Catalysts: Catalysts, typically platinum (Pt), palladium (Pd) and rhodium (Rh), are used in the form of their precursor salts, such as chloroplatinic acid (H2PtCl6), platinum nitrate (Pt(NO3)2), palladium nitrate (Pd(NO3)2), palladium chloride (PdCl2), rhodium nitrate (Rh(NO3)2) and rhodium chloride (RhCl3) - NB: The list of precursors is not exhaustive.

[0049] • Dissolution process: These metal salts are dissolved in a solvent, usually water, forming a solution where the metal ions are dissociated from their anions and exist in ionic form. This ionic state is crucial, as it allows for uniform distribution and deep penetration into the porous structure of the washcoat.

[0050] • Application (impregnation): The ionic solution is applied to the Washcoat often by dipping (the honeycomb is immersed in the solution).

[0051] • Drying: After application, the honeycombs are dried to remove excess solvent. This process can be done in air or under vacuum at moderate temperatures. After drying, the rare metals revert to their precursor salt forms at the surface of the washcoat (H2PtCl6, Pt(NO3)2, Pd(NO3)2, PdCl2, Rh(NO3)2, RhCl3...).

[0052] Calcination: Calcination follows drying. It aims to convert metal precursors into their metallic form by heating at high temperatures (for example, between 500 °C and 600 °C). The honeycomb structure is thus heated to transform mineral salts into rare metals (Pt, Pd, Rh, and others). The catalyst metals are then aggregated on the surface of the washcoat as metallic nanoparticles (see element 3 in Figure 4).

[0053] 4. Quality Control

[0054] • Finally, the manufactured catalytic converters undergo quality control checks to ensure their performance and characteristics.

[0055] One of the main avenues for technological advancement in the field of catalytic converters concerns the use of single-atom catalysts (SACs). Unlike standard catalysts that use nanoparticles of precious metals such as platinum or palladium, SACs utilize isolated metal atoms, uniformly dispersed on a substrate surface. This atomic-scale dispersion optimizes catalytic efficiency by maximizing the exposure of active atoms and reducing the amount of precious metals required.

[0056] Indeed, single-atom catalysts (SACs) offer significant advantages in terms of precious metal conservation, particularly for platinum group metals (PGMs). Studies have shown that SACs enable much more efficient use of precious metals, reducing the required quantity by up to five times compared to traditional nanoparticle-based catalysts [3]. This reduction is primarily due to atomic dispersion, which maximizes the use of active metal atoms, achieving almost 100% atomic utilization. The savings in platinum group metal (PGM) usage can generate substantial benefits for industry.Indeed, in 2019, approximately 39% of global platinum production (196 tonnes), 77% of global palladium production (249 tonnes) and 85% of global rhodium production (24 tonnes) were used for the manufacture of catalytic converters for the automotive industry [4].

[0057] In terms of performance, single-atom catalysts (SACs) offer the advantage of operating at relatively low temperatures. Remarkable results for the oxidation of carbon monoxide (CO) and hydrocarbons, with 90% conversion at temperatures as low as ~160 °C under simulated diesel exhaust conditions, have been achieved [3], whereas traditional converters often require much higher temperatures to achieve similar conversion levels. This will reduce emissions of harmful pollutants such as nitrogen oxides (NOx). X) and unburned hydrocarbons in certain operating phases of catalytic converters.

[0058] Regarding the manufacturing methods for single-atom catalysts (SACs), several techniques allow for the efficient and controlled deposition of single atoms of precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh). Here is a description of the main methods currently in use:

[0059] • Chemical Vapor Deposition (CVD): CVD is a method in which vapor-phase precursors are decomposed on a solid surface. This process generally requires high temperatures (up to 1000 °C) to ensure efficient precursor decomposition. For Pt, Pd, and Rh SACs, specific precursors containing these metals are introduced into a reaction chamber. Below is an example of precursor decomposition for platinum atoms [5]:

[0060] Pt(PF3)4: Evaporation temperature 0 °C / Deposition / decomposition temperature: 200-300 °C / Decomposition formula: Pt(PF3)4^Pt + 4 PF3.

[0061] At high temperatures, the precursors decompose to release metal atoms which attach uniformly to the substrate, often in the presence of gases such as hydrogen or helium to facilitate the reduction and anchoring of the metal atoms.

[0062] • Physical Vapor Deposition (PVD): PVD is a method in which the source material is vaporized or sprayed by techniques such as laser ablation, electric arc evaporation, sputtering, electron beam evaporation, etc., and then condensed onto a substrate (solid surface) to form a thin film.

[0063] For Pt, Pd and Rh SACs, metallic targets are vaporized or sprayed and the process is controlled (deposition time, pressure, temperature and deposition chamber conditions) so that single atoms condense on the substrate, thus forming single-atom catalysts.

[0064] • Atomic Layer Deposition (ALD): ALD is a thin-film deposition technique based on the sequential use of a gas-phase chemical process. It involves repeated cycles of exposure to gaseous precursors, followed by purging to remove residues; it is a subclass of chemical vapor deposition (CVD). However, it is often mentioned in the scientific literature as an independent method for synthesizing single-atom catalysts.

[0065] Single-atom platinum catalysts on graphene have been synthesized simply by adjusting the number of cycles of atomic layer deposition (ALD) and carefully controlling the nucleation sites on the supports [6],

[0066] • Chemical Synthesis in Solution: This approach includes impregnation, coprecipitation, and sol-gel processes:

[0067] • Impregnation: Impregnation is a commonly used method for manufacturing single-atom catalysts (SACs) due to its simplicity and efficiency. It involves soaking a suitable support, such as graphdiyne (GDY), in a solution containing dissolved metal precursors like K2PtCl4 for several hours. After drying, the support is annealed under an inert atmosphere, such as argon (Ar), at a high temperature (e.g., 200 °C) to fix the metal atoms [7]. Specific conditions, such as temperature and the type of inert gas, can vary depending on the particular requirements of the process and the materials used. SACs obtained using this method exhibit good dispersion of metal atoms on the support (although nanoparticle formation can also occur), which maximizes their catalytic efficiency.This method can also be used for other precious metals such as palladium (Pd) and rhodium (Rh).

[0068] • Co-precipitation: Used to create SACs by simultaneously precipitating the metal and the support from a solution, this method ensures uniform dispersion of atoms. For example, a Pt / FeOx SAC catalyst was fabricated by co-precipitation. The platinum (hexachloroplatinic acid - H2PtCl6) and iron oxide precursors were precipitated, which anchored individual platinum atoms to the iron oxide support [8].

[0069] • Sol-Gel: The sol-gel method allows the formation of a solid matrix incorporating metal atoms (or other elements). It is an ideal method for single-atom catalysts (SACs) due to its ability to form materials with specific porosities and structures. The metal precursors are sometimes metal alkoxides which, through hydrolysis and condensation, form gels containing Pt, Pd, or Rh atoms. After drying and calcination, the metal atoms are trapped within the porous matrix of the gel, which becomes a solid, ensuring uniform atomic dispersion. In one study, the sol-gel process was used for the synthesis of single-atom platinum (Pt) catalysts. The metal precursor H2PtCl6 was mixed with aluminum isopropoxide and a triblock copolymer in an ethanol solution. After evaporation of the solvent, the gel formed was calcined at 400°C and then reduced in an atmosphere composed of 5% hydrogen (H2) and 95% nitrogen (N2) at the same temperature.This process made it possible to obtain a catalyst with Pt atoms dispersed uniformly on a mesoporous Al2O3 structure[9].

[0070] • Electrochemical Deposition: This technique uses electrochemical reactions to reduce metal ions to metal atoms directly onto a conductive substrate. For Pt, Pd, and Rh SACs, solutions containing metal ions are used, and a voltage is applied to reduce these ions to metal atoms that are deposited onto the substrate. Precise control of the current density allows regulation of the number of atoms deposited, thus ensuring a uniform atomic dispersion of the metals on the support.

[0071] A study has shown that it is possible to use electrochemical deposition to fix single atoms of gold (Au), platinum (Pt) and palladium (Pd) onto molybdenum disulfide (MoS2) and other two-dimensional materials

[0010] .

[0072] • Pyrolysis: In this method, precursors are heated in an inert atmosphere at high temperature, causing their decomposition and leaving metal atoms anchored to a suitable support. During pyrolysis, these precursors decompose, and the precious metal atoms are dispersed atomically on the support, often a carbonaceous material. It should be noted that pyrolysis includes a sub-method involving flame spray pyrolysis.

[0073] In one study, single-atom platinum (Pt) catalysts were stabilized on metal oxide supports using high-temperature (>1000 °C) flame spray pyrolysis. Among the supports tested were Al2O3, SiO2, TiO2, and ZrO2. The catalysts obtained by flame pyrolysis showed superior catalytic performance for CO oxidation, methane combustion, and partial methane oxidation

[0011] .

[0074] It is important to note that other techniques also exist in this research area and in the scientific literature. Among these, we can mention Metal-Organic Structure (MOF) Derivation, photoreduction, ball milling, ion exchange, galvanic replacement, mass-selected soft-landing technique, deposition-precipitation method, anti-Ostwald Ripening, high-temperature atom trapping, laser ablation, microwave-assisted synthesis, and cyclic voltammetry. These methods enrich the spectrum of possibilities for the fabrication of SACs, thus offering a wider range of techniques [

[0012] ,

[0013] ,

[0014] ,

[0015] ].Stabilizing single atoms on support materials is crucial but challenging, as single-atom catalysts can experience problems such as aggregation, where the atoms clump together, losing much of their catalytic property. Not all materials provide the necessary stability for single-atom catalysts (SACs), and the effectiveness of a support material can vary considerably depending on the specific catalytic system and reaction conditions. Support materials are chosen for their ability to firmly anchor single atoms, preventing migration and aggregation, and for their interaction with active sites, which can enhance catalytic activity and selectivity.

[0075] For example, single atoms placed on simple metallic surfaces often face stability problems. Metals generally have surface energy that can cause single atoms to migrate and aggregate, especially under reaction conditions. For example, single-atom catalytic converters (SACs) made using single platinum atoms on a metallic surface will quickly lose their properties. This is because atoms tend to cluster at high temperatures (catalytic converters typically operate at temperatures of 400 °C to 600 °C).

[0076] Below is a non-exhaustive list of materials that can serve as supports for single-atom catalysts:

[0077] • Metal Oxides: Many metal oxides, including FeO xCeO2, TiO2, ZnO, and Al2O3 are promising supports for SACs. The surface cations and anions of a metal oxide support can be replaced by single-atom catalysts. In this regard, a stability study of platinum (Pt) single-atom catalysts on an alumina (Al2O3) support showed that this catalyst retained its single-atom catalyst profile even after 60 temperature change cycles from 100 °C to 400 °C over one month [9].

[0078] • Carbon-Based Materials Several research studies have led to the development of relatively stable SACs on carbon-based materials such as activated carbon, graphene, and carbon nanotubes (CNTs). The large specific surface area of ​​these materials allows for uniform dispersion of metal atoms, thus preventing their aggregation and the formation of larger, less reactive particles.

[0079] • Zeolites: Some zeolites such as silicalite, ZSM-5 and beta-zeolite, have structured microporous frameworks that can enclose single atoms in their channels, preventing them from aggregating while remaining accessible for catalytic reactions (it is worth noting that zeolite structures generally include oxide molecules such as SiO2 and Al2O3).

[0080] • Metal-Organic Frameworks (MOFs): such as MOF-74, UiO-66, and ZIF-8, are structures engineered with molecular-level precision. These materials are specifically designed to create suitable environments that facilitate the precise positioning and stabilization of single atoms. • Silica (SiO2): certain variants of silica (which is an oxide), such as amorphous silica and mesoporous silica (e.g., SBA-15, MCM-41), are used for their inert properties and large surface areas, making them suitable for stabilizing single atoms under various conditions.

[0081] • Layered Materials and Nitrides: such as layered double hydroxides (LDHs), transition metal dichalcogenides like MoS2, and titanium nitride (TiN), offer layered structures and strong metal-support interactions, which are beneficial for stabilizing single atoms.

[0082] • Phosphides and Carbides - such as nickel phosphide (Ni2P) and tungsten carbide (WC) offer sites where metal atoms can be firmly anchored; these materials are sometimes used for their hardness, stability, and conductive properties, useful in environments requiring high durability.

[0083] • Sulfides and Selenides such as molybdenum disulfide (MoS2) and cobalt selenide (CoSe2) effectively stabilize metal atoms, thus improving catalytic performance.

[0084] Other support materials such as various ceramics and conductive polymers expand the range of possible SAC supports, meeting specific catalytic needs.

[0085] Support materials for single-atom catalysts (SACs) are essential for the performance and durability of catalytic systems, particularly in automotive catalytic converters where operating conditions are extremely demanding. Among the various support material options—including metal oxides, carbon-based materials, zeolites, metal-organic frameworks (MOFs), silica, layered materials and nitrides, as well as phosphides and carbides—oxides (metallic or non-metallic, such as silica, in addition to elements containing oxides in their composition) stand out particularly for their properties.

[0086] In particular, metal oxides such as FeOx, CeO2, TiO2, SiO2, and Al2O3 offer excellent thermal and chemical stability, crucial characteristics for catalytic converters that must operate efficiently at high temperatures and in potentially corrosive environments. These materials can withstand frequent temperature fluctuations without significant degradation, thus ensuring a long catalyst lifespan. Furthermore, metal oxides facilitate the oxygen exchange necessary for the NOx reduction and hydrocarbon and carbon monoxide oxidation reactions, which are essential for reducing vehicle emissions.

[0087] An additional and significant argument in favor of oxides and metal oxides is their established use in current catalytic converters. These materials are not merely theoretical or experimental; they are already widely used in the automotive industry. This widespread adoption testifies not only to their effectiveness but also to their reliability. Their presence in existing systems provides concrete evidence of their performance, thus facilitating integration and reducing the risks associated with adopting new technologies.

[0088] Although single-atom catalysts (SACs) offer significant advantages in terms of catalytic performance, the cost-effective industrialization of SAC synthesis methods for large-scale production remains complex. For example, techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) require specialized equipment and precise control conditions to achieve uniform dispersion of single atoms on a support. While efficient in the laboratory, these methods involve high infrastructure costs in an industrial setting, making their large-scale application less economically viable.

[0089] Solution chemical synthesis represents a potentially more affordable method for the production of single-atom catalysts (SACs), but it faces significant challenges that complicate its large-scale industrialization. While this technique can be less expensive in terms of equipment and infrastructure compared to methods like CVD or PVD, it requires precise control of reaction conditions to ensure the uniform dispersion of metal atoms on a support. The main problem lies in the reproducibility of the results: even minimal variations in synthesis conditions, such as reactant concentration, temperature, or reaction time, can lead to significant differences in the quality and activity of the catalysts produced.

[0090] In general, there is currently no easily scalable method for manufacturing single-atom catalysts (SACs). The challenges associated with their large-scale production, particularly in terms of cost, reproducibility, and stability, hinder the adoption of these advanced technologies in the industrial sector. Faced with these constraints, manufacturers continue to rely primarily on standard catalyst production processes that do not require a single-atom dispersion level. These well-established and optimized conventional methods allow for the production of efficient catalysts with greater ease of scaling and at a significantly lower cost, thus more practically meeting the industry's current needs.

[0091] Description of the invention:

[0092] The aim of the present invention is to provide manufacturers with a manufacturing process for single-atom catalysts that is industrializable, scalable to an industrial scale, and whose parameters are easy to control.

[0093] Among the methods for manufacturing single-atom catalysts (SACs) previously discussed, Electrochemical Deposition presents a notable avenue for providing an adequate solution to the constraints related to the industrial sector.

[0094] Indeed, electrochemical deposition is a widespread technology used on an industrial scale in various industries for manufacturing and improving the properties of materials. It involves several techniques for depositing metals or other substances onto substrates via controlled electrochemical processes. These methods are important for applications in electronics, the automotive industry, the aerospace industry, and the decorative arts.

[0095] Electrochemical deposition is a process very well known to manufacturers (industrial use since the 19th century). e century) and whose large-scale industrialization is relatively inexpensive and easy.

[0096] Furthermore, this process shares similarities with the processes currently used by industrial units for manufacturing catalytic converters. Indeed, in current catalytic converter manufacturing processes, the honeycomb or monolithic components are immersed in basins containing solutions to deposit the washcoat and load the catalysts (platinum, palladium, and rhodium).

[0097] The use of electrochemical deposition will only require the replacement of catalyst loading basins with electrochemical deposition basins.

[0098] However, a major difficulty prevents this solution from currently being used in industry. Indeed, we have seen that oxides, and more specifically metal oxides, remain the most rational solution currently known and used in industry for washcoats. However, oxides are generally electrical insulators. This makes the use of electrochemical deposition difficult, or even sometimes impossible, for loading catalysts onto the washcoats of catalytic converters.

[0099] The present invention proposes to use conductive oxides to make it possible to use electrochemical deposition processes to load the contact surface of catalytic convectors with catalyst atoms.

[0100] Before explaining the concept of conductive oxides and their manufacturing and application processes in the context of the present invention, we will describe in more detail the various electrochemical deposition technologies. Electrochemical deposition comprises several sub-technologies, including:

[0101] ■ Electrolytic Deposition (Electroplating): Electroplating uses an external power source to reduce metal ions from a solution and deposit them onto a conductive substrate.

[0102] ■ Immersion Deposition: Immersion deposition involves immersing a substrate in a solution containing metal ions without using an external power supply. In this process, the metal ions in the solution are spontaneously reduced and deposited onto the substrate due to the difference in affinity between the metal ions and electrons. ■ Autocatalytic Deposition: Autocatalytic deposition, also known as non-electric chemical deposition, involves the chemical reduction of metal ions on a catalytic surface of the substrate without the use of external electricity. In this process, a reducing agent present in the solution provides the electrons necessary for the reduction of the metal ions.

[0103] ■ Electrophoretic Deposition: This technique uses an electric field to direct charged particles (colloidal particles) suspended in a fluid towards a substrate.

[0104] It should be noted that other electrochemical deposition methods are available in the scientific literature, namely Ion Exchange Deposition, Electroplating, Anodic Deposition and Selective Plating.

[0105] Selective electrochemical plating is an electrodeposition method used to treat only targeted areas of a component, without immersion in a bath. It is performed using techniques such as brush plating.

[0106] It is also worth mentioning the "Pulse Electroplating" or pulsed electrochemical deposition method, which uses pulsed currents to more precisely control the process and the amount of material deposited. It is used in the electronics industry to produce high-quality circuit boards and in the automotive industry for components requiring a high level of finish and precision.

[0107] In the discussion and presentation of our invention, we will focus on the case of an electrochemical deposition where an external source of electricity is used to apply an electrical voltage to the solution comprising the metal ions and to the substrate on which we want to deposit catalyst atoms (platinum, palladium and rhodium or other catalysts).

[0108] Applying this electrical voltage to our system comprising the ionic solution and the substrate will allow the catalyst ions present in the solution to be moved to fix or deposit them on the surface of the substrate composed of conductive oxides by processes which we will see after the explanation of the concept of conductive oxides.

[0109] Conductive oxides are materials that combine the properties of metals and oxides, offering sufficient electrical conductivity while maintaining the stability and most of the properties of oxides. Conductive oxides play a vital role in numerous applications across various fields, including electronics and sensor technologies.

[0110] There are certain oxides that sometimes exhibit low intrinsic conductivity, occasionally due to defects in their matrix structures, such as zinc oxide (ZnO) and copper oxides (Cu2O). These oxides, possessing intrinsic conductivity, can obviously be used directly in the context of the present invention. However, it should be noted that the oxides widely used in catalytic converter washcoats, due to their mechanical and thermal stability, exhibit very low electrical conductivities, making their use difficult, if not nearly impossible, for the electrochemical deposition of catalyst atoms onto the washcoats.

[0111] The table below gives approximate orders of magnitude for the electrical conductivity and resistivity of certain metal oxides. It should be noted that these values ​​vary according to several conditions, including the synthesis methods used and the calculation methods, as well as calculation conditions such as temperature. Other values ​​can be found in the scientific literature. The values ​​in the table are used only to illustrate the difficulty of using certain metal oxides for electrochemical deposition.

[0112] Table 1: Approximate values ​​of electrical conductivity and resistivity of certain metal oxides.

[0113] It is noted that the two metal oxides widely used in washcoats (Al₂O₃ and CeO₂) exhibit relatively high electrical resistivities, making their use difficult for the electrochemical deposition of catalyst atoms. This difficulty particularly concerns alumina (Al₂O₃), which has a band gap sometimes exceeding 7 eV for γ-alumina, making it a strong insulator.

[0114] Indeed, a simple calculation of the resistance of a 50-micrometer-thick layer of aluminum oxide washcoat deposited on a metallic honeycomb surface gives a value of approximately 1.67 x 10 8 Q (assuming the average resistivity of aluminum oxide is 10 13 Qm and that the total geometric surface area of ​​the Washcoat inside the honeycomb is approximately 3 m 2 ).

[0115] Regarding ceramic honeycombs, which make up approximately 90% of the catalytic converters on the market, the electrical resistance of the washcoat layer will be higher. This is because, in this case, the direction of the electric current will tend to be parallel to the washcoat surface, unlike on a metallic surface where the direction of the electric current is perpendicular to the washcoat surface. This is explained by the high electrical resistivity of cordierite (around 10 Ω·m). 16 Qm at room temperature - values ​​may vary depending on conditions and calculation methods). Figure 5 shows the direction of the current for a ceramic honeycomb (Figure 5 - A) and for a metallic honeycomb (Figure 5 - B).

[0116] Thus, the same calculation (simplified by assuming the current is 100% parallel to the washcoat surface) of the resistivity of a 50-micrometer-thick layer of aluminum oxide washcoat deposited on the surfaces of a ceramic (cordierite) honeycomb structure yields very high resistance values ​​that vary depending on the honeycomb geometry (resistance that can exceed 10 13 Q).

[0117] It should be noted that for ceramic honeycombs, several solutions will be proposed later to facilitate the transport of electricity from the Washcoat to the power source, including one solution which consists of using a metal plate (which may contain a network of metal bars) to connect the portions of the conductive Washcoat (layer of conductive oxides) deposited on the internal surfaces of the ceramic honeycombs, the prior deposition of a conductive layer at the internal surfaces of the honeycomb before the deposition of the conductive Washcoat and the creation of highly conductive paths within the Washcoat of conductive oxides through the use of metallic particles or through the introduction of oxide paths with high conductivities such as indium tin oxide (ITO).

[0118] To conclude our discussion regarding the difficulty of using non-conductive oxides for electrochemical deposition, we note that for both cases (metallic and ceramic honeycomb), the washcoat resistance values ​​make the electrochemical deposition of catalyst atoms on the surface of aluminum oxide washcoats impractical (very long deposition times or excessive heating of the system due to Joule heating, or both simultaneously, without achieving results applicable in an industrial context). For example, the deposition of one gram of platinum requires the passage of an electrical charge of approximately 2000 coulombs through the honeycomb and washcoats (deposition of platinum ions). 4+ ).

[0119] The use of metallic (or non-metallic) oxides less resistant than aluminum oxide remains possible within the scope of the present invention. However, it should be noted that this replacement remains difficult for several reasons related to the thermal and mechanical stability of the washcoat. Currently, a significant proportion of washcoats used in catalytic converters comprise at least 80% aluminum oxides.

[0120] To address the electrical resistivity problem of oxides and metal oxides widely used in washcoats, it is proposed to increase the conductivity of these oxides through several methods, including: Doping (introduction of impurities to increase free charge carriers), Defect Creation (such as oxygen vacancies or metallic interstitials to provide free electrons or holes), Non-stoichiometry (adjustment of the metal-oxygen ratio), Composites (combination with conductive metals or carbonaceous materials), Surface Treatments (chemical reduction or thermal annealing to induce defects), Hydrogenation (introduction of hydrogen to passivate defects), Alloying (formation of conductive mixed oxides), etc.

[0121] Certain deposition methods (including precipitation / co-precipitation, sol-gel deposition, and electrochemical deposition) also allow the production of oxides with sufficient electrical conductivities for the purposes of our invention. This result is due to the introduction of defects into the crystalline structure of the synthesized oxides during the deposition phases.

[0122] Although all methods for increasing the conductivity of oxides could be used within the scope of this invention, we will focus in our discussion on the most common method: doping the oxides. Doping is generally performed with N-type or P-type dopants. N-type doping adds extra electrons, forming a cloud of free electrons near the conduction band, which facilitates electron movement and increases electrical conductivity. Conversely, P-type doping creates holes in the valence band by removing electrons, thus creating positive charge carriers. This cloud of free electrons or the availability of holes reduces the oxide's resistance to electrical flow.

[0123] Doping can also be achieved using elements with valence shells similar to those of the metallic (or non-metallic) elements constituting the oxide. This increases the oxide's electrical conductivity by introducing defects into its crystalline structure. This is a possible option within the scope of the present invention. However, it will not be discussed further since it is less advantageous than N- and P-type doping.

[0124] Doping metallic oxides (or non-metallic oxides such as SiO2) not only increases their conductivity but also modifies many of their characteristics. Indeed, oxide doping is also used to increase their thermal stability. For example, several dopants such as silicon (Si), lanthanum (La), cerium (Ce), zirconium (Zr), and boron (B) have been evaluated to increase the thermal stability of alumina-y

[0016] .

[0125] In the context of our invention, doping the oxides constituting the washcoat will play a crucial role in the binding of catalyst atoms (platinum, palladium, rhodium, and any other elements). Studies have shown that oxides with a high capacity to bind single catalyst atoms are those containing a significant number of defects in their crystal structures. Doping metallic (or non-metallic) oxides with other elements introduces a large number of defects into their structures and surfaces, creating areas where catalyst atoms can bind. More specifically, doping creates oxygen vacancies within the oxides' crystal structures.

[0126] To optimize the creation of these oxygen vacancies, it is essential to control the oxygen content during the doping process. Fine-tuning this content maximizes the oxygen vacancy density, thereby promoting the efficient anchoring of single catalyst atoms within the doped matrix.

[0127] It is important to note that doped oxides only become conductive after exceeding a certain temperature threshold, which varies depending on the material but is generally close to or above room temperature. This temperature dependence is due to the energy required to excite free electrons or activate holes.

[0128] Oxide doping can be achieved through the use of metals, other oxides, or even by introducing other molecules or non-metallic elements. It is also important to note that N-type and P-type dopants are not the same as semiconductor dopants, and each oxide has a specific list of N-type and P-type dopants. For example, titanium dioxide (TiO2) has N-type dopants such as niobium (Nb) and niobium pentoxide (Nb2O5) and P-type dopants such as nickel (Ni) and chromium(III) oxide (Cr2O3), while zinc oxide (ZnO) has aluminum (Al) and aluminum oxide (Al2O3) as N-type dopants.

[0129] Numerous methods exist for manufacturing conductive oxides, each with its own advantages and applications. These methods include complex and expensive techniques such as ion implantation and atomic layer deposition (ALD). While all methods for manufacturing conductive oxides could be used within the scope of this invention, we will focus in our discussion on simpler and easily industrialized methods.

[0130] We will focus particularly on Solid State Reaction methods, the Sol-Gel Process, co-precipitation, and electrochemical deposition. Below is a brief description of these methods:

[0131] ■ Solid-state reaction: This is a widely used method for manufacturing conductive oxides, involving the mixing of oxide particles with other oxides (of a different chemical composition) or with metallic particles (or even with particles of non-metallic elements) to obtain the desired doping and properties. The process generally begins by mixing fine powders of the host oxide and the dopant, whether it is another oxide or another chemical element. Particle sizes often range from a few nanometers to 100 micrometers or more (dopant particles are sometimes on the order of nanometers, while the particles of the oxide to be doped are often larger) to ensure uniform distribution and optimal reactivity.These mixtures are then subjected to high temperatures, up to 800°C and 1500°C or even higher, depending on the specific materials involved. During heating, several processes occur: the dopant atoms or ions diffuse into the oxide lattice, substituting for atoms of the host material or occupying interstitial sites. This diffusion creates defects such as oxygen vacancies and holes, which act as free charge carriers, thus increasing the electrical conductivity of the oxide. This method is advantageous due to its simplicity and scalability, making it suitable for the mass production of conductive oxides. This method is widely cited in the scientific literature [

[0017] ,

[0018] ,

[0019] ,

[0020] ].

[0132] ■ The sol-gel process: This is another method used to manufacture conductive oxides by incorporating dopants into the oxide structures. The process begins with the dissolution of oxide precursors and dopants, the oxide precursors often being in the form of alkoxides (although other forms of precursors can also be used). In a mixture containing solvents such as water and alcohol, these precursors undergo hydrolysis, forming uniformly dispersed colloidal particles. As hydrolysis and condensation progress, the solution transforms into a gel where the particles interact to form a solid network. This gel is then dried to remove the solvents and subsequently calcined at high temperature, producing a dense and homogeneous final oxide. The dopant ions integrate into the oxide network, altering its structure and improving the material's conductivity.The sol-gel method has been used several times successfully for the synthesis of conducting oxides. For example, the use of this method has made it possible to synthesize aluminum-doped ZnO

[0021] .

[0133] ■ Co-precipitation: Unlike the sol-gel method, which involves the formation of colloidal particles, the co-precipitation method for the synthesis of doped conducting oxides uses aqueous solutions of metallic (or non-metallic) salts that precipitate. In this method, after dissolving the precursors of the base oxide and the dopant in an aqueous solution, a precipitating agent is added to react with the metallic (or non-metallic) ions, generally forming insoluble hydroxides or oxides (or other materials such as organometallic compounds). This precipitation incorporates the dopant ions into the crystal lattices of the base oxide as soon as they are formed (or of the hydroxide or any other component).The components thus formed (oxides, hydroxides, organometallic compounds, and others) are then subjected to a drying phase to remove excess solvent and moisture, followed by a calcination phase where the material is heated to a high temperature. This calcination step is crucial because it transforms, for example, hydroxides and organometallic compounds into oxides (in cases where hydroxides or organometallic compounds are precipitated) and, most importantly, ensures the integration of the dopant into the crystalline structure of the oxide, thereby increasing the electrical conductivity of the final material.

[0134] This method was used to synthesize rAl2O3 doped with Fe ions 3+ , Neither 2+ , and Co 2+

[0022] .

[0135] It should be noted that oxides obtained by precipitation methods (without doping) can sometimes exhibit sufficiently high electrical conductivities

[0022] for use in the context of the present invention. This can potentially be achieved through the use of methods similar to precipitation, such as electrochemical deposition and the sol-gel method (since these synthesis methods are closely related). However, our discussion will focus on the use of doping to increase the conductivity of oxides, given these various advantages.

[0136] ■ Electrochemical Deposition: Electrodeposition is a technique used to create thin films of materials by introducing a base material and a dopant through electrochemical processes. In this method, a conductive substrate serves as the cathode in an electrochemical cell. The ions of the base material and the dopant, both dissolved in an electrolytic solution, are then reduced by applying a voltage between the anode and the cathode. This reduction causes the deposition of these ions onto the cathode, forming a thin film that homogeneously integrates the dopant into the crystalline structure of the base material, improving or modifying its physical or chemical properties.

[0137] A practical example of this method involves doping tin oxide (SnO2) with antimony (Sb). In this scenario, an electrolytic solution containing tin(II) chloride (SnCl2) and antimony(III) chloride (SbCl3) is used. When voltage is applied, the Sn ions 2+ and Sb 3+ are reduced and deposited on the cathode, the result is a layer of SnO2 doped with antimony. This method has been used for example to fabricate SnO2-doped nanoparticles with antimony (Sb) on a carbon foil, an additional heating step at 350 °C was used

[0023] .

[0138] It should be noted that for all methods, it is possible to dope the oxides with metallic and non-metallic elements.

[0139] Having explained the techniques and materials used in the present invention, we will now describe in detail the steps of the single-atom catalyst manufacturing process. The proposed manufacturing process comprises the following two steps:

[0140] 1. The creation or synthesis of conductive oxide substrates or layers.

[0141] 2. The deposition or fixation of catalyst atoms on conductive oxide substrates or layers by the electrochemical deposition method.

[0142] The order of these two steps is not mandatory; it is possible to deposit or attach the catalyst atoms before the final stage of creating the substrate or the conductive oxide layer. For example, it is possible to attach the catalyst atoms first to oxide precursors before converting these precursors into oxides onto which the catalysts are attached or deposited.

[0143] These two steps cover the application of the process of the present invention for the manufacture of all catalytic devices and catalytic supports. These steps are particularly applicable to the honeycomb structures of catalytic converters.

[0144] It should be clarified that, in the remainder of this document, the concepts, processes, and configurations described as applicable to honeycomb structures are also, equivalently, applicable to all monoliths and three-dimensional structures with internal channels or passages allowing the circulation and / or diffusion of fluids. This functional equivalence notably covers monoliths, ceramic foam structures, and extruded blocks with porous or complex geometries. Therefore, the use of the term "honeycomb" in the following paragraphs should be understood as generically designating all such structures with a similar function in the transport, diffusion, or treatment of fluids within catalytic devices.

[0145] To these two steps of the process, an optional step must be added for ceramic honeycombs. This involves creating or depositing a highly conductive layer on the inner surfaces of the honeycomb (or on the contact surface of the device or catalytic support to be manufactured in general) before creating the conductive oxide layer (Figure 6). This step is not necessary for metallic honeycombs.

[0146] In Figure 6, (1) represents an internal surface of the honeycomb, (2) represents a highly conductive layer and (3) represents a conductive Washcoat (i.e., a layer of conductive oxides) on which catalyst atoms can be deposited.

[0147] Adding a highly conductive layer is proposed as an option, since the oxides most commonly used in washcoats (especially Al₂O₃) are highly insulating and can exhibit relatively high electrical resistivities even after doping for certain synthesis methods

[0024] ,

[0025] , making the time required for the electrochemical deposition of catalyst atoms long enough to prevent excessive heating by Joule heating. A conductive layer beneath the conductive washcoat will address this problem.

[0148] Another method for addressing the high resistivity of certain doped oxides involves creating highly conductive pathways within the conductive washcoat. These pathways can be introduced during the washcoat creation process. This aspect will be discussed later in the section on methods for creating the conductive washcoat (i.e., the conductive oxide layer).

[0149] Finally, other methods which consist of using metal plates optionally including a network of metal bars will be discussed in the section explaining the electrochemical deposition of catalyst atoms.

[0150] For a better understanding of the present invention, it should be noted that the proposed method is to increase the electrical conductivity of the oxides so that electric current can pass through the crystals of these oxides to ensure the electrochemical deposition and fixation of catalyst atoms onto the oxides (more specifically onto oxygen vacancies). The solutions involving the addition of a highly conductive layer beneath the conductive washcoat, the addition of highly conductive pathways within the conductive washcoat, and the use of metal plates and bars primarily serve to reduce the overall electrical resistance of the system to better conduct the electric current to the power source.

[0151] As mentioned in the "Technical Field" section, the present invention may have various applications and uses in the field of catalysis. However, its initial design is intended for catalytic converters in internal combustion engine vehicles.

[0152] We will therefore subsequently focus on the application of the proposed manufacturing process to honeycomb structures intended for catalytic converters. However, this same process can be applied to various other areas of catalysis and to different geometric shapes of catalysts. The focus of the description of the invention and the description of its embodiments on catalytic converters does not in any way imply the limitation of the invention to this field, nor does it imply that the proposed process is limited to monoliths and honeycomb structures. Indeed, the process of the present invention can be applied to different geometric shapes. For example, it can be applied to simple plates or to different shapes of catalytic supports.

[0153] We will now explain the first part of the process of the present invention, which is the creation (or synthesis) of a conductive oxide layer (conductive Washcoat) or the creation of a conductive oxide substrate.

[0154] The creation of the conductive oxide layer or conductive oxide substrate aims to prepare a support on which the catalyst atoms will be deposited or fixed and also aims to increase the contact surface of the catalytic converter (or other device or support) and to give it the ability to store oxygen when needed.

[0155] The creation of the conductive oxide layer at the contact surface of monoliths or honeycombs (or other structures and supports) can be achieved through several methods, including:

[0156] ■ The deposition of previously synthesized conductive oxides on the internal surfaces of the honeycomb.

[0157] ■ The deposition of oxide particles and dopant particles on the internal surface of the honeycomb followed by the synthesis of conductive oxides at the surfaces of the honeycomb through the solid state reaction method.

[0158] ■ The synthesis of conductive oxides at the contact surface of the honeycomb using the sol-gel method.

[0159] ■ The synthesis of conductive oxides at the contact surface of the honeycomb through the use of the co-precipitation method.

[0160] ■ The synthesis of conductive oxides at the contact surface of the honeycomb through the use of the electrochemical deposition method.

[0161] ■ The use of honeycombs made of conductive oxides.

[0162] It should be noted that all the methods mentioned above can be applied to different geometric shapes and different catalytic supports other than monoliths and honeycombs.

[0163] It should also be noted that the methods cited are not exhaustive and that other manufacturing process options are possible within the scope of the present invention. It should also be noted that the metrics (such as temperature) subsequently cited in the description of these methods are not exhaustive.

[0164] In the following sections, we will describe in detail the aforementioned methods for creating conductive oxide layers or substrates:

[0165] - Deposition of pre-prepared conductive oxides: this is perhaps the most obvious method for creating the Washcoat layer of conductive oxides on the surface of the monolith or honeycomb. This method consists of using pre-synthesized conductive oxides; these oxides can be synthesized by any possible method, including the aforementioned methods (solid-state reaction, sol-gel, coprecipitation, and electrodeposition).

[0166] As previously mentioned, washcoats typically use more than one oxide to ensure multiple catalytic functions. For example, washcoats very often use a mixture of aluminum oxide (Al₂O₃) and cerium oxide (CeO₂). The aluminum oxide serves to increase the contact surface area of ​​the catalytic converter, while the cerium oxide serves to increase the oxygen storage capacity.

[0167] Washcoats can also use other metal oxides and semiconductor oxides: SiO2, TiO2, ZrO2, V2O5, La2O3, ZnO...

[0168] To achieve the desired properties of catalytic converters, a material must be synthesized that includes a mixture of the oxides used in the final washcoat production. This can be achieved through:

[0169] ■ Simultaneous doping of the oxides that make up the desired final washcoat. This can be achieved using various methods, including those already discussed (solid-state reaction, sol-gel, co-precipitation, and electrodeposition). For example, the co-precipitation method simply involves precipitating all the oxides to be doped and all the dopants simultaneously.

[0170] ■ Mixing the conducting oxides after their synthesis. This method is perhaps more advantageous than the first (only the dopants specific to each oxide are introduced for doping). The mixing of conducting oxides can be achieved, for example, by the ball milling process, which will be discussed later.

[0171] Generally, pretreatment will be necessary in certain contexts before the conductive oxides are deposited on the surface of the honeycomb (or catalytic substrate). Indeed, one of the important properties of washcoats is their large contact area, which maximizes the interaction of the gases with the catalysts.

[0172] A simple solution to this need is to grind conductive oxides using the ball milling process. A ball mill (synonyms: ball mill and grinding wheel) is a device designed to grind solids into very fine powders. It consists of a drum that rotates during operation. This drum is partially filled with the material to be ground and with grinding elements (metal balls or spheres). Once rotation begins, a cascading effect grinds the substance into a fine powder.

[0173] The ball milling process is widely used to manufacture metal oxide nanoparticles and microparticles and can be used in the context of our invention for the synthesis of conductive oxide nanoparticles and microparticles. The use of these particles will significantly increase the contact surface area of ​​the conductive oxides (similar to washcoats currently used in industry).

[0174] The ball milling process will also allow the different pre-synthesized conductive oxides to be mixed in order to apply the desired composition of the Washcoat which will be applied to the surface of the honeycomb (or the catalyst support in general).

[0175] The next step after the synthesis of conductive oxide nanoparticles and microparticles is to deposit them onto the honeycomb contact surface. Several options exist for this. However, the most practical option is to use the same process currently employed by manufacturers to deposit Washcoat layers (dip coating).

[0176] Conductive oxide nanoparticles or microparticles are then mixed with a liquid such as water (and potentially with other solvents, binders, and additives such as colloidal silica). This mixture forms a slurry, which is a liquid suspension containing solid particles.

[0177] Next, the slurry must be applied to our honeycomb structure. The simplest method is to immerse the honeycomb in a basin filled with slurry to load it (other methods can also be used to apply the slurry). Once the honeycomb is filled, some of the slurry is removed for reuse (often by draining or using compressed air), while a sufficient amount of slurry remains adhered to the internal contact surface of the honeycomb. It should be noted that there are parameters and techniques currently in use that ensure a uniform distribution of the slurry across the honeycomb's contact surface.

[0178] The method of immersing the honeycomb in a slurry bath can be applied to both types of honeycomb (ceramic and metallic) and to any other structure. For metallic honeycombs, it is worth noting the possibility of depositing a washcoat layer of conductive oxides onto the stainless steel sheets before the honeycomb fabrication (an option sometimes used today for applying washcoats).

[0179] An alternative to conventional immersion involves applying a negative pressure (or partial vacuum) to one end of the structure to draw the slurry through its channels. This method, already described in several industrial patents, allows for a more homogeneous distribution of the slurry. It remains compatible with all variations of the process of the present invention based on the synthesis and application of oxide slurries.

[0180] After applying the slurry to the internal surface of the honeycomb (the surface in contact with the exhaust gases), the next step is drying, which can be done using an oven or simply in the open air. This step is necessary to evaporate the solvents and to fix the washcoat to the honeycomb surface.

[0181] The process then moves to the final stage, which involves heating the washcoat to temperatures sufficient to ensure the calcination process (for example, between 500°C and 800°C). Calcination physically transforms the washcoat into a porous and adherent layer; this can be achieved by placing the honeycomb panels in suitable ovens.

[0182] Since some doped oxides still exhibit significant electrical resistivity values, it is advisable to use (for ceramic honeycombs) the option of creating a conductive layer on the sometimes internal surfaces of the honeycomb before the synthesis of the washcoat from conductive oxides and creating highly conductive pathways within the conductive washcoat.

[0183] The creation of the conductive layer can be done through the use of metallic powders (such as aluminum) and by following the same steps as the creation of the Washcoat (formation of a slurry, application of the slurry to the honeycomb and heating).

[0184] Creating a conductive layer beneath the conductive washcoat allows for the creation of highly conductive pathways to carry electrical current during the electrochemical deposition process. This conductive layer can also be synthesized using highly conductive oxides.

[0185] Regarding highly conductive pathways, a configurable quantity of metallic particles (such as aluminum, copper, or chromium particles) or particles of oxides with high electrical conductivity (or the oxides used to synthesize them after heating) is added to the slurries used to create the conductive oxide washcoat. After the drying and calcination steps, highly conductive pathways are created within the conductive washcoat (Figure 7).

[0186] In Figure 7, (1) represents the basic elements of the conductive Washcoat such as doped aluminum and cerium oxides, (2) represents particles or portions containing highly conductive components such as metallic elements and ITO (indium tin oxide), and (3) represents highly conductive pathways within the Washcoat of conductive oxides.

[0187] This technique has already been used successfully to increase the conductivity of a highly insulating Al2O3 plate (electrical conductivity increasing from 10⁻¹⁰⁴). 16 at 10" 1 S / cm) through the creation of highly conductive paths introduced by the synthesis of indium tin oxide (ITO) bridges from microparticles of ln2O3 and SnO2 (metal oxide powder)

[0026] .

[0188] It should be noted that the mention of ITO (indium tin oxide) in this example is purely illustrative, intended to explain the principle of creating highly conductive paths in the washcoat. Given the high cost of indium, other, more economical conductive oxides, such as AZO (aluminum-doped zinc oxide), can be advantageously used. These perform the same electrical functions, ensuring comparable conductive paths, while improving the industrial viability of the process. Furthermore, the option of simply using metallic particles, such as aluminum particles, can be added. The use of metallic particles allows for significantly higher electrical conductivity in the highly conductive paths.

[0189] The most important parameters to consider for optimizing the addition of particles used to create highly conductive paths in slurry are:

[0190] ■ The particles to be used (materials).

[0191] ■ Particle concentration.

[0192] ■ Particle size.

[0193] In general, it is advisable that the addition of highly conductive paths be done in moderation, as these paths can sometimes be more favorable for the deposition of catalyst atoms than the crystalline structures of Al2O3 and CeO2, especially in the case of the use of metallic particles.

[0194] However, when oxides are used to bind catalyst atoms, it is possible to create a large number of highly conductive pathways. It is even possible to use highly conductive oxides (such as ITO or AZO) to create most or all of the substrate or conductive oxide layer.

[0195] - Deposition of oxide and dopant particles on the internal surfaces of the honeycomb: this method involves depositing oxide particles alongside dopant particles of those oxides. All the oxide particles intended for use in Washcoat synthesis (e.g., Al2O3 and CeO2) are mixed with suitable dopant particles.

[0196] The potential dopants of the most commonly used oxides in conductive washcoats (Al2O3 and CeO2) will be discussed later.

[0197] The mixing process is the same as in the previous method. The oxide particles and dopant particles are mixed in a liquid to form a slurry.

[0198] After the slurry has formed, it is applied to the internal surface of the honeycomb structures in the same way as the previous method. It is then dried by dripping or using compressed air.

[0199] After the slurry has dried, the oxide particles are doped to form conductive oxides. This doping is carried out using the solid-state reaction method and is performed in parallel with the calcination step.

[0200] To ensure these two steps (doping and calcination), the honeycomb structure containing the particle mixture is heated to temperatures of up to 800°C and 1300°C or even higher. This results in a porous and adherent Washcoat layer of conductive oxides.

[0201] This method also offers the possibility of creating highly conductive pathways. To do this, simply add metallic particles or highly conductive oxide particles (or the oxides used to synthesize them) to the slurry before application.

[0202] - Synthesis of conductive oxides using the sol-gel method: this method consists of depositing a layer of conductive oxides on the internal surface of the honeycomb or monolith using the sol-gel method. To achieve this result, the honeycombs (ceramic or metallic) are simply immersed in a basin containing an aqueous solution in which precursors of the oxides to be doped (such as alkoxides or any other precursors suitable for the sol-gel method) and dopants or their precursors are dissolved.

[0203] The sol-gel process is carried out through hydrolysis and condensation reactions (or other reactions), resulting in a gel containing oxide and dopant particles within the honeycomb (internal walls). The gel is then dried to remove residual solvents and heated to a high temperature to ensure oxide doping and calcination. This results in a conductive oxide layer on the surface of the honeycomb's internal walls; this layer can be considered a conductive washcoat.

[0204] Synthesis of conducting oxides using the co-precipitation method: This method involves immersing (dipping) honeycomb structures or monoliths in a basin of aqueous solution containing precursors of the base oxide and dopant. The oxide and dopant layers are then formed on the internal walls of the honeycomb structure through co-precipitation. The composition of the conducting oxides to be deposited can be controlled by modifying the precursors in the aqueous solution and their concentrations. By controlling the composition of the aqueous solution, it is possible to synthesize conducting oxides composed of several oxides necessary for the optimal functioning of catalytic converters (e.g., Al₂O₃ and CeO₂).

[0205] There are a significant number of co-precipitation options applicable within the scope of the present invention. For example, a sufficiently conductive layer of amorphous Al2O3 has been successfully synthesized by the co-precipitation method, which ensured doping of the amorphous Al2O3 with Fe ions. 3+ , Neither 2+ , and Co 2+ A conductivity of approximately 0.55 ohms -1 cm -1 A temperature above 327 K was obtained by this method through the doping of Al2O3 with 1 mol% Co 2+

[0022] . For cobalt doping, co-precipitation is carried out by adding an appropriate amount of pure cobalt oxalate to a well-stirred solution of aluminum tartrate before its precipitation. A layer of aluminum tartrate is then deposited on the surface of the internal walls of the honeycomb or monolith. This layer is then dried and heated to temperatures that convert the aluminum tartrate to Al₂O₃, thus completing the doping and ensuring the calcination of the oxides. This results in a layer of conductive oxides covering the internal contact surface of the honeycomb.

[0206] However, regarding the co-precipitation method, it is worth noting that it may be advantageous to proceed to the step of depositing catalyst atoms onto the conducting oxides before moving on to the calcination and crystallization phase. Indeed, amorphous Al₂O₃ is generally obtained by co-precipitation, and this form of alumina is more conductive than its crystalline form (γ-alumina).

[0207] In this case, there will be two heating stages. The first stage transforms the aluminum tartrate into Al2O3. After electrochemical deposition, a second heating stage is carried out to ensure the crystallization of the Al2O3.

[0208] This observation can be generalized to all cases where alumina (or generally oxide) forms are created that are more conductive than their final form after calcination / crystallization. In these cases, it is necessary to deposit the catalyst atoms before proceeding to calcination / crystallization.

[0209] It is even possible to deposit catalyst atoms onto doped oxide precursors that are deposited on the surface of the catalyst support before converting them into oxides by heating or other methods as described in the present invention. In this case, the catalyst atoms remaining on the surface will bind to or be deposited onto the surfaces of the oxides formed. However, this method offers no real advantages over the conventional methods presented.

[0210] It is also worth recalling the possibility of obtaining sufficiently conductive oxides by simple precipitation (without using co-precipitation).

[0211] - Synthesis of conductive oxides using the electrodeposition method: This option for synthesizing a conductive washcoat (layer of conductive oxides) involves simultaneously depositing the oxides that constitute the washcoat and their respective dopants using the electrodeposition method. An electrical voltage is applied to the honeycomb or monolith immersed in an electrolytic solution containing chemical precursors of the oxides and their dopants. At the end of the electrodeposition process, a conductive washcoat is obtained on the surface, sometimes internal, of the honeycomb structure of the catalytic converter.

[0212] For ceramic honeycombs with high electrical resistance, it is necessary to synthesize a conductive layer on the inner surfaces of the honeycomb before beginning electrochemical deposition. It is also worth noting the possibility of depositing oxide precursors and dopants instead of directly depositing oxides. The use of honeycombs made with conductive oxides: This method involves using honeycombs or monoliths composed of conductive oxides (a solution also applicable to any other form of catalyst support) instead of using cordierite ceramic honeycombs or metallic honeycombs.

[0213] In this method, there isn't really a creation of a conductive oxide washcoat in the linguistic sense of the term. The focus is more on creating a conductive oxide substrate, but the surface or layer in contact with the sometimes internal honeycomb structure can be considered a conductive oxide washcoat.

[0214] There are several possible methods for creating a honeycomb of conductive oxides. The most obvious involves using the following process:

[0215] ■ The mixing of a powder comprising oxide particles with a solvent such as water to form a malleable paste. The solvent may include additives such as colloidal silica.

[0216] ■ The resulting paste is extruded through a die to form a honeycomb structure (or any other structure).

[0217] ■ After obtaining the honeycomb structure, we move on to the drying and baking stage: the formed honeycomb is dried to remove moisture, then baked at high temperature to ensure sintering as well as doping of oxides if necessary (doping by the solid state reaction method).

[0218] Regarding the composition of the powder to be used, there are several options. For example, it is possible to use pre-synthesized conductive oxide particles, it is also possible to mix oxide particles with oxide dopant particles (for example, a mixture of alumina and ceria with their dopants - the doping is done during the baking step by the solid-state reaction method).

[0219] In the context of manufacturing conductive oxide honeycombs, it is advisable to create sufficiently strong conductive pathways within the solid structure of these honeycombs. This can be achieved by introducing into the powder used to obtain the paste highly conductive metallic particles or oxide particles such as indium tin oxide or aluminum-doped zinc oxide, or particles used to synthesize highly conductive pathways after heating, such as indium oxide (ln2O3) and tin oxide (SnO2) particles.

[0220] By fabricating a honeycomb of conductive oxides, it is possible to deposit catalyst atoms directly onto the honeycomb surface using electrochemical deposition without having to go through the steps of creating a conductive oxide washcoat, because the surface of these honeycombs includes a layer that can be considered a conductive oxide washcoat. As mentioned previously, the methods for creating conductive oxide layers and substrates described in the context of this invention are not limiting. For example, the creation of the conductive oxide layer or substrate can be achieved simply by introducing a large number of highly conductive paths while limiting the size of the insulating blocks (particularly the Al2O3 blocks).In this case, doping the Washcoat oxides (especially Al2O3) is not necessarily required, as the electric current only travels short distances on the insulating blocks. The resulting layer or substrate can then be considered a conductive oxide layer or substrate, given the conductivity provided by the created pathways.

[0221] However, it is recommended to dope the base oxides of the Washcoat or substrate in order to create sites for attaching single atoms (i.e., increasing the number of potential sites for attaching catalyst atoms compared to the case without doping the oxides).

[0222] After discussing the methods of creating conductive oxide layers and substrates, we will discuss the dopants that can be used to dope the most commonly used oxides currently in Washcoats (Al2O3 and CeO2).

[0223] When choosing a dopant for an oxide, several key parameters must be considered to ensure the desired improvement in material properties, particularly electrical conductivity. First, the valence state of the dopant relative to the host lattice ions is crucial, as it determines the type of charge carriers (electrons or holes) introduced, which affects the type of conductivity (N or P). Second, the ionic radius of the dopant must be compatible with the host lattice to avoid significant distortion of the crystal structure and maintain material integrity. Third, the solubility of the dopant in the host material must be sufficient to ensure uniform distribution without forming secondary phases. Furthermore, the stability of the dopant under operating conditions and its interaction with the electronic band structure of the host oxide are essential to ensure the dopant remains effective over time.

[0224] Below is a non-exhaustive list of potential dopants for alumina (Al2O3) and ceria (CeO2):

[0225] Table 2: List of potential dopants of rAl2O3 and CeO2.

[0226] Among the dopants listed in the table, tin oxides and indium oxides deserve particular attention. Indeed, from these two oxides, it is possible to create highly conductive pathways within the washcoat or substrate through the synthesis of conductive ITO while doping Al₂O₃ and CeO₂. Furthermore, ITO is highly stable at high temperatures. As an alternative to ITO, AZO (aluminum-doped zinc oxide) can also be used, offering good electrical conductivity at a significantly lower cost.

[0227] Alumina (Al2O3) remains one of the most widely used elements in catalytic converter washcoats. Doping with atoms having a different valence than aluminum can offer an additional benefit in terms of creating sites for the binding of catalyst atoms (Pt, Pd, Rh, and others).

[0228] Indeed, several studies have shown that the pentacoordinates of Al 3+ (aluminium) which are configurations where an aluminium atom is bonded to five other atoms around it, rather than the usual six (loss of a bond with oxygen) have a high capacity to fix platinum atoms [

[0027] ,

[0028] ] and doping with elements having a different valence to aluminium can introduce oxygen vacancies and thus help to create pentacoordinate or even tetracoordinate sites.

[0229] It is worth mentioning that studies on the stability of platinum atoms attached to Al2O3, and more specifically to pentacoordinate sites, have shown high stability. Indeed, a Pt / m-Al2O3 catalyst remained stable even after 60 cycles of CO oxidation reactions between 100 and 400 °C, over a period of one month [9].

[0230] This observation is not limited to alumina: in general, oxides doped or modified according to the methods previously mentioned to improve their conductivity generally have oxygen vacancies favorable to the fixation of catalytic atoms such as platinum or palladium, particularly in the case of materials like CeO2 or ZrO2.

[0231] To this, we must add that the pentacoordinate sites of Al 3+sites in contact with the electrolytic solution during electrochemical deposition may have higher probabilities of deposition and fixation of catalyst atoms since the electrical conductivity of the oxide structure is largely ensured by these sites (a remark that can be generalized to other doped oxides).

[0232] It is also interesting to note that, even if catalytic atoms (such as platinum or palladium) do not initially deposit in oxygen vacancies, they can migrate across the surface of the support to these sites, via surface diffusion or atomic mobility phenomena, to stabilize there preferentially.

[0233] Having seen the first step of our single-atom catalyst manufacturing process, we will now move on to the part concerning the electrochemical deposition or fixation of catalyst atoms onto the washcoat or conductive oxide substrate.

[0234] Indeed, after creating a conductive oxide surface, it becomes easier to deposit catalyst atoms (Pt, Pd, Rh, and others) onto it. To do this, simply immerse the honeycomb structure (metallic or ceramic) in a basin containing a suitable aqueous solution and apply an electrical voltage to the structure (Figure 8). Ions of catalyst atoms will then be deposited and potentially fixed to suitable sites.

[0235] In Figure 8, (1) represents a honeycomb, (2) represents an anode made of rare metals or inert elements, (3) represents an electrolytic solution in which precursors of rare metals (Pt, Pd, Rh and others) are dissolved, (4) represents a voltage or electric current source generating a series of pulses to ensure pulse electrochemical deposition and (5) represents a basin.

[0236] It should be noted that the process of the present invention is not limited to the deposition of platinum group metals (PGMs), which also include iridium and ruthenium, but can also be applied to other atoms with catalytic properties (nickel and cobalt, for example). However, we will focus on the use of PGMs in the remainder of this presentation of our invention.

[0237] With regard to platinum group metals, electrochemical deposition is generally a technique used to coat a surface with a precious metal from a solution containing metal ions. This process takes place in an electrochemical cell composed of a cathode (the surface to be coated), an anode (which may be either inert or made of the same metal to be deposited), and usually an electrolyte containing dissolved metal ions. When an electric current is applied, the metal ions migrate to the cathode, where they are reduced and deposited as solid metal. This deposition is influenced by various parameters, including precursors, electrolyte composition, pH, temperature, and current density.

[0238] The table below lists the options available in the current state of the art for the Electrochemical Deposition of Platinum Group Metals (PGMs); this list is not exhaustive:

[0239] Table 3: List of possible options for the Electrochemical Deposition of Platinum Group Metals (PGMs) [

[0029] ,

[0030] ]. In the context of the present invention, the objective is not to deposit a layer of catalyst metals, but to deposit a small but sufficient number of catalyst atoms to maximize the efficiency of the catalytic converters. Our ultimate goal is to deposit single atoms on the surface of the conducting oxides.

[0240] This result can be achieved by controlling the density and total intensity of the electric current applied to the honeycombs or monoliths and by controlling the deposition time. The objective is to deposit a number of catalyst atoms sufficient to meet the performance requirements of the catalytic converter.

[0241] The catalyst atoms will then be deposited on the surface of the oxides or attach to defects present in the crystal structure of the conducting oxides. As a reminder, doping the oxides increases the number of defects present in their crystal structures and, in particular, creates oxygen vacancies that are conducive to the stabilization of the catalyst atoms.

[0242] Within the framework of the present invention, it is possible to obtain, at the end of the process, certain blocks where several atoms are deposited (non-single atoms). The various parameters of the process of the present invention must be controlled to minimize this possibility (especially the current density and the deposition time).

[0243] It is also possible within the scope of the present invention to intentionally deposit quantities of catalyst atoms far exceeding the number of defects present on the surface of the conducting oxides, or to obtain complete blocks of catalyst atoms. However, such an option offers no economic advantage.

[0244] Electrochemical deposition of catalyst atoms can be performed on any geometric shape. For honeycombs and monoliths in general, the most optimal method is to completely immerse the honeycomb structures in electrochemical deposition tanks.

[0245] Once the honeycomb structure is immersed in the basin, the aqueous solution is allowed to fill all the internal walls of the honeycomb, and the deposition or fixation process is initiated by applying an electrical voltage (Figure 8). To ensure rapid filling of the internal walls, the honeycomb can be immersed vertically.

[0246] As mentioned previously, the electrochemical deposition of group metals (PGMs) is carried out under specific conditions. In addition, it is necessary to operate at temperatures where the conductivity of the conductive oxides is sufficient. The other parameters listed in Table 3 must be adjusted according to the desired characteristics for deposition on the internal walls of the honeycomb (current density, solute concentration, etc.).

[0247] Regarding the application of electrical voltage to honeycomb structures, two scenarios are possible:

[0248] ■ The application of electrical voltage to a metallic honeycomb.

[0249] ■ The application of electrical voltage to a ceramic honeycomb.

[0250] Applying electrical voltage to metallic honeycombs can be easily done by connecting a part of the honeycomb with a wire or a metallic support onto which an electrical voltage is applied (Figure 9).

[0251] In Figure 9, (1) represents an electrical wire, (2) represents a metallic honeycomb, (3) a support used to connect the honeycomb with the electrical wire and (4) a metallic support for a honeycomb.

[0252] Regarding ceramic honeycombs, it is possible to use a metal (or conductive) plate to connect the different portions of the conductive oxide washcoat present in the internal walls of the honeycomb (Figure 10).

[0253] In Figure 10, (1) represents the metal plate used to connect the different portions of the conductive Washcoat, (2) represents a layer of conductive Washcoat, (3) represents internal walls of the honeycomb, (4) represents the internal walls of the honeycomb, (5) represents a support used to carry the honeycomb and (6) represents connections between the metal plate and the different portions of the conductive Washcoat, these connections allow the electric current to pass through.

[0254] It should be noted that it is advisable to cover all parts of the metal plate not part of the plate / Washcoat bonds with an insulating material in order to prevent the deposition of rare metals on this plate.

[0255] This plate may include metal bars (or conductive bars in general) which are inserted inside the internal walls of the honeycomb to fix it and to increase the electrical conductivity of the system (Figure 11).

[0256] In Figure 11, (1) represents metal bars, (2) represents a metal plate, (3) represents the honeycomb structure (walls and internal surfaces) and (4) represents a support used to carry the honeycomb.

[0257] Long metal bars (Element 1 in Figure 12) can be used as an alternative for depositing a metallic layer prior to the creation of the conductive washcoat and for creating highly conductive pathways within the conductive washcoat. Long metal bars can also be used simultaneously with both techniques. When metal bars are used, the portion in contact with the aqueous solution should be protected with a suitable insulator such as PVC to prevent the deposition of catalyst atoms on the bars and thus avoid the need to recycle them for the extraction of rare metals (Figure 13).

[0258] In Figure 13, (1) represents an insulator that will be in contact with the electrolytic solution (PVC or other), (2) represents a metal bar that will be in contact with the conductive Washcoat, (3) a metal plate and (4) a support.

[0259] It should be noted that electrochemical pulse deposition (Figure 14) can be very beneficial in the context of the present invention. Indeed, the electrical conductivity of conductive oxides generally increases with increasing frequency of the electric current (sometimes with a peak at a given frequency). For example, the conductivity of zinc oxide (doped and undoped with Cr ions) 3+ ) increases with the applied frequency

[0031] . It should also be noted that the impact of the skin effect can be neglected in our context since the Washcoat thickness is generally less than 100 micrometers.

[0260] In Figure 14, elements (1) represent the components of an electrochemical deposition system (anode, cathode, solution, and power source), and element (2) represents an example of an electric current graph including pulses. Various other forms of electric current can be applied within the scope of the present invention, with current frequencies ranging from a few Hz or less to several MHz or more.

[0261] The supply of rare metals to the electrochemical deposition basin for electrochemical deposition can be done by three main methods:

[0262] ■ Adding metallic precursors to dissolve in the electrolyte is a common method. These precursors are chemical complexes containing the desired rare metals, such as (NH4)2PtCl6 for platinum or Pd(NH3)4Cl2 for palladium.

[0263] ■ Complete or partial replacement of the electrolytic solution is also possible to ensure the supply of rare metals to the basin.

[0264] ■ In acidic electrolytes, such as those containing hydrogen chloride (HCl) or sulfuric acid (H2SO4), a metallic anode made of group metals (PGMs) can corrode, releasing metal ions into the solution. These ions can then be deposited on the internal surfaces of the honeycomb structure. While this method may seem advantageous in terms of ease of implementation, care must be taken regarding the corrosive effect of HCl and H2SO4 on washcoats and honeycomb structures in general.

[0265] It should be noted that it is possible to use a basin containing the precursors of the three catalyst atoms (Pt, Pd, Rh) used in catalytic converters (Figure 15) to avoid inserting the honeycomb into three basins to deposit each catalyst (Figure 16).

[0266] An important step in our manufacturing process involves recovering the electrolytic solution that remains inside the honeycomb after any electrochemical deposition of catalyst atoms. Indeed, if the concentration of rare metal precursors in the electrolytic solution is high, there is a risk of nanoparticles containing these metals forming after drying, thus negating the cost savings achieved by creating catalysis sites with single catalyst atoms.

[0267] The recovery of this solution can be done by several methods, such as draining or using compressed air (Figure 17). In Figure 17, compressed air is used for the recovery of the electrolyte solution. Element (1) in the figure represents a fan, element (2) represents a channel through which compressed air flows, (3) represents a honeycomb structure, (4) represents droplets of the electrolyte solution, and (5) represents the electrolyte solution.

[0268] During electrochemical deposition, the composition of the aqueous solution must be parameterized according to the quantities of each metal to be deposited. Furthermore, the composition of the anode must also be parameterized if the rare metal supply is achieved through anode corrosion.

[0269] It should also be added that selective electrochemical deposition (selective electroplating) solutions can be used to simplify the process of filling the internal walls of honeycombs with the electrolytic solution instead of immersing the honeycomb in a large tank. For example, Figure 18 describes a filling process in which conductive syringes containing a pressurized electrolytic solution (1) are used to inject said solution into the internal walls of the honeycomb to be filled (3). The honeycomb is enclosed in a holder comprising a cylinder (4) and connected to a power source (2). Once the honeycomb is filled (5), the electrochemical deposition process begins. It should be noted that the syringes are connected only to the electrolytic solution and not to the honeycomb.It should also be noted that this solution is impractical for honeycombs where the walls have dimensions less than 0.2 mm.

[0270] Another, simpler solution for selective electrochemical deposition involves drawing the electrolytic solution from a basin under pressure to fill the internal walls of the honeycomb (Figure 19-A and Figure 19-B). In Figure 19, element (1) is the electrolytic solution, element (2) is a fan, and element (3) is a honeycomb whose internal walls have been filled with the electrolytic solution. Once the honeycomb is filled with the electrolytic solution, it is moved (7) under pressure to be deposited and fixed onto a support comprising a cylinder (8). This support is then connected to a voltage source (4) via components such as a conducting wire (6) and bars immersed in the electrolytic solution but not touching the honeycomb (5), and the electrochemical deposition process begins.

[0271] Finally, it is possible to use the supports comprising a cylinder illustrated in element (4) of Figure 18 and element (8) of Figure 19 to fix the honeycombs to fill them with the electrolytic solution simply by pouring it onto the monolith.

[0272] In the selective electrochemical deposition methods discussed, it is possible to reuse the electrolytic solutions several times after recovery.

[0273] The uniform deposition of catalyst elements on the surfaces, sometimes internal, of honeycombs and monoliths remains a significant challenge for our invention. This problem is less pronounced for metallic honeycombs and monoliths due to their high electrical conductivity, which results in a low voltage gradient throughout the structure (U=RI). 2). The catalyst atoms then tend to be deposited uniformly throughout the honeycomb structure.

[0274] However, for ceramic honeycombs and monoliths, the conductivity of the conductive oxide layer and thus of the honeycomb and the system generally remains limited, especially if highly conductive paths, a conductive layer under the conductive oxide layer, or metal bars are not used.

[0275] Indeed, with low electrical conductivity of the system there will be a significant gradient of electrical voltage throughout the honeycomb and this can lead to a non-uniform deposition of catalysts on the sometimes internal surfaces of the monoliths.

[0276] To remedy this problem, several options exist. For example, it is possible to connect the electrical voltage source to the first end of the honeycomb and perform the electrochemical deposition for a duration T1 before connecting the second end of the honeycomb to the voltage source and performing the electrochemical deposition for a duration T2 (which may be equal to or different from T1).

[0277] Figure 20 illustrates this solution. In Figure 20-A, the first end of the honeycomb (4) is connected to a plate comprising conductive bars (3), which is itself connected to a voltage generator (2). The system also includes an anode (1). In Figure 20-B, it is the second end that is connected to the voltage source.

[0278] Another, simpler solution involves using two grids that connect the conductive Washcoat sections at both ends of the honeycomb structure. Figure 21 illustrates this solution.

[0279] In Figure 21, elements (1) relate to the two grids previously exposed, element (2) is a voltage generator, (3) represents an anode, (4) represents the honeycomb, (5) illustrates the surface of one face of the honeycomb, (6) represents a plan view of one of the two grids and (7) represents the surface of one face of the honeycomb on which a grid is fixed.

[0280] As previously stated, the process of the present invention can be applied to the manufacture of various types of catalytic devices or catalytic supports. For example, the process of the present invention can be used to manufacture electrodes for water electrolysis.

[0281] The process of the present invention can be particularly used for the manufacture of catalytic supports. Catalytic supports are solid materials comprising catalysts; these supports are used in several industries such as the refining industry, the pharmaceutical industry, and the chemical industry in general.

[0282] Catalytic supports come in various geometric shapes, including cylindrical pellets, trilobed or quadrilobed extrudates, spheres, Raschig rings, and others. Figure 22 provides some examples of catalytic support shapes. Regarding their application, there are several ways to use catalytic supports. For example, they can be loaded into a fixed-bed reactor to facilitate the cracking of heavy hydrocarbons.

[0283] It is possible to apply all the steps and options of the process of the present invention discussed in the context of the manufacture of catalytic converters from honeycombs on catalytic supports.

[0284] This can be achieved by starting with substrates made of any material onto which a washcoat or a layer of conductive oxides is applied. Alternatively, the substrates can be manufactured using conductive oxides. This can be obtained, for example, by using a powder containing conductive oxide particles or oxide particles that produce conductive oxides (and potentially create highly conductive pathways), and by using the known process (mixing with a solvent, forming a paste, extruding to the desired shape, heating and baking with oxide doping if necessary).

[0285] It is also possible to manufacture structures in any shape and cut them into the desired shapes after applying the process of the present invention to obtain catalytic supports at the end.

[0286] Industrial application, advantages and benefits of the invention:

[0287] The process of the present invention makes it possible to manufacture higher-performance catalytic converters at an affordable cost using less precious metal (especially platinum, palladium, and rhodium) than standard processes. Indeed, single-atom catalysts allow for a considerable reduction in the use of precious metals while improving catalytic performance, particularly at relatively low temperatures [3].

[0288] In addition to the manufacture of catalytic converters for motor vehicles, the catalytic devices and supports obtained by the process of the present invention can also be used in all areas of catalysis in various industries. For example, the process of the present invention can be used to manufacture water electrolysis electrodes, catalytic supports for the refining and chemical industries in general, as well as various other applications.

[0289] Detailed description of embodiments of the invention:

[0290] In the following, we will describe (10) ten embodiments of the present invention; these embodiments are mentioned by way of example and do not in any way limit the scope of the present invention:

[0291] Implementation method I:

[0292] In this embodiment, we start from a cordierite ceramic honeycomb. This honeycomb is immersed (soaked) in a basin containing a slurry of microparticles and nanoparticles of Al2O3, CeO2, SnO2, ln2O3, CoO and ZnO.

[0293] The composition and size of the particles can be adjusted according to the manufacturer's needs. For example, the following particle composition is possible for the slurry: 80% Al₂O₃, 10% CeO₂, and 10% each of SnO₂, ln₂O₃, CoO, and ZnO. Zeolites can also be added to the particle mixture.

[0294] Regarding particle sizes, this is also a parameter adjustable by the industrial manufacturer who can even use several particle sources with different average particle sizes for the same oxide (generally between 10 nm and a few micrometers).

[0295] The honeycomb is then removed from the slurry tank, and the excess slurry is eliminated, either by draining or using compressed air. The honeycomb is then dried (in an oven or drying chamber).

[0296] Once dry, the washcoat is baked at high temperatures to ensure the calcination and doping of the various oxides that compose it (temperatures can reach up to 1300 °C or more). The SnO2 and ln2O3 oxides serve (in addition to doping) to create highly conductive pathways through the synthesis of ITO (indium tin oxide).

[0297] It should be noted that highly conductive paths can also be obtained by introducing metallic particles (aluminum or titanium powder for example) instead of SnO2 and ln2O3 at the slurry.

[0298] After obtaining a layer of conductive Washcoat on the surface of the sometimes internal parts of the honeycomb, the process moves to the electrochemical deposition stage. The honeycomb is then bonded to a metal plate, which may include bars that serve to better support the honeycomb and increase the electrical conductivity of the system (Figure 11, Figure 12 and Figure 13).

[0299] The honeycomb structure is then immersed in one or more tanks (Figure 15 and Figure 16) to be loaded with catalyst atoms (Pt, Pd, Rh, and others). An electrical voltage is applied to the metal support plate of the honeycomb structure (and therefore to the conductive washcoat) to initiate the deposition process. The duration and intensity of the electrical current are parameters that control the amount of catalyst atoms deposited on the washcoat surface.

[0300] In Figure 15, element (1) represents an electrolytic solution, text (2) represents the chemical composition of the electrolytic solution, (3) represents a honeycomb, (4) represents an anode made of an inert element or a mixture of Pt, Pd and Rh and (5) a source of electricity.

[0301] In Figure 16, text (1) gives the chemical composition of the solution for platinum deposition, element (2) represents a platinum anode or platinum-coated element, the text

[0302] (3) gives the chemical composition of the solution for the deposition of palladium, the element

[0303] (4) represents a palladium or palladium-coated anode, text (5) gives the chemical composition of the solution for rhodium deposition and element (6) represents a rhodium or rhodium-coated anode.

[0304] As mentioned previously, electrochemical pulse deposition can be applied within the scope of the present invention given its advantages. This applies to all of its embodiments, including the present embodiment.

[0305] It is also necessary to ensure that the temperature within the different electrochemical deposition basins allows for sufficient electrical conductivity for the conductive oxides while maintaining optimal conditions for electrochemical deposition.

[0306] For electrochemical deposition tanks, it is possible to immerse the honeycomb structure onto which the catalyst atoms are to be deposited in a single tank containing all the precursors of the catalyst atoms. For example, it is possible to use a solution in which (NH₄PtCk₂, PdCl₂, and Na₃RhCl₆ are dissolved in the presence of electrolytes such as sodium citrate, potassium phosphate, and sodium chloride (Figure 15).

[0307] For better control of the catalysts to be deposited, the honeycomb can be immersed in three or more basins consecutively to deposit the atoms of each catalyst element. For example, the honeycomb can be immersed first in a basin containing a solution of (NH4)2PtCl6 with sodium citrate, then in a basin containing a solution of PdCl2 with potassium phosphate, and finally in a solution of Na3RhCl6 with sodium chloride (Figure 16).

[0308] After the completion of each electrochemical deposition step, it is advisable to recover the remaining electrolytic solution inside the honeycombs for reuse. This can be achieved by draining or by using compressed air, and this is applicable to all embodiments of the present invention.

[0309] For the electrochemical deposition of rare metals, a significant number of options exist in the prior art in terms of precursors, electrolytes, temperature, and current density. All of the options available in the global prior art can be applied within the scope of the present invention and the various embodiments presented. This step will be briefly described in the subsequent embodiment descriptions.

[0310] Implementation method II:

[0311] The second embodiment is similar to embodiment I except that it starts from a metallic honeycomb.

[0312] The process is exactly the same, except that in this case, and since the honeycomb is conductive, a metal plate is not needed to connect the internal surfaces of the honeycomb walls to the electrical voltage source. The honeycomb is connected directly to the electrical current source (Figure 9).

[0313] It is also possible to omit SnO2 and ln2O3 (and to avoid using metallic powders) in the powder composition applied through the slurry. Indeed, creating highly conductive pathways does not provide significant gains in system conductivity in this context. However, it is still recommended.

[0314] Implementation method III:

[0315] In the third proposed implementation, we start with a ceramic honeycomb onto which a conductive layer is first deposited. The deposition of this conductive layer can be carried out through the following steps:

[0316] ■ Metal powder (for example, aluminum powder) is added to a solvent to form a slurry. ■ The honeycomb is dipped into a basin containing the slurry formed, then the excess slurry is removed.

[0317] ■ We then move on to drying the slurry, which can be done in an oven or in any other drying solutions.

[0318] ■ Once the slurry has dried, we move on to the sintering phase. The honeycomb is then heated until it reaches the melting temperature of the particles forming the applied metal powder (for example, the melting temperature of aluminum is 660 °C - or less for particles a few nanometers in size).

[0319] After the formation of the conductive layer, which will serve as a pathway for the electric current during the electrochemical deposition phase, the process moves on to creating the conductive washcoat. For this method, prefabricated conductive oxide particles are proposed.

[0320] For example, it is possible to use alumina particles (Al2O3) doped with cobalt (Co) and ceria particles (CeO2) doped with gadolinium (Gd).

[0321] As mentioned previously, the average particle sizes to be used are adjustable by the industrialist and can vary from a few nanometers to several micrometers (for example, it is possible to use particles with an average size of 1 pm for all oxides).

[0322] The creation of the conductive Washcoat involves the process described several times: the honeycomb is immersed in a slurry containing conductive oxide particles, then most of the slurry is removed, the process moves to the drying phase, and then a sufficient temperature is applied to ensure the calcination of the Washcoat in order to ensure its adhesion.

[0323] The resulting honeycomb is then attached to a metal plate (Figure 10, Figure 11, Figure 12 and Figure 13) to connect the different portions of the conductive Washcoat with an electrical voltage source.

[0324] Subsequently, the electrochemical deposition phase of the catalyst atoms is carried out in one or more basins depending on the available options, some of which are mentioned as an indication in Table 3 (Figure 15, Figure 16).

[0325] Implementation method IV:

[0326] Embodiment IV is somewhat similar to embodiment III; a conductive layer is first deposited following the same steps described in embodiment III. However, prefabricated conductive oxide particles are not used, but the doping operation is proposed to be carried out after the slurry has been deposited.

[0327] For this, it is possible for example to use the same particle configuration mentioned in embodiment I using a basin comprising a slurry of microparticles and nanoparticles of Al2O3, CeO2, SnO2, ln2O3, CoO and ZnO.

[0328] After application, the excess is removed and the slurry is dried. The doping and calcination stages then begin. The honeycomb is placed in a furnace and heated to temperatures sufficient to ensure oxide doping and calcination.

[0329] After obtaining a honeycomb structure whose internal wall surfaces contain a layer of conductive Washcoat deposited on a highly conductive metallic layer, the next step is the electrochemical deposition of catalyst atoms.

[0330] Implementation method V:

[0331] Embodiment V is similar to embodiments I and II. The same steps are followed, except that at the slurry stage, metallic particles are used instead of conductive oxide particles to dope the Al2O3 and CeO2 particles.

[0332] In other words, alumina and ceria particles are not mixed with SnO2, ln2O3, CoO, and ZnO particles, but rather with metal particles. For example, it is possible to mix Al2O3 and CeO2 with cobalt (Co) and titanium (Ti) particles.

[0333] After heating the honeycomb to reach doping and calcination temperatures, doped oxides and highly conductive pathways are obtained.

[0334] We then proceed to the electrochemical deposition stage to charge the catalyst atoms.

[0335] Implementation method VI:

[0336] In this embodiment, a metallic honeycomb is used onto which prefabricated conductive oxide particles are deposited. For example, it is possible to use alumina (Al2O3) particles doped with cobalt (Co) and ceria (CeO2) particles doped with gadolinium (Gd).

[0337] The pre-synthesized conductive oxide particles are mixed with a solvent such as water to form a slurry. The honeycomb structure is then immersed (dipped) in a basin containing the slurry.

[0338] The excess slurry is then removed, and the remaining slurry is dried. The next step is calcination, where the honeycomb and slurry (washcoat) are heated to a suitable temperature. After a conductive washcoat is obtained on the surfaces of the internal honeycomb, the process proceeds to the electrochemical deposition of catalyst atoms (Pt, Pd, Rh, and others).

[0339] This deposition can use the concept of pulsed electrochemical deposition (a technique applicable to all embodiments of the present invention) and can be carried out in one or more electrochemical deposition basins.

[0340] Method of implementation Vil:

[0341] In this embodiment, we propose to use the co-precipitation method to create a layer of conductive Washcoat (layer of conductive oxides) on the surface of the sometimes internal parts of a metallic honeycomb.

[0342] As mentioned previously, a sufficiently conductive layer of amorphous Al2O3 was successfully synthesized by the co-precipitation method, which ensured doping of the amorphous Al2O3 with Co ions 2+ (source 22). We propose to use the same process within this execution mode.

[0343] The metallic honeycomb is then immersed in a basin containing a solution of dissolved gelatinous amorphous aluminum hydroxide (Figure 23), tartaric acid, and cobalt oxalate. An excess of tartaric acid ensures the complete dissolution of the aluminum hydroxide, while cobalt oxalate is added to uniformly incorporate Co ions into the solution (and subsequently into the aluminum oxide matrix). The addition of ethanol precipitates the aluminum tartrate.

[0344] The concentrations of the solutes and the amount of ethanol in the solution must be controlled to ensure optimal precipitation.

[0345] In Figure 23, element (1) represents an aqueous solution, text (2) represents the chemical composition of the aqueous solution, (3) represents a honeycomb immersed in the aqueous solution to deposit the aluminum tartrate layer, (4) a valve to control the amount of ethanol to be introduced into the aqueous solution and (5) an ethanol reservoir.

[0346] It is also possible to add other dopants and elements to the solution. For example, it is possible to add precursors to simultaneously deposit CeO2 (or one of its precursors) and its dopants such as Gadolinium (Gd).

[0347] After the precipitation process, a layer of aluminum tartrate forms within the inner pores of the honeycomb (on the surface of the pores). This layer is then washed (for example, with acetone) and dried.

[0348] We then move on to the heating stage, the honeycomb and the aluminum tartrate layer are heated to temperatures allowing the transformation of aluminum tartrate into Al2O3 and the calcination and crystallization of alumina (for example 1200 K).

[0349] We then move on to the phase of depositing the catalyst atoms; the honeycomb is then connected to a current source (preferably a current with pulses) and is immersed in one or more basins in order to carry out the electrochemical deposition phase of the catalysts.

[0350] As already explained, in the case of using the co-precipitation method, it is possible to carry out the electrochemical deposition phase before the crystallization of the alumina. In this case, there will be two heating phases (for example, the substrate is heated to 1000 K and allowed to cool to perform the electrochemical deposition, then heating is resumed at around 1200 K to ensure the crystallization of the Al2O3).

[0351] Implementation method VIII:

[0352] This involves applying the same process as embodiment VII to a ceramic honeycomb. The same steps are used except for these two differences:

[0353] ■ The co-precipitation phase is preceded by the deposition of a conductive layer with a process similar to that mentioned in Execution Mode III where a conductive layer is synthesized at the level of the internal surfaces (surface of the surfaces) of the honeycomb using metallic powder.

[0354] ■ The use of a conductive plate preferably containing bars to link the different portions of the conductive Washcoat (Figure 10, Figure 11, Figure 12 and Figure 13) and to connect them with the source of the electric current.

[0355] It should be noted that the use of the conductive plate is not necessary when the ends of the honeycomb are covered with the previously deposited metallic layer. This observation can be applied to all embodiments of the present invention where a ceramic honeycomb is used.

[0356] Implementation method IX:

[0357] In this embodiment, honeycomb structures of conductive oxides comprising highly conductive paths are used.

[0358] It is possible to manufacture these honeycombs using the following process:

[0359] ■ The mixing of a powder of oxide particles with a solvent such as water to create a malleable paste.

[0360] ■ Extrusion of the paste to form the honeycombs.

[0361] ■ Heating the honeycomb to ensure sintering and doping of oxides.

[0362] Regarding the powder composition, there are several possible options depending on the manufacturer's needs. For example, the following powder composition (by mass) can be used: ■ 60% aluminum oxide powder (Al2O3).

[0363] ■ 20% cerium oxide powder (CeO2).

[0364] ■ 10% tin dioxide powder (SnO2).

[0365] ■ 10% indium oxide powder (ln2O3).

[0366] Regarding particle size, sizes on the order of nanometers (e.g., 100 nm or larger) are proposed to avoid large blocks with low conductivity within the honeycomb structure. It should be noted that prefabricated conductive oxides can also be used in this embodiment.

[0367] After obtaining the honeycomb structures, electrochemical deposition of the catalyst atoms can be performed by immersing the honeycombs in one or more electrochemical deposition tanks and applying an electrical voltage (preferably pulsed) to them. At the end of the electrochemical deposition process, it is advisable to collect the electrolytic solution remaining inside the honeycombs.

[0368] Implementation method X:

[0369] In this embodiment, the process of the present invention is to be applied to manufacture catalytic supports for the chemical and petrochemical industries. As previously explained, catalytic supports come in several forms.

[0370] In this embodiment, the process begins with long cylinders made of conductive oxides and containing highly conductive paths. These cylinders can be manufactured using the same steps as those described for the fabrication of honeycomb structures from conductive oxides (mixing the powder with a solvent to form a paste, then extrusion, followed by baking and doping).

[0371] Once the conductive oxide cylinders are obtained, they are immersed directly in an electrochemical deposition tank to deposit or fix catalyst atoms (Figure 24). After the catalyst atoms have been deposited / fixed, the long cylinders are cut to obtain cylindrical pellets.

[0372] In Figure 24, elements (1) represent conductive oxide cylinders, element (2) represents a support for carrying the conductive oxide cylinders, (3) represents an anode, (4) an electrical pulse generator and (5) an electrolytic solution.

[0373] It is also possible to directly load catalytic supports without having to cut bulky structures. For example, Figure 25 shows the loading of Raschig rings with catalyst atoms into an electrochemical deposition tank. These rings are deposited onto a conductive plate; the parts of the plate in contact with the electrolytic solution are protected by a suitable insulator such as PVC, while the parts onto which the rings are deposited remain free.

[0374] In Figure 25, (1) represents a raschig ring, (2) represents a conductive plate, (3) represents the part of the plate protected by an insulator such as PVC, (4) represents the free parts of the plate on which the rings are placed and (5) represents a support for connecting the plate to a source of electricity.

[0375] Brief description of the drawings

[0376] Figure 1 shows a catalytic converter (or catalytic pot) from a motor vehicle (Figure 1-A) and its function in reducing harmful gas emissions (Figure 1-B). The honeycomb structure is located inside the catalytic converter.

[0377] Figure 2 shows a simplified drawing of a ceramic honeycomb.

[0378] Figure 3 gives a simplified drawing of a metallic honeycomb.

[0379] Figure 4 shows a Washcoat layer deposited on a honeycomb surface and how it increases the contact area with gases. The figure also shows catalyst nanoparticles deposited on the Washcoat layer.

[0380] Figure 5 shows the direction of the electric current for a ceramic honeycomb (Figure 5-A) and for a metallic honeycomb (Figure 5-B).

[0381] Figure 6 shows a highly conductive layer created before the creation of the conductive oxide layer to reduce the total electrical resistance of the system.

[0382] Figure 7 shows highly conductive pathways present within the conductive oxide layer or substrate.

[0383] Figure 8 shows the electrochemical deposition of catalyst atoms on a honeycomb by immersing it in a basin containing ions of catalyst atoms.

[0384] Figure 9 shows the application of electrical voltage to a metallic honeycomb using an electrical wire (Figure 9-A) or using a metallic support (Figure 9-B).

[0385] Figure 10 shows and explains the use of a metal plate to connect the different portions of the conductive Washcoat (layer of conductive oxides) present at the surface of the sometimes internal honeycomb before (Figure 10-A) and after (Figure 10-B) the application of the plate.

[0386] Figure 11 shows a metal plate comprising bars which support the honeycomb and facilitate the electrical connection between the portions of conductive oxides present at the internal sometimes points of the honeycomb.

[0387] Figure 12 shows a metal plate comprising long metal bars. Figure 13 shows the protection of the parts of the metal bars in contact with the aqueous solution using suitable insulators such as PVC.

[0388] Figure 14 shows and explains the use of pulse electrochemical deposition to charge a honeycomb immersed in an electrochemical deposition basin used to deposit or fix catalyst atoms.

[0389] Figure 15 shows the deposition of platinum (Pt), palladium (Pd) and rhodium (Rh) atoms on the internal surfaces of the honeycomb (on the conductive oxides) using a single electrochemical deposition basin.

[0390] Figure 16 shows the electrochemical deposition of platinum (Pt) atoms in basin A, palladium (Pd) in basin B and rhodium (Rh) in basin C.

[0391] Figure 17 shows the recovery of the electrolytic solution remaining inside the honeycombs after electrochemical deposition using compressed air.

[0392] Figure 18 shows the filling of the internal walls of a honeycomb using conductive syringes containing a pressurized electrolytic solution (Figure 18-A). The electrochemical deposition is then carried out in a cylindrical basin containing the honeycomb (Figure 18-B).

[0393] Figure 19 shows the filling of the internal walls of the honeycomb by aspirating an electrolytic solution from a basin (Figure 19-A and Figure 19-B). The electrochemical deposition is then carried out in a cylindrical basin containing the honeycomb (Figure 19-C).

[0394] Figure 20 represents the realization of the electrochemical deposition by applying the electrical voltage to the first end of the honeycomb initially (Figure 20-A) and then to the second end (Figure 20-B) to ensure a homogeneous electrochemical deposition of the catalytic elements.

[0395] Figure 21 illustrates the use of two conductive grids applied to both ends of the honeycomb. These two grids electrically connect the Washcoat sections while allowing the electrolytic solution to penetrate the internal walls of the honeycomb.

[0396] Figure 22 shows some examples of geometric shapes of catalytic supports.

[0397] Figure 23 shows a honeycomb immersed in a basin to create a conductive Washcoat layer through the use of the co-precipitation method.

[0398] Figure 24 shows the loading of conductive oxide cylinders with catalyst atoms into an electrochemical deposition basin. Figure 25 shows the loading of Raschig rings with catalyst atoms into an electrochemical deposition basin.

[0399] Bibliographical references:

[0400] [1] Jiang, Pingping, Guanzhong Lu, Yun Guo, Yanglong Guo, Shunhai Zhang, et Xingyi Wang.

[0401] « Preparation and Properties of a y-A12O3 Washcoat Deposited on a Ceramic Honeycomb ». Surface and Coatings Technology 190, n° 2-3 (janvier 2005): 314-20. https: / / doi.Org / 10.1016 / j.surfcoat.2004.05.029.

[0402] [2] Agra, Christos. « The effect of Powder Characteristics on Washcoat Quality. Part I: Alumina

[0403] Washcoats », s. d.

[0404] [3] Hoang, Son, Yanbing Guo, Andrew J. Binder, Wenxiang Tang, Sibo Wang, Jingyue Liu,

[0405] Huan Tran, et al. « Activating Low-Temperature Diesel Oxidation by Single-Atom Pt on TiO2 Nanowire Array ». Nature Communications 11, n° 1 (26 février 2020): 1062. https : / / doi . org / 10.1038 / s41467-020-14816-w.

[0406] [4] Matthey, Johnson. « Pgm Market Report February 2019 », s. d.

[0407] [5] Zinn, Alfred A., Lutz Brandt, Herbert D. Kaesz, et Robert F. Hicks. « Chemical Vapor

[0408] Deposition of Platinum, Palladium and Nickel ». In The Chemistry of Metal CVl), édité par Toivo T. Kodas et Mark J. Hampden- Smith, l re end., 329-55. Wiley, 1994. https: / / doi.org / 10.1002 / 9783527615858.ch7.

[0409] [6] Sun, Shuhui, Galicia Zhang, Nicolas Gauquelin, Ning Chen, Jigang Zhou, Songlan Yang,

[0410] Weifeng Chen, et al. « Single-Atom Catalysis Using Pt / Graphene Achieved through Atomic Layer Deposition ». Scientific Reports 3, n° 1 (3 mai 2013): 1775. https: / / doi.org / 10.1038 / srep01775.

[0411] [7] Zhang, Huimin, Wenhao Liu, Dong Cao, et Daojian Cheng. « Carbon-Based Material-

[0412] Supported Single-Atom Catalysts for Energy Conversion ». iScience 25, n° 6 (juin 2022): 104367. https: / / doi.Org / 10.1016 / j.isci.2022.104367.

[0413] [8] Qiao, Botao, Aiqin Wang, Xiaofeng Yang, Lawrence F. Allard, Zheng Jiang, Yitao Cui

[0414] Jingyue Liu, Jun Li, et Tao Zhang. « Single-Atom Catalysis of CO Oxidation Using Ptl / FeOx ». Nature Chemistry 3, n° 8 (août 2011): 634-41. https: / / doi.org / 10.1038 / nchem.1095.

[0415] [9] Zhang, Zailei, Yihan Zhu, Hiroyuki Asakura, Bin Zhang, Jiaguang Zhang, Maoxiang Zhou

[0416] Yu Han, et al. « Thermally Stable Single Atom Pt / m-A12O3 for Selective Hydrogenation and CO Oxidation ». Nature Communications 8, n° 1 (27 juillet 2017): 16100. https: / / doi.org / 10.1038 / ncommsl6100.

[0417]

[0010] Xuan, Ningning, Jinhang Chen, Jianjian Shi, Yawei Yue, Peiyuan Zhuang, Kun Ba

[0418] Yangye Sun, et al. « Single-Atom Electroplating on Two Dimensional Materials ». Chemistry of Materials 31, n° 2 (22 janvier 2019): 429-35. https : / / doi . org / 10.1021 / acs . chemmater.8b03796.

[0419]

[0011] Ding, Shipeng, Hsi-An Chen, Okorn Mekasuwandumrong, Max J. Hülsey, Xinpu Fu, Qian

[0420] He, Joongjai Panpranot, Chia-Min Yang, et Ning Yan. « High-Temperature Flame Spray Pyrolysis Induced Stabilization of Pt Single-Atom Catalysts ». Applied Catalysis B: Environmental 281 (février 2021): 119471. https: / / doi.Org / 10.1016 / j.apcatb.2020.119471.

[0421]

[0012] Guo, Jiawen, Huimin Liu, Dezheng Li, Jian Wang, Xavier Djitcheu, Dehua He, et Qijian

[0422] Zhang. « A Minireview on the Synthesis of Single Atom Catalysts ». RSC Advances 12, n° 15 (2022): 9373-94. https: / / doi.org / 10.1039 / D2RA00657J.

[0423]

[0013] Asikin-Mijan, Nurul, Haslinda Mohd Sidek, Abdulkareem G. Al Sultan, Nurul Ahtirah

[0424] Azman, Nur Athirah Adzahar, et Hwai Chyuan Ong. « Single-Atom Catalysts: A Review of Synthesis Strategies and Their Potential for Biofuel Production ». Catalysts 11, n° 12 (30 novembre 2021): 1470. https: / / doi.org / 10.3390 / catall l l21470.

[0425]

[0014] Yu, Xiaohui, Jiguang Deng, Yuxi Liu, Lin Jing, Zhiquan Hou, Wenbo Pei, et Hongxing

[0426] Dai. « Single-Atom Catalysts: Preparation and Applications in Environmental Catalysis ». Catalysts 12, n° 10 (14 octobre 2022): 1239. https: / / doi.org / 10.3390 / catall2101239.

[0427]

[0015] Li, Siqi, Ziwang Kan, He Wang, Jiaxiao Bai, Yunyi Liu, Song Liu, et Yingjie Wu.

[0428] « Single-Atom Photo-Catalysts: Synthesis, Characterization, and Applications ». Nano Materials Science 6, n° 3 (juin 2024): 284-304. https: / / doi.Org / 10.1016 / j.nanoms.2023. l 1.001.

[0429]

[0016] Shabani, Shaghay egh, Seyed Mohammad Mirkazemi, Hamidreza Rezaie, Yaser

[0430] Vahidshad, and Stefano Trasatti. 2022. “A Comparative Study on the Thermal Stability, Textural, and Structural Properties of Mesostructured y-A12O3 Granules in the Presence of La, Sn, and B Additives.” Ceramics International 48 (5): 6638-48. https : / / doi .org / 10.1016 / j .ceramint.2021.11.213.

[0431]

[0017] Zhu, Yan-Lin, Shuai Liu, Xiao-Kun Zhang, et Yong Xiang. « Effects of Cr3+

[0432] Concentration on the Crystallinity and Optical Properties of Cr-Doped A12O3 Powders by Solid-State Reaction Method ». IOP Conference Series: Materials Science and Engineering 382 (juillet 2018): 022037. https: / / doi.org / 10.1088 / 1757-

[0433] 899X / 382 / 2 / 022037.

[0434]

[0018] Tian, Cheng, Hui Lin, Dawei Zhang, Peiping Zhang, Ruijin Hong, Zhaoxia Han, Xinglu

[0435] Qian, et Jun Zou. « Mn 4+Activated AI2O3 Red-Emitting Ceramic Phosphor with Excellent Thermal Conductivity ». Optics Express 27, n° 22 (28 octobre 2019): 32666. https: / / doi.org / 10.1364 / OE.27.032666.

[0436]

[0019] Ruiz-Trejo, Enrique, Gustavo Tavizôn, et Hector Garcia-Ortega. « Structure and

[0437] Electronic Conductivity of Reduced Gd-Doped CeO[Sub 2] ». Journal of The Electrochemical Society 154, n° 2 (2007): A70. https: / / doi.org / 10.1149 / L2402111.

[0438]

[0020] Sebayang, Kerista, Saufa Taslima, Masno Ginting, Perdamean Sebayang, et Nurdin Bukit.

[0439] « Cr-DOPED ZnO Prepared by Solid State Reaction Method ». Chemistry and Materials Research, s. d.

[0440]

[0021] Chen, Wen-Jauh, Wei-Long Liu, Shu-Huei Hsieh, et You-Gang Hsu. « Synthesis of

[0441] ZnO:Al Transparent Conductive Thin Films Using Sol-Gel Method ». Procedia Engineering 36 (2012): 54-61. https: / / doi.Org / 10.1016 / j.proeng.2012.03.010.

[0442]

[0022] El-Shaarawy, M.G, et W.A.A Bayoumy. « Doping Effect on the Electrical Properties of

[0443] Amorphous A12O3 ». Materials Chemistry and Physics 78, n° 2 (février 2003): 405-11. https : / / doi .org / 10.1016 / S0254-0584(02)00201 -8.

[0444]

[0023] Zhang, Ruochen, Ke Li, Shouzhen Ren, Jiafu Chen, Xiaojian Feng, Yingqiao Jiang,

[0445] Zhangxing He, Lei Dai, et Ling Wang. « Sb-Doped SnO2 Nanoparticle-Modified Carbon Paper as a Superior Electrode for a Vanadium Redox Flow Battery ». Applied Surface Science 526 (octobre 2020): 146685. https: / / doi.Org / 10.1016 / j.apsusc.2020.146685.

[0446]

[0024] Brook, R. J., J. Yee, et F. A. Kroger. « Electrochemical Cells and Electrical Conduction of

[0447] Pure and Doped Al 2 O 3 ». Journal of the American Ceramic Society 54, n° 9 (septembre 1971): 444-51. https: / / doi.Org / 10. l l l l / j.1151-2916.1971.tbl2382.x.

[0448]

[0025] Kelly, Paul. « Studies of the Electrical Energy Storage and Loss Mechanisms in Aluminum

[0449] Oxide. » Doctor of Philosophy, Carleton University, 1965. https: / / doi.org / 10.22215 / etd / 1965-00203.

[0450]

[0026] Kusunose, Takafumi, Asuka Fujita, et Tohru Sekino. « Making Insulating A12O3

[0451] Electrically Conductive without Loss of Translucency Using a Small Amount of ITO Grain Boundary Phase ». Scripta Materialia 159 (janvier 2019): 24-27. https: / / doi.Org / 10.1016 / j.scriptamat.2018.09.009.

[0027] Wang, Yan, Chunlei Pei, Xianhui Wang, Guodong Sun, Zhi-Jian Zhao, et Jinlong Gong.

[0452] « The Role of Pentacoordinate A13+ Sites of Pt / A12O3 Catalysts in Propane Dehydrogenation ». Fundamental Research, septembre 2022, S2667325822003624. https: / / doi.Org / 10.1016 / j.fmre.2022.08.020.

[0453]

[0028] Li, Runze, Lei Luo, Xinlong Ma, Wenlong Wu, Menglin Wang, et Jie Zeng. « Single

[0454] Atoms Supported on Metal Oxides for Energy Catalysis ». Journal of Materials Chemistry A 10, n° 11 (2022): 5717-42. https: / / doi.org / 10.1039 / DlTA08016D.

[0455]

[0029] Rao, C, et D Trivedi. « Chemical and Electrochemical Depositions of Platinum Group

[0456] Metals and Their Applications ». Coordination Chemistry Reviews 249, n° 5-6 (mars 2005): 613-31. https: / / doi.Org / 10.1016 / j.ccr.2004.08.015.

[0457]

[0030] Langerock, Steven, et Luc Eleerman. « Study of the Electrodeposition of Rhodium on

[0458] Polycrystalline Gold Electrodes by Quartz Microbalance and Voltammetric Techniques ». Journal of The Electrochemical Society 151, n° 3 (2004): C155. https: / / doi.org / 10.1149 / L1643071.

[0459]

[0031] Snowden, D.P., H. Saltsburg, et J.H. Pereue. « The Frequency -Dependent Electrical

[0460] Conductivity of Powders: Nickel Oxide ». Journal of Physics and Chemistry of Solids 25, n° 10 (octobre 1964): 1099-1106. https: / / doi.org / 10.1016 / 0022-3697(64)90132-5.

Claims

AMENDED CLAIMS received by the International Bureau on February 28, 2026 (28.02.2026) 1. A method for manufacturing single-atom catalytic devices, applied to three-dimensional catalytic structures of the honeycomb or monolithic type intended for integration into catalytic converters for motor vehicles, comprising the following steps: ■ The creation or synthesis of conductive oxide substrates or conductive oxide layers having oxygen vacancies in their crystalline structure, said vacancies being introduced to create sites suitable for the attachment of catalytic atoms in the form of single atoms; ■ The electrochemical deposition of catalytic atoms, in the form of single atoms, on said oxide substrates or on said oxide layers, said oxygen vacancies participating in the anchoring and stabilization of said catalytic atoms; The process being implemented on said three-dimensional catalytic structures, in particular ceramic or metallic, said structures, of the honeycomb type, comprising internal channels or passages allowing the circulation or diffusion of fluids within said passages or channels; Electrochemical deposition is a deposition carried out by the application of an electric current or an electric voltage, the prefabricated three-dimensional structure of the honeycomb or monolith type being used as an electrode, and an electrolytic solution containing the catalytic species being brought into contact with the internal walls of said structure.

2. A method according to claim 1, wherein the single atoms of catalysts, linked to said oxygen vacancies, remain stable during several thermal cycles at temperatures up to 400 °C, said oxygen vacancies being carried by thermally stable oxides, capable of retaining, during said thermal cycles, their structure as well as the accessibility of said catalytic sites to air and exhaust gases. 3- A method according to any one of claims 1 or 2, wherein the electrochemical deposition is carried out under control of electrical parameters including at least current density and deposition time, so as to promote the deposition of catalytic atoms in the form of single atoms and to limit the formation of catalytic nanoparticles or aggregates of catalytic atoms. 4- A method according to any one of claims 1 to 3, wherein said oxides are doped to induce said oxygen vacancies used for the fixation of catalytic atoms as single atoms within the crystalline structure of the oxides.

5. A method according to claim 4, wherein the doping of the oxides is carried out with an adjustment of the oxygen content, so as to increase the density of oxygen vacancies within the crystal structure of said oxides.

6. A method according to claims 1 to 5, wherein the doping of the oxides is carried out by at least one of the following methods: ■ Solid state reaction; ■ Co-precipitation; ■ Sol-gel; ■ Electrochemical deposition. 7- A process according to claims 1 to 6, wherein the oxides are synthesized by one of the following methods: ■ Precipitation; ■ The sol-gel method; ■ Electrochemical deposition. These methods are likely to introduce defects in the structure of the synthesized oxides, in particular oxygen vacancies.

8. A method according to any one of claims 1 to 7, wherein the three-dimensional honeycomb or monolithic structure is a ceramic or electrically insulating structure, in particular based on cordierite.

9. A method according to claim 8, applied to three-dimensional ceramic or insulating structures with internal channels or passages, particularly of the honeycomb or monolithic type, wherein electrical continuity between the layers of conductive oxides deposited in the different channels is ensured by at least one of these methods: ■ The deposition of a conductive layer covering the ends of the three-dimensional structure, ensuring the electrical link between the different portions of the conductive oxide layers; ■ The use of a metallic or conductive plate or grid, placed at one or both ends of the structure, to ensure electrical continuity between said layers of conductive oxides; ■ The use of conductive elements, in particular metal bars or rods, capable of being inserted at least partially inside the pipes or internal passages of the structure; The process may further include an electrochemical deposition strategy aimed at obtaining a substantially uniform deposit along the structure, in particular by implementing at least one of the following provisions: ■ The modification of electrical connection points during electrochemical deposition; ■ The simultaneous application of a voltage or electric current to both ends of the three-dimensional structure; ■ The use of a highly conductive layer under the conductive oxide layers, in order to promote a homogeneous distribution of the electrical potential; The use of highly conductive pathways integrated within the layers of conductive oxides, capable of promoting a homogeneous distribution of the electrical potential. 10- A method according to any one of claims 1 to 9, wherein the electrolytic solution intended for electrochemical deposition is selectively introduced into the internal channels or passages of the three-dimensional structure, in particular by injection, aspiration, or pouring after fixing said structure onto a support.

11. A method according to any one of claims 1 to 10, wherein the three-dimensional honeycomb or monolithic structure is made from at least one conductive oxide comprising oxygen vacancies, the catalytic atoms being fixed directly onto said structure by electrochemical deposition, without prior formation of a separate layer of conductive oxides. 12- A method according to any one of claims 1 to 11, comprising the following steps for creating conductive oxide layers on the surfaces of the internal walls of the three-dimensional honeycomb or monolithic structure: ■ The mixing of a powder comprising pre-synthesized conductive oxide particles with a solvent, in particular water, to form a slurry. ■ The application of slurry to the surfaces of sometimes internal three-dimensional structures of the honeycomb or monolith type. ■ Drying the slurry. ■ Optionally, heating or calcination of the conductive oxide layer.

13. A method according to any one of claims 1 to 12, comprising the following steps for creating layers of doped conductive oxides on the surfaces of the internal walls of a three-dimensional honeycomb or monolithic structure: ■ The mixing of a powder comprising oxide particles and dopant particles of said oxides with a solvent, in particular water, to form a slurry ■ The application of slurry to the surfaces of the internal walls of the three-dimensional structure of the honeycomb or monolith type; ■ Drying the slurry; ■ Heating to ensure doping and calcination operations.

14. A method according to any one of claims 1 to 13, comprising the implementation of at least one method for depositing or forming layers of conductive oxides on the surfaces of the internal walls of a previously manufactured three-dimensional honeycomb or monolithic structure, said method comprising at least one of the following methods: ■ The precipitation or co-precipitation of oxides or oxide precursors, with or without dopants, from an aqueous solution; ■ A sol-gel process allowing the formation of oxides or oxide precursors, with or without dopants; ■ An electrochemical deposition process of conductive oxides or precursors of conductive oxides from an electrolytic solution.

15. A process according to claim 14, further comprising one or more steps of drying, heating, calcining, crystallizing or transforming oxide precursors into oxides.

16. A method according to any one of claims 1 to 15, comprising a step of using at least one oxide from Al2O3, CeO2 or ZrO2, comprising a step of introducing oxygen vacancies into said oxide, and a step of attaching single atoms of catalysts to said oxygen vacancies, so as to form single-atom catalytic sites.

17. A method according to any one of claims 1 to 16, comprising an electrochemical deposition step of at least one catalytic element among platinum, palladium, rhodium, iridium, ruthenium, nickel and cobalt, said catalytic elements being preferentially fixed on oxygen vacancies present in the oxides, so as to form single-atom catalytic sites.

18. Catalytic converter for motor vehicle, comprising at least one catalytic structure comprising single-atom catalysts, said structure being obtainable by a process according to any one of claims 1 to 17.

19. Catalytic converter for motor vehicle according to claim 18, wherein the catalytic structure is a three-dimensional channeled or internally channeled structure, in particular of the honeycomb or monolithic type, allowing the circulation or diffusion of fluids within said passages or channels.

20. Catalytic converter for motor vehicle according to any one of claims 18 or 19, wherein the catalytic structure comprises at least one layer of conductive oxides or a substrate of conductive oxides having oxygen vacancies in their crystalline structure, said vacancies constituting anchoring sites for single catalytic atoms.

21. Catalytic converter for motor vehicle according to any one of claims 18 to 20, wherein the three-dimensional catalytic structure of the honeycomb or monolith type is a ceramic or insulating structure, in particular based on cordierite.

22. Catalytic converter for motor vehicle according to any one of claims 18 to 21, wherein the catalytic structure comprises at least one oxide among Al2O3, CeO2, ZrO2, TiO2, V2O5, ZnO, La2O3, SnO2 and SiO2, said oxide having oxygen vacancies, single atoms of catalyst being fixed to said oxygen vacancies, so as to form single-atom catalytic sites.

23. Catalytic converter according to any one of claims 18 to 22, wherein the catalytic structure comprises catalytic atoms deposited or fixed as single atoms on said oxygen vacancies, said catalytic atoms comprising at least one element from platinum, palladium, rhodium, iridium, ruthenium, nickel and cobalt. [0001] [0002]Declaration according to Article 19.1 [0003] Claim 1, as well as all the claims that depend on it, have been modified, rewritten or added in order to make one of the central aspects of the application more explicit, namely the fixation of catalytic atoms on oxygen vacancies present in oxides. [0004]It should be noted that none of the documents in the preliminary research report use the concept of oxygen vacancies (D4 and D2 do not mention any fixation technique, DI is based on cationic vacancies, and D3 implements the fixation of catalytic atoms by chemical bonding with heteroatomic elements present on the surface). [0005]The transition from the approaches described in DI and D3 to the use of oxygen gaps is not obvious to a person skilled in the art. [0006]■ DI is based on cationic vacancies, the formation of which is simple in nanowires which exhibit thermal instability at high temperature, but which is difficult to reproduce on forms of oxides suitable for catalytic converters, particularly on microparticles; [0007]■ D3 relies on the addition of heteroatomic elements, such as oxygen, to create anchoring sites, in contrast to the present application which aims at the creation of catalytic sites by removing oxygen to form vacancies. [0008] Claim 1 has been limited to electrochemical deposition using electricity, allowing direct attachment of atoms to oxygen vacancies. Other approaches, such as immersion or impregnation, do not offer a comparable advantage; they generally involve the prior deposition of the entire desired quantity of precursors, followed by heating for calcination, leading to significant nanoparticle formation. [0009]These modifications also aim to restrict the protection sought to catalytic converters for motor vehicles using honeycomb-type structures. Consequently, other applications of the invention are no longer subject to a protection request. [0010] Claim 1 has been amended to explicitly limit the protection sought to the application of the process to prefabricated honeycomb-type structures. This limitation clearly distinguishes the invention from D4, in which the steps of the process are carried out on flat metal supports, these elements then being shaped to form a honeycomb-type structure. [0011]This modification also renders unsuitable the techniques described in D3, which concern UV or plasma treatment, as these are incompatible with the small dimensions of the honeycomb channels of the catalytic converters (approximately 1 mm). Even with pretreatment of oxide microparticles, this treatment remains limited to the initial surface area of ​​the particles and does not correspond to the final catalytically active surfaces after integration of the microparticles into the channels. [0012] Claims 8 and 9 introduce the implementation of the process on ceramic honeycombs, which are the most common in catalytic converters. This option is not covered by D4, which is based on metallic structures, as the shaping steps described in D4 are not easily applicable to ceramic structures, which cannot be bent or readily subjected to electrochemical deposition by the application of an electric current.

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