Metal Oxide-Supported Atomic Quantum Cluster (AQC) Catalysts as Oxygen Carriers for Chemical Looping Processes

Abstract

The present invention relates to a process comprising an atomic quantum cluster (AQC) consisting of 3 to 10 metal atoms supported on a metal oxide as a catalyst for oxygen release, which can be applied to the oxidation of fuels. Further, the present invention relates to the use of an AQC consisting of 3 to 10 metal atoms supported on a metal oxide as an oxygen carrier in a chemical looping reaction, as well as to catalysts and chemical compositions comprising an AQC consisting of 3 to 10 metal atoms supported on a metal oxide.

Description

Technical Field

[0001] The present invention relates to the field of chemical looping (CL) technology, and more particularly to atom quantum cluster (AQC)-based oxygen carriers supported on metal oxides and their use in chemical looping processes.

Background Art

[0002] Global warming and climate change are highly likely to be associated with the increasing concentration of carbon dioxide (CO2), a greenhouse gas in the atmosphere. Therefore, it is urgent to develop and implement processes to avoid CO2 emissions from human activities. One of the intermediate solutions is carbon-dioxide capture and storage (CCS).

[0003] In the search for promising technologies to reduce global CO2 emissions, the so-called chemical looping combustion (CLC) process, a state-of-the-art third-generation CCS technology, is particularly attractive because the predicted CO2 capture cost is very low compared to currently available technologies. In CLC, an oxygen carrier that transports oxygen from the atmosphere to the fuel is used, thereby avoiding direct contact between the atmosphere and the fuel. A CLC system typically includes an air and a fuel reactor. In the fuel reactor, lattice oxygen from a solid oxygen carrier is used to burn a hydrocarbon fuel, and after condensing the steam, a pure CO2 stream suitable for carbon separation is obtained. In the gas reactor, an air stream is used to regenerate the oxygen carrier material.

[0004] Chemical looping technology was mainly developed for so-called chemical looping combustion (CLC) of fuels such as coal or natural gas. Recently, however, the focus of chemical looping has shifted towards the production of hydrogen and other chemicals. In this way, it is possible to produce high-value-added products. When focusing on chemical production, in this technology, instead of air, the oxygen carrier material is regenerated by other oxidants such as CO2, and even H2O. Along with this, CO and H2 are produced respectively. Therefore, chemical looping technology has the potential to become a conversion method for clean and efficient conversion of fuels into electricity, hydrogen, and synthesis gas.

[0005] The key point of this process is to find a suitable solid oxygen carrier, and the most commonly used materials are metal oxides. The temperature and oxygen partial pressure at which the reaction of the oxide material occurs are controlled by the thermodynamic equilibrium regarding reduction and oxidation. This can be done using the Ellingham diagram for the target process (Annu.Rev.Chem.Biomol.Eng.2015.6:3.1 - 3.23).

[0006] However, in addition to having such suitable redox thermodynamics, the ideal material needs to meet several other requirements regarding reaction rate, durability, etc. For example, from a thermodynamic perspective, an ideal candidate is MnO2 / Mn2O3 with an equilibrium temperature of 730K in air. However, since the reoxidation of Mn2O3 to MnO2 is extremely slow, MnO2 / Mn2O3 is not suitable as an oxygen carrier (Energy Environ.Sci.,2017,10,818 - 831).

[0007] Therefore, in this technical field, there remains a strong need to develop suitable oxygen carrier materials with high oxygen carrier capacity, good reaction rate, and versatility for more efficient chemical looping technology applications.

Brief Description of the Drawings

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Summary of the Invention

[0009] The inventors have surprisingly found that by depositing clusters of a small number of atoms on various metal oxides, the activation energies of both the oxidation and reduction reactions involved in chemical looping are dramatically reduced, thereby either reducing the temperature of the processes involved or increasing the reaction rate at the same temperature as that used in processes without the clusters, realizing a new catalytic method.

[0010] Advantageously, since there is a possibility of reducing the temperature of the chemical looping process, it may further promote the improvement of the oxygen carrier ability of the oxide, thereby avoiding the deterioration of the oxide that occurs at high temperatures and generates many pores at a level significantly lower than the theoretical one. This reduces the amount of oxygen that the oxygen carrier can hold at a lower temperature.

[0011] Based on this finding, it has been found that these catalysts are suitable solid oxygen carriers for various chemical looping processes that focus on heat and chemical production.

[0012] Accordingly, a first aspect of the present invention is i. preparing a catalyst comprising an atomic quantum cluster (AQC) consisting of 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide; ii. contacting the catalyst with a reducing agent at a temperature from room temperature to 800 °C to release oxygen from the metal oxide; and iii. optionally, contacting the catalyst with an oxidizing agent to at least partially replenish the oxygen in the metal oxide comprising a catalytic process, wherein the reducing agent is selected from an inert atmosphere, a reducing atmosphere, or a combination thereof, relating to the catalytic process.

[0013] A second aspect of the present invention relates to an oxygen-deficient catalyst obtainable by the above process.

[0014] A third aspect is a) A catalyst comprising an atomic quantum cluster (AQC) composed of 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide; and b) A reducing agent selected from an inert atmosphere, a reducing atmosphere, or a combination thereof relates to a catalyst composition.

[0015] A fourth aspect is the use of a catalyst comprising an AQC composed of 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide, as an oxygen carrier for a chemical looping reaction.

[0016] These aspects and their preferred embodiments are further defined below in the detailed description and the claims.

Mode for Carrying Out the Invention

[0017] Unless otherwise defined, all technical and scientific terms used herein have the meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0018] As defined above, in a first aspect, the present invention i. A step of preparing a catalyst comprising an atomic quantum cluster (AQC) composed of 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide; ii. A step of contacting the catalyst with a reducing agent at a temperature from room temperature to 800 °C to release oxygen from the metal oxide; and iii. Optionally, a step of contacting the catalyst with an oxidizing agent to at least partially replenish oxygen in the metal oxide comprises a catalyst process, wherein the reducing agent is selected from an inert atmosphere, a reducing atmosphere, or a combination thereof, relates to a catalyst process.

[0019] In the process of the present invention, when the metal oxide of the catalyst comes into contact with a reducing agent, it releases lattice O atoms, thereby generating oxygen vacancies (OVs), and an oxygen-deficient metal oxide (MO x-δ )(i.e., a metal oxide in a reduced state or a state with a lower degree of oxidation) is produced. As a result, (i) the release of O2 from the lattice; (ii) the formation of peroxides by the partial oxidation of oxygen; or (iii) the extraction of O2 - from the lattice due to the oxidation of a reducing agent (e.g., hydrogen or fuel) can occur. Subsequently, the reduced metal oxide is partially or completely oxidized back to its original state (MO x ) by a process of re-oxidizing the reduced metal in the presence of a suitable agent that provides oxygen incorporated into the metal oxide to partially or completely remove the oxygen vacancies.

[0020] Step (i) The process of the present invention includes step (i) of preparing a catalyst comprising a metal atom quantum cluster (AQC) having 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide.

[0021] The term "atomic quantum cluster" (abbreviated as AQC) is understood to be a metal atom quantum cluster. The metal AQC is formed only from metal atoms (Mn) in a zero oxidation state, the number of metal atoms is less than 500 (Mn, n < 500), and the size is less than 2 nm. The AQC is stable over a long period. The AQC no longer behaves like a "metal" and is known to behave like a molecule. Therefore, these clusters exhibit new properties that are not observed in nanoparticles, microparticles, or bulk metals as reported in EP1914196A1. Therefore, the physicochemical properties of the AQC cannot be simply inferred from the properties of nano / microparticles.

[0022] The AQC according to the present invention consists of 3 to 10 metal atoms, preferably 4 to 8 or 5 to 7 metal atoms.

[0023] In a preferred embodiment, the metal AQC is a monodisperse metal AQC, for example, a monodisperse metal AQC having 3, 4, 5, 6, 7, 8, 9, or 10 metal atoms. As used herein, a monodisperse population is a population in which the size of the metal clusters is uniform and can be determined by currently used analytical methods. Preferably, the metal AQC is a monodisperse metal AQC having 3, 4, or 5 metal atoms, and more preferably, the metal AQC is a monodisperse metal AQC having 5 metal atoms.

[0024] Thus, in a preferred embodiment, the metal AQC consists of 3, 4, 5, 6, 7, 8, 9, or 10 metal atoms, more preferably, the metal AQC consists of 3, 4, or 5 metal atoms, and most preferably, the metal AQC consists of 5 metal atoms.

[0025] Throughout this specification, unless the context requires otherwise, variations such as the terms "consisting of" and "consists of" are to be construed as meaning including the recited integers, steps, groups of numerical values or groups of steps and not including other integers, steps, groups of numerical values or groups of steps. Thus, the description of an AQC consisting of "n" metal atoms (where n is an integer) refers to an AQC containing only "n" transition metal atoms.

[0026] The metal of the AQC suitable for the process of the present invention is a transition metal, preferably a transition metal selected from Ag, Cu, Au, Pt, Pd, Fe, Co, Ni, or a combination of two or more of these metals, more preferably a transition metal selected from Pt, Ag, Cu, or a combination of two or more of these metals. In a preferred embodiment, the metal is Cu. In another preferred embodiment, the metal is Pt. In a further preferred embodiment, the metal is Ag.

[0027] In the process of the present invention, suitable metal AQC can be obtained by any suitable means known in the art. As a non-limiting example, methods for the preparation of metal AQC are disclosed in S Huseyinova et al., J. Phys. Chem. C, 2016, 120, 15902-15908, or V. Porto et al. Adv. Funct. Mater. 2022, 2113028 (1-14).

[0028] As a non-limiting example, the catalyst of the present invention can be obtained by impregnating a solution of metal AQC onto a metal oxide and drying the resulting mixture. For example, the catalyst can be prepared by a general method known in the art, such as the method disclosed in V. Meille et al, Appl. Catal. A Gen. 2006, 315, 1-17.

[0029] In certain embodiments, the catalyst according to the present invention may be subjected to an activation treatment before step (i). For example, the catalyst may be calcined in a reducing atmosphere. Preferably, the calcination may be carried out at a temperature of 500-600 °C for about 1 hour while flowing Ar / H2.

[0030] The metal oxide of the present invention may include any metal oxide known as an oxygen carrier in a chemical looping reaction. Non-limiting examples of metal oxides typically used in chemical looping include pure metal oxides such as CuO, CdO, NiO, Mn2O3, Fe2O3, and CoO; as well as oxide mixtures; perovskite-type oxides; and substituted perovskite-type oxides.

[0031] In certain embodiments, the metal oxide is selected from metal oxides containing rare earth elements, preferably La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, or combinations thereof; for example, selected from the group consisting of La2O3, CeO2, Ce2O3, Ce3O4, Nd2O3, Sm2O3, Eu2O3, Gd2O3, or combinations thereof.

[0032] In another specific embodiment, the metal oxide may be a perovskite-type metal oxide. In a further specific embodiment, the metal oxide has the formula ABO3 (where the sites of A and B may have the structure of A1 1-x A2 x and / or B1 1-y B2 y ); here, A contains at least one rare earth element and B is at least one transition metal element. In a preferred embodiment, A is at least one rare earth element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, and combinations thereof. B is at least one transition metal element selected from the group consisting of Cr, Mo, Mn, Fe, Ru, Co, Ni, and Cu. Preferably, the perovskite-type metal oxide is LaMnO3, La 1-x Sr x MnO3, and La 1-x Ce x MnO3. More preferably, the perovskite-type metal oxide is La 0.65 Sr 0.35 MnO3.

[0033] In a further specific embodiment, the metal oxide may be a metal oxide containing a transition metal element selected from Cr, Mo, Mn, Fe, Ru, Co, Ni, Cu, or combinations thereof, such as MnO2, Mn2O3, Co3O4, Fe2O3, Fe3O4, CoFe2O4, NiFe2O4, ZnFe2O4, or combinations thereof.

[0034] In one embodiment, the metal oxide is TiO2, WO3, MnO2, Mn2O3, Co3O4, Fe2O3, Fe3O4, CoFe2O4, NiFe2O4, ZnFe2O4, FeAl2O4, BiFeO3, FeAl2O4, CoAl2O4, La2O3, CeO2, Ce2O3, Ce3O4, Nd2O3, Sm2O3, Eu2O3, Gd2O3, LaMnO3, La 1-x Sr x MnO3, and La1-x Ce x is selected from the group consisting of MnO3, or combinations thereof.

[0035] In a preferred embodiment, the metal oxide is CeO2, Ce2O3, Ce3O4, MnO2, Mn2O3, Co3O4, BiFeO3, La 1-x Sr x MnO3, and La 1-x Ce x MnO3, or a combination thereof. In a more preferred embodiment, the metal oxide is cerium oxide, and more preferably, the metal oxide is CeO2, and most preferably, the metal oxide is La 0.65 Sr 0.35 MnO3.

[0036] In certain embodiments, the metal oxide is in any form that maximizes its surface area, and preferably can be in particulate or powder form. In certain embodiments, the metal oxide can be in the form of a nanostructure (i.e., at least one dimension is 1000 nm or less), such as nanopowder, nanowire, nanorod, nanoparticle, nanoplatelet, or combinations thereof. In a preferred embodiment, the average particle size of the nanostructure is 10 - 200 nm.

[0037] In certain embodiments, the metal oxide has a surface area of 1 m 2 / g - 2000 m 2 / g, preferably 5 - 1000 m 2 / g, more preferably 10 - 500 m 2 / g, even more preferably 10 - 100 m 2 / g, and most preferably 20 - 80 m 2 / g.

[0038] In certain embodiments, 0.01% - 20% of the surface area of the metal oxide is covered by AQC, preferably, 0.1% - 10%, more preferably 0.5% - 5% of the surface area of the metal oxide is covered by AQC.

[0039] In certain embodiments, the loading amount of AQC in the catalyst ranges from 0.01 to 10 wt%, preferably from 0.1 to 5 wt%, based on the total weight of the catalyst.

[0040] Additionally, or alternatively, the metal oxide can be defined as a volatile or non-volatile metal oxide. In the context of the present invention, "non-volatile metal oxide" refers to a metal oxide species that remains in the solid phase throughout the process. Non-limiting examples of non-volatile metal oxides include titanium oxide, cerium oxide, iron oxide, cobalt oxide, hercynite, or perovskite.

[0041] For volatile oxides, the temperature required for reduction is higher than the vaporization temperature of the metal oxide, whereby a phase transition occurs during the high-temperature thermal reduction process. Preferably, the metal oxide of the present invention is a non-volatile metal oxide.

[0042] In certain embodiments, the catalyst comprises Cu AQC deposited on the surface of CeO2. Preferably, the Cu AQC consists of 5 metal atoms.

[0043] In a preferred embodiment, the catalyst comprises Ag AQC deposited on the surface of CeO2. Preferably, the Ag AQC consists of 5 metal atoms.

[0044] In another preferred embodiment, the catalyst is La 0.65 Sr 0.35 and comprises Cu AQC consisting of 5 metal atoms deposited on the surface of MnO3.

[0045] Step (ii) The process of the present invention further comprises step (ii) of contacting the catalyst of step (i) with a reducing agent to release oxygen from the metal oxide of the catalyst.

[0046] In the context of the present invention, "releasing oxygen from a metal oxide" means the reduction of the metal oxide by the generation of oxygen vacancies (OVs), and simultaneously, the release of O2 from the lattice, the partial oxidation of oxygen to form peroxides, or the oxidation of a reducing agent that extracts O2 - from the lattice occurs.

[0047] The expression "bringing into contact" in step (ii) refers to the physical contact between the catalyst and the reducing agent. The contact in step (ii) can be carried out by any suitable means. In a preferred embodiment, the contact in step (ii) can be carried out by flowing a gaseous reducing agent through the catalyst.

[0048] In the context of the present invention, a reducing agent means an atmosphere suitable for promoting the removal of oxygen from the catalyst. Suitable reducing agents for the present invention can be an inert atmosphere, a reducing atmosphere, or a combination thereof.

[0049] As used herein, the term "inert atmosphere" means a vacuum; an oxygen partial pressure lower than the thermodynamic partial pressure required to make the value of ΔG (Gibbs free energy) negative for pore formation at the process temperature, preferably an oxygen partial pressure of less than 1 bar, more preferably an oxygen partial pressure of less than 0.1 bar; or an inert gas atmosphere. As used herein, the term "reducing atmosphere" refers to an atmosphere containing a reducing gas.

[0050] Thus, in certain embodiments, the reducing agent is selected from the group consisting of a vacuum; an oxygen partial pressure of less than 1 bar, preferably less than 0.1 bar; an inert gas; a reducing gas; or a combination thereof. Preferably, the reducing agent is an inert gas, a reducing gas, or a combination thereof. In a more specific embodiment, the inert gas is selected from helium, nitrogen, argon, and combinations thereof. In another more specific embodiment, the reducing gas is selected from hydrogen, methane, low-carbon fuels (C2 - C5), carbon monoxide, and combinations thereof. In certain embodiments, the reducing gas may be derived from a raw material such as coal or biomass.

[0051] In some specific embodiments, the reducing agent in step (ii) reacts with at least a part of the oxygen released from the catalyst, thereby forming oxidized by-products. In certain embodiments, the reducing agent can undergo complete, partial, or selective oxidation. In certain embodiments, the reducing agent in step (ii) is hydrogen and the oxidized by-product is water. In another specific embodiment, the reducing agent in step (ii) is methane and the oxidized by-products are carbon dioxide, carbon monoxide, syngas, or a combination thereof.

[0052] In certain embodiments, the hourly space velocity (GHSV) of the reducing agent with respect to the catalyst in step (ii) is 10 h -1 ~1000000 h -1 , preferably 1000~500000 h -1 , more preferably 10000~100000 h -1 . GHSV can be defined as the volume of gas entering the reactor per hour (typically expressed under standard conditions) per unit volume of the catalyst.

[0053] In certain embodiments, step (ii) is carried out for between 1 second and 24 hours, preferably between 10 seconds and 10 hours, more preferably between 30 seconds and 2 hours. In certain embodiments, step (ii) is carried out for about 30 seconds, about 1 minute, about 5 minutes, about 10 minutes, about 30 minutes, about 1 hour, about 2 hours, about 4 hours, about 8 hours, about 16 hours, about 24 hours. In a preferred embodiment, step (ii) is carried out for about 5 minutes.

[0054] Step (ii) is carried out at a temperature in the range from room temperature to 800 °C, preferably in the range from 200 to 700 °C, preferably in the range from 350 to 600 °C, more preferably at a temperature of about 550 °C.

[0055] In another preferred embodiment, step (ii) is carried out at room temperature.

[0056] In the context of the present invention, the term "room temperature" means a temperature of 10°C to 40°C, preferably 15°C to 30°C, more preferably 20°C to 25°C.

[0057] In a preferred embodiment, step (ii) is carried out at a temperature of 250°C to 600°C, and the reducing agent is an inert gas selected from argon, helium, or a combination thereof.

[0058] In another preferred embodiment, step (ii) is carried out at a temperature of 250°C to 600°C, and the reducing agent is a reducing gas such as hydrogen, methane, or a combination thereof.

[0059] In a specific embodiment, step (ii) is carried out under a pressure of 0.1 bar to 100 bar. In a preferred embodiment, step (ii) is carried out at atmospheric pressure.

[0060] In a specific embodiment, step (ii) further includes irradiating the catalyst with light.

[0061] In a more specific embodiment, the light irradiated in step (ii) is derived from sunlight. In a further embodiment, the light irradiated in step (ii) is derived from an artificial light source such as a simulated sunlight lamp, a UV lamp, or an Xe lamp. In a specific embodiment, the artificial light source can be used in combination with sunlight.

[0062] In a specific embodiment, the light irradiated in step (ii) is selected from sunlight, visible light, UV light, or a combination thereof. In a preferred embodiment, the light is visible light.

[0063] In a specific embodiment, the irradiation in step (ii) is carried out using a light beam of about 0.1 to 20 mW / cm 2 or 0.5 to 10 mW / cm 2 .

[0064] In certain embodiments, concentrated solar energy is used to obtain at least a portion of the energy required for the irradiation in step (ii). In certain embodiments, the solar energy may be concentrated using a solar concentrator such as a tower system and a dish system.

[0065] Step (iii) The process of the present invention may further include step (iii) of contacting the catalyst with an oxidizing agent to at least partially replenish oxygen in the metal oxide. Thus, if carried out, in this step, the oxygen-deficient or reduced metal oxide is partially or completely oxidized to its original state (MO x ) to return. As a result, the oxidizing agent is replenished with oxygen, and at the same time a reduced product may be formed.

[0066] In certain embodiments, the oxidizing agent may be selected from air, carbon dioxide, carbon monoxide, water, and combinations thereof.

[0067] The contact in step (iii) can be carried out by any suitable means. In certain embodiments, the contact in step (iii) can be carried out by dispersing the catalyst in the oxidizing agent. In a preferred embodiment, the contact in step (iii) is carried out by flowing the oxidizing agent through the catalyst.

[0068] In some specific embodiments, the oxidizing agent in step (iii) is reduced when transferring oxygen to the catalyst, thereby forming a reduced by-product. In certain embodiments, the oxidizing agent in step (iii) is water, and hydrogen is formed as the reduced by-product. In another specific embodiment, the oxidizing agent in step (iii) is carbon dioxide, and methane is formed as the reduced by-product.

[0069] In certain embodiments, the hourly space velocity (GHSV) of the oxidizing agent with respect to the catalyst in step (iii) is 10 h -1~1000000 h -1 、 preferably 1000 to 500000 h -1 、 preferably 10000 to 100000 h -1 It is.

[0070] In certain embodiments, step (iii) is carried out for 1 second to 24 hours, preferably 10 seconds to 10 hours, more preferably 30 seconds to 2 hours. In certain embodiments, step (iii) is carried out for about 30 seconds, about 1 minute, about 5 minutes, about 10 minutes, about 30 minutes, about 1 hour, about 2 hours, about 4 hours, about 8 hours, about 16 hours, about 24 hours. In a preferred embodiment, step (iii) is carried out for about 5 minutes.

[0071] In certain embodiments, step (iii) is carried out under a pressure in the range of 0.1 to 100 bar. In a preferred embodiment, step (iii) is carried out at atmospheric pressure.

[0072] In some embodiments, step (iii) further comprises irradiating the catalyst with light.

[0073] In a further particular embodiment, the light irradiated in step (iii) is derived from sunlight. In a further embodiment, the light irradiated in step (iii) is derived from an artificial light source such as a simulated sunlight lamp, a UV lamp, or a Xe lamp. In certain embodiments, the artificial light source can be used in combination with sunlight.

[0074] In certain embodiments, the light irradiated in step (iii) is selected from sunlight, visible light, UV light, or a combination thereof. In a preferred embodiment, the light is visible light.

[0075] In certain embodiments, the irradiation in step (iii) is carried out using a light beam of about 0.1 to 20 mW / cm 2 、 or 0.5 to 10 mW / cm 2 .

[0076] In certain embodiments, concentrated solar energy is used to obtain at least a portion of the energy required for the irradiation of step (iii).

[0077] In some alternative embodiments, step (iii) may be carried out in a substantially light-free state. In certain embodiments, step (iii) is carried out in a completely light-free state.

[0078] For the purposes of the disclosure herein, the term in a substantially light-free state in step (iii) means the amount of light reaching the catalyst that can result in the formation of oxygen in an amount of up to 10 mol%, preferably up to 1 mol%, more preferably up to 0.1 mol% with respect to the total amount of the corresponding reduced by-products generated during step (iii), such as the total amount of hydrogen or methane.

[0079] The oxidizing agent for the contacting of step (iii) can be in any suitable form, such as a liquid phase or a gas phase.

[0080] In certain embodiments, the oxidizing agent is water. In further certain embodiments, the water is in the form of liquid water, water vapor, or steam, or a combination thereof. In a preferred embodiment, the water is water vapor. In another certain embodiment, the oxidizing agent is carbon dioxide.

[0081] In one embodiment, step (iii) is carried out at a temperature in the range from room temperature to 800 °C, preferably in the range from 200 to 700 °C, preferably in the range from 350 to 600 °C, more preferably at a temperature of about 550 °C.

[0082] In another preferred embodiment, step (iii) is carried out at room temperature.

[0083] In a further embodiment, steps (ii) and (iii) are carried out in the reverse order, i.e., first step (iii) and then step (ii).

[0084] In certain embodiments, the process of the present invention further includes repeating steps (ii) and (iii) at least once to release oxygen and replenish the catalytic metal oxide lattice.

[0085] In certain embodiments, steps (ii) and (iii) are repeated at least once, at least twice, at least three times, at least five times, at least ten times, at least fifty times, at least one hundred times, at least one thousand times, at least ten thousand times, or at least one hundred thousand times. In a preferred embodiment, steps (ii) and (iii) are repeated at least three times. In a more preferred embodiment, steps (ii) and (iii) are repeated at least one hundred times. In an even more preferred embodiment, steps (ii) and (iii) are repeated at least one thousand times.

[0086] In certain embodiments, steps (ii) and (iii) are performed in reverse order, i.e., first step (iii) and then step (ii), where steps (iii) and (ii) are repeated at least once, at least twice, at least three times, at least five times, at least ten times, at least fifty times, at least one hundred times, at least one thousand times, at least ten thousand times, or at least one hundred thousand times. In a preferred embodiment, steps (iii) and (ii) are repeated at least three times. In a more preferred embodiment, steps (iii) and (ii) are repeated at least one hundred times. In an even more preferred embodiment, steps (iii) and (ii) are repeated at least one thousand times.

[0087] In a preferred embodiment, the process of the present invention i. preparing a catalyst comprising an atomic quantum cluster (AQC) consisting of 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide; ii. contacting the catalyst with CH4 at a temperature from room temperature to 800 °C to release oxygen from the metal oxide, preferably, contacting the catalyst with CH4 while irradiating the catalyst with light at a temperature from room temperature to 800 °C to release oxygen from the metal oxide, wherein hydrogen and CO are formed as oxidized by-products; and iii. contacting the catalyst with CO2 in the substantial absence of light to at least partially replenish the oxygen in the metal oxide, wherein CH4 is formed as a reduced by-product is included.

[0088] In another preferred embodiment, the process of the present invention comprises i. preparing a catalyst comprising an atomic quantum cluster (AQC) consisting of 3 to 10 metal atoms and a non-volatile metal oxide, wherein the AQC is deposited on the surface of the non-volatile metal oxide; ii. contacting the catalyst with an inert atmosphere at a temperature from room temperature to 800 °C to release oxygen from the metal oxide, preferably, contacting the catalyst with an inert atmosphere while irradiating the catalyst with light at a temperature from room temperature to 800 °C to release oxygen from the metal oxide; and iii. contacting the catalyst with water in the substantial absence of light to produce hydrogen to at least partially replenish the oxygen in the metal oxide is included.

[0089] In this particular embodiment, the term in the substantial absence of light in step (iii) means the amount of light reaching the catalyst that can result in the formation of oxygen in an amount up to 10 mol%, preferably up to 1 mol%, more preferably up to 0.1 mol% based on the total amount of hydrogen produced.

[0090] In a more preferred embodiment, steps (ii) and (iii) are performed in the reverse order.

[0091] In another more preferred embodiment, steps (ii) and (iii) are performed at least once, preferably at least 3 times, more preferably at least 100 times.

[0092] It is further assumed that this procedure can appropriately utilize the low - energy part of the solar spectrum to reach and maintain the temperature required for the entire process. In certain embodiments, the low - energy part of the solar spectrum can be infrared light with less than 0.5 eV, preferably less than 0.1 eV.

[0093] In certain embodiments, concentrated solar energy is used to obtain at least a part of the energy required to reach the temperature of steps (ii) and / or (iii). In a further embodiment, concentrated solar energy is used to obtain at least a part of the energy required for the irradiation in step (ii). In certain embodiments, the solar energy may be concentrated using solar concentrators such as tower - type systems and dish - type systems.

[0094] As described above, the metal AQC supported on the metal oxide has surprisingly high conversion efficiency even at low temperatures. This is an important advantage over the prior art as it avoids the deterioration of the oxide that occurs at high temperatures. Thus, the higher oxygen - carrier ability of the catalyst is realized with higher durability in continuous repeated reactions.

[0095] catalyst In a second aspect, the present invention relates to an oxygen - deficient catalyst obtainable by the process defined in the first aspect, in any of its specific and preferred embodiments.

[0096] In the context of the present invention, the term "oxygen deficient" with respect to a catalyst means an excess of metal and / or a deficiency of oxygen in a metal oxide relative to its stoichiometric composition. Thus, any metal oxide having a higher atomic concentration ratio of metal to oxygen relative to the ideal stoichiometric composition of the metal oxide is considered to be oxygen deficient and therefore has an excess of oxygen vacancies greater than 0%.

[0097] In certain embodiments, the catalyst has an excess of oxygen vacancies of at least 0.1%, preferably at least 1%, more preferably at least 5%, and even more preferably at least 10% relative to the stoichiometric composition of the metal oxide. In another particular embodiment, the catalyst has an excess of oxygen vacancies of 0.1 - 100%, preferably 1 - 80%, more preferably 10 - 60%, which may be determined by techniques well known in the art such as Raman spectroscopy or XPS (X-ray photoelectron spectroscopy).

[0098] In certain embodiments, the metal AQC is a monodisperse metal AQC, preferably a monodisperse metal AQC having 3, 4, or 5 metal atoms, and more preferably a monodisperse metal AQC having 5 metal atoms.

[0099] In a preferred embodiment, the oxygen-deficient catalyst comprises a Cu AQC or an Ag AQC, preferably a Cu AQC or an Ag AQC consisting of 5 metal atoms. In a more preferred embodiment, the metal oxide is CeO2.

[0100] In a preferred embodiment, the oxygen-deficient catalyst comprises a Cu AQC or an Ag AQC consisting of 5 metal atoms deposited on the surface of CeO2.

[0101] composition A third aspect is a) a catalyst comprising an atomic quantum cluster (AQC) consisting of 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide; and b) A reducing agent selected from an inert atmosphere, a reducing atmosphere, or a combination thereof relates to a catalyst composition containing the same.

[0102] In certain embodiments, the catalyst has at least 0.1%, preferably at least 1%, more preferably at least 5%, and even more preferably at least 10% excess oxygen vacancies relative to the stoichiometric composition of the metal oxide. In another specific embodiment, the catalyst has 0.1 - 100%, preferably 1 - 80%, more preferably 10 - 60% excess oxygen vacancies relative to the stoichiometric composition of the metal oxide.

[0103] In certain embodiments, the metal AQC is a monodisperse metal AQC, preferably a monodisperse metal AQC having 3, 4, or 5 metal atoms, more preferably a monodisperse metal AQC having 5 metal atoms.

[0104] In a preferred embodiment, the catalyst of the composition comprises a Cu AQC or an Ag AQC, preferably a Cu AQC or an Ag AQC consisting of 5 metal atoms. In a more preferred embodiment, the metal oxide is CeO2.

[0105] In the most preferred embodiment, the catalyst of the composition comprises a Cu AQC or an Ag AQC consisting of 5 metal atoms deposited on the surface of CeO2.

[0106] In certain embodiments, the reducing agent of the composition is an inert gas. Preferably, the inert gas is selected from argon, helium, nitrogen, or a combination thereof.

[0107] In another specific embodiment, the reducing agent is a reducing gas. Preferably, the reducing gas is selected from H2, CO, methane, or a combination thereof.

[0108] Even more specific preferred embodiments regarding the catalyst and the reducing agent in the composition are the same as those described for the above aspects.

[0109] use A fourth aspect relates to the use of a catalyst comprising an atomic quantum cluster (AQC) composed of 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide, as an oxygen carrier for a chemical looping reaction.

[0110] The present invention further relates to the use of an oxygen-deficient catalyst or catalyst composition defined in the second and third aspects in any of the specific preferred embodiments for a chemical looping reaction.

[0111] In a specific embodiment, the chemical looping reaction is selected from the group consisting of chemical looping combustion, syngas production, water gas shift reaction, steam methane reforming, selective oxidation of hydrocarbons, hydrogen production, photo / thermochemical water splitting, thermochemical water splitting, and thermochemical carbon dioxide splitting. In a preferred embodiment, the use is for thermochemical water splitting or photo / thermochemical water splitting.

[0112] Other embodiments 1. One embodiment is i. preparing a catalyst comprising an atomic quantum cluster (AQC) composed of 3 to 10 metal atoms and a non-volatile metal oxide, wherein the AQC is deposited on the surface of the non-volatile metal oxide; ii. contacting the catalyst with water to produce hydrogen in a substantially light-free state; iii. irradiating the catalyst with light in an inert atmosphere to form oxygen vacancies (OVs), and then releasing oxygen from the metal oxide; and iv. optionally, repeating steps ii) and iii) at least once for hydrogen production and oxygen release A process for hydrogen production, comprising A process for hydrogen production, wherein steps ii) and iii) may be performed in the reverse order.

[0113] 2. Another embodiment relates to the process according to embodiment 1, wherein the AQC consists of 5 metal atoms.

[0114] 3. Another embodiment relates to the process according to embodiment 1 or 2, wherein the metal of the AQC is selected from Ag, Cu, Au, Pt, Pd, Fe, Co, Ni, or a combination of two or more of these metals.

[0115] 4. Another embodiment relates to the process according to any one of embodiments 1 to 3, wherein the metal of the AQC is Cu, Ag, Pt, or a combination of two or more of these metals.

[0116] 5. Another embodiment relates to the process according to any one of embodiments 1 to 4, wherein the loading amount of the AQC deposited on the surface of the non-volatile metal oxide is an amount such that the surface coverage is 0.01% to 20%.

[0117] 6. Another embodiment relates to the process according to any one of embodiments 1 to 5, wherein the non-volatile metal oxide is selected from TiO2, WO3, MnO2, Mn2O3, Co3O4, Fe2O3, Fe3O4, CoFe2O4, NiFe2O4, ZnFe2O4, FeAl2O4, BiFeO3, FeAl2O4, CoAl2O4, La2O3, CeO2, Ce2O3, Ce3O4, Nd2O3, Sm2O3, Eu2O3, Gd2O3, LaMnO3, La 1-x Sr x MnO3, and La 1-x Ce x MnO3, or a combination thereof.

[0118] 7. Another embodiment relates to the process according to any one of embodiments 1 to 6, wherein the non-volatile metal oxide has a surface area of 1 m 2 / g to 2000 m 2 / g.

[0119] 8. Another embodiment relates to the process according to any one of embodiments 1 to 7, wherein step (ii) and / or (iii) is carried out at a temperature from room temperature to 800 °C, preferably at a temperature of 350 to 600 °C, more preferably at a temperature of about 550 °C.

[0120] 9. Another embodiment relates to the process according to any one of embodiments 1 to 8, wherein step (ii) is carried out for 1 second to 24 hours, preferably for 30 seconds to 2 hours, more preferably for about 5 minutes.

[0121] 10. Another embodiment relates to the process according to any one of embodiments 1 to 9, wherein step (iii) is carried out for 1 second to 24 hours, preferably for 30 seconds to 2 hours, more preferably for about 5 minutes.

[0122] 11. Another embodiment relates to the process according to any one of embodiments 1 to 10, wherein the water is in the form of liquid water, water vapor, or steam, or a combination thereof, preferably water vapor.

[0123] 12. Another embodiment relates to the process according to any one of embodiments 1 to 11, wherein the light irradiated in step (iii) is sunlight, visible light, UV light, or a combination thereof.

[0124] 13. Another embodiment relates to the process according to any one of embodiments 8 to 12, wherein a solar concentrator is used to obtain at least part of the energy required to reach the temperature of step (ii) and / or (iii), and / or to obtain at least part of the energy required for the irradiation in step (iii).

[0125] 14. Another embodiment is i) preparing a catalyst comprising Ag or Cu AQC consisting of 5 metal atoms deposited on the surface of CeO2 or La 0.65 Sr 0.35 MnO3 respectively; ii) A step of generating hydrogen by bringing a catalyst into contact with steam at a temperature of 350°C to 600°C in a state where there is substantially no light; iii) A step of releasing oxygen from a metal oxide by bringing the catalyst into contact with an inert atmosphere while irradiating the catalyst with visible light; and iv) Optionally, a step of repeating steps ii) and iii) at least once for the production of hydrogen and the release of oxygen; relates to the process according to any one of Embodiments 1 to 13, comprising the above.

[0126] 15. Another embodiment relates to the use of a catalyst comprising an AQC consisting of 3 to 10 metal atoms and a non-volatile metal oxide, wherein the AQC is deposited on the surface of the non-volatile metal oxide, for thermocatalytic hydrogen production and / or thermocatalytic water splitting, and / or photocatalytic / thermocatalytic hydrogen production.

Examples

[0127] The present invention will be described below by examples that are useful for explaining the structure and tests of the embodiments for the purpose of explanation. However, it is understood that the present invention is not limited to the following examples in any sense.

[0128] Example 1. Preparation of Catalyst Typically, 0.1 g of CeO2 or La 0.65 Sr 0.35MnO3 (purchased from Alfa Aesar) metal oxide was impregnated with 400 μL or 2 mL of metallic Cu or Ag AQC having an appropriate concentration (procedures previously reported in S. Huseyinova et al., J. Phys. Chem. C, 2016, 120, 15902 - 15908 or V. Porto et al., Adv. Funct. Mater. 2022, 2113028 (1 - 14), and the process for manufacturing atomic quantum clusters (application number EP18382038.0); method for preparing purified atomic quantum clusters (application number PCT / ES2019 / 070403)), and the desired loading amount was obtained.

[0129] For Examples 2 - 5, next, the obtained solution was dried in an incubator in air at 25 °C for 48 hours, and then a drying process was carried out at 80 mbar and 80 °C overnight.

[0130] For Examples 6 - 8, the obtained solution was dried in air overnight, and then a calcination process was carried out at 550 °C for 1 hour under an Ar / H2 flow (9:1 by volume).

[0131] Example 2. Vacancy Formation Cycle by He under Dark Conditions 100 mg of the Ag5 - CeO2 catalyst with a loading amount of 0.5 wt% was placed inside a gas - phase reactor. The reactor was heated to 550 °C at P = 1.1 bar. A He flow was introduced into the reactor at a rate of 20 mL / min for 1 hour to form pores in the metal oxide. Then, a He flow containing 20% O2 was introduced into the reactor at a rate of 20 mL / min for 1 hour to remove the oxygen vacancies by replenishing the oxygen in the catalyst.

[0132] The color - phase change of the catalyst material (which indicates the presence or absence of O2 vacancies in the metal oxide) was observed. The formation of oxygen vacancies can also be determined by diffuse reflectance spectroscopy (DRS). The presence of a band at ≒514 nm indicates the presence of O2 vacancies on CeO2. As shown in Figure 1, after treatment with O2, this band disappears.

[0133] Example 3. H 2 Vacancy Formation Cycle by 100 mg of the Ag5-CeO2 catalyst with a loading of 0.5 wt% was placed inside the gas-phase reactor. The reactor was heated to 550 °C at P = 1.1 bar. A first treatment with a He flow containing 20% O2 was carried out for 1 h (dV / dt = 20 mL / min) to remove any oxygen vacancies present in the initial sample. Subsequently, a step of forming new vacancies was carried out by introducing an H2 flow for 90 min.

[0134] As shown by the presence or absence of the ≈514 nm band shown in Figure 2, DRS showed that the initial vacancies (t0) formed to some extent during the deposition process in the sample were removed (left figure), and that new vacancies were formed by H2 (right figure).

[0135] Example 4. Vacancy Formation by Ar and Light and Subsequent H 2 Generation by Water 50 mg of the Cu5-CeO2 catalyst with a loading of 0.02 wt% was placed inside the gas-phase reactor. The reactor was heated to 450 °C at P = 1.1 bar. An argon flow was introduced for 2 h inside the reactor while irradiating with light (Irradiation = 19.6 cm 2 , dV / dt = 10 mL / min, φ = 30%, irradiation light source: 200 W Hg(Xe) lamp). Subsequently, without irradiating with light inside the reactor, using a saturator, water vapor was introduced at a rate of 3 mL / min for 1 h with Ar as the carrier (volume fraction φ = 30%).

[0136] Figure 3 shows the XPS analysis results of CeO2 of the Cu5@CeO2 sample before (a) and after (b) Ar and light treatment at 450 °C, and an increase in the Ce 3+ signal due to vacancy formation in the metal oxide can be confirmed.

[0137] The cycle of Ar / light irradiation and H2O / dark conditions was repeated 8 times. For each cycle, as shown in Figure 4, the generation of hydrogen was analyzed by GC-TCD.

[0138] Example 5. Vacancy Formation by Ar:CH 4 (2:1) and Light and Subsequent CH 2 Generation by CO 4 Example 6. Hydrogen Generation Experiment Using Cu5 Supported on CeO 50 mg of the Ag5-CeO2 catalyst with a loading amount of 1 wt% was placed inside the gas-phase reactor. The reactor was heated to 500 °C at P = 1.1 bar. While irradiating the reactor with light (Irradiation = 19.6 cm 2 , dV / dt = 10 mL / min, φ = 30%, irradiation light source: 200 W Hg(Xe) lamp), an Ar:CH4 (2:1) flow was introduced for 0.5 h. CH4 was converted to CO + H2 in this step. Then, inside the reactor, under dark conditions, with Ar as the carrier, CO2 was introduced at a rate of 20 mL / min for 0.5 h (Ar:CO2 = 2:1). CO2 was converted to CH4 in this step.

[0139] The cycle of CH4 / light and CO2 / dark was repeated 40 times. CO and H2 during this pore formation cycle were detected by analysis with GC-TCD as shown in Figure 5a. The generation of CH4 and CO2 detected by mass spectrometry is shown in Figure 5b.

[0140] as Catalyst 2 Example 7. Hydrogen Generation Experiment Using Cu5 Supported on LSM 35 as Catalyst 50 mg of the Cu5-CeO2 catalyst was dispersed in water and placed on a 20 cm 2 of a 30 cm sintered plate 2After depositing in the range of, this catalyst was placed inside a gas-phase reactor. The reactor and its surroundings were evacuated three times. Then, the entire apparatus was purged with argon for 30 minutes to remove air. While purging the reactor with argon, it was heated to 450 °C over 2 hours. After that, using a saturator, water vapor was introduced into the reactor at a rate of 3 mL / min for 1 hour with Ar as the carrier (volume fraction φ = 30%). Following this step, under an argon flow rate of 10 mL / min, an irradiation step was carried out for 2 hours using a 200 W xenon lamp. The generation of hydrogen was analyzed by a gas chromatograph [column: GC-2014 (Shimadzu Corporation) connected with Molsieb 13x60 / 80 and Porapak M 80 / 100]. The steps of water vapor introduction (ii) and photo-irradiation (iii) were repeated 7 more times. In the 8 cycles performed, on average, 2 mL / g of H2 was generated as shown in Figure 7.

[0141] Example 8. Hydrogen Generation Experiment Using Ag5 Supported on CeO 50 mg of Cu5-La 0.65 Sr 0.35 The SrMnO3 catalyst was dispersed in water and placed on a 20 cm sintered plate of 30 cm 2 2 ​After depositing in the range, this catalyst was placed inside a gas-phase reactor. The reactor and its surroundings were evacuated three times. Then, the entire apparatus was purged with argon for 30 minutes to remove air. The reactor was heated to 550 °C over 2.5 hours while purging with argon, and then, inside the reactor, using a saturator, steam was introduced at a rate of 3 mL / min for 0.5 hour with Ar as the carrier (volume fraction φ = 30%). Following this step, under an argon flow at a rate of 10 mL / min, an irradiation step was carried out for 1 hour using a 200 W xenon lamp. The generation of hydrogen was analyzed by a gas chromatograph [column: GC-2014 (Shimadzu Corporation) connected with Molsieb 13x60 / 80 and Porapak M 80 / 100]. The steam introduction step (ii) and the light irradiation step (iii) were repeated 31 more times. Among the 32 cycles performed, in the first 23 cycles, as shown in Figure 8, on average, 20 mL / g of H2 was generated. After the H2 per cycle slowly decreased to nearly 0 mL / g (starting from the 24th cycle), when the catalyst was irradiated for 90 minutes under Ar using a 200 W xenon lamp, in the last cycle (32nd cycle), H2 became 20 mL / g.

[0142] as Catalyst 2 Example 9. Hydrogen Generation Experiment Using Ag5 Supported on LSM 35 as Catalyst 50 mg of the Ag5-CeO2 catalyst was dispersed in water, and 12.25 cm 2After depositing on the steel plate, this catalyst was placed inside the gas-phase reactor. The reactor and its surroundings were evacuated three times. Then, the entire apparatus was purged with argon for 30 minutes to remove air. The reactor was heated to 500 °C over 1 hour while purging with argon, and then steam was introduced into the reactor at a rate of 2.5 mL / min for 1 hour using a Bronkhorst CEM evaporator system (volume fraction φ = 50%). Following this step, an irradiation step was carried out for 2 hours using a 200 W xenon lamp under an argon flow rate of 5 mL / min. The generation of hydrogen was analyzed using a mass spectrometer (ThermoStar GSD 320 T1 (Pfeiffer Vacuum)) and a gas chromatograph (Agilent 8890 GC system). The steam introduction step and the light irradiation step were repeated two more times. In the three cycles carried out, on average, 5.7 mL / g of H2 was produced as shown in Figure 9.

Claims

1. The following steps: i. Preparing a catalyst comprising an atomic quantum cluster (AQC) composed of 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide; ii. Contacting the catalyst with a reducing agent at a temperature from room temperature to 800 °C to release oxygen from the metal oxide; and iii. Optionally, contacting the catalyst with an oxidizing agent to at least partially replenish oxygen in the metal oxide A catalyst process comprising: The reducing agent is selected from an inert atmosphere, a reducing atmosphere, or a combination thereof. The catalyst process.

2. The process according to claim 1, wherein the AQC is composed of 5 metal atoms.

3. The process according to claim 1 or 2, wherein the metal of the AQC is selected from Ag, Cu, Au, Pt, Pd, Fe, Co, Ni, or a combination of two or more of these metals.

4. The process according to any one of claims 1 to 3, wherein the metal of the AQC is Cu, Ag, Pt, or a combination of two or more of these metals.

5. wherein the metal oxide is TiO ２ , WO ３ , MnO ２ , Mn ２ O ３ , Co ３ O ４ , Fe ２ O ３ , Fe ３ O ４ , CoFe ２ O ４ , NiFe ２ O ４ , ZnFe ２ O ４ , FeAl ２ O ４ , BiFeO ３ , FeAl ２ O ４ , CoAl ２ O ４ , La ２ O ３ , CeO ２ , Ce ２ O ３ , Ce ３ O ４ , Nd ２ O ３ , Sm ２ O ３ , Eu ２ O ３ , Gd ２ O ３ , LaMnO ３ , La １－ｘ Sr ｘ MnO ３ , and La １－ｘ Ce ｘ MnO ３ The process according to any one of claims 1 to 4, selected from the group consisting of.

6. The process according to any one of claims 1 to 5, wherein the reducing agent is selected from vacuum; an oxygen partial pressure of less than 1 bar; an inert gas; a reducing gas; or a combination thereof.

7. The process according to any one of claims 1 to 6, wherein the reducing agent is an inert gas, a reducing gas, or a combination thereof.

8. The process according to any one of claims 1 to 7, wherein step (ii) is performed at room temperature.

9. The process according to any one of claims 1 to 7, wherein step (ii) is performed at a temperature of 250 °C to 600 °C, and the reducing agent is an inert gas selected from Ar, He, or a combination thereof.

10. Step (ii) is carried out at a temperature of 250°C to 600°C, and the reducing agent is a reducing gas such as hydrogen, CH ４ , or a combination thereof. The process according to any one of claims 1 to 7.

11. The process according to any one of claims 1 to 10, wherein step (ii) further comprises irradiating the catalyst with light.

12. The process according to any one of claims 1 to 8, further comprising step (iii) of contacting the catalyst with an oxidizing agent to at least partially replenish oxygen in the metal oxide, wherein the oxidizing agent is selected from air, carbon dioxide, water, or a combination thereof.

13. The process is i. Preparing a catalyst comprising an atomic quantum cluster (AQC) composed of 3 to 10 metal atoms and a non-volatile metal oxide, wherein the AQC is deposited on the surface of the non-volatile metal oxide; ii. A step of contacting the catalyst with an inert atmosphere while irradiating the catalyst with light at a temperature from room temperature to 800 °C to release oxygen from the metal oxide; and iii. A step of generating hydrogen by contacting the catalyst with water in a substantially light-free state to at least partially replenish oxygen in the metal oxide The process according to claim 12, comprising.

14. The process according to claim 12 or 13, wherein step (iii) is carried out at a temperature of 350 °C to 600 °C.

15. An oxygen-deficient catalyst obtainable by the process according to any one of claims 1 to 14.

16. The catalyst according to claim 15, wherein the metal AQC is a monodisperse AQC.

17. The catalyst according to claim 15 or 16, wherein the catalyst has at least 0.1% excess oxygen vacancies relative to the stoichiometric composition of the metal oxide.

18. The catalyst contains Cu or Ag AQC consisting of 5 metal atoms deposited on the surface of CeO ２ and is the catalyst according to any one of claims 15 to 17.

19. a) A catalyst comprising an atomic quantum cluster (AQC) composed of 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide; and b) A reducing agent selected from an inert atmosphere, a reducing atmosphere, or a combination thereof A catalyst composition comprising.

20. The catalyst composition according to claim 19, wherein the metal AQC is a monodisperse metal AQC.

21. The catalyst composition according to claim 19 or 20, wherein the catalyst has at least 0.1% excess oxygen vacancies relative to the stoichiometric composition of the metal oxide.

22. The catalyst contains Cu or Ag AQC composed of 5 metal atoms deposited on the surface of CeO ２ The catalyst composition according to any one of claims 19 to 21.

23. The reducing agent is an inert gas, preferably an inert gas selected from argon, helium, nitrogen, or a combination thereof, and / or a reducing gas selected from H ２ , CO, methane, or a combination thereof. The catalyst composition according to any one of claims 16 to 19.

24. Use of a catalyst comprising an AQC composed of 3 to 10 metal atoms and a metal oxide, wherein the AQC is deposited on the surface of the metal oxide, as an oxygen carrier in a chemical looping reaction.

25. The use according to claim 24, wherein the chemical looping reaction is selected from the group consisting of chemical looping combustion, syngas production, water gas shift reaction, steam methane reforming, selective oxidation of hydrocarbons, hydrogen production, photo / thermochemical water splitting, thermochemical water splitting, and thermochemical carbon dioxide splitting.

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