Metal catalyst technology for producing formic acid and methane oxygenate from methane

Abstract

Disclosed are a metal catalyst, a method for producing a methane oxygenate from methane, a method for recycling methane, and an apparatus for removing and recycling methane. The metal catalyst comprises: a support; and metal nanoparticles formed on the support. The irradiation of the metal nanoparticles with light can promote a reaction for producing a methane oxygenate from methane via plasmon resonance.

Description

Metal catalyst technology for the production of formic acid and methane oxidase from methane

[0001] The present invention relates to a method for producing a methane oxidant from methane using a metal catalyst, a methane resource conversion method, and a methane removal and resource conversion device.

[0002] Converting methane into energy-dense and transportable liquid compounds offers an important way to optimize the efficient utilization of fossil fuels while mitigating greenhouse gas emissions. Among the various available strategies, aerobic oxidation of methane has attracted attention as a direct conversion method to produce valuable methane oxidates such as methanol, formaldehyde, formic acid, and methanol derivatives. This process follows a thermodynamically favorable mechanism characterized by a negative Gibbs free energy change (ΔG°<0), i.e., an energy-releasing reaction (Fig. 1a). The key to achieving selective synthesis of the desired product lies in controlling the reaction progress. However, this goal is hindered by the high first bond-dissociation energy (439.3 ± 0.1 kJ mol) of the nonpolar CH3-H covalent bond. -1 ) is hindered by the application of energy for methane activation, which inadvertently promotes complete oxidation of both reactants and intermediates, ultimately leading to their conversion primarily to carbon dioxide.

[0003] CH3-H bond cleavage can occur with the assistance of a series of reactive species, including superoxide (O2·-), hydroperoxyl (·OOH), and hydroxyl (·OH) radicals derived from oxygen (O2) and / or hydrogen peroxide (H2O2) molecules. A notable example concerns a previous study that demonstrated the efficiency of colloidal AuPd nanoparticles in converting methane to methanol with a selectivity exceeding 90%. This improvement was driven by the hydroxyl (·OH) radical generated from the strong oxidizing agent hydrogen peroxide. The reaction mechanism involving the radicals was reported to have a specific energy of 39 kJ mol -1As can be seen from the activation energy, it is related to the kinetic barrier associated with methane activation. Interestingly, the colloidal catalyst showed much higher efficiency than the same nanoparticles supported on TiO2.

[0004] Rather than relying on sacrificial oxidants, there is growing interest in exploring alternative approaches that integrate metal nanoparticle catalysts into photochemical systems. Metal nanoparticles exhibit intense light absorption via excitation of localized surface plasmon resonances (LSPRs). The synergistic effects of their quantum properties (or photoexcitation due to light absorption), catalytic activity, and high surface area make these nanoparticles ideal photocatalysts. Consequently, these nanoparticles have demonstrated the ability to drive a range of reactions under mild conditions, including H2O decomposition, CO oxidation, NH3 oxidation, C2H4 and C3H6 epoxidation, CO2 reduction, and the azocoupling of p-aminothiophenol.

[0005] Plasmonic metal nanoparticles exhibit strong absorption channels at the high energy side of the plasmon resonance arising from their unique interband transitions. The utilization of localized surface plasmon resonance excitation for interband transitions is particularly advantageous for hot electrons (e) due to intraband transitions. - ) considering the limits of energy-rich electrons and holes (e - -h + ) presents a promising route to generate pairs and promote chemical reactions.

[0006] The present inventors have used surface plasmon excitation of gold (Au) nanoparticles as a unique photocatalyst for the selective oxidation of methane without using light-absorbing semiconductors. The results show that C is produced at ambient conditions (i.e., 298 K and 1 atm) without the addition of strong sacrificial oxidants. 1+ It was shown that methane oxidase was produced. This photoreaction was derived from the high chemical potential of charge carriers generated through interband transitions of gold (Au) nanoparticles. This e - and h +participates in interfacial interactions with O2 adsorbates and Dexter-type e - Through the exchange process, singlet oxygen ( 1 O2) Forms a species. Formed 1 O2 relaxes the inherent energy barrier associated with CH4 activation, facilitating direct intermolecular bonding with adjacent CH4 molecules. Finally, this process initiates CH bond activation under ambient conditions, inhibiting complete oxidation of methane and selectively producing formic acid (HCOOH) rather than carbon dioxide.

[0007] The challenge of the present invention is to minimize the energy loss and environmental impact that can occur during the oxidation and resource conversion of methane gas. To this end, the present invention explores sustainable energy resource utilization by developing a metal catalyst that enhances the efficiency of the reaction that occurs during the conversion of methane into useful oxides while reducing the production of byproducts. This approach can overcome the limitations of existing methane utilization methods and help achieve a balance between energy production and environmental protection. Furthermore, the present invention can provide new technological solutions for industries related to methane gas processing, thereby expanding the potential of methane utilization in various fields.

[0008] In one aspect, the present invention provides a metal catalyst comprising a support; and metal nanoparticles formed on the support, wherein when light is irradiated on the metal nanoparticles, the metal catalyst promotes a reaction of producing a methane oxidant from methane by plasmon resonance.

[0009] In one embodiment, the support is a solid organic and inorganic or organic / inorganic composite that stabilizes metal nanoparticles, and may include, but is not particularly limited to, SiO2, Al2O3, TiO2, or WO3.

[0010] In one embodiment, the metal nanoparticles may include gold (Au), silver (Ag), or copper (Cu).

[0011] In one embodiment, the metal nanoparticles may have a size of about 1 to 100 nm.

[0012] In one embodiment, the metal nanoparticles may have a size of about 10 to 60 nm.

[0013] In one embodiment, the metal catalyst may have a maximum absorption wavelength at a wavelength of about 510 to 530 nm.

[0014] In one embodiment, the oxidant of methane may include methanol (CH3OH), formaldehyde (HCHO), formic acid (HCOOH), or acetaldehyde (CH3CHO).

[0015] In another aspect, the present invention provides a method for producing an oxidant of methane from methane, comprising the step of exposing or flowing methane gas to the metal catalyst while irradiating the metal catalyst with light.

[0016] In another aspect, the present invention provides a method for producing a methane resource using a method for producing an oxidant of methane from the methane, wherein the oxidant of methane is obtained in a liquid phase.

[0017] In another aspect, the present invention provides a methane removal and resource recovery device comprising: a reactor capable of injecting or flowing a reaction gas containing methane therein; a metal catalyst positioned within the reactor; and a light source capable of irradiating light onto the metal catalyst.

[0018] In one embodiment, the metal catalyst may be another metal catalyst in the embodiments of the present invention described above.

[0019] In one embodiment, the methane removal and resource recovery device can remove and resource recovery methane generated from livestock, factories, garbage, fuel gas, natural gas, sewage, or wetlands.

[0020] In one embodiment, the methane removal and resource recovery device may further include a collection unit for obtaining the oxidant of methane obtained in the reactor in a liquid phase.

[0021] The effectiveness of the present invention lies in optimizing the oxidation and resource utilization processes of methane, thereby improving energy efficiency and reducing environmental impact. Specifically, the developed catalyst can reduce greenhouse gas emissions that may arise during the methane conversion process, contributing to climate change responses. Furthermore, the invention opens up new industrial applications by converting methane into high-value-added chemicals, which can contribute not only to economic benefits but also to sustainable environmental management. Furthermore, these technological advancements can foster innovation in the energy sector and guide industries toward greater reliance on renewable energy sources.

[0022] Figure 1. Progress control of methane oxidation (CH4OR) over plasmonic gold (Au) nanoparticles (NPs). (a) Change in standard Gibbs free energy (ΔG°) of methane oxidation at 298 K in kJ mol -1Thermodynamic diagram showing methane oxidation in units of 10; this value was determined using literature values ​​of standard Gibbs formation energies taken from the CRC Handbook. This diagram shows that methane oxidation proceeds in a downslope (ΔG°<0) process, where methane molecules are converted to various compounds. However, the energy applied to the reaction system to overcome the significant activation barrier of methane molecules tends to lead to complete oxidation of both reactants and intermediates, producing carbon dioxide, an undesired byproduct. This process therefore inhibits the selective production of methane oxidant (blue line). Gray lines indicate arbitrary transition states. The chemical species in parentheses are other compounds co-formed in that step. (b) Representative transmission electron microscope (TEM) image of gold (Au) nanoparticles (black arrows) supported on SiO2 particles. These nanoparticles were used as photocatalysts in this study. The scale bar is 50 nm. Additional transmission electron microscopy (TEM) images and the size distribution of gold (Au) nanoparticles are shown in Figures 6 and 7, respectively. (c) UV-vis absorption spectra of SiO2 (blue curve) and Au / SiO2 (orange curve) measured by a UV-vis diffuse reflectance spectrophotometer equipped with an integrating sphere. The vertical dashed line indicates the peak position at approximately 520 nm of the localized surface plasmon resonance (LSPR) band. All spectra are shown without baseline subtraction or normalization. (d) Gas chromatograph (GC-FID) chromatograms equipped with a flame ionization detector measured at 2-h intervals during the photocatalytic oxidation of methane by gold (Au) nanoparticles. Photocatalytic activity was performed using gold (Au) nanoparticles in a gas mixture of 3.8% (i.e., 3.8 kPa) CH4, 59.3% (i.e., 60.0 kPa) O2, and 36.9% (i.e., 37.5 kPa) helium at 298 K and 1 atm. The gold (Au) nanoparticles were irradiated with 1.0 W cm for 8 h. -2Exposure to light with energies less than 3.60 eV at a dose of . The chromatograms are arranged from bottom to top in ascending order of illumination time. This chromatogram shows peaks corresponding to CH3CHO and HCOOH, the area of ​​which is observed to increase with illumination time. The quantification of each detected product was determined from the integrated peak area.

[0023] Figure 2. Plasmon modulation of the oxidation reaction of methane.

[0024] Figure 3. Reaction kinetics at various concentrations.

[0025] Figure 4. Singlet oxygen by local surface plasmon resonance ( 1 O2) generation.

[0026] Figure 5. Proposed mechanism.

[0027] Figure 6. Transmission electron microscope (TEM) image of gold (Au) nanoparticles supported on SiO2 particles having a gold (Au) nanoparticle content of 0.92 wt%.

[0028] Figure 7. Histogram and Gaussian fitting curve showing the size distribution of gold (Au) nanoparticles.

[0029] Figure 8. Photograph of the experimental reactor setup for the photocatalytic methane oxidation reaction.

[0030] Figure 9. Mass fragmentation patterns of the oxidized product showing (a) HCOOH (measurement indicated by blue bars) and (b) CH3CHO (measurement indicated by red bars).

[0031] Figure 10. Long-term methane oxidation reaction experiment and experimental kinetic model.

[0032] Fig. 11. Energy less than 3.60 eV and 1.0 W cm -2 TEM images of 0.92 wt% gold (Au) nanoparticles used in the photocatalytic methane oxidation reaction performed under ambient light conditions for 80 h. (a-g) Scale bar is 200 nm. (h) Scale bar is 100 nm.

[0033] Figure 12. Histogram and Gaussian fitting curve showing the size distribution of gold (Au) nanoparticles after 80 hours of photocatalytic methane oxidation.

[0034] Figure 13. UV-vis absorption spectra of Au / SiO2 before photoreaction (orange curve) and after 80 hours of photoreaction (blue curve).

[0035] Fig. 14. X-ray crystal structure study.

[0036] Figure 15. Linear scale plots showing the production rates of (a) HCOOH, (b) CH3CHO, (c) CO2, and (d) H2 as a function of O2 pressure while maintaining a constant pressure of 4.3 ± 0.4 kPa CH4.

[0037] Figure 16. Linear scale plots showing the production rates of (a) HCOOH, (b) CH3CHO, (c) CO2, and (d) H2 as a function of CH4 pressure while maintaining a constant pressure of 2.3 ± 0.4 kPa O2.

[0038] Figure 17. UV-vis absorption spectra of 9,10-Anthracenediyl-bis(mylene)dimalonic acid (ABDA) reagent solution before photoreaction (orange curve) and 4 hours after photoreaction at various energies of incident light.

[0039] Figure 18. UV-vis absorption spectra of the 9,10-Anthracenediyl-bis(mylene)dimalonic acid (ABDA) reagent solution before photoreaction (orange curve) and 4 hours after photoreaction with varying incident light irradiance.

[0040] Figure 19. Comparison of methane oxidation by gold (Au) nanoparticles supported on different carriers. q-SiO2 represents quartz support and a-SiO2 represents amorphous silica.

[0041] Figure 20. Comparison of methane oxidation reactions promoted by Au, Ag, and Cu nanoparticles.

[0042] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. The present invention may be modified in various ways and may take various forms. Therefore, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, but should be understood to include all modifications, equivalents, and substitutes included in the spirit and technical scope of the present invention. In describing each drawing, similar reference numerals are used to indicate similar components. In the attached drawings, the dimensions of structures are shown larger than actual size to ensure clarity of the present invention.

[0043] The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprise" or "have" are intended to specify the presence of a feature, number, step, operation, component, or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, or combinations thereof. In the context of this specification, the term "about" or the like can mean about ± 1%, about ± 2%, about ± 3%, about ± 4%, about ± 5%, about ± 6%, about ± 7%, about ± 8%, about ± 9%, or about ± 10% of a numerical value described in the specification.

[0044] Additionally, the description of one aspect of the present invention may be applied identically or similarly to the same or similar configurations or terms in the description of other aspects.

[0045] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0046] A metal catalyst according to an embodiment of the present invention may include a support; and metal nanoparticles formed on the support. In the context of this specification, the support refers to a material that provides a base on which metal nanoparticles can be distributed. This structure can maximize the activity of the catalyst and increase the selectivity of the reaction. In addition, the support can play a role in extending the life of the catalyst by enhancing the stability of the metal nanoparticles. This can provide economic advantages while maintaining the efficiency of the catalyst under reaction conditions. In particular, by experimentally exploring and optimizing supports of various shapes and compositions, it is possible to develop a catalyst system most suitable for a specific reaction. Variables that can be considered in this process include the physical structure of the support, chemical properties, and interactions with the metal nanoparticles, but the scope of the present invention is not necessarily limited thereto.

[0047] In the context of this specification, the term "nanoparticle" refers to very small particles, typically ranging from about 1 to 100 nm. These nanoparticles can significantly influence the chemical and physical properties of materials. Catalysts using metal nanoparticles, in particular, enable efficient reaction promotion due to their large surface area and high reactivity. This allows for reactions to be activated even at low temperatures and provides the opportunity to more precisely control reaction conditions. Furthermore, by modifying the size, shape, and composition of the nanoparticles, the properties of the catalyst can be customized. This can contribute to the development of new types of catalysts and overcoming the limitations of existing catalysts.

[0048] The metal catalyst of the present invention, which includes a support and metal nanoparticles formed on the support, can be expected to exhibit even distribution of the metal nanoparticles and enhanced chemical stability. This configuration optimizes the reaction zone of the catalyst and enhances the interaction between the reactants and the catalyst, offering the potential to increase overall reaction efficiency. Furthermore, by preventing recombination of the metal nanoparticles, the support can maintain the active sites of the catalyst for a longer period of time, thereby increasing the long-term stability and reusability of the catalyst. These characteristics can offer economic advantages, particularly in industrial-scale reaction processes, and can contribute to the development of sustainable processes that reduce environmental impact.

[0049] The reaction that the metal catalyst can promote and the promotion principle are not particularly limited. In one embodiment, when light is irradiated on the metal nanoparticles, the reaction of producing a methane oxidant from methane can be promoted by plasmon resonance. In the context of this specification, the dictionary meaning of plasmon resonance refers to a phenomenon in which electrons within the particles collectively oscillate when light is irradiated on the metal nanoparticles. This resonance phenomenon can provide a mechanism for effectively transferring light energy to the active site of the catalyst, thereby potentially significantly improving the efficiency of the photocatalytic reaction. In particular, it can be useful for promoting the chemical conversion of substances with low reactivity, such as methane, and this can be applied in various fields such as energy conversion and storage, and environmental purification. In addition, the catalytic process using plasmon resonance can consume less energy than traditional thermal methods, and can provide a method for increasing the activity, selectivity, and specificity of the reaction.

[0050] In one embodiment, the support may comprise SiO2, Al2O3, TiO2, or WO3. In one embodiment, the support may comprise SiO2. By selecting the support material as described above, there is the potential to significantly improve the stability and activity of the catalyst. Materials such as SiO2 have excellent physical and chemical stability even at high temperatures, and can increase the dispersion of catalytically active sites through interaction with metal nanoparticles. This ultimately provides a method to improve the accessibility of reactants and increase the overall efficiency of the catalyst. Furthermore, the use of a support such as SiO2 increases the possibility of extending the reusability and lifespan of the catalyst, which can provide significant economic advantages in industrial applications. In particular, additional research, such as surface treatment or structural modification of the support, may be necessary to optimize the performance of the catalyst under various reaction conditions, thereby finding a method to further enhance the selectivity and activity of the catalyst for a specific reaction.

[0051] In one embodiment, the metal nanoparticles may include gold (Au), silver (Ag), or copper (Cu). In one embodiment, the metal nanoparticles may include gold (Au). By selecting the material of the metal nanoparticles as described above, there is a possibility that the light absorption and conversion efficiency can be significantly improved by utilizing the plasmon properties of the metal nanoparticles. In particular, gold (Au) has excellent electrical conductivity and chemical stability, and can induce strong plasmon resonance in the visible and near-infrared regions. These properties can significantly increase the efficiency in photocatalytic reactions and broaden the light absorption range in the process of converting light energy into chemical energy. In addition, gold (Au) nanoparticles can enhance catalytic activity in certain chemical reactions and can contribute to improving the selectivity and speed of the reaction. This has the potential to be applied in various fields such as environmental purification, energy conversion, and detailed chemical synthesis. By controlling the size, shape, distribution, composition, etc. of the above metal nanoparticles, a method can be sought to optimize the performance of the catalyst according to specific reaction conditions.

[0052] In one embodiment, the metal nanoparticles may have a size of about 1 to 100 nm. When the size of the metal nanoparticles is within the range of about 1 to 100 nm, this can be a significant factor that can affect the surface plasmon resonance characteristics. In this size range, metal nanoparticles can enhance their optical properties by optimizing their interaction with light. For example, the ability to effectively absorb and scatter light can vary depending on the size, which offers the potential to enhance performance in photocatalytic applications or sensor technology. Furthermore, by controlling the size of the nanoparticles, the reactivity to light of specific wavelengths can be adjusted, thereby enhancing their usability in customized applications. These characteristics are important considerations in the research and development of nanotechnology, and can lead to research directions that can contribute to promoting various chemical reactions, improving the sensitivity of optical sensing, and enhancing the detection accuracy of specific substances through controlling the size of the nanoparticles.

[0053] In one embodiment, the metal catalyst may have a maximum absorption wavelength at a wavelength of approximately 510 to 530 nm. Metal catalysts with a maximum absorption wavelength in this range may exhibit high light absorption capabilities, particularly in the visible light region. This has the potential to significantly enhance the efficiency of photocatalytic reactions and may be effective in promoting chemical reactions. Furthermore, these characteristics offer potential applications in optical sensors, solar cells, and various light-based technologies. High light absorption capabilities at appropriate wavelengths can help effectively utilize light to promote catalytic reactions or improve light conversion and storage processes. To this end, a process of optimizing wavelength characteristics and finely controlling reaction conditions accordingly may be followed.

[0054] In one embodiment, the oxidant of methane may include methanol (CH3OH), formaldehyde (HCHO), formic acid (HCOOH), or acetaldehyde (CH3CHO). In one embodiment, the oxidant of methane may include formic acid (HCOOH) and acetaldehyde (CH3CHO). A metal catalyst capable of producing an oxidant of methane containing formic acid has the potential to be usefully utilized in various industrial fields. In particular, formic acid can be used as a source of fuel cells or as an intermediate in organic synthesis, thereby contributing to the search for environmentally friendly energy solutions. In addition, efficient conversion of methane gas can also help reduce greenhouse gas emissions.

[0055] Meanwhile, a method for producing a methane oxidant from methane according to an embodiment of the present invention may include a step of exposing or flowing methane gas to a metal catalyst while irradiating the metal catalyst with light. The metal catalyst may be the metal catalyst according to an embodiment of the present invention described above. In the context of the present specification, exposing a specific element and a gas to each other means placing them under each other's chemical or physical influence. In this process, the oxidation reaction of methane can be promoted through the interaction of methane, oxygen gas, and the metal catalyst, thereby efficiently producing an oxidant of methane such as methanol, formaldehyde, formic acid, or acetaldehyde. In the context of the present specification, flowing a gas to a specific element means moving or causing the gas to flow along a specific path or location. Through this process, the contact area between the gas and the catalyst can be maximized, thereby increasing the efficiency of the reaction. The gas flow can help ensure even gas distribution within the reactor, allowing all catalyst particles to participate in the reaction.

[0056] In the context of this specification, the term "methane oxidizer" refers to compounds produced during the oxidation of methane. These oxidizers primarily appear in the form of methanol, formaldehyde, formic acid, and acetaldehyde, and these compounds can play an important role in energy production, as raw materials for the chemical industry, and in environmental purification processes. These oxidizers obtained through methane oxidation have potential applications in various industrial fields and are particularly valuable as clean energy raw materials. Methanol can be used as a fuel additive or solvent, formaldehyde in the production of resins and adhesives, and formic acid in the production of preservatives and industrial chemicals. Because methane oxidizers have such a wide range of applications, research and technological development for their efficient production are continuously considered important.

[0057] The above-described light irradiation is a crucial process that can stimulate catalytic activity and promote the methane oxidation reaction. Specifically, when metal nanoparticles exhibit plasmonic properties, light irradiation can significantly increase catalytic activity through electron resonance at the surface. This light irradiation process can also help increase reaction selectivity and conversion by using light of a specific wavelength. Furthermore, this method can provide energy-efficient reaction conditions and enable environmentally friendly reaction pathways. The heat or photochemical energy generated by light irradiation can lower the activation energy of methane gas, facilitating the oxidation reaction and enabling the reaction to proceed at lower temperatures. This can contribute to reduced energy consumption and increased reaction stability and sustainability. Ultimately, this process enhances the production of methane oxidants and provides an efficient method for producing industrially useful chemicals.

[0058] Meanwhile, the methane resource conversion method according to an embodiment of the present invention uses the "method for producing an oxidant of methane from methane" according to the embodiment of the present invention described above, and the methane oxidant can be obtained in a liquid phase. In the context of this specification, "resource conversion" means a process of converting a specific material or energy into a useful resource. This process promotes efficient use of resources by converting low-value raw materials or unused resources into valuable products or energy. The methane resource conversion method according to an embodiment of the present invention achieves this by utilizing methane, particularly methane-rich resources, to produce useful chemicals such as methanol, formaldehyde, and formic acid, which are oxidants of methane. These chemicals are obtained in a liquid phase and can be used in various industrial fields. For example, methanol can be utilized as a fuel, solvent, or raw material for other chemical products, and formaldehyde and formic acid can be used in the manufacture of industrial adhesives, preservatives, and synthetic resins, respectively. Therefore, this method can contribute to the efficient use of energy resources and the development of the chemical industry by converting methane into high value-added chemicals.

[0059] Meanwhile, a methane removal and resource recovery device according to an embodiment of the present invention may include a reactor capable of injecting or flowing a reaction gas containing methane therein; a metal catalyst positioned within the reactor; and a light source capable of irradiating light onto the metal catalyst.

[0060] The role of the above reactor is to create an environment that can receive light from a light source so that the reactant gas containing methane can effectively contact the metal catalyst and be converted into products. This creates conditions in which the methane gas can react with oxygen activated on the surface of the metal catalyst and be converted into a methane oxidant. This process within the reactor enables the efficient processing and resource utilization of methane gas and can provide the optical conditions necessary to promote the methane oxidation reaction. The light source can increase the activity of the catalyst and accelerate the reaction by irradiating the metal catalyst with light of a specific wavelength. This process may involve the plasmon effect or a photocatalytic reaction.

[0061] In one embodiment, the metal catalyst may be any of the metal catalysts described in the embodiments of the present invention. The role of the metal catalyst is to promote the oxidation reaction of methane through direct interaction between methane and oxygen gas, thereby efficiently producing methane oxidants such as methanol, formaldehyde, formic acid, and acetaldehyde. During this process, the metal catalyst activates oxygen molecules by being irradiated with light, and these activated oxygen molecules react with methane to form oxidants. This process of catalyst activation and reaction by light absorption is called a photocatalytic reaction, and it can help lower the energy barrier of the reaction and increase the reaction rate. In particular, the metal catalyst absorbs light of a specific wavelength from a light source and utilizes this absorbed energy to promote the oxidation reaction of methane. This mechanism makes the methane gas treatment and resource utilization process more efficient, and can also have a positive impact on environmental protection and energy recovery.

[0062] The role of the light source is to provide energy for the catalytic reaction and activate the methane gas reaction on the catalyst surface. This light source can enhance the plasmonic effect or photocatalytic activity occurring on the catalyst surface by emitting light of a specific wavelength. This optical stimulation can accelerate the methane oxidation reaction, shortening the reaction time and increasing the reaction efficiency. Furthermore, the energy provided by the light source lowers the activation energy required for methane and oxygen to react on the catalyst surface to produce an oxidant. This helps achieve high reaction efficiency while reducing overall energy consumption.

[0063] The use of the methane removal and resource conversion device according to an embodiment of the present invention is not particularly limited as long as methane can be obtained or is generated anywhere. In one embodiment, the methane removal and resource conversion device can remove and resource-convert methane generated from livestock, factories, waste, fuel gas, natural gas, sewage, or wetlands. For example, methane generated during the digestion process of livestock in livestock farming, methane that may be generated during the production process in factories or industrial facilities, methane generated from organic matter decomposing in landfills, methane leaked during the mining and processing of natural gas, methane generated during the sewage treatment process, methane naturally generated in natural environments such as wetlands, etc., methane removal and resource conversion through this device is possible in almost any location where methane is generated. The application of this device reduces greenhouse gas emissions by reducing methane gas emissions, and at the same time, provides an opportunity to create additional economic value by converting methane into useful chemicals. Therefore, this invention can be an important tool for environmental protection and sustainable resource management, and provides flexibility for various applications tailored to the characteristics and needs of methane-producing regions.

[0064] In one embodiment, the methane removal and resource recovery device may further include a collection unit for collecting the oxidant of methane obtained within the reactor in a liquid phase. By further including the collection unit, the oxidants generated through the oxidation reaction of methane can be efficiently recovered. The collection unit is structured to liquefy and collect the oxidant generated within the reactor, and the liquid oxidant thus generated can be converted into a form that can be used or stored directly without further processing. The methane oxidant obtained during this process can be utilized as a useful chemical raw material in various industrial fields, which means that additional economic value can be created during the methane gas processing and conversion process. Furthermore, by processing and resource recovery of methane gas in this manner, it offers the possibility of reducing the burden on the environment and promoting the utilization of sustainable energy resources.

[0065] Hereinafter, embodiments of the present invention will be described. However, the embodiments described below are merely some embodiments of the present invention, and the scope of the present invention is not limited to the embodiments described below.

[0066] Photocatalytic oxidation of CH4 by gold nanoparticles. The present inventors have designed a gas-phase plasmonic reaction system for the oxidation of methane (Fig. 8). Gold nanoparticles were placed in a reactor filled with a 1 atm gas mixture of CH4 and O2 at defined concentrations. The photoreaction was initiated by illuminating the gold nanoparticles with a collimated beam emitted by a 300 W Xe arc lamp equipped with a condenser lens, typically maintained at a constant temperature of 25°C. This plasmonic reaction system operates without the need for elevated temperatures, high reactant pressures, or the inclusion of additional oxidants such as H2O2 and N2O.

[0067] For the gas-phase plasmonic methane oxidation reaction, a pellet-like powdered photocatalyst consisting of gold nanoparticles supported on inert and insulating SiO2 particles was used. The gold nanoparticles were supported on the SiO2 particles using a reducing agent of NaBH4. The gold nanoparticles were quantified as 0.92 wt% using inductively coupled plasma-optical spectroscopy (ICP-OES) analysis, a value chosen to minimize the influence of localized surface plasmon resonance (LSPR)-driven local heating on the reaction due to the sparse and isolated distribution of gold nanoparticles on the SiO2 particles (Figures 1b and 6). No auxiliary additives, such as nanoparticle ligands or capping agents, were used to avoid affecting the reaction. Consequently, a relatively broad size and shape distribution was observed. The shape of the gold nanoparticles was approximated as quasi-spherical, with a mean diameter of 35.9 nm and a corresponding standard deviation (SD) of 26.9 nm, which is represented as 35.9 ± 26.9 nm (Figure 7). Gold nanoparticles attached to SiO2 supports exhibited an optical absorption profile from ultraviolet to visible wavelengths, with a maximum wavelength of 520 nm. This absorption feature arises as a result of the dipole localized surface plasmon resonance (LSPR) of gold nanoparticles (Fig. 1c). The LSPR band is a shift to higher energy levels within the 6sp band. - Here (transition within the band) and e from 5d to 6sp band - This includes the range of (inter-band transitions).

[0068] As described above, the oxidation reaction of gaseous plasmonic methane was performed under standard conditions of 25°C and 1 atm pressure. The photon energy (E) of 3.60 eV, which induces an interband transition in gold nanoparticles, was ph ) lower than E phWhen incident light was applied, the production of C1(HCOOH) and C2(CH3CHO) methane oxidants was observed continuously for 8 hours in the oxidation reaction of methane (Fig. 1d, Fig. 9, and Fig. 2a). This change was accompanied by the simultaneous production of CO2 and H2 (Fig. 2b).E ph As the spectral overlap region of the interband and intraband transitions decreases to 2.34 eV, the production rates of these species decrease rapidly (Figs. 2a and 2b). In particular, the production rates of three carbon-containing products, namely HCOOH, CH3CHO, and CO2, decrease with E ph showed a superlinear response to H2 production. However, this behavior was not observed at the H2 production rate, which is E ph , which shows linear proportionality. The difference in trend may be due to different reaction pathways dominating H2 production.

[0069] Figure 2. Plasmon modulation of the oxidation reaction of methane. (a) HCOOH (blue circle, left y-axis (mmol g -1 h -1 Unit)) and CH3CHO (orange square, right y-axis (μmol g -1 h -1 (b) Production rates of additional products, CO2 (gray diamonds) and H2 (yellow triangles), detected in the same set of reactions as in panel (a) as a function of photon energy. These rates are expressed in μmol g for appropriate comparison. -1 h -1 mmol g instead -1 h -1The y-axis scale is indicated in units. The exponential curves shown as dashed lines in panels (a) and (b) are used to provide the best fits for HCOOH, CH3CHO, and CO2. For H2, the dashed line is a linear fit to the data points. (c) Cumulative selectivity (left y-axis, in %) for each product formed in the oxidation of methane and conversion of CH4 (right y-axis, in %) as a function of photon energy. The photoreaction was performed using gold nanoparticles in a gas mixture of 4.2% (i.e., 4.3 kPa) CH4, 2.3% (i.e., 2.3 kPa) O2, and 93.5% (i.e., 94.7 kPa) helium at 298 K and 1 atm pressure. The gold nanoparticles were exposed to light of various energies, particularly light less than 3.60, 3.10, 2.73, and 2.34 eV, at a dose of 1.0 W cm for 8 h. -2 were exposed to a dose of . (d) Plot of RTln(rate) as a function of photon energy for HCOOH, CH3CHO, and CO2 products, where R is the gas constant and T is the reaction temperature. The dashed line shows the linear best-fit curve. The zero production rate measured at an incident light energy of 2.34 eV is excluded during the logarithmic scale transformation. The slopes of the linear fits for HCOOH, CH3CHO, and CO2 are 5.4, 5.6, and 5.7 kJ mol, respectively. -1 eV -1 (e) HCOOH as a function of dose (blue circle; left y-axis (in mmol) g -1 h -1 ) and CH3CHO (orange squares; μmol g -1 h -1 (f) Production rates of additional products, CO2 (gray diamonds) and H2 (yellow triangles), detected in the same set of reactions as in panel (e) as a function of irradiance. These rates are expressed in μmol g for appropriate comparison. -1 h -1 mmol g instead -1 h -1The y-axis scale is indicated in units. The dashed lines for all products show the linear dependence on irradiance. This photoreaction was performed using gold nanoparticles in a gas mixture of 4.2% (i.e., 4.3 kPa) CH4 and 2.3% (i.e., 2.3 kPa) O2, the remainder being helium, balanced with He, at 298 K and 1 atm pressure. The gold nanoparticles were exposed to irradiances of 0 (i.e., dark control performed at elevated temperature of 323 K), 0.4, 0.7, and 1.0 W cm -2 were exposed to light with energies less than 3.60 eV for 8 hours at various irradiances. Each data point shown in this figure is the average determined from at least three experiments performed under identical conditions. Error bars are the standard error of the mean for this set of trials.

[0070] C 1+ E, where oxidants, CO2 and H2 are produced ph In the range, HCOOH production exhibited a selectivity exceeding 97%, with a methane conversion of approximately 20% (Fig. 2c). The residual fraction, which comprised less than 3%, included compounds such as CH3CHO, CO2, and H2. It is important to note that the selectivity for HCOOH remained constant even under conditions where CH4 conversion was increased. This observation contrasts with the competitive dynamic between CH4 conversion and the selectivity of the oxidant product typically observed in methane oxidation.

[0071] The inventors performed a photocatalytic methane oxidation reaction using gold nanoparticles for 80 hours (Fig. 10). The oxidant production rate showed an upward trend during the illumination period and eventually reached a plateau. The experimental kinetic data were derived from the steady-state approximation for the sequential reaction, y = a(1-e -bx) was modeled using the formula (detailed information about this model is described later in other examples). By analyzing the kinetic parameters a and b, the inventors confirmed that the oxidation reaction activity of methane and the selectivity for HCOOH product were favorable under plasmon excitation. In addition, the plasmonic catalyst was stable during extended testing periods (see FIGS. 11 to 14 and the examples described below).

[0072] Plasmon control of catalytic activity. e generated by interband attenuation of gold nanoparticles. - -h + When there is a pair of photovoltaic and light excitations, the incident E ph The relationship between them can be described by the following model equation:

[0073]

[0074] Here, R is the gas constant, T is the reaction temperature, r light is the net reaction rate under light excitation, ΔG° dark is the standard Gibbs free energy of the dark reaction, n is the photoinduced initiation step, e is the - -h + The number of pairs, F is the Faraday constant. zFE ph The term represents the Gibbs free energy of the reaction under light irradiation.

[0075] According to the prediction described in equation 1, the experimentally observed RTln(rate light ) and E ph The relationship between the two is shown by a linear correlation (Fig. 2d), a consistent feature observed across all carbon-containing products. The plots associated with these products exhibit similar slopes. Irradiance, another parameter that could potentially affect the slope, was fixed according to the specific conditions of the photoreaction. Consequently, the only determinant of the slope is z. This observation implies that all carbon-containing products undergo the same initiation step, regardless of the number of carbons or the degree of oxidation. One example of such a step is CH4 to 1H+ The methyl radical (·CH3) is formed through extraction. After the formation of this intermediate, a series of oxidation steps will follow, culminating in the production of HCOOH. According to the principle presented in Equation 1, the y-intercept is ΔG°. dark This inference is experimentally supported by the different y-intercept values ​​observed in each plot (Fig. 2d), which indicate differences in the free energy contributions controlling the production of various oxidants from CH4.

[0076] Plasmon-driven energy conversion involves rapid carrier relaxation, resulting in the dissipation of stored energy in the form of heat. A local temperature increase around gold nanoparticles can potentially affect catalytic activity. In the experimental design of this experimental example, the inventors developed a method for preparing controlled, low-density, specifically less than 1%, gold nanoparticles on a SiO2 substrate. The photoreaction involving the gold nanoparticles was performed at a constant bulk temperature of 25°C. This dual approach contributed to the efficient release of thermal energy from the nanoparticles.

[0077] E ph No catalytic activity was observed for gold nanoparticles under light irradiation of < 2.34 eV (Figs. 2a and 2b). Moreover, no discernible product was observed under conditions without light excitation (Figs. 2e and 2f) while keeping all other parameters constant except the reaction temperature of 50°C. The observation of a linear relationship between production rate and irradiance (Figs. 2e and 2f) demonstrates that the acceleration of the forward reaction during photoexcitation is due to an energy carrier transfer process and not a simple thermal plasmon effect. However, the potential influence of photothermal heating on the energy distribution of charge carriers induced by localized surface plasmon resonance excitation of gold nanoparticles and its partial contribution to the reaction kinetics cannot be ruled out.

[0078] Kinetic dependence of methane oxidation on reactant concentration. The kinetics of methane oxidation show a slight dependence on O2 concentration within the considered pressure range (0.5–70.6 kPa, Fig. 3a). This indicates a high O2 coverage on the gold surface. The pseudo-reaction order n is determined to be 0.20 for HCOOH, 0.16 for CH3CHO, 0.17 for CO2, and nearly zero for H2. In contrast, within the investigated pressure range (0.4–42.6 kPa), variations in CH4 concentration were found to have a negligible effect on the methane oxidation process rate (Fig. 3b). In particular, the regression analysis applied to the CO2 production rate yielded a value of m of 0.36. However, this estimate is limited by variation within the data set, suggesting that CH4 is hardly adsorbed on the gold catalyst during the catalytic process. These results are consistent with the unfavorable adsorption properties of CH4 on the gold surface due to its symmetric molecular structure and relatively weak polarity of the C–H bonds.

[0079] Figure 3. Reaction kinetics at various concentrations. (a) Logarithmic scale plot of the production rate for each product as a function of O2 pressure under a fixed pressure of 4.3 ± 0.4 kPa CH4. The slope, n, of the dotted fitting line represents the pseudo-reaction order with respect to O2 concentration. (b) Logarithmic scale plot of the production rate for each product as a function of CH4 pressure under a fixed pressure of 2.3 ± 0.4 kPa O2. The slope, m, of the dotted fitting line represents the pseudo-reaction order with respect to CH4 concentration. The corresponding linear scale plots are the best-fit equations and R 2 The values ​​are shown in Fig. 15 for panel (a) and in Fig. 16 for panel (b). The photoreactions were performed using gold nanoparticles in a gas mixture of CH4 and O2 at 1 atm pressure and 298 K with various compositions, respectively. The gold nanoparticles were irradiated with 1.0 W cm for 8 hours. -2were exposed to light with energies less than 3.60 eV at a dose of . Each data point shown in this figure is the average determined from at least three experiments performed under identical conditions. Error bars are the standard error of the mean for this set of trials.

[0080] The observed effect of reactant concentration on the kinetics of methane oxidation supports the involvement of the Eley-Rideal mechanism at the catalyst surface. The Eley-Rideal mechanism entails a scenario in which gaseous molecules directly react with molecules adsorbed on active sites. Consequently, the inventors hypothesize that methane oxidation occurs through the interaction between gaseous CH4 molecules and O2 molecules bound to the gold surface. A similar Eley-Rideal pathway has been reported for methane oxidation on platinum and palladium surfaces, highlighting the essential role of activated O2 species located on the catalyst surface in the potent CH4 bond cleavage inherent in CH4.

[0081] Singlet oxygen generation induced by photoirradiation of gold nanoparticles. The inventors have discovered that spin-forbidden O2 transitions occur in the system of the present invention. Specifically, the photoreactive system generates a triplet state ( 3 Σ g - ) in a singlet state (i.e., 1 Δ g ) induces the sensitivity of O2, which is 0.98 eV (94.5 kJ mol) compared to the energy of the triplet ground state. -1 ) is at an energy level as high as .

[0082] 1 Detection of O2 followed the same method as that used for the photocatalytic oxidation of methane (see the examples below for detailed procedures). 1The O2 scavenger, 9,10-Anthracenediyl-bis(mylene)dimalonic acid (ABDA), was positioned beneath the substrate containing gold nanoparticles. The photocatalytic layer was exposed to light for 2 h under standard conditions of 25°C and 1 atm pressure in a 1 atm gas mixture of 4% (v / v) CH4, 60% (v / v) O2, and the remainder helium, which resulted in bleaching of ABDA. This bleaching 1 It refers to a selective reaction with O2 and endo peroxide (ABDA- 1 O2) is formed.

[0083] Incident light E directed at gold nanoparticles ph If you modify it, it will be generated 1 The amount of O2 is controlled.E ph As it increases 1 The equilibrium of O2 production was reached more quickly (Fig. 4a and Fig. 17). This trend is similar to the superlinear behavior observed in the methane oxidation experiment (Fig. 2a). In both cases, the acceleration of the photocatalytic reaction kinetics was mainly caused by inter-band rather than intra-band transitions. Moreover, the generated 1 The amount of O2 showed a linear relationship with the irradiance (Fig. 4b and Fig. 18), which reproduced the trend observed between the oxidation of methane and the irradiance (Fig. 2e).

[0084] Figure 4. Singlet oxygen by localized surface plasmon resonance (LSPR) 1 O2) Generation. (a) Generated as a function of incident photon energy. 1 Changes in the O2 moles. These measurements were performed using gold nanoparticles in a gas mixture of 4% (v / v) CH4 and 60% (v / v) O2, the remainder being helium, at 298 K and 1 atm pressure. The gold nanoparticles were irradiated with light of various energies, particularly those less than 2.95, 2.73, 2.51, and 2.25 eV, at a dose of 1.0 W cm for 4 h. -2 were exposed to a dose of . The dotted line represents the curve fitted by an exponential function. The shaded area is the selective1 The region where ABDA, an O2 probe, self-decomposes by light absorption is shown. (b) Generated as a function of irradiance. 1 Changes in the molarity of O2. These measurements were performed using gold nanoparticles in a gas mixture of 4% (v / v) CH4 and 60% (v / v) O2, the remainder being helium, at 298 K and 1 atm pressure. The gold nanoparticles exhibited radiative efficiencies of 0 (i.e., dark reaction), 0.4, 0.7, and 1.0 W cm -2 were exposed to light with energies less than 2.95 eV for 4 h at various irradiances. The dashed line is the linear regression curve for the data points. (c) Arrhenius plot of the HCOOH production rate, i.e., the natural logarithm of the HCOOH production rate versus the reciprocal of the oxidation reaction temperature of plasmonic methane. The data are fitted by slope (-E app / R) is the apparent activation energy E app is fitted with a straight line proportional to . Each data point shown in this figure is the mean determined from at least three experiments performed under identical conditions. The error bars are the standard error of the mean for this set of trials.

[0085] In principle, the electronic configuration of the triplet O2 molecule prevents direct reaction with the singlet CH4 molecule because spin is not conserved. This deviation in spin states increases the activation barrier, limiting the progress of the partial oxidation reaction. In the experiment of this experimental example, the apparent activation energy for the oxidation of methane was 24.8 ± 3.9 kJ mol -1 was measured (Fig. 4c), which is significantly lower or similar in size to the alternative process.

[0086] These findings 1 This suggests that the generation of O2 is associated with an energy carrier-mediated mechanism on the surface of gold nanoparticles (Fig. 5a). Under illumination, gold nanoparticles generate charge carriers with redox potential. O2 adsorbates are formed by the transfer of a single electron (1e) from the photocharged gold nanoparticles. -) is accepted. 1e to the adsorbed O2 - Adding degenerate π * Orbit (e.g. π x * ) is filled and a superoxide anion is produced:

[0087]

[0088] The inventors of the present invention have developed a temporary O2 ·- Different occupied π in paper gold nanoparticles * State (e.g. π y * ) with opposite spin h + It is assumed that the electrons undergo sequential transfer. Often called back electron transfer (back e - This step is called transfer. 1 Produces O2:

[0089]

[0090] The redox coupling process is Dexter e - Similar to the exchange mechanism (Fig. 5b). This process requires sufficient energy e - -h + This becomes thermodynamically feasible when pairs can participate in the reaction at the nanoparticle interface. The energy distribution of these charge carriers, generated by the decay of the excited surface plasmon resonance before inelastic relaxation, is determined by the electronic band structure of the metal, particularly the Fermi level E F It strongly depends on the position of the d band for gold. For gold, the allowed interband transition near the resonant surface plasmon polariton energy is E F It occurs in the d band state located about 2 eV below the E of gold. F is at a potential of 0.66 V compared to SHE at pH 0.

[0091] For example (Fig. 5a), E ph= When photoexcitation occurs at 2.34 eV (energy region partially overlapping with the LSPR transition), h formed through interband decay of localized surface plasmon resonance (LSPR) excitation in gold + Assume that occupies the d band. Therefore, the d band h + has a maximum potential of 2.66 V compared to SHE, which is more positive than the E° value in Equation 3. The corresponding photogenerated e - is E F It is estimated to exist in the sp band just above and have a maximum potential of 0.32 V, which is not enough energy to be transferred to the O2 molecule (Eq. 2). Therefore, the attenuation of the plasmon resonance occurred at an energy lower than the interband absorption of 3.0 eV (corresponding to a wavelength longer than 410 nm), which is the energy of the methane oxidation reaction. 1 This causes little or no production of O2 and HCOOH, i.e., from gold nanoparticles. 1 Dexter-type evolution of the oxidation reactions of O2 and methane can occur by harvesting energy carriers generated by photons with energies greater than 3.0 eV.

[0092] Figure 5. Proposed mechanism. (a) Schematic depicting the transport of electrons (- signs) and holes (+ signs) generated through interband transitions in gold under steady-state illumination with incident light having different photon energies hv. The schematic shows the predicted carrier distribution (blue and orange areas) from the standard experimental band offsets. Following localized surface plasmon resonance excitation, dephasing / relaxation occurs within the gold nanoparticle, leading to a shift in the Fermi level (E F ) electrons occupying the above states are generated. Some of these electrons are scattered to the lowest unoccupied molecular orbital (LUMO) state of the adsorbed O2, and O2 ·- is formed. O2 is formed simultaneously or temporarily. ·- is a singlet oxygen ( via Dexter-type electron exchange (blue and orange arrows). 1O2) promotes the production of photons. The higher the photon energy potential, the 1 O2 production increases further. However, this process requires a photon energy of at least 2.86 eV. Otherwise, charge carriers primarily recombine. (b) Two degenerate 2pπ states showing the triplet ground state (bottom image) and singlet excited state (top image) of O2. * Occupied and spin states of electrons in antibonding orbitals. Triplet ground state ( 3 Σ g - In the O2 molecule (indicated by π * It has two unpaired electrons with parallel spins of +1 / 2 (upper red arrows) in an antibonding orbital. One electron is transferred to the πx electron carrier through a Dexter-type electron exchange process between the photoexcited gold nanoparticle and the O2 molecule, as depicted in panel (a). * orbit (blue dotted arrow) and other electrons move to πy * It is extracted from the orbit (orange dotted arrow). Therefore, 3 Σ g - The state is 0.98 eV (94.5 kJ mol) higher than the ground state. -1 ) main singlet state with higher energy ( 1 Δ g ) is excited. The solid arrows indicate the direction of the electron spin, with +1 / 2 pointing upward and -1 / 2 pointing downward. (c) Energy diagram of the oxidation reaction of methane driven by plasmon excitation as the reaction progresses. It is promoted by the band transition of gold nanoparticles. 1 The promotion of O2 increases the energy of the reactant by 94.5 kJ mol -1 It increases to . Then, 1 O2 species combines with free CH4 molecules. During this interaction, 1 The energy barrier governing the oxidation reaction of methane with O2 is 119.3 kJ mol according to the Eley-Rideal mechanism. -1 (ΔG ‡dark ) is 24.8 ± 3.9 kJ mol; theoretically predicted -1 (ΔG ‡ light is observed to decrease (determined experimentally). This decrease results in the selective formation of HCOOH.

[0093] conclusion

[0094] Based on the present invention, the inventors propose a novel mechanism for the partial oxidation of methane. This mechanism focuses on the generation of singlet oxygen through spin transfer of triplet oxygen, which represents a departure from the radical-mediated process discussed previously. Specifically, as shown in Figure 5c, the band-to-band transition of gold nanoparticles induces the sensitization of O2 from the triplet ground state to the singlet state. 1 The O2 species has an energy barrier of 24.8 ± 3.9 kJ mol for the reaction. -1 By lowering the spin selection rule between singlet CH4 and triplet O2 molecules, we overcome the constraints. As a result, 1 The generation of O2 leads to an oxidative interaction with nearby CH4 molecules, resulting in the highly selective production of HCOOH (>97%) under suitable conditions, while limiting CO2 production to less than 1%. This process follows the Eley-Rideal model and exhibits a significant dependence on the O2 concentration. The overall mechanism depends on the photon energy, which determines the chemical potential of charge carriers generated through interband transitions in gold nanoparticles. These observations highlight the role of surface plasmon resonance-driven catalysis in controlling partial oxidation and product distribution.

[0095] Experimental example

[0096] Preparation of gold nanoparticles supported on SiO2. AuCl using NaBH4 as a reducing agent. 4- Anion Au 0Gold nanoparticles were fixed on the surface of SiO2 by direct reduction. Specifically, 1.0 g of SiO2 powder (particle size range: approximately 0.5–5 μm, Samchun, model number S0170) was added to 100 mL of deionized (DI) water in a 250 mL beaker. After stirring the solution for 20 min, 0.1 g mL was added to deposit 1 wt% of gold nanoparticles. -1 A 204.5 μL aqueous stock solution of HAuCl4·3H2O (≥ 99.9% purity, supplied by Sigma-Aldrich, model number 520918-1G) was added to the SiO2 suspension while maintaining continuous stirring. The mixture was gradually adjusted to pH 2.0 by adding 0.1 M HNO3 solution (≥ 68.0-70.0% purity, Samchun, model number N1056) and stirred for an additional 1 h. Subsequently, 50 mL of 0.01 M NaBH4 (> 98.0% purity, supplied by Samchun, model number S2032) solution was added dropwise to the pH-adjusted mixture. At this stage, the color of the colloidal solution changed from pale yellow to deep purple. The suspension was further stirred for 3 h. The resulting solution was then evenly distributed into six 50 mL conical tubes (SPL, model number 50050). To ensure uniform weight distribution across all tubes, DI water was added to each tube based on the weight of the heaviest tube. The total volume was maintained at less than 40 mL. The tubes were centrifuged at 10,000 rpm (equivalent to 15,596 g) for 15 minutes. The supernatant from the tubes was decanted into a separate waste container. Next, 40 mL of DI water was added to the tube containing the sediment, which was redispersed in the water by vortexing and sonication. The tubes were then subjected to three additional centrifugation and supernatant extraction cycles. The final sediment was dried overnight at 80°C. The dried mass was collected and ground into a fine powder using an agate mortar and pestle.

[0097] Analysis. Transmission electron microscopy (TEM) analysis was performed using a JEOL JEM-2100F instrument operating at an accelerating voltage of 200 kV. Micrographs were taken in bright-field mode using a charge-coupled device (CCD) camera. For TEM imaging of gold nanoparticles, a small amount (approximately 15 mg) of Au / SiO2 powder was dispersed in ethanol by sonication for 15 minutes. The colloidal droplets were then deposited on a 400-mesh Cu grid coated with an ultrathin carbon film (Ted Pella). The grid was then dried in an oven at 80°C for more than 12 hours. Micrographs were analyzed using Digital Micrograph software to determine the size of the gold nanoparticles. The particle size distribution, represented as a histogram, was fitted using a Gaussian function in OriginPro software to confirm the particle size distribution. X-ray diffraction (XRD) patterns were obtained using a Rigaku SmartLab X-ray diffractometer operating at 50 kV and 100 mA using Cu Kα radiation at a wavelength of 1.54 Å. Patterns were acquired at a step size of 0.02° and a resolution of 3° min -1The XRD patterns of the samples were recorded in the 2θ range of 20° to 80° at a scan rate of 1000 s. The XRD patterns of the samples were compared with those obtained from the International Center for Diffraction Data (ICDD). The gold content was quantified using a Thermo Fisher Scientific iCAP PRO XP Duo inductively coupled plasma-optical emission spectrometer (ICP-OES). The diffuse reflectance of the solid powder samples was measured using a Shimadzu UV-3600i Plus UV-vis spectrophotometer equipped with an integrating sphere covering the wavelength range of 300–800 nm. Prior to the sample measurement, the detector was calibrated with BaSO4 (ultrapure water, Nacalai Tesque, model number 03834-55). For liquid samples, the samples were placed in quartz cuvettes with a path length of 10 mm. The samples and reference samples were positioned so that the dual beams from the dual monochromator could pass through both specimens. The sample spectra were measured simultaneously with the baseline to allow real-time correction for potential instrumental variations and solvent-related contributions to the sample spectra.

[0098] Photocatalytic CH4 oxidation reaction (CH4OR). Methane oxidation was performed in a jacketed photoreaction cell with a capacity of 150 mL. 100 mg of catalyst was loaded onto a 47 mm diameter, 0.45 mm thick ultrafine borosilicate glass substrate (Chmlab, GF5) without chemical additives. This process resulted in a final diameter of 2 cm (area of ​​3.14 cm). 2) and a fixed catalyst layer with a thickness of 0.58 ± 0.02 (SD) mm was produced. The prepared substrate was placed in a photoreaction cell, and a cross-shaped stirring bar was used underneath to assist gas convection. The cell was sealed using a rubber septum, and a 5-mm-thick circular quartz window was fixed on top with an O-ring. Then, the inside of the reactor was purged with a feed gas mixture consisting of CH4 and O2 balanced with helium (He) at a total flow rate of 20 standard cubic centimeters per minute (sccm) for 20 min. The composition of the gas mixture was controlled through a digital mass flow controller (MKP VIC-D210) connected to gas cylinders of CH4 (> 99.999% purity), O2 (> 99.999% purity), and He (> 99.999% purity). The concentration of the mixture gas was controlled by controlling the flow rates of each gas. The reactor was then placed on a stirrer in the dark and allowed to equilibrate for 30 min. From this point on, a temperature-controlled cooling or heating fluid was circulated through the jacket of the photoreaction cell to maintain the desired temperature until the photoreaction was complete. The experimental setup is shown in Figure 8. The photoreaction was initiated by illuminating the prepared reaction cell with a collimated beam from a Newport 300 W Xe arc lamp (model 6258) equipped with a condenser lens. For light energy-dependent experiments, a long-pass edge filter (Edmund) was installed on the arc lamp to selectively attenuate wavelengths shorter than 345, 400, 455, and 530 nm in the irradiating light. The average irradiance was measured using a digital power meter console (ThorLabs PM100D) connected to a thermal power sensor (ThorLabs S425C). The incident light was transmitted from above through a quartz window on the photocatalyst substrate. The intensity of the incident light was modulated by varying the distance from the lamp.Gas components within the reaction cell were periodically analyzed using a Shimadzu GC-2030 system equipped with a barrier discharge ionization detector (BID) and a YL6500 gas chromatograph (GC) system equipped with a flame ionization detector (FID). All experiments were performed at least three times to ensure the robustness and reliability of subsequent data analysis.

[0099] GC data analysis. Component peaks in the GC chromatogram were identified by comparing their retention times with those of established standards. Specifically, oxygenated products, i.e., HCOOH and CH3CHO, were cross-validated using the characteristic patterns of fragment ions (Figures 9a and 9b) generated using an Agilent 6890N GC system equipped with a 5975B series mass-selective detector (MSD). Each peak was integrated using a designated function within the GC software. If a component (e.g., CO2) was present in the chromatogram obtained prior to the reaction (i.e., reaction time t = 0), the peak area recorded at subsequent time intervals was subtracted from the area measured at t = 0. This subtraction procedure can result in negative peak areas when the GC signal approaches the background noise level, potentially due to instrumental measurement inaccuracies. In such circumstances, the amount of species produced during methane oxidation was considered zero. The measured peak areas were substituted into a calibration curve equation obtained using standard samples of a specific concentration. This allowed the calculation of the number of moles of compound present in the sample. The amount of detected components was converted to their concentrations within the reactor by considering the ratio of the internal reactor volume to the volume injected into the GC system. To account for the cumulative loss of each component within the reactor due to sample injection for GC measurements, the aforementioned calculations accounted for sample loss during the GC measurement. This correction was implemented to determine the actual amount of sample present in the reactor at a given time. The CH4 conversion (%) was calculated by dividing the amount of CH4 consumed by the amount of CH4 fed (i.e., the difference between the initial and final measurements) and multiplying the result by 100. If a product was present in the sample, the amount in moles was divided by the grams of gold nanoparticles. This serves as a measure of catalytic activity, similar to the turnover rate, which quantifies the number of substrate molecules converted to product per active site.The production rate was obtained from the slope of a linear regression applied to a time-course plot depicting the amount of each product versus reaction time. This linear interval was chosen based on the results of an 80-h long-term photoreaction (Fig. 10). The percent selectivity for each product was calculated by multiplying the ratio of the production rate of a specific product to the overall production rate of all products in the methane oxidation reaction by 100. The apparent activation energy, E, was calculated. app is the slope of the natural logarithm of the reaction rate linearly with respect to the reciprocal of the temperature (-E app / R, where R is the gas constant, i.e. 8.314 J mol -1 K -1 ) was determined from. The experimentally determined production rate of the major product HCOOH with >97% selectivity under optimized conditions was used in these calculations. All data analyses were performed using the average results derived from at least three experimental runs performed under identical conditions and the corresponding standard error of the mean for this set of experiments.

[0100] Singlet oxygen ( 1 O2) detection. 1 O2 was detected by the bleaching reaction of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA; ≥ 90% purity, Sigma-Aldrich, model number 75068-50MG). ABDA, an anthracene derivative, was present in a 1:1 stoichiometry. 1 It reacts with O2 to form the corresponding endoperoxide (ABDA- 1 O2) is formed. This reaction resulted in a decrease in the characteristic anthracene absorption band, which is typically observed between 300 and 410 nm. The molar concentration C of ABDA was determined using the Beer-Lambert law.

[0101]

[0102] Here, A represents the absorbance recorded at 399 nm, and ε is the extinction coefficient of ABDA at this wavelength (11,990 M -1 cm-1 ) represents the path length of the solution in the UV-vis spectrophotometer cuvette (10 mm). Molar concentration is given in a given volume of ABDA solution. 1 It was used to determine the amount of O2. The reagent solution of ABDA was prepared in dimethyl sulfoxide (DMSO), and an aliquot was introduced into deionized water to produce a concentration of 80 μM. The resulting ABDA solution exhibited an initial absorbance close to 1 at 399 nm. In the plan of this experimental example, 1 O2 detection was performed using the same setup used for the photocatalytic methane oxidation reaction. However, 4 mL of the reagent solution and a cross-shaped stir bar were added before introducing the photocatalytic substrate into the photoreaction cell. The ABDA solution did not come into direct contact with the photocatalytic substrate. After this step, the procedure was identical to that described in the photocatalytic methane oxidation reaction section. The reaction cell was sealed and purged with a gas mixture consisting of 4% (v / v) CH4, 60% (v / v) O2, and the remainder helium. The reactor was then placed on a stir plate in the dark and allowed to stabilize for 30 min. From this point on, the cell temperature was maintained at 25°C by circulating fluid through the jacket of the photoreaction cell. Wavelength-dependent experiments were performed by exposing the system to light with wavelengths greater than 420, 455, 495, or 550 nm. This illumination was provided by a Newport 300 W Xe arc lamp with the same down-flow configuration used for the photocatalytic methane oxidation reaction. ABDA self-decomposes when exposed to wavelengths shorter than 420 nm. The intensity of the incident light was controlled by adjusting the distance from the light source. After 4 hours of exposure, the ABDA solution in the reactor was transferred to a quartz cuvette and an absorbance spectrum was acquired. To ensure reliability, the test was performed at least three times in the same manner. The resulting absorbance spectrum shows characteristic absorption bands of ABDA in the range of 300–410 nm. A decrease in the intensity of these absorption bands compared to those measured before the photoreaction indicates that ABDA is1 It indicates that it was converted into endoperoxide by O2 in the gas phase. 1 The lifespan of O2 is known to be on the order of a few seconds. Consequently, the generated 1 It is reasonable that some of the O2 is dissolved in the ABDA solution while illuminating the photocatalyst, thereby cooling the ABDA. The generated 1 The number of moles of O2 is the observed change in ABDA concentration and the reaction with ABDA. 1 It was estimated based on the stoichiometric relationship between O2. However, this estimation does not include the dissolved oxygen in the solution. 1 Only the number of O2 moles was considered. Therefore, the derived amount represents a conservative lower limit and is generated in this system. 1 The actual amount of O2 is likely to be higher.

[0103] Figure 6. TEM images of gold nanoparticles supported on SiO2 particles with a gold nanoparticle content of 0.92 wt%. Gold nanoparticles were deposited on the SiO2 surface via direct reduction using NaBH4 as a reducing agent without the use of additional additives such as ligands or capping agents. (a-d) The scale bar is 100 nm. (e-h) The scale bar is 50 nm.

[0104] Figure 7. Histogram and Gaussian fitting curve showing the size distribution of gold nanoparticles. A total of 79 samples were randomly selected from the TEM images of Au / SiO2, including those shown in Figures 1b and 6, for size analysis of gold nanoparticles. The diameter of each individual gold nanoparticle was estimated using Digital Micrograph software under the assumption of a quasi-circular plane, and the average diameter of the gold nanoparticles was measured to be 35.9 ± 26.9 (SD) nm.

[0105] Figure 8. Photograph of the experimental reactor setup for photocatalytic methane oxidation. The setup consists of the following components: (1) a quartz window, (2) an O-ring, (3) a clamp, (4) a 150-mL borosilicate reactor body, (5) a photocatalyst-loaded substrate, (6) a jacket wall, (7) a rubber diaphragm, and (8) a circulating fluid inlet (the outlet is located on the opposite side). The incident light is positioned at the top of the photoreactor.

[0106] Figure 9. Mass fragmentation patterns of (a) HCOOH (measurements indicated by blue bars) and (b) CH3CHO (measurements indicated by red bars) oxidized products sampled during 24-h gold nanoparticle photocatalytic methane oxidation. The photoreaction was performed using gold nanoparticles in a gas mixture of 4% (v / v) CH4 and 60% (v / v) O2, the remainder being helium, at 298 K and 1 atm pressure. The gold nanoparticles were exposed to light with energies less than 3.60 eV at a dose of 1.0 W cm for 24 h. -2 were exposed to the same dose. For comparison, reference fragmentation patterns (gray bars) of HCOOH and CH3CHO from the National Institute of Standards and Technology (NIST) Chemistry Webbook are provided in panels (a) and (b), respectively.

[0107] Figure 10. Long-term methane oxidation experiment and experimental kinetic model. (a) HCOOH (blue circles, left y-axis (mmol g)) as a function of illumination time -1 h -1 Units)) and CH3CHO (orange squares; μmol g -1 h -1 (b) Production rates of additional products, CO2 (gray diamonds) and H2 (yellow triangles), detected in the same set of reactions as in panel (a) as a function of illumination time. These rates are expressed in μmol g for appropriate comparison. -1 h -1 mmol g instead -1 h -1The y-axis scale is indicated in units. (c) The cumulative selectivity (%) of each product produced in the methane oxidation reaction during the illumination period is determined from the relative amounts of each product. This photoreaction was performed using gold nanoparticles in a gas mixture of 3.8% (i.e., 3.8 kPa) CH4 and 59.3% (i.e., 60.0 kPa) O2, with the remainder being helium, at 298 K and 1 atm pressure. The gold nanoparticles were exposed to light with energies less than 3.60 eV for 80 h at a power of 1.0 W cm -2 was exposed to the amount of investigation. A detailed discussion can be found in other examples described below.

[0108] Fig. 11. Energy less than 3.60 eV and 1.0 W cm -2 TEM images of 0.92 wt% gold nanoparticles used in the photocatalytic methane oxidation reaction performed under ambient light conditions for 80 h (Fig. 10). (a-g) The scale bar is 200 nm. (h) The scale bar is 100 nm.

[0109] Figure 12. Histogram and Gaussian fitting curve showing the size distribution of gold nanoparticles after 80 hours of photocatalytic methane oxidation. A total of 62 samples were randomly selected from the TEM images of Au / SiO2, including the sample shown in Figure 11, for size analysis of the gold nanoparticles. The diameter of each individual gold nanoparticle was estimated using Digital Micrograph software under the assumption of a quasi-circular shape in a plane. This evaluation revealed an average diameter of 41.8 ± 22.4 (SD) nm. Given the limited number of samples, TEM analysis alone is not sufficient to confirm the size change of the gold nanoparticles. We additionally performed UV-vis absorption (Figure 13) and PXRD (Figure 14) measurements of the Au / SiO2 bulk powder after 80 hours of photocatalytic methane oxidation.

[0110] Figure 13. UV-vis absorption spectra of Au / SiO2 before (orange curve) and after 80 h of photoreaction (blue curve). The gold nanoparticle content is 0.92 wt%. These measurements were performed using a UV-vis diffuse reflectance spectrophotometer equipped with an integrating sphere. The vertical dashed line indicates the peak position of the surface plasmon resonance band located at 520 nm.

[0111] Figure 14. X-ray crystal structure studies. (a) Experimental PXRD patterns of SiO2 (blue curve), Au / SiO2 pre-photoreaction (orange curve), and Au / SiO2 after 80 h of photoreaction (gray curve). Spectra are displayed in vertically stacked format without baseline subtraction or normalization. The scale bar represents 500,000 counts s. -1 corresponds to the height of the (111) and (200) planes, respectively. (b) A zoomed-in pattern from panel (a) in the range of 37° to 45° to allow for proper comparison of the two major peaks (38.2° and 44.4°) appearing around 2θ corresponding to gold nanoparticles on the (111) and (200) planes, respectively. The spectra are presented in raw form without baseline subtraction or normalization. The scale bar represents 5,000 counts s. -1 corresponds to the height of the . For reference, stick patterns for ICDD standard SiO2 (blue bars) and Au (orange bars) are included. A detailed description of the PXRD data analysis can be found in other examples described below.

[0112] Figure 15. Linear scale plots showing the production rates of (a) HCOOH, (b) CH3CHO, (c) CO2, and (d) H2 as a function of O2 pressure while maintaining a constant pressure of 4.3 ± 0.4 kPa CH4. This photoreaction was performed using gold nanoparticles in gaseous mixtures of CH4 and O2 with various compositions under a pressure of 1 atm at 298 K. The gold nanoparticles were irradiated with light of energy less than 3.60 eV for 8 h at a dose of 1.0 W cm -2were exposed to a dose of . The fitting parameter n, which represents the order of the pseudo-response to O2 concentration, was determined using a power function fitting of the form y = axn (shown as a dotted line). Each plot is accompanied by R, which serves as a measure of goodness of fit. 2 The fitted equations are shown with the values. The n values ​​were 0.20 for HCOOH, 0.16 for CH3CHO, and 0.17 for CO2. The fit to the H2 production rate is relatively low with R 2 This yields a value of -0.02, indicating a low confidence level for the estimated n-value for H2. Each data point is the mean derived from at least three experiments performed under identical conditions. Error bars represent the standard error of the mean for this set of trials. A log-scale plot of these dynamics is shown in Figure 3a.

[0113] Figure 16. Linear scale plots showing the production rates of (a) HCOOH, (b) CH3CHO, (c) CO2, and (d) H2 as a function of CH4 pressure while maintaining a constant pressure of 2.3 ± 0.4 kPa O2.

[0114] This photoreaction was performed using gold nanoparticles in a gas mixture of CH4 and O2 with various compositions under 1 atm pressure at 298 K. The gold nanoparticles were exposed to light with energy less than 3.60 eV at a dose of 1.0 W cm for 8 h. -2 was exposed to the amount of y = bx m The power function fitting in the form (shown as a dotted line) determines the fitting parameter m, which represents the pseudo-reaction order of CH4 concentration. Each plot is shown with R, which serves as a measure of goodness of fit. 2 The fitted equations are shown with the values. The relatively low R obtained from the fitting results for the production rates of all products 2The values ​​indicate a relatively low confidence level for the estimated m value. This result stems from the weak correlation between production rate and CH4 concentration. Consequently, the m value is considered zero. Each data point is the average determined from at least three experiments performed under identical conditions. Error bars represent the standard error of the mean for this set of trials. A log-scale plot of these dynamics is shown in Figure 3b.

[0115] Figure 17. UV-vis absorption spectra of the ABDA reagent solution before photoreaction (orange curve) and 4 h after photoreaction as a function of the incident light energy. The measurements were performed in the same top-down configuration as the setup used for the photocatalytic methane oxidation reaction. This involved using gold nanoparticles in a gas mixture of 4% (v / v) CH4 and 60% (v / v) O2, the remainder being helium, at 298 K and 1 atm pressure. The gold nanoparticles were irradiated for 4 h at 1.0 W cm 2 by light of various energies, particularly light less than (a) 2.95, (b) 2.73, (c) 2.51, and (d) 2.25 eV. -2 The spectrum was investigated with the help of a 1:1 stoichiometry. The spectrum shows characteristic absorption bands of ABDA in the range of 300–410 nm. The ABDA solution self-decomposes when exposed to wavelengths below 420 nm. The decrease in intensity of these absorption bands compared to that measured before the photoreaction is due to the 1:1 stoichiometry. 1 It indicates that ABDA is converted to endoperoxide by O2. The observed change in ABDA concentration is generated from 1 The moles of O2 were estimated, and the results are shown in Figure 4a. Each data point is the average of at least three experiments performed under identical conditions. Error bars represent the standard error of the mean for this set of trials.

[0116] Figure 18. UV-vis absorption spectra of the ABDA reagent solution before photoreaction (orange curve) and 4 h after photoreaction with varying incident light irradiance. These measurements were performed in the same top-down configuration as the setup used for photocatalytic methane oxidation. This involved using gold nanoparticles in a gas mixture of 4% (v / v) CH4 and 60% (v / v) O2, the remainder being helium, at 298 K and 1 atm pressure. The gold nanoparticles were exposed to irradiances of 0 (i.e., dark reaction), 0.4, 0.7, and 1.0 Wcm for 4 h. -2 was illuminated by light with energy less than 2.95 eV at various irradiances. The spectra show characteristic absorption bands of ABDA in the range of 300–410 nm. The ABDA solution self-decomposes when exposed to wavelengths less than 420 nm. The decrease in intensity of these absorption bands compared to that measured before the photoreaction is due to the 1:1 stoichiometry. 1 It indicates that ABDA is converted to endoperoxide by O2. The observed change in ABDA concentration is generated from 1 The molar amount of O2 was estimated, and the results are shown in Figure 4b. Each data point is the average determined from at least three experiments performed under identical conditions. The error bars represent the standard error of the mean for this set of trials.

[0117] Determination of time-dependent concentrations of methane oxidase products in methane oxidation reactions

[0118] Consider the following sequential scheme for converting CH4 to HCOOH (Fig. 1a):

[0119]

[0120] In this reaction, the formation of HCOOH occurs through the formation and decay of two intermediate species: CH3OH (designated I1) and HCHO (designated I2). The sequential reaction scheme in Equation (5) is assumed to involve a series of first-order elementary reactions. Accordingly, the differential rate equations for each species are as follows:

[0121]

[0122]

[0123]

[0124]

[0125] Given that [I1] and [I2] vary little with time t, their time derivatives are approximately zero. Applying this steady-state approximation to I1 in the example reaction yields the following expression for [I1]:

[0126]

[0127]

[0128] Equation (11) is the result of integrating the differential rate expression for [CH4] under the initial condition [CH4]0≠0, and all other initial concentrations are zero. In the steady-state approximation, the expression corresponding to [I2] is:

[0129]

[0130]

[0131] Finally, the differential expression for HCOOH is:

[0132]

[0133] Integrating equation (14) yields the expression for [HCOOH]:

[0134]

[0135] According to equation (15), [HCOOH] is predicted to exhibit apparent kinetics consistent with the first-order decay of CH4. Similar logic applies to CH3CHO, for which the steady-state approximation holds true.

[0136]

[0137] Figure 10 shows a comparison between experimental kinetic data and numerically predicted data (dashed line) using a steady-state approximation for sequential reactions. The parameters are the Box-Lucas model y = a(1 - e -bx ) was determined using the exponential function, and for HCOOH, a = 83.8 mmol and b = 0.485 h -1 , for CH3CHO, a = 53.0 μmol and b = 0.317 h -1 It produces.

[0138] Calculation of the crystal size of gold nanoparticles

[0139] PXRD patterns of Au / SiO2 before and after 80 h of photoreaction were obtained (Fig. 14a). With respect to the SiO2 particles, the Au / SiO2 composite exhibits four additional peaks at 2θ = 38.2°, 44.3°, 64.6°, and 77.5°, corresponding to the (111), (200), (220), and (311) planes of the space group Fm-3m(225), respectively, indicating gold nanoparticles with a face-centered cubic (fcc) crystal structure. Analysis of the peak widths and positions of the planes allows the determination of the corresponding crystal size using the Scherrer equation (equation (17)), which relates the line broadening pattern to the size.

[0140]

[0141] Hered hkl where is the average crystallite size in the direction perpendicular to the lattice plane, hkl is the Miller index of the plane under analysis, K is a dimensionless numerical factor, also called the crystallite shape factor (0.94; assumed for a spherical crystal with a cubic unit cell), λ is the incident wavelength of the X-ray source (0.15406 nm), β is the full width at half maximum (FWHM) of the XRD peak in radians, and θ is the Bragg diffraction angle in radians. We calculated two major peaks associated with the (111) and (200) planes (Fig. 14b). The relevant parameters are listed in the table below:

[0142]

[0143] a- 1 degree is equal to 0.01745 rad, i.e. 1° = 0.01745 rad.

[0144] b- The number in parentheses indicates the precision uncertainty for the same number of least significant figures.

[0145] The results in the far right column of the table show that the dimensional change of the (111) plane is minimal, while the (200) crystal plane shows an increase of approximately 5% before and after the photoreaction.

[0146] Comparison of methane oxidation by gold nanoparticles supported on different carriers

[0147] Figure 19 shows the comparative results of methane oxidation by gold nanoparticles supported on different carriers. In Figure 19, q-SiO2 represents quartz crystalline silica, and a-SiO2 represents amorphous silica. Referring to Figure 19, the HCOOH product selectivity is approximately 97% for q-SiO2 and 99.9% for a-SiO2. All photoreactions were performed in a gas mixture of 3.8% (i.e., 3.8 kPa) CH4, 59.3% (i.e., 60.0 kPa) O2, and the remainder helium at 298 K and 1 atm, and the amount of photoreaction products produced for 1 hour was compared.

[0148] Comparison of methane oxidation reactions promoted by Au, Ag, and Cu nanoparticles

[0149] Figure 20 shows the comparative results of methane oxidation reactions promoted by Au, Ag, and Cu nanoparticles. All photoreactions were performed in a gas mixture of 3.8% (i.e., 3.8 kPa) CH4 and 59.3% (i.e., 60.0 kPa) O2 in balance with He at 298 K and 1 atm, and the amount of photoreaction products produced for 1 hour was compared. Referring to Figure 20, it can be confirmed that the amount of methane oxidation products is high in the order of gold, copper (Cu), and silver (Ag), and while trace amounts of H2, CO2, and CH3CHO are produced, HCOOH accounts for the majority of the product, confirming that the reaction of the present invention has high selectivity.

[0150] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below.

Claims

1. A support; and metal nanoparticles formed on the support; When light is irradiated on the above metal nanoparticles, the reaction of producing methane oxidant from methane is promoted by plasmon resonance. Metal catalyst.

2. In paragraph 1, The support comprises SiO2, Al2O3, TiO2 or WO3. Metal catalyst.

3. In paragraph 1, The above metal nanoparticles include gold (Au), silver (Ag) or copper (Cu). Metal catalyst.

4. In paragraph 1, The above metal nanoparticles have a size of 1 to 100 nm. Metal catalyst.

5. In paragraph 1, The above metal catalyst has a maximum absorption wavelength at a wavelength of 510 to 530 nm. Metal catalyst.

6. In paragraph 1, The oxidants of the above methane include methanol (CH3OH), formaldehyde (HCHO), formic acid (HCOOH), or acetaldehyde (CH3CHO). Metal catalyst.

7. A method for obtaining an oxidized form of methane from methane, A method comprising the step of irradiating light to a metal catalyst while exposing or flowing methane gas to the metal catalyst according to any one of claims 1 to 6. A method for producing a methane oxidase from methane.

8. Using the method of Article 7, The oxidizer of the above methane is obtained in a liquid phase, Methane resource utilization method.

9. A reactor capable of injecting or flowing a reaction gas containing methane into the interior; a metal catalyst positioned within the reactor; and A light source capable of irradiating light onto the metal catalyst; The above metal catalyst is a metal catalyst according to any one of claims 1 to 6. Methane removal and resource recovery unit.

10. In paragraph 9, The above methane removal and resource recovery device removes and resources methane generated from livestock, factories, garbage, fuel gas, natural gas, sewage, or wetlands. Methane removal and resource recovery unit.

11. In paragraph 9, The above methane removal and resource recovery device further includes a collection unit for obtaining the oxidant of methane obtained in the reactor in a liquid phase. Methane removal and resource recovery unit.

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