A single metal atom that enables photomodification of hydrogen vectors

Abstract

The method is provided for photoreforming a large amount of low-molecular-weight hydrogen vector using a single-atom metal or semimetallic catalyst to produce hydrogen and value-added by-products.

Description

Technical Field

[0001] The present invention relates to a method for photo-reforming one or more abundant low molecular weight hydrogen vectors in the presence of a light-absorbing single metal atom enabler. The low molecular weight hydrogen vector may be represented as MH where M = C, N, or O. In this method, both hydrogen and valuable carbon, nitrogen, and oxygen-containing co-products (or co-products) are generated. The present invention also relates to a method for producing hydrogen and a catalyst useful in the production of hydrogen and such co-products. In particular, the present invention relates to a method for photo-reforming hydrogen vectors using a single metal atom catalyst. X As described above.

Background Art

[0002] Hydrogen is the basis for the transition from the use of fossil fuels to sustainable energy. Unlike fossil fuels, hydrogen combustion simply generates water and heat, so hydrogen is a very attractive alternative energy source for achieving goals related to de-carbonization and de-fossilization. However, despite the potential benefits resulting from the transition to hydrogen, there are important issues related to the transportation and storage of hydrogen, mainly due to the difficulty of liquefying hydrogen, its high flammability and tendency to leak, and the significant risk of forming an explosive mixture with air.

[0003] To address these problems, hydrogen vectors can be used as a means of storing, transporting, and releasing hydrogen. Hydrogen vectors are stable compounds that can safely and easily store and release hydrogen. Examples of these vectors include methane (CH4), ethane (C2H6), ammonia (NH3), and water (H2O). These low-molecular-weight compounds can store hydrogen and release it on demand through catalytic reforming or dissociation processes. Methods used to convert these hydrogen vectors back into hydrogen generally involve thermochemical, electrochemical, or photochemical reactions requiring some form, varying degrees of energy input. The required energy can come from non-renewable sources such as natural gas or coal, or from renewable sources such as solar or wind energy. Regardless of the source, many conventional conversion processes require high temperatures and the associated high energy input, and depending on the source and process, carbon, CO, and / or CO2 can become undesirable byproducts if not properly recovered.

[0004] In one embodiment, the present invention is a hydrogen production process or method using a photocatalyst.

[0005] Catalysts are crucial for the photocatalytic production of hydrogen from a hydrogen vector. By definition, a catalyst is a substance that facilitates a chemical reaction without being consumed. In photocatalysis, the catalyst takes photons from light and converts them into charge carriers and / or heat, which then excite reactants at a surface-active center, triggering a chemical change with an effective and / or low-energy barrier. In reported hydrogen-producing photocatalysts, the catalyst consists of a light absorber and a catalytic center attached to a solid support. Typically, the light absorber includes metal nanoparticles that can strongly absorb photons through plasmon effects, such as Au, Cu, and Ag. These catalysts help decompose the hydrogen vector, releasing hydrogen gas and other co-products, such as carbon from methane, nitrogen from ammonia, and oxygen from water.

[0006] For example, U.S. Patent No. 10766024 discloses a multicomponent photocatalyst comprising a plasmon material and a reactive component optically, electronically, or thermally coupled; a method for carrying out a catalytic reaction comprising filling a reaction chamber with the multicomponent photocatalyst comprising a plasmon material and a reactive component optically, electronically, or thermally coupled; supplying molecular reactants to the reaction chamber; and irradiating the reaction chamber with a light source. The plasmon material is a metal incorporated into a bulk metal structure that imparts the ability to promote plasmons to the metal. A single metal atom cannot have plasmons.

[0007] Regardless of their effectiveness, conventional metal nanoparticle photocatalysts have several drawbacks. For example, plasmon nanoparticles only allow the outermost surface atoms to react, and considering the number of active sites or atoms of the metal used, this leads to inefficiencies such as reduced conversion or yield, and decreased atomic efficiency. Furthermore, plasmon metals are usually expensive, and high loading amounts of 20% or more are typically required to achieve satisfactory results. In addition, the electronic properties of these metal nanoparticles can worsen catalytic activity efficiency due to collective electronic effects that are not optimized for specific reactions. [Overview of the project]

[0008] Unlike metal nanoparticle catalysts, single-atom catalysts (SACs) generally consist of individual metal atoms dispersed on a solid support and offer several advantages over conventional multi-atom catalysts used in prior art. SACs significantly reduce the cost of metal loading, catalyst material, and conversion processes by maximizing the atomic efficiency of each metal atom. The unique electronic properties of a single metal atom can be fine-tuned with coordination elements and coordination numbers to optimize specific reactions, enabling those particular reactions to be highly efficient for the target catalytic process.

[0009] In terms of hydrogen production by the process or method of the present invention, single-atom catalysts are highly promising for photoreforming hydrogen vectors by reducing catalyst costs while maintaining high efficiency for specific reactions. Furthermore, single-atom catalysts eliminate the possibility of plasmon effects, which are collective oscillations of free electrons typically observed in metal nanoparticles. While plasmon effects can enhance certain catalytic reactions, they are not always beneficial and introduce complexity that reduces overall efficiency. The absence of plasmon effects in single-atom catalysts leads to more predictable and controllable catalytic behavior, simplifying reaction dynamics and making them particularly useful in the photoreformation of low-molecular-weight hydrogen vectors.

[0010] The development of single-atom catalysts for the photoreformation of hydrogen vectors represents a significant advance in hydrogen production technology. By addressing the limitations of conventional multi-atom catalysts, single-atom catalysts offer a more effective, sustainable, and safer method for generating hydrogen. This invention leverages the unique properties of a single metal atom to enhance catalytic performance, presenting a novel approach to hydrogen production that aligns with global sustainability goals.

[0011] The present invention offers advantages over known prior art by using a single metal atom attached to a solid support instead of a metal particle catalyst for photomodifying a hydrogen vector into hydrogen and value-added co-products. The present invention is characterized by the following: The process or method of the present invention comprises the use of a single metal atom attached to a solid support, the single atom including transition metal atoms and main-group atoms such as Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Os, Ir, Pt, Au, Sn, Pb, Sb, Bi, N, P, F, and S.

[0012] The use of such single metal atoms and light allows these photoreformation reactions to proceed in a way that enables the conversion of hydrogen vectors into co-products of hydrogen and value-added carbon, nitrogen, and oxygen.

[0013] By using a single-metal atom catalyst that enables the photoreformation reaction of hydrogen vectors according to the present invention, instead of known polymetallic atomic particles of the prior art, (i) atomic efficiency, (ii) orbital efficiency, (iii) surface area efficiency, and (iv) cost efficiency are improved.

[0014] Furthermore, the localized variance electrons of a single metal atom attached to a solid support do not induce collective electron plasmon resonance, which is only possible with the delocalized electrons found in polymetallic atomic particles described in the prior art. Therefore, the single-metal enablers on solid supports described in this book are entirely different from all known plasmon polymetallic atomic particles and differ in their use for photomodification of hydrogen vectors.

[0015] The photoactivity of these single-metal atom enablers is believed to originate from the electronic effects of excited states associated with localized electrons in the single metal atom. This differs from the collective multi-electron effect of delocalized electrons in plasmon polymetallic atom particles used for the photomodification of hydrogen vectors in conventional techniques. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a conceptual diagram of a single-atom catalyst that enables photoreformation of hydrogen vectors. The single-atom catalyst consists of a single atom arranged on a solid support, and the hydrogen vectors described include CH4, NH3, H2O, and C2H6. [Figure 2] Figure 2 shows a scanning transmission electron microscope image of the Ru1 / CARBON1 catalyst, where Ru atoms (bright dots) dispersed on the carbon support can be seen. [Figure 3]Figure 3 shows the on-stream H2 generation rates for single-metal atom (Ru1) carbon-supported catalysts and nanoparticle (RuNP) carbon-supported catalysts under NH3 flow rate of 2 sccm and light intensities of 0–48 suns. Figure 3 confirms that single-atom catalysts are stable and highly efficient in reforming ammonia to H2. In a flow catalytic reactor, the light intensity was increased from 0 (dark) to 48 suns (bright), and then gradually decreased to 39, 31, 26, 21, and 17. [Figure 4] Figure 4 shows the relative H2 generation rates under steady state for Ru1 carbon-supported catalysts and nanoparticle (RuNP) carbon-supported catalysts. Figure 4 confirms that single-atom catalysts have higher atomic efficiency than nanoparticle (RuNP) catalysts. [Figure 5] Figure 5 shows the on-stream H2 generation rate for a single metal atom (Fe1) carbon-supported catalyst under NH3 flow rate of 2 sccm and light intensity of 0–48 suns. Figure 5 confirms that a single iron atom is stable and highly efficient in reforming ammonia to H2. In a flow catalytic reactor, the light intensity was increased from 0 (dark) to 48 suns (bright), and then gradually decreased to 39, 31, 26, 21, and 17. [Figure 6] Figure 6 shows the production rates of photocatalytic ethane conversion to ethylene for single metal atom (Ru1)-supported carbon catalysts and particle (RuNP)-supported carbon catalysts at a flow rate of 2.2 sccm under a light intensity of 48 suns. [Modes for carrying out the invention]

[0017] According to the present invention, a process or method for photomodifying one or more low molecular weight hydrogen vectors is achieved by exposing such vectors to a light source in the presence of a light-absorbing single metal or semimetal atom catalyst dispersed on a solid support.

[0018] The single metal or metalloid atom may be one of the metal or metalloid elements in the periodic table. In some embodiments, the single metal or metalloid atom catalyst is selected from the group consisting of Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Os, Ir, Pt, Au, Sn, Pb, Sb, Bi, N, P, F, S, and B. The single metal or metalloid atom catalyst may be a metal. In some embodiments, the single metal or metalloid atom catalyst is selected from the group consisting of Ru and Fe.

[0019] The solid support may be an insulator or a semiconductor. In some embodiments, the solid support may be in the form of a metal oxide, nitride, sulfide, phosphide, boride, silicide, carbide, a mixture of silicon and carbon, or a doped form.

[0020] The single atom metal or metalloid catalyst is prepared by dispersing and arranging single atoms of the selected metal or metalloid catalyst on a solid support. Such a prepared catalyst with a solid support is used in a reactor into which a low molecular weight hydrogen vector is introduced. In some embodiments, the low molecular weight hydrogen vector may be selected from the group consisting of organic alkanes, linear or cyclic alcohols, or ethers. In other embodiments, the low molecular weight hydrogen vector may be selected from the group consisting of ethane, hydrogen sulfide, methane, ammonia, and water. In a further embodiment, the low molecular weight hydrogen vector is selected from the group consisting of ethane, methane, ammonia, and water. In a further embodiment, one or more low molecular weight hydrogen vectors include a mixture of one or more of ethane, methane, ammonia, and water.

[0021] The surface of the solid support is irradiated with light having an intensity in the range of about 10 to about 50 suns, which may be supplied by sunlight, by a light emitting diode source, or by other artificial light sources. In some embodiments, the light intensity may be in the range of about 1 to about 50 W cm-1, or about 10 to about 50 W cm-1. The intensity of the light may be adjusted optically or electronically to obtain the desired result. The wavelength of the light may be in the range from ultraviolet through the visible spectrum to the infrared spectrum.

[0022] The resulting gas stream may be separated by conventional means to separate hydrogen gas from the co-products of the photoreforming process.

[0023] In some embodiments, by photoreforming a low molecular weight hydrogen vector, the hydrogen vector dissociates into gaseous hydrogen separable therefrom and co-products of the photoreforming process.

[0024] The process or method of the present invention can be more easily understood by referring to the following specific embodiments.

[0025] [Synthesis of Single-Atom Catalysts] The synthesis of single-atom catalysts, such as Ru1 / CARBON, can be carried out using the obtained carbon by pyrolysis of biomass at a temperature of 5,00 - 1,800 K using base chemicals, for example, in an inert atmosphere. Subsequently, the obtained carbon is washed and dried at 273 - 473 K to give a product designated as CARBON1. CARBON1 is mixed with base chemicals in an inert atmosphere and the carbon obtained by pyrolyzing again is designated as CARBON2. A 300 mg carbon sample is dispersed in a 1 wt% solution of tris(acetylacetonato)Ru(III) with stirring for 24 hours, then washed several times with water, and dried and calcined at 400 °C or higher to prepare a catalyst sample. The obtained catalysts were designated as Ru1 / CARBON1 and Ru1 / CARBON2. As shown in Figure 2, it was confirmed by scanning transmission electron microscope images that Ru atoms are primitively dispersed on the carbon support at the nanoscale. This is different from the nanoparticle catalysts used in the reported prior art.

[0026] The prepared catalyst was tested in a laboratory-scale reactor. This reactor may have a stainless steel reactor body with one or more quartz glass windows arranged around it, and valves to control the inflow of gas into and outflow of the reactor body. The quartz glass windows of the reactor allow light from a Xe lamp or simulated solar light to irradiate the surface of the carbon support where the single-atom catalyst is dispersed within the reactor, thereby promoting photoreformation of the hydrogen vector. For laboratory-scale reactors, a thermocouple thermometer and a pressure gauge may be connected. In one embodiment, it was used with a 300W Xe lamp from a Perfect Light® solar simulator. A Newport® power meter with an 18 mm detector spot diameter may also be used. Light intensity was changed by manually changing the power to the Xe lamp. Further adjustments to achieve the desired intensity may also be made by changing the light intensity, for example, by changing the light spot diameter when using a focusing lens.

[0027] Prepared carbons, such as CARBON1 and CARBON2, may be set by placing them on the bed of the reactor.

[0028] [Photomodification of ammonia] According to one embodiment of the present invention, a single Ru atom (Ru1) on carbon (CARBON1 and CARBON2) is used to obtain 9-5000 mmol H2 / g Ru With an extremely high conversion rate per hour, it is possible to reform ammonia into hydrogen under atmospheric pressure.

[0029] Following this process, the activity of catalysts Ru1-CARBON1 and Ru1-CARBON2 was evaluated by placing a known amount of catalyst in a reactor and repeatedly running tests (runs) while varying the light intensity by flowing an ammonia-containing gas fluid through the reactor at a flow rate of 2 sccm and atmospheric pressure. The light intensity was increased from 0 (dark) to 48 suns (bright) in the reactor, and then gradually decreased to 39, 31, 26, 21, and 17. This process was repeated for Ru nanoparticle catalysts within the same light intensity range. Metal-free carbon was used as a control.

[0030] As shown in Figure 3, 13-48 suns (kW / m 2 The conversion rate increases at light intensities within the range of ). In particular, the activity of the single-atom Ru catalyst supported on CARBON1 was found to be superior to that of the Ru nanoparticle (RuNP) catalyst across the entire light intensity range, being 5-10 times higher.

[0031] In contrast, the activity of the single-atom Ru catalyst supported on CARBON2 was 2-3 times that of the Ru nanoparticle (RuNP) catalyst at 39-48 suns and 17-26 suns, respectively, but the Ru nanoparticle catalyst was slightly superior to the single-atom catalyst at a moderate light intensity of 26-31 suns (Figure 4).

[0032] Furthermore, as observed for both the Ru catalyst supported on CARBON1 carbon and the Ru catalyst supported on CARBON2 carbon, the single Ru metal atom catalyst exhibited better durability, i.e., it could withstand higher light intensities than the nanoparticle catalyst. Extending this, under 48 suns, the RuNP-carbon nanoparticle catalyst became inactive as the reaction progressed, while the Ru1-carbon single atom catalyst showed a gradual increase in activity and stabilized within 1.5 hours. The highest ammonia conversion yield was approximately 15% observed with Ru nanoparticles supported on CARBON2 when irradiated under 48 suns. However, the single metal atom catalyst had significantly higher atomic efficiency than its nanoparticle counterparts. As a result, the single metal atom catalyst can be prepared and manufactured at a very low cost.

[0033] [Fe single-atom catalyst for ammonia] By using the iron (Fe) active site, it is possible to explain the efficiency of other transition metal atoms and main group atoms. Two samples, Fe1-CARBON1 and Fe1-CARBON2, were prepared using the above method for preparing Ru catalysts, except that tris(acetylacetonate)Fe(III) was used instead of tris(acetylacetonate)Ru(III).

[0034] Under an ammonia flow rate of 2 sccm and 48 suns, the hydrogen evolution activity of both Fe1-CARBON1 and Fe1-CARBON2 was 9000 mmol H2 / g Fe Approximately 45 mmol H2 / g, equivalent to / h catalyst The activity was 2000 / h at 39, 31, 26, 21, and 17 suns, respectively, for 2000, 120, 20, 20, and 20 mmol H2 / g. Fe The level decreased to below / h. The results are shown in Figure 5, confirming that the single-atom iron catalyst is effective and stable for reforming ammonia to H2.

[0035] Single metal atoms can enable similar photoreform reactions for methane and water. Gaseous products in the reforming of ammonia (nitrogen and hydrogen) and water (hydrogen and oxygen) can be separated by a selective permeable membrane incorporated into the reactor or by other methods known to those skilled in the art. As mentioned above, a characteristic unique to single metal atom catalysts, compared to nanoparticle metal catalysts, is that the plasmonic collective electron character in the latter cannot be achieved with the localized electron properties of the former.

[0036] [Dehydrogenation of ethane to ethylene] A single Ru atom catalyst (Ru1) on a carbon support can be used to dehydrogenate ethane to ethylene under LED light at atmospheric pressure. In particular, as shown in Figure 6, the activity of the carbon-supported single-atom Ru catalyst in converting ethane to ethylene at an intensity of 48 suns and a flow rate of 2.2 sccm surpassed that of the Ru nanoparticle (RuNP) catalyst, showing a three-fold increase in activity. The single-atom catalyst also exhibited greater activity stability. With the single-atom Ru catalyst, ethylene production increased and then decreased. However, with the Ru nanoparticle (RuNP) catalyst, the activity consistently decreased.

Claims

1. A method for photomodifying one or more low molecular weight hydrogen vectors, characterized by exposing such vectors to a light source in the presence of a light-absorbing single metal or semimetal atom catalyst dispersed on a solid support.

2. The method according to claim 1, characterized in that the low molecular weight hydrogen vector is selected from the group consisting of organic alkanes, linear or cyclic alcohols, or ethers.

3. The method according to claim 1, characterized in that the low molecular weight hydrogen vector is selected from the group consisting of ethane, hydrogen sulfide, methane, ammonia, and water.

4. The method according to claim 1, characterized in that the low molecular weight hydrogen vector is selected from the group consisting of ethane, methane, ammonia, and water.

5. The method according to claim 1, wherein the one or more low molecular weight hydrogen vectors include a mixture of one or more ethane, methane, ammonia, and water.

6. The method according to any one of 1 to 3, characterized in that the low molecular weight hydrogen vector is dissociated into separable gaseous hydrogen and co-products by photomodification.

7. The method according to any one of claims 1 to 3, characterized in that the single metal or metalloid atom described in claim 1 may be one of the metal or metalloid elements of the periodic table.

8. The method according to claim 1, characterized in that the single metal or metalloid atom catalyst is selected from the group consisting of Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Os, Ir, Pt, Au, Sn, Pb, Sb, Bi, N, P, F, S, and B.

9. The method according to claim 1, characterized in that the single metal or metalloid atom catalyst is a metal.

10. The method according to claim 1, characterized in that the single metal or metalloid atom catalyst is selected from the group consisting of Ru and Fe.

11. The photomodification of the aforementioned low molecular weight hydrogen vector is performed at approximately 1 to approximately 50 W / cm². －１ The method according to any one of 1 to 3, characterized in that it is performed under light intensity within the range.

12. The photomodification of the aforementioned low molecular weight hydrogen vector is performed at approximately 10 to 50 W / cm². －１ The method according to any one of 1 to 3, characterized in that it is performed under light intensity within the range.

13. The method according to any one of 1 to 3, characterized in that the light is supplied by sunlight, a light-emitting diode, or another artificial light source.

14. The method according to any one of 1 to 3, characterized in that the wavelength of the light may be in the range from the ultraviolet spectrum through the visible spectrum to the infrared spectrum.

15. The method according to any one of 1 to 3, characterized in that the solid carrier may be an insulator or a semiconductor.

16. The method according to any one of 1 to 3, characterized in that the solid carrier may be a mixture or doped form of metal oxides, nitrides, sulfides, phosphides, borides, silicides, carbides, silicon, and carbon.

Images