Patent Application
20240286119
The present invention relates to a nanocatalyst for methane dry reforming.
As greenhouse gas emissions and global warming issues have become a major concern around the world, research on ways to reduce and treat carbon dioxide emissions is actively progressing. A representative chemical method for reducing carbon dioxide is the methane-reforming reaction, which reacts carbon dioxide (CO2) and methane (CH4) to generate syngas such as CO and H2.
As a reforming reaction of methane, dry reforming of methane, unlike wet reforming of methane (steam reforming of methane; reaction of natural gas and water), has the advantage of producing syngas of great industrial value because the H2/CO ratio is close to 1.
Reaction Equation (1) below represents a dry reforming reaction of methane with carbon dioxide.
CH4+CO2→2CO+2H2 (1)
During dry reforming of methane in Reaction Equation (1), the following side reactions occur together.
CO2+H2→CO+H2O (2)
2CO→C+CO2 (3)
CO+H2→C+H2O (4)
CH4→C+H2 (5)
CO2→C+O2 (6)
Thermodynamically, the methane dry reforming in Reaction Equation (1) proceeds spontaneously at 640° C. or higher, while the reverse water gas shift reaction in Reaction Equation (2) and the Boudouard reaction in Reaction Equation (3) proceed spontaneously at 815° C. and 710° C. or lower, respectively. Therefore, in order to suppress side reactions and allow the syngas conversion reaction to predominantly occur, a methane dry reforming reaction needs to be performed at a high temperature of 700° C. or higher.
Depending on the reaction conditions, a carbon precipitation reaction as shown in Reaction Equations (3) to (6) may occur, in particular, carbon deposition occurs easily in nickel-based catalysts, leading to rapid deactivation of the catalyst. On the other hand, when using a noble metal catalyst, resistance to carbon deposition increases, but economic feasibility becomes an issue due to the high price. Therefore, in order to commercialize methane dry reforming technology, it is necessary to develop a cost-competitive catalyst that has a high syngas conversion rate and carbon deposition inhibition ability.
As the dispersion of the catalyst formed on the ceramic support increases, the utilization rate of the material increases. In other words, since the thermochemical reaction occurs on the surface of the catalyst, the finer and more uniformly distributed the catalyst is on the surface of the support, the greater the effect may be achieved with a small amount. However, as the size of the catalyst gets smaller, the tendency to agglomerate becomes stronger, which intensifies the problem of thermal stability in a high-temperature reaction. Accordingly, there is a need for a catalyst for methane dry reforming that is stable at high temperature while having catalyst particles finely distributed on the surface of the ceramic support.
The present invention is directed to providing a catalyst for methane dry reforming, which has high catalytic activity and is stable for a long time even when operated at high temperature.
According to an aspect of the present invention, there is provided a nanocatalyst for methane dry reforming, which has a fluorite structure represented by the following Chemical Formula 1 and has a plurality of transition metal or noble metal particles dispersed on a surface thereof:
A1-aCeaO2-δ [Chemical Formula 1]
in Chemical Formula 1, A is selected from rare earth elements excluding Ce, and a and δ are real numbers of 0<a<1 and 0≤δ≤1, respectively.
A catalyst of the present invention has a high conversion rate because the transition metal or noble metal particles are uniformly distributed on the surface of the catalyst. In addition, since the transition metal or noble metal particles form strong bonds in an ionic state, agglomeration does not occur at high temperatures, and the risk of carbon deposition is significantly low, so excellent conversion rates can be maintained even when used at high temperatures for a long period of time. In addition, the catalyst of the present invention can be prepared by a chemical solution synthesis method that is simple and easy to mass produce. When methane dry reforming is applied to industry in earnest, it is expected to greatly contribute to reducing greenhouse gases and efficiently producing syngas.
Hereinafter, the present invention will be described in detail.
The terms used in the present application are only used to describe specific embodiments and are not intended to limit the present invention. Unless defined otherwise, 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 the present invention belongs.
Throughout the specification, when it is said that a part “includes,” “contains,” or “has” a certain component, this means that it may further include other components, unless specifically defined otherwise.
Terms such as first and second are used to distinguish one component from another component, and the components are not limited by the above-mentioned terms.
When a part of a layer, a membrane, and the like is said to be “above’ or “on” another part, this includes not only cases where one part is in contact with another part by being “directly above” or “directly on” another part, but also cases where another part is present in the middle. Conversely, when a part is said to be ‘directly above” or “directly on” another part, it means that there are no other parts therebetween.
The nanocatalyst for methane dry reforming according to the present invention has a fluorite structure represented by the following Chemical Formula 1 and has a plurality of transition metal or noble metal particles dispersed on a surface thereof:
A1-aCeaO2-δ [Chemical Formula 1]
in Chemical Formula 1, A is selected from rare earth elements excluding Ce, and a and δ are real numbers of 0<a<1 and 0≤δ≤1, respectively.
According to one embodiment of the present invention, in Chemical Formula 1, A may be selected from the group consisting of Y, Sc, Gd, Sm, La, Nb, Nd, Pr, Yb, Er, and Tb. According to another embodiment of the present invention, in Chemical Formula 1, A may be an element selected from the lanthanide group, for example, Gd, Sm, La, Nb, Nd, Pr, Yb, Er, and Tb.
According to one embodiment of the present invention, in Chemical Formula 1, a may be a real number of 0.5≤a<1, and 6 may be a real number of 0≤δ≤0.5.
According to another embodiment of the present invention, the nanocatalyst for methane dry reforming of the present invention may have a fluorite structure represented by the following Chemical Formula 2 and have a plurality of transition metal or noble metal particles dispersed on the surface thereof:
Gd1-aCeaO2-δm [Chemical Formula 2]
in Chemical Formula 1, a and 6 are real numbers of 0<a<1 and 0≤δ≤1, respectively.
According to one embodiment of the present invention, in the nanocatalyst for methane dry reforming of the present invention, the transition metal or noble metal particle may be selected from the group consisting of Pt, Au, Ag, Pd, Ir, Rh, Ru, Pd, Os, Ni, Co, and Fe. For example, the transition metal or noble metal particle may be Pt, Au, Ag, Ni, or Co.
According to one embodiment of the present invention, the transition metal or noble metal particles may be present in an ionic state or in both an ionic and a metallic state. For example, since the transition metal or noble metal particles are present in an ionic state, they may be strongly bonded to the base material of the fluorite structure in a doped form. Accordingly, since they do not easily move even at high temperature, for example, 800° C. or higher, and the particles may maintain a fine and uniform distribution, they may maintain excellent activity for a long period of time without causing agglomeration.
According to one embodiment of the present invention, the transition metal or noble metal particles may form fine particles or atomic clusters on the surface or may be present in a single atomic state. According to one embodiment of the present invention, the transition metal or noble metal particles may have a size of 0.1 to 5 nm, for example, 0.5 to 2.5 nm. Meanwhile, in the case of the nanocatalyst of the present invention, the catalyst particle size may be 5 to 200 nm, for example, 5 to 50 nm.
According to one embodiment of the present invention, the transition metal or noble metal particles may be present in an amount of 0.1 to 10% by weight, for example, 3 to 5% by weight, based on the weight of the nanocatalyst.
According to another embodiment of the present invention, the nanocatalyst may be used at a temperature of 700° C. or higher. As can be seen from the examples described later, when the nanocatalyst according to the present invention is used for dry reforming of methane at a temperature of 700° C. or higher, CH4 and CO2 conversion rates of 70% or more may be achieved.
According to one embodiment of the present invention, the nanocatalyst may exhibit a CH4 conversion rate of 90% or more and a CO2 conversion rate of 95% or more at a temperature of 800° C. or higher.
The catalyst of the present invention may be prepared by a solution synthesis method and thus it is easy to prepare and may be applied to mass production.
According to one embodiment of the present invention, the nanocatalyst of the present invention may be prepared by a method including (a) mixing a precursor of the fluorite structure material of Chemical Formula 1 and a precursor of the transition metal or noble metal particles as a solution and (b) heat-treating the mixture.
The precursor of the fluorite structure material in step (a) may be, for example, in the form of one or more selected from ceramic nanopowder, chlorides, bromides, iodides, nitrates, nitrites, sulfates, acetates, sulfites, acetylacetonate salts, and hydroxides, but is not limited thereto. Preferably, the precursor may be in the form of a nitrate.
In step (a), the precursor of the transition metal or noble metal particles may be, for example, in the form of one or more selected from metal nanopowder, chlorides, bromides, iodides, nitrates, nitrites, sulfates, acetates, sulfites, acetylacetonate salts, and hydroxides, but is not limited thereto. Preferably the precursor may be in the form of a chloride.
In step (a), water, alcohol, or a mixed solvent of water and alcohol may be used as a solvent in the solution. Here, the alcohol may be appropriately selected from alcohols having 1 to 4 carbon atoms, for example, methanol, ethanol, propanol, or butanol. An amount of solvent may be at a concentration of 0.05 to 1 M. When a mixed solvent of water and alcohol is used as the solvent, a mixing ratio between these solvents may be a volume ratio of 1:0 to 3:1 based on the volume of the total solvent.
In step (a), the solution may further contain a complexing agent in addition to the precursor of the fluorite structure material, the precursor of the transition metal or noble metal particles, and the solvent.
The complexing agent may be, for example, one or more selected from urea, melamine, diethylenetriamine, glycine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, diaminocyclohexane-N,N′-tetra-acetic acid, diethylenetriaminepentaacetic acid, and ethylene glycol-bis-(2-aminoethyl ether), but is not limited thereto. Preferably, urea may be used. In addition, an amount of the complexing agent may be 3 to 15 times that of the cations in the solution.
In step (b), the heat treatment may be performed at 50° C. to 900° C., for example, 300° C. to 900° C. or 600° C. to 900° C. The heat treatment may be divided into two or more steps so that the temperature may be reached in two or more steps, for example, five steps.
Hereinafter, the present invention will be described in more detail with reference to examples of the present invention. Since the examples are presented to explain the present invention, the present invention is not limited thereto.
Ce(NO3)3-6H2O, Gd(NO3)3-6H2O, K2PtCl4, and urea were added to distilled water and dissolved using a magnetic stirrer for about 10 minutes. Thereafter, ethanol was added and the solution was mixed using the magnetic stirrer for 10 minutes. At this time, the composition of the solution for synthesizing Pt (4 mol %)-GDC powder is shown in Table 1 below. Thereafter, the solution was heat-treated using an electric furnace according to the heat treatment schedule shown in Table 2 below to obtain Pt (4 mol %)-GDC nanocatalyst powder.
A transmission electron microscope (TEM) image of the Pt(4 wt %)/Gd0.2Ce0.8O1.9 (GDC) nanocatalyst particles prepared in the Preparation Example is shown in
The methane dry reforming characteristics of the Pt (4 wt %)/GDC catalyst were evaluated. The reactor size was a ½ inch tube and 0.2 g of catalyst was used. A composition ratio of the input gas was CH4:CO2:He=1:1.12:0.96, and the evaluation was performed under the condition of WHSV 30,000 cc/g h.
The long-term stability of the Pt (4 wt %)/GDC catalyst was evaluated at 800° C.
Although the present invention has been described above with reference to the preferred embodiments, a person having ordinary skill in the art can understand that various modifications and changes of the present invention are possible within the spirit and scope of the present invention set forth in the following patent claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2021-0086382 | Jul 2021 | KR | national |
This application is a National Stage Patent Application of PCT International Application No. PCT/KR2022/009271 (filed on Jun. 28, 2022), which claims priority to Korean Patent Application No. 10-2021-0086382 (filed on Jul. 1, 2021), which are all hereby incorporated by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/KR2022/009271 | 6/28/2022 | WO |
