Carbon dioxide conversion catalyst and method for producing the same

Abstract

The present invention relates to a carbon dioxide conversion catalyst including a protective layer formed on its surface. By controlling the surface coverage of the catalyst particles by the protective layer, the selectivity for high-value hydrocarbons with 5 or more carbon atoms can be increased in the carbon dioxide conversion reaction, while maintaining a high carbon dioxide conversion rate.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2023-0123490 dated September 15, 2023, and all content disclosed in the documents of the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a novel carbon dioxide conversion catalyst that can increase the selectivity of hydrocarbons having 5 or more carbon atoms in a reaction that converts carbon dioxide to hydrocarbons, and to a method for producing the same. [Background technology]

[0003] Since carbon dioxide accounts for a large proportion of greenhouse gases, technologies to reduce the amount of carbon dioxide in the atmosphere are being researched in various fields. Typically, carbon capture and storage (CCS) technologies, which capture and store carbon dioxide, and carbon capture and utilization (CCU) technologies, which capture carbon dioxide and then utilize it in other fields, are being researched using various methods.

[0004] Of the two categories of carbon dioxide treatment technologies mentioned above, a representative example of a CCU technology that goes beyond simply storing captured carbon dioxide and can be utilized is a technology that produces economically valuable hydrocarbons from captured carbon dioxide. Methods that can produce hydrocarbons from carbon dioxide include electrochemical, photochemical, and thermochemical methods. However, electrochemical and photochemical methods have difficulty producing long-chain hydrocarbons and have low carbon dioxide conversion rates, so more in-depth research is needed before they can be actually applied to industrial fields. On the other hand, thermochemical methods produce various hydrocarbon gases from carbon dioxide using various catalysts under high temperature and a hydrogen atmosphere, and because they have a higher carbon dioxide conversion rate compared to the two methods mentioned above, they are currently the most widely used method.

[0005] The reaction to produce hydrocarbons from carbon dioxide is generally known to consist of two sequential reactions. The first reaction is the conversion of carbon dioxide to carbon monoxide via a reverse water-gas shift (RWGS) reaction, and the second reaction is the conversion of the carbon monoxide produced in the first reaction to hydrocarbons via a Fischer-Tropsch reaction. The first reaction is endothermic, while the second reaction is exothermic. A large amount of energy is required to efficiently carry out the first reaction, but in the second reaction, the reaction heat must be rapidly removed to prevent catalyst sintering and deactivation. Therefore, due to the characteristics of such a two-stage reaction, efficiently operating the reaction process is by no means easy. In particular, if the reaction heat generated during the second reaction process is not quickly removed, the reaction heat can accumulate inside the catalyst particles, causing a sintering phenomenon where the catalyst particles aggregate, leading to a degradation problem where the activity of the catalyst itself decreases, and potentially reducing the selectivity of the target hydrocarbon.

[0006] Known methods to address these issues include controlling the reactivity of the catalyst layer by using inert supports or particles along with catalyst particles when converting carbon dioxide using a fixed-bed reactor, or by using catalysts with new structures and properties. However, the former method has the problem of side effects caused by the inert supports or particles used, and newly developed catalysts have not yet achieved results that satisfy both aspects: the conversion rate of carbon dioxide and the selectivity of high-carbon hydrocarbons.

[0007] Therefore, there is a need to develop a novel catalyst that can produce hydrocarbons from carbon dioxide without requiring another two-stage reaction process, while also satisfying two aspects: the conversion rate of carbon dioxide and the selectivity of high-carbon hydrocarbons. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] KR10-2023-0040742A [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to solve the above problems by introducing a thin and uniform protective layer on the surface of metal catalyst particles by atomic film deposition, and by optimizing the proportion of the catalyst particle surface covered by such protective layer. This invention aims to provide a novel carbon dioxide conversion catalyst that minimizes sintering at high temperatures and can produce high-carbon hydrocarbons, particularly those with 5 or more carbon atoms, with high selectivity. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides a novel carbon dioxide conversion catalyst, a method for producing the same, and a carbon dioxide conversion method using the catalyst.

[0011] Specifically, (1) the present invention provides a carbon dioxide conversion catalyst comprising Fe-based catalyst particles and a protective layer formed on the surface of the catalyst particles, wherein the coverage rate of the surface of the catalyst particles by the protective layer is 10 to 90%, and the protective layer comprises Al, Ce, Cu, Co, Mo, oxides or nitrides thereof.

[0012] (2) The present invention provides the carbon dioxide conversion catalyst described in (1) above, wherein the thickness of the protective layer is 0.5 to 10 nm.

[0013] (3) The present invention relates to a surface area of ​​catalyst particles not covered by the protective layer that is 0.05 to 2 m². 2 The present invention provides a carbon dioxide conversion catalyst according to (1) or (2) above, wherein the concentration is / g.

[0014] (4) The present invention relates to a catalyst having a specific surface area of ​​1 to 250 m². 2Provided is a carbon dioxide conversion catalyst according to any one of (1) to (3) above, which is / g.

[0015] (5) The present invention provides a carbon dioxide conversion catalyst according to any one of (1) to (4) above, wherein the content of the protective layer based on the total weight of the catalyst is 1 to 50% by weight.

[0016] (6) The present invention provides a carbon dioxide conversion catalyst according to any one of (1) to (5) above, wherein the Fe-based catalyst particles are Fe bulk catalysts or catalyst particles in which Fe is supported as an active component on a support.

[0017] (7) The present invention provides a carbon dioxide conversion catalyst according to any one of (1) to (6) above, wherein the Fe-based catalyst particles are Fe bulk catalysts, and the coverage rate of the surface of the catalyst particles by the protective layer is 30% or more and 90% or less.

[0018] (8) The present invention provides a carbon dioxide conversion catalyst according to any one of (1) to (7) above, wherein the support is alumina or silica.

[0019] (9) The present invention provides a carbon dioxide conversion catalyst according to any one of (1) to (8) above, wherein the Fe-based catalyst particles are Fe / Si, and the coverage rate of the surface of the catalyst particles by the protective layer is 10% or more and 20% or less.

[0020] (10) The present invention provides a carbon dioxide conversion catalyst according to any one of (1) to (9) above, wherein the Fe-based catalyst particles are Fe / γ-Al, and the coverage rate of the surface of the catalyst particles by the protective layer is 5% or more and 15% or less.

[0021] (11) The present invention provides a carbon dioxide conversion catalyst according to any one of (1) to (10) above, wherein the Fe-based catalyst particles are Fe / δ-Al, and the coverage rate of the surface of the catalyst particles by the protective layer is 20% or more and 30% or less.

[0022] (12) The present invention provides a catalyst for carbon dioxide conversion according to any one of (1) to (11) above, wherein the Fe-based catalyst particles are catalyst particles in which Fe is supported as an active component on a support, and one or more selected from Na, K, and Cu are further supported as a promoter component.

[0023] (13) The present invention provides a catalyst for carbon dioxide conversion according to any one of (1) to (12) above, wherein the Fe-based catalyst particles are Fe / K / Cu / Si, and the coverage rate of the surface of the catalyst particles by the protective layer is 10% or more and 50% or less.

[0024] (14) The present invention provides a method for producing a catalyst according to any one of (1) to (13) above, including a step of forming a protective layer on the surface of Fe-based catalyst particles by atomic film deposition.

[0025] (15) The present invention provides a method for converting carbon dioxide, including a step of heating a reaction gas containing carbon dioxide to synthesize a mixed hydrocarbon gas in the presence of the catalyst according to any one of (1) to (13) above.

Advantages of the Invention

[0026] The carbon dioxide conversion catalyst of the present invention has a structure in which a part of the surface of the catalyst particles showing catalytic activity is covered by a thin and uniform protective layer, so that it exhibits excellent catalytic activity, and the sintering phenomenon at high temperatures is suppressed, and carbon dioxide can be stably and efficiently converted into hydrocarbons. In particular, among hydrocarbons, hydrocarbons having 5 or more carbon atoms and high added value can be produced with high selectivity.

Brief Description of the Drawings

[0027] [Figure 1] It is a diagram for observing the change in the morphology of the catalyst of Example 4-3 of the present invention and the catalyst of Comparative Example 4 before and after heat treatment.

Embodiments for Carrying Out the Invention

[0028] The present invention will be described in more detail below.

[0029] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0030] Catalysts for carbon dioxide conversion The present invention provides a carbon dioxide conversion catalyst comprising Fe-based catalyst particles and a protective layer formed on the surface of the catalyst particles, wherein the coverage rate of the surface of the catalyst particles by the protective layer is 10 to 90%, and the protective layer contains Al, Ce, Cu, Co, Mo, or oxides or nitrides thereof.

[0031] As mentioned above, the reaction to convert carbon dioxide to hydrocarbons is carried out in two steps, and Fe-based catalysts are known to exhibit relatively superior activity in both of these steps. However, when Fe-based catalyst particles are used as is, their activity decreases due to sintering of the catalyst during the reaction process, resulting in the drawback that one or more of the above-mentioned selectivity and conversion rate are not sufficiently high to be satisfactory. To overcome this drawback, the present invention introduces a thin and uniform protective layer covering a portion of the surface of Fe-based catalyst particles by atomic layer deposition (ALD). This protective layer enhances the high-temperature stability of the catalyst itself, and also provides a novel carbon dioxide conversion catalyst that can obtain hydrocarbons with a relatively high addition value of 5 or more carbon atoms with high selectivity among the hydrocarbon mixture ultimately produced.

[0032] The catalyst of the present invention will be described in more detail below.

[0033] Fe-based catalyst particles Fe-based catalyst particles refer to catalyst particles containing iron (Fe) that have been used in conventional carbon dioxide conversion reactions. The activity of these Fe-based catalyst particles enables the conversion of carbon dioxide into hydrocarbons.

[0034] More specifically, the Fe-based catalyst particles may be an Fe bulk catalyst or catalyst particles on which Fe is supported as an active component on a support. The Fe bulk catalyst means a catalyst composed solely of Fe-based components, which are the active components, without the need for another support. More specifically, Fe metal or a compound containing Fe can be used as the bulk catalyst.

[0035] On the other hand, if the Fe-based catalyst particles are catalyst particles on which Fe is supported as an active component on a support, the support may be alumina or silica. These types of support have a large specific surface area, which is advantageous for supporting the active component, and are particularly excellent in terms of catalytic activity and durability when Fe is supported on them.

[0036] Furthermore, if the Fe-based catalyst particles are catalyst particles in which Fe is supported as an active component on a support, co-catalyst components may be supported together with the active component Fe for the purpose of further increasing the catalytic activity of the active component, and one or more co-catalyst components selected from Na, K, and Cu may be used.

[0037] The Fe-based catalyst particles may be in the form of secondary particles formed by the aggregation of multiple primary particles. The primary particles may be nanoparticles with a diameter in the nanometer range, and more specifically, the diameter of the primary particles may be 100 nm or less, particularly preferably 80 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, or 30 nm or less, and may also be 1 nm or more, 3 nm or more, 5 nm or more, or 10 nm or more. Furthermore, the diameter of the secondary particles formed by the aggregation of multiple primary particles may be 10 μm or more, more preferably 30 μm or more, 50 μm or more, 70 μm or more, or 100 μm or more, and may also be 1,000 μm or less, 800 μm or less, 600 μm or less, or 500 μm or less. When the diameters of the primary and secondary particles of the Fe-based catalyst particles are within the above ranges, a balance is appropriate in terms of mechanical strength and catalytic activity.

[0038] protective layer The protective layer covers a portion of the surface of the catalyst particles, thereby suppressing catalyst sintering during the carbon dioxide conversion reaction process, and thus improving the carbon dioxide conversion rate and the selectivity of high-carbon hydrocarbons.

[0039] More specifically, when a protective layer is formed on the surface of the catalyst particles by atomic film deposition, the protective layer is thin and uniform in thickness, and is formed in a shape that covers only a portion of the surface of the catalyst particles. However, when the percentage of the catalyst particle surface covered by the protective layer, i.e., the coverage rate, is adjusted to a range of 10-90%, the conversion rate of carbon dioxide by the catalyst is improved, and the selectivity of high-carbon hydrocarbons also increases. Although the specific mechanism of this effect is not clear, it was expected that the effect in terms of selectivity would decrease because the surface area that exhibits activity becomes smaller when the catalyst surface is covered by the protective layer. However, as in the present invention, when the coverage rate is set within a specific range, it has been confirmed that not only the conversion rate, which is expected to be improved by the protective layer, but also the selectivity is actually improved.

[0040] Furthermore, the coverage rate may vary depending on the type and composition of the Fe-based catalyst particles. More specifically, if the pore size inside the Fe-based catalyst particles is small, some pores may become clogged during the formation of the protective layer, resulting in a low coverage rate. Conversely, if the pore size inside the Fe-based catalyst particles is large, a high coverage rate may be observed after the formation of the protective layer. Moreover, the coverage rate may be adjusted by changing the process conditions during the formation of the protective layer. More specifically, if a thick protective layer is formed, the thickened protective layer may clog some pores, resulting in a low coverage rate. Conversely, if a thin protective layer is formed, the coverage rate can be adjusted over a wide range.

[0041] As mentioned above, the coverage rate varies depending on the type and composition of the Fe-based catalyst particles, and may be between 10% and 90%. If the Fe-based catalyst particles include a support, the coverage rate is 10% or more, and may be 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, or 30%. On the other hand, if the Fe-based catalyst particles are a bulk catalyst without a support, the coverage rate is 10% or more, 20% or more, 30% or more, or 35% or more, and may be 90% or less. More specifically, if the Fe-based catalyst particles are Fe / Si, the coverage rate may be between 10% and 20%. If the Fe-based catalyst particles are Fe / γ-Al, the coverage rate may be between 5% and 15%. If the Fe-based catalyst particles are Fe / δ-Al, the coverage rate may be between 20% and 30%. When the Fe-based catalyst particles are Fe / K / Cu / Si, the coverage range may be 10% or more and 50% or less, preferably 10% or more and 50% or less, 45% or less, 40% or less, 35% or less, or 30% or less. When the coverage is within the above range, excellent selectivity for high-carbon hydrocarbons and carbon dioxide conversion rate can be achieved.

[0042] On the other hand, the "coverage rate" can be calculated by dividing the content of the protective layer by (thickness of the protective layer (coating layer) * specific surface area of ​​the catalyst * theoretical true density of the protective layer). In the above formula, the theoretical true density of the protective layer refers to the theoretical value known as the density of the components that form the protective layer.

[0043] Further, the protective layer may contain Al, Ce, Cu, Co, Mo, their oxides or nitrides. The above components can, without reducing the catalytic activity of the Fe-based catalyst particles, be excellent in high-temperature and mechanical stability, and enable the performance to be sufficiently maintained even when the catalyst is used under high-temperature conditions. More preferably, the protective layer may contain Al. When the protective layer contains Al, its oxide or nitride, the performance of the protective layer described above can be maximized. In particular, the catalytic activity can be increased due to the surface interaction between the Fe-based catalyst particles and Al of the protective layer.

[0044] Furthermore, the thickness of the protective layer may be 0.5 to 10 nm, preferably 0.5 nm or more, 1 nm or more, 1.5 nm or more, or 2 nm or more, and may be 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, or 5 nm or less. When the thickness of the protective layer is too thin, there is a risk that the effect of the protective layer, specifically, the effect of suppressing the sintering of the catalyst at high temperature, cannot be significantly exerted. When the thickness of the protective layer is too thick, there is a risk that the catalytic activity will instead decrease. On the other hand, in the present invention, controlling the thickness of the protective layer within the above-described thin range and making it uniform is due to forming the protective layer by the atomic film deposition method. The thickness of the protective layer can be measured from the cross-sectional TEM of the manufactured catalyst.

[0045] In the catalyst of the present invention, the surface area of the surface of the catalyst particles not covered by the protective layer is 0.05 to 2 m 2 / g, preferably 0.05 m 2 / g or more, 0.07 m 2 / g or more, or 0.1 m 2 / g or more, and 2 m 2 / g or less, 1.8 m 2 / g or less, or 1.5 m 2 / g or less. When the surface area of the catalyst particles not covered by the protective layer is within the above range, a sufficient degree of catalytic activity can be provided.

[0046] In the catalyst of the present invention, the specific surface area of ​​the catalyst after the protective layer is formed may vary slightly depending on the type of Fe-based catalyst particles, but is generally between 1 and 250 m². 2 It may be / g, preferably 1 to 100m 2 It may be / g. Since the catalyst of the present invention has a sufficiently large specific surface area as described above, the contact area between the catalyst and carbon dioxide is sufficiently large, and as a result, a high carbon dioxide conversion rate can be achieved.

[0047] In the catalyst of the present invention, the content of the protective layer relative to the total weight of the catalyst may be 1 to 50% by weight, preferably 2% or more by weight, 3% or more by weight, 5% or more by weight, or 10% or more by weight, and may also be 30% or less by weight, 25% or less by weight, or 23% or less by weight. When the content of the protective layer is within the above range, the improvement effect of the protective layer can be maximized.

[0048] Catalyst manufacturing method The present invention provides a method for producing the aforementioned carbon dioxide conversion catalyst. Specifically, the present invention provides a method for producing a catalyst, which includes the step of forming a protective layer on the surface of Fe-based catalyst particles by atomic film deposition.

[0049] A key technical feature of the catalyst of the present invention is the protective layer, which is formed by atomic film deposition. When using atomic film deposition, a protective layer of uniform thickness can be formed even on Fe-based catalyst particles with complex 3D morphologies, and the thickness of the protective layer can also be adjusted to be thin.

[0050] The process of forming a protective layer by atomic film deposition may be carried out by conventional methods, and may be performed by loading Fe-based catalyst particles into an atomic film deposition apparatus, injecting and depositing the protective layer raw material, oxidizing or reducing, and purging, all of which together constitute a single cycle, and repeating this cycle multiple times. In the above process, water (H2O), ozone (O3), or oxygen (O2) plasma may be injected to form a metal oxide, and hydrogen gas may be injected to form a metal layer.

[0051] Methods for converting carbon dioxide The present invention provides a method for converting carbon dioxide using the catalyst described above. More specifically, the present invention provides a method for converting carbon dioxide, comprising the step of heating a reaction gas containing carbon dioxide in the presence of the catalyst to synthesize a mixed hydrocarbon gas.

[0052] The selectivity of high-carbon hydrocarbons with 5 or more carbon atoms in the mixed hydrocarbon gas produced using the catalyst of the present invention may be 40% or more, preferably 45% or more. The catalyst of the present invention is characterized by the introduction of the aforementioned protective layer, which results in high carbon dioxide conversion rate and high selectivity of high-carbon hydrocarbons during the carbon dioxide conversion reaction using the catalyst.

[0053] The aforementioned conversion reaction can be carried out without particular limitations under conditions applicable to the thermochemical conversion reaction of carbon dioxide, and the reactor and other equipment used in the present invention are not particularly limited. Furthermore, the temperature at which the reaction takes place is not particularly limited, as long as it is a temperature at which carbon dioxide is sufficiently converted. The catalyst of the present invention has a protective layer, which minimizes the sintering phenomenon even under high-temperature conditions, and allows the carbon dioxide conversion reaction to proceed stably even at relatively high temperatures.

[0054] The present invention will be described in more detail below with reference to examples and experimental examples, but the present invention is not limited to these examples and experimental examples. The examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples herein are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0055] material Fe / Si, Fe / γ-Al, Fe / δ-Al, Fe bulk catalyst, Fe / Na, and Fe / K / Cu / Si catalyst were used as Fe-based catalyst particles. The Fe / Na catalyst refers to a catalyst in which Na, as a co-catalyst component, is added to the Fe bulk catalyst, and the Fe / K / Cu / Si catalyst refers to a catalyst in which Fe is supported as the main catalyst component and Cu and K components are supported as co-catalyst components on a Si support.

[0056] Examples and Comparative Examples 0.5 g of prepared Fe-based catalyst particles were spread onto a square tray and loaded. The tray was then placed into a chamber within the ALD equipment, and the chamber temperature was set to 150°C and the process pressure to 1 Torr. Subsequently, 20°C trimethylaluminum (TMA) was pulsed into the chamber with 100 sccm of nitrogen gas as a carrier gas for 3 seconds, maintained for 100 seconds, and then purged for 20 seconds. This process was repeated three times. After that, the chamber was purged for another 600 seconds, and water was pulsed in for 3 seconds instead of trimethylaluminum in the same process as above, maintained for 100 seconds, and then purged for 20 seconds. This process was repeated three more times. This process constituted one cycle, and by repeating the above cycle 8 to 40 times, a protective layer containing aluminum oxide was formed on the surface of the Fe-based catalyst particles.

[0057] Tables 1 and 2 below summarize the details of the catalysts produced in each example and comparative example. Example 5-2, on the other hand, had the same conditions as Example 5-1, but the amount of TMA and water added was doubled, the thickness of the protective layer remained the same, and a catalyst with a higher coverage rate was produced. Example 5-3 involved crushing and classifying the catalyst particles to reduce their size from the existing 300-500 μm to 100-300 μm, after which a protective layer was formed. In Example 5-3, as the size of the catalyst particles decreased, the exposed surface area increased, resulting in a higher coverage rate of the protective layer.

[0058] [Table 1]

[0059] [Table 2]

[0060] On the other hand, the characteristics measured in Tables 1 and 2 above were measured by the following method. 1) Thickness of the protective layer: Platinum (Pt) or carbon is deposited (sputtered) to a thickness of 100 nm onto the protective layer of the catalyst particles, followed by FIB (Focused Ion Beam) or Ar + Cross-sectional specimens were prepared using ion milling. The thickness of the catalyst layer was measured by TEM analysis of the prepared specimens. 2) Content of the protective layer: The catalyst content was confirmed by ICP component analysis, and 0.1 g of catalyst particles was dissolved in 1 ml of hydrochloric acid, then diluted 10-fold and subjected to ICP-OES analysis. On the other hand, the content of the protective layer refers to the content of Al contained only within the protective layer, excluding the Al content originating from the support. Measurement equipment: ICP-OES Agilent 5110 Measurement conditions: RF Power 1300W, Torch Height 15mm, Plasma gas flow 15L / min, Sample Gas flow 0.8L / min, Auxiliary Gas flow 0.2L / min, Pump Speed ​​1.5ml / min 3) Coverage: This was calculated using the content of the protective layer measured above, the thickness of the protective layer, the specific surface area of ​​the catalyst, and the catalyst density, and was calculated using the following formula. Coverage = Catalyst content / (Thickness of protective layer * Specific surface area of ​​catalyst * Theoretical true density of catalyst) 4) Fe surface area: After reducing the catalyst by heat treatment at 400°C for 3 hours, CO gas was injected into the reactor and the adsorbed surface area was measured. On the other hand, if the Fe surface area decreases despite an increase in the protective layer, it is confirmed that this is because the catalyst particles solidify during the reduction process, causing a decrease in the Fe surface area.

[0061] Considering the results in Tables 1 and 2, the Fe bulk catalyst, which has a relatively large internal pore size, showed a higher coverage rate compared to other catalysts. It was confirmed that as the thickness of the protective layer increased, some pores became clogged, resulting in a decrease in coverage rate. On the other hand, other catalysts using a support showed a lower coverage rate compared to the bulk catalyst due to the relatively smaller internal pore size. In all types of catalysts, it was confirmed that some pores became clogged by the formed protective layer, resulting in a decrease in the specific surface area of ​​the catalyst compared to catalysts without a protective layer.

[0062] Experimental Example 1. Measurement of conversion rate and selectivity in a carbon dioxide conversion reaction using a catalyst. Mixed hydrocarbons were produced from carbon dioxide using the catalysts prepared in Examples 5-1 to 5-3 and Comparative Example 5. Specifically, after introducing the prepared catalysts into the reactor, they were pretreated by heating to 500°C while flowing 5% CO / N2 (250 sccm) for 3 hours. Then, the temperature in the reactor was lowered to 350°C, and the reaction was carried out under a pressure of 20 bar by flowing 25% CO2 / H2 (75 sccm) for 6 hours.

[0063] The reaction products formed as a result of the reaction were passed through a constant-temperature water bath trap adjusted to 0°C to collect liquid hydrocarbons with 5 or more carbon atoms, and the gas phase products were analyzed in real time by gas chromatography. The reaction was carried out continuously for more than 48 hours.

[0064] The carbon dioxide conversion rate and the selectivity of hydrocarbons with 5 or more carbon atoms were measured / calculated using the following methods. 1) Conversion rate: Calculated using the following formula. Carbon dioxide conversion rate = (Input CO2 flow rate - Exhaust CO2 flow rate) / (Input CO2 flow rate) * 100% 2) Selectivity: Calculated using the following formula. Selectivity of gas-phase products = (C A H B Flow rate*A) / (Input CO2 flow rate - Exhaust CO2 flow rate)*100% Selectivity of liquid hydrocarbons with 5 or more carbon atoms = 100% - (sum of selectivity of gas-phase products)

[0065] The measured conversion rates and selectivity values ​​are summarized in Table 3 below.

[0066] [Table 3]

[0067] As can be seen from Table 3 above, it was confirmed that when the catalyst of the present invention was used, the carbon dioxide conversion rate and the selectivity for liquid hydrocarbons with 5 or more carbon atoms and high added value were higher compared to when the catalyst of the comparative example was used. Furthermore, although the thickness of the protective layer was the same, the aluminum content in the protective layer was higher in Examples 5-2 and 5-3, which resulted in a higher coverage rate, and even higher conversion rates and selectivity values ​​were observed than in Example 5-1. From this, it was confirmed that under the same conditions, the conversion rate and selectivity can be improved by increasing the coverage rate.

[0068] Experimental Example 2. Confirmation of changes in properties of catalysts after heat treatment. We investigated how the specific surface area of ​​the catalysts of Comparative Example 4 and Example 4-3 changed and how particle clumping occurred after heat treatment.

[0069] Specifically, each catalyst was heat-treated at 700°C for 2 hours, and the results are summarized in Figure 1.

[0070] As can be seen from Figure 1, the catalyst of Example 4-3 of the present invention showed little change in specific surface area and little particle clumping despite being heated for a long time under high temperature conditions, whereas the catalyst of Comparative Example 4 underwent a sintering phenomenon in which particles solidified, resulting in a significant decrease in specific surface area.

[0071] This confirms that the catalyst of the present invention can maintain stable performance even under high-temperature conditions by having a protective layer covering a portion of its surface.

Claims

1. Fe-based catalyst particles and The catalyst particles include a protective layer formed on the surface of the catalyst particles, The coverage rate of the catalyst particles surface by the protective layer is 10 to 90%. A carbon dioxide conversion catalyst wherein the protective layer comprises Al, Ce, Cu, Co, Mo, or oxides or nitrides thereof.

2. The carbon dioxide conversion catalyst according to claim 1, wherein the thickness of the protective layer is 0.5 to 10 nm.

3. The surface area of ​​the catalyst particles not covered by the protective layer is 0.05 to 2 m². ２ The catalyst for carbon dioxide conversion according to claim 1, wherein the concentration is / g.

4. The specific surface area of ​​the catalyst is 1 to 250 m². ２ The catalyst for carbon dioxide conversion according to claim 1, wherein the concentration is / g.

5. The carbon dioxide conversion catalyst according to claim 1, wherein the content of the protective layer, based on the total weight of the catalyst, is 1 to 50% by weight.

6. The carbon dioxide conversion catalyst according to claim 1, wherein the Fe-based catalyst particles are Fe bulk catalysts or catalyst particles on which Fe is supported as an active ingredient on a support.

7. The Fe-based catalyst particles are Fe bulk catalysts, The carbon dioxide conversion catalyst according to claim 6, wherein the coverage rate of the surface of the catalyst particles by the protective layer is 30% or more and 90% or less.

8. The carbon dioxide conversion catalyst according to claim 6, wherein the support is alumina or silica.

9. The Fe-based catalyst particles are Fe / Si, The carbon dioxide conversion catalyst according to claim 6, wherein the coverage rate of the surface of the catalyst particles by the protective layer is 10% or more and 20% or less.

10. The Fe-based catalyst particles are Fe / γ-Al, The carbon dioxide conversion catalyst according to claim 6, wherein the coverage rate of the surface of the catalyst particles by the protective layer is 5% or more and 15% or less.

11. The Fe-based catalyst particles are Fe / δ-Al, The carbon dioxide conversion catalyst according to claim 6, wherein the coverage rate of the surface of the catalyst particles by the protective layer is 20% or more and 30% or less.

12. The Fe-based catalyst particles are catalyst particles in which Fe is supported on a support as an active component. The catalyst for carbon dioxide conversion according to claim 6, wherein one or more components selected from Na, K, and Cu are further supported as co-catalyst components.

13. The Fe-based catalyst particles are Fe / K / Cu / Si, The carbon dioxide conversion catalyst according to claim 6, wherein the coverage rate of the surface of the catalyst particles by the protective layer is 10% or more and 50% or less.

14. A method for producing a catalyst according to claim 1, comprising the step of forming a protective layer on the surface of Fe-based catalyst particles by atomic film deposition.

15. A method for converting carbon dioxide, comprising the step of heating a reaction gas containing carbon dioxide in the presence of the catalyst described in claim 1 to synthesize a mixed hydrocarbon gas.

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