Carbon dioxide conversion catalyst and method for manufacturing same

Abstract

The present invention relates to a catalyst for converting carbon dioxide, comprising a protective layer formed on the surface thereof, wherein by controlling the amount of coverage of the catalyst particle surface by the protective layer, high selectivity for high-carbon-number hydrocarbons having 5 or more carbon atoms, which have high value in carbon dioxide conversion reactions, can be achieved while maintaining the conversion rate of carbon dioxide at high levels.

Description

Carbon dioxide conversion catalyst and method for producing the same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0123490, filed September 15, 2023, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a novel carbon dioxide conversion catalyst capable of increasing the selectivity for hydrocarbons having 5 or more carbon atoms in a reaction for converting carbon dioxide into hydrocarbons, and a method for producing the same.

[0005] Carbon dioxide accounts for a significant portion of greenhouse gases, and technologies to reduce its presence in the atmosphere are being studied in various fields. Representative examples include Carbon Capture and Storage (CCS), which captures and stores carbon dioxide, and Carbon Capture and Utilization (CCU), which captures carbon dioxide and then utilizes it for other purposes.

[0006] Among the two categories of carbon dioxide treatment technologies mentioned above, the representative CCU technology that can utilize captured carbon dioxide beyond simple storage is the technology that produces economically valuable hydrocarbons from captured carbon dioxide. Methods for producing 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, requiring further research before they can be applied in actual industrial fields. On the other hand, thermochemical methods use various catalysts under high temperatures and a hydrogen atmosphere to produce various hydrocarbon gases from carbon dioxide. Compared to the two methods described above, thermochemical methods have a higher carbon dioxide conversion rate and are therefore the most widely used method at present.

[0007] It is generally known that the reaction for producing hydrocarbons from carbon dioxide consists of two consecutive reactions. The first reaction is a reaction in which carbon dioxide is converted into carbon monoxide through the reverse water gas shift (RWGS) reaction, and the second reaction is a reaction in which the carbon monoxide produced through the first reaction is converted into hydrocarbons through the Fischer-Tropsch reaction. While the first reaction is endothermic, the second reaction is exothermic. In order to efficiently perform the first reaction, a large amount of energy must be supplied, but in the second reaction, the heat of reaction must be quickly removed to prevent sintering and deactivation of the catalyst. Therefore, operating the reaction process efficiently due to the characteristics of this two-step reaction is by no means easy. In particular, if the heat of reaction generated during the second reaction process is not quickly removed, the heat of reaction may accumulate inside the catalyst particles, causing a sintering phenomenon in which the catalyst particles coagulate, and a deterioration problem in which the activity of the catalyst itself decreases may occur, resulting in a decrease in selectivity for the desired hydrocarbon.

[0008] Known methods to address these issues include controlling the reactivity of the catalyst layer by using inert supports or particles together with the catalyst particles in a fixed-bed reactor for carbon dioxide conversion, or using catalysts with novel structures and properties. However, the former approach suffers from the problem of side effects caused by the inert supports or particles used, and newly developed catalysts have not yet achieved satisfactory results in both carbon dioxide conversion and high-carbon hydrocarbon selectivity.

[0009] Therefore, there is a need to develop a novel catalyst that can produce hydrocarbons from carbon dioxide without a separate two-stage reaction process, while also achieving satisfactory results in both carbon dioxide conversion and high-carbon hydrocarbon selectivity.

[0010]

[0011] Prior art literature

[0012] (Patent Document 1) KR 10-2023-0040742 A

[0013]

[0014] The present invention is intended to solve the above-mentioned problem, and provides a novel carbon dioxide conversion catalyst capable of producing high-carbon hydrocarbons, particularly hydrocarbons having 5 or more carbon atoms, with high selectivity while minimizing sintering at high temperatures by introducing a thin and uniform protective layer on the surface of a metal catalyst particle using an atomic layer deposition method and optimizing the ratio of the surface of the catalyst particle covered by the protective layer.

[0015] In order to solve the above-mentioned problem, the present invention provides a novel carbon dioxide conversion catalyst, a method for producing the same, and a method for converting carbon dioxide using the catalyst.

[0016] Specifically, (1) the present invention provides a catalyst for carbon dioxide conversion, which comprises Fe-based catalyst particles and a protective layer formed on the surface of the catalyst particles, wherein the coverage 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, or an oxide or nitride thereof.

[0017] (2) The present invention provides a catalyst for carbon dioxide conversion in the above (1), wherein the thickness of the protective layer is 0.5 to 10 nm.

[0018] (3) In the present invention, in the above (1) or (2), the surface area of ​​the catalyst particle surface not covered by the protective layer is 0.05 to 2 m 2 / g provides a catalyst for carbon dioxide conversion.

[0019] (4) In any one of the above (1) to (3), the specific surface area of ​​the catalyst is 1 to 250 m 2 / g provides a catalyst for carbon dioxide conversion.

[0020] (5) The present invention provides a catalyst for carbon dioxide conversion, wherein the content of the protective layer based on the weight of the entire catalyst is 1 to 50 wt% in any one of (1) to (4).

[0021] (6) The present invention provides a catalyst for carbon dioxide conversion, wherein the Fe-based catalyst particles are Fe bulk catalysts or catalyst particles in which Fe is supported as an active ingredient on a support, in any one of the above (1) to (5).

[0022] (7) The present invention provides a catalyst for carbon dioxide conversion, wherein the Fe-based catalyst particles are Fe bulk catalysts in any one of the above (1) to (6), and the coverage of the surface of the catalyst particles by the protective layer is 30% or more and 90% or less.

[0023] (8) The present invention provides a catalyst for converting carbon dioxide, wherein the support is alumina or silica, in any one of (1) to (7).

[0024] (9) The present invention provides a catalyst for carbon dioxide conversion, wherein the Fe-based catalyst particles are Fe / Si, and the coverage of the surface of the catalyst particles by the protective layer is 10% or more and 20% or less, in any one of the above (1) to (8).

[0025] (10) The present invention provides a catalyst for carbon dioxide conversion, wherein the Fe-based catalyst particles are Fe / γ-Al, and the coverage of the surface of the catalyst particles by the protective layer is 5% or more and 15% or less, in any one of the above (1) to (9).

[0026] (11) The present invention provides a catalyst for carbon dioxide conversion, wherein the Fe-based catalyst particles are Fe / δ-Al, and the coverage of the surface of the catalyst particles by the protective layer is 20% or more and 30% or less, in any one of the above (1) to (10).

[0027] (12) The present invention provides a catalyst for carbon dioxide conversion, wherein the Fe-based catalyst particle is a catalyst particle in which Fe is supported as an active component on a support, and at least one selected from Na, K, and Cu is further supported as a cocatalyst component, in any one of the above (1) to (11).

[0028] (13) The present invention provides a catalyst for carbon dioxide conversion, wherein the Fe-based catalyst particles are Fe / K / Cu / Si, and the coverage of the surface of the catalyst particles by the protective layer is 10% or more and 50% or less, in any one of the above (1) to (12).

[0029] (14) The present invention provides a method for manufacturing a catalyst according to any one of (1) to (13), including a step of forming a protective layer on the surface of an Fe-based catalyst particle using an atomic layer deposition method.

[0030] (15) The present invention provides a method for converting carbon dioxide, including a step of synthesizing a mixed hydrocarbon gas by heating a reaction gas containing carbon dioxide in the presence of a catalyst according to any one of (1) to (13).

[0031] The carbon dioxide conversion catalyst of the present invention has a structure in which a portion of the surface of the catalyst particles exhibiting catalytic activity is covered with a thin and uniform protective layer, thereby exhibiting excellent catalytic activity, while suppressing sintering at high temperatures, thereby stably and efficiently converting carbon dioxide into hydrocarbons, and in particular, producing high value-added hydrocarbons having 5 or more carbon atoms with high selectivity.

[0032] Figure 1 is a diagram showing changes in the shape of the catalyst of Example 4-3 of the present invention and the catalyst of Comparative Example 4 before and after heat treatment.

[0033] Hereinafter, the present invention will be described in more detail.

[0034] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0035]

[0036] Catalyst for carbon dioxide conversion

[0037] The present invention provides a catalyst for carbon dioxide conversion, comprising Fe-based catalyst particles and a protective layer formed on the surface of the catalyst particles, wherein the coverage 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, or an oxide or nitride thereof.

[0038]

[0039] As explained above, the reaction of converting carbon dioxide into hydrocarbons is carried out in a two-step reaction, and it is known that the Fe-based catalyst exhibits relatively excellent activity in both of these reactions. However, when Fe-based catalyst particles are used as they are, the activity decreases due to sintering of the catalyst during the reaction process, and thus, at least one of the selectivity and conversion rate mentioned above is not sufficiently high to be satisfied. To overcome this drawback, the present invention introduces a thin and uniform protective layer covering a portion of the surface of the Fe-based catalyst particles using atomic layer deposition (ALD). Through the action of this protective layer, the high-temperature stability of the catalyst itself can be increased, and a novel catalyst for carbon dioxide conversion can be provided that can obtain a high selectivity for high-carbon hydrocarbons having a carbon number of 5 or more, which are relatively high in added value among the hydrocarbon mixture ultimately produced.

[0040]

[0041] Hereinafter, the catalyst of the present invention will be described in more detail.

[0042]

[0043] Fe-based catalyst particles

[0044] Fe-based catalyst particles refer to catalyst particles containing Fe, which have been conventionally used in carbon dioxide conversion reactions. A reaction of converting carbon dioxide into hydrocarbons can be performed by the activity of the Fe-based catalyst particles.

[0045] More specifically, the Fe-based catalyst particles may be Fe bulk catalysts or catalyst particles in which Fe is supported as an active ingredient on a support. The Fe bulk catalyst refers to a catalyst composed only of an Fe-based component as an active ingredient without a separate support. More specifically, Fe metal or a compound containing Fe may be used as the bulk catalyst.

[0046] Meanwhile, when the Fe-based catalyst particles are catalyst particles in which Fe is supported as an active ingredient on a support, the support may be alumina or silica. The above types of supports have a large specific surface area, making them advantageous for supporting the active ingredient, and when Fe is supported, they can be particularly excellent in terms of catalytic activity and durability.

[0047] Furthermore, when the Fe-based catalyst particle is a catalyst particle in which Fe is supported as an active component on a support, a co-catalyst component may be supported together with the active component Fe for the purpose of further increasing the catalytic activity of the active component, and at least one selected from among Na, K, and Cu may be used as the co-catalyst component.

[0048]

[0049] The above Fe-based catalyst particles may be in the form of secondary particles formed by agglomeration of a plurality of primary particles. The primary particles may be nanoparticles having a diameter in the nm range, and more specifically, the diameter of the primary particles may be 100 nm or less, and particularly preferably 80 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, or 30 nm or less, and at least 1 nm, 3 nm or more, 5 nm or more, or 10 nm or more. In addition, the diameter of the secondary particles formed by agglomeration of a plurality of primary particles may be 10 μm or more, and more preferably 30 μm or more, 50 μm or more, 70 μm or more, or 100 μm or more, and at most 1,000 μm, 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-described range, the balance in terms of mechanical strength and catalytic activity can be appropriate.

[0050]

[0051] protective layer

[0052] The above protective layer suppresses catalyst sintering during the carbon dioxide conversion reaction process by covering a portion of the surface of the catalyst particles described above, thereby improving the conversion rate of carbon dioxide and the selectivity for high-carbon hydrocarbons.

[0053] More specifically, when a protective layer is formed on the surface of the catalyst particle described above using the atomic layer deposition method, the protective layer is formed in a shape in which the thickness is thin and uniform while covering only a portion of the surface of the catalyst particle, and when the ratio of the catalyst particle surface covered by the protective layer formed in this way, that is, the coverage, is adjusted to a range of 10 to 90%, the conversion rate of carbon dioxide by the catalyst is improved while the selectivity of high-carbon hydrocarbons also increases. Although the specific mechanism of this action cannot be clearly identified, it was expected that the selectivity would decrease because the surface area that exhibits activity would be narrowed when the catalyst surface is covered by the protective layer. However, on the contrary, when the coverage is within a specific range as in the present invention, it was confirmed that the selectivity was also improved along with the conversion rate expected to be improved by the protective layer.

[0054] Furthermore, the coverage may vary depending on the type or composition of the Fe-based catalyst particles described above. More specifically, when the internal pore size of the Fe-based catalyst particles is small, the coverage may decrease as some of the pores are blocked during the protective layer formation process. Conversely, when the internal pore size of the Fe-based catalyst particles is large, the coverage may exhibit a high value after the protective layer formation. Furthermore, the coverage may be controlled by varying the process conditions during the protective layer formation process. More specifically, when the protective layer is formed thickly, the coverage may decrease as the thickened protective layer blocks some of the pores. When the protective layer is formed thinly, the coverage can be controlled within a high range.

[0055] The above coverage may vary depending on the type and component of the Fe-based catalyst particles as described above, and may be 10 to 90%. When the Fe-based catalyst particles include a support, it may be 10% or more and 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, or 30%. Meanwhile, when the Fe-based catalyst particles are bulk catalysts that do not include a support, it may be 10% or more, 20% or more, 30% or more, or 35% or more and 90% or less. More specifically, when the Fe-based catalyst particles are Fe / Si, the coverage range may be 10% or more and 20% or less. When the Fe-based catalyst particles are Fe / γ-Al, the coverage range may be 5% or more and 15% or less. When the Fe-based catalyst particles are Fe / δ-Al, the coverage range may be 20% or more and 30% or less. When the Fe-based catalyst particles are Fe / K / Cu / Si, the coverage range may be 10% or more and 50% or less, and 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-described range, the selectivity for high-carbon hydrocarbons and the conversion rate of carbon dioxide can be excellent at the same time.

[0056]

[0057] Meanwhile, the above "coverage" can be calculated by dividing the content of the protective layer by (protective layer (covering layer) thickness * catalyst specific surface area * theoretical density of the protective layer). In the above formula, the theoretical density of the protective layer refers to a theoretical value known as the density of the component formed into the protective layer.

[0058]

[0059] In addition, the protective layer may include Al, Ce, Cu, Co, Mo, or oxides or nitrides thereof. These components do not lower the catalytic activity of the Fe-based catalyst particles, and have excellent high-temperature and mechanical stability, so that the performance can be sufficiently maintained even when the catalyst is used under high-temperature conditions. More preferably, the protective layer may include Al. When the protective layer includes Al, its oxide or nitride, the performance of the above-described protective layer can be maximized, and in particular, the catalytic activity can be enhanced due to the surface interaction between the Fe-based catalyst particles and the Al of the protective layer.

[0060]

[0061] Furthermore, the thickness of the protective layer may be 0.5 to 10 nm, and preferably 0.5 nm or more, 1 nm or more, 1.5 nm or more, or 2 nm or more, and 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. If the thickness of the protective layer is too thin, the effect of the protective layer, specifically, the effect of inhibiting catalyst sintering at high temperatures, may not be significantly exerted, and if the thickness of the protective layer is too thick, the catalytic activity may rather decrease. Meanwhile, in the present invention, the fact that the thickness of the protective layer can be controlled within the above-described thin range and made uniform is due to the formation of the protective layer using an atomic layer deposition method. The thickness of the protective layer can be measured from a cross-sectional TEM of the manufactured catalyst.

[0062] In the catalyst of the present invention, the surface area of ​​the catalyst particle surface not covered by the protective layer is 0.05 to 2 m 2 / g may be, preferably 0.05m 2 / g or more, 0.07m 2 / g or more or 0.1m 2 / g or more, 2m 2 / g or less, 1.8m 2 / g or less or 1.5m 2 / g or less. The surface area of ​​the catalyst particles not covered with a protective layer must be within the above-mentioned range to provide sufficient catalytic activity.

[0063] In the catalyst of the present invention, the specific surface area of ​​the catalyst after the protective layer is formed may vary depending on the type of Fe-based catalyst particles, but is 1 to 250 m 2 / g may be, preferably 1 to 100 m 2 / g. The catalyst of the present invention has a sufficiently large specific surface area as described above, so that the contact area between the catalyst and carbon dioxide can be sufficiently large, and thus the carbon dioxide conversion rate can be high.

[0064] In the catalyst of the present invention, the content of the protective layer based on the weight of the entire catalyst may be 1 to 50 wt%, preferably 2 wt% or more, 3 wt% or more, 5 wt% or more, or 10 wt% or more, and 30 wt% or less, 25 wt% or less, or 23 wt% or less. When the content of the protective layer is within the above-described range, the improvement effect by the protective layer can be maximized.

[0065]

[0066] Method for manufacturing a catalyst

[0067] The present invention provides a method for manufacturing a catalyst for carbon dioxide conversion as described above. Specifically, the present invention provides a method for manufacturing a catalyst, comprising the step of forming a protective layer on the surface of iron-based catalyst particles using an atomic layer deposition method.

[0068]

[0069] A key technical feature of the catalyst of the present invention is its protective layer, which is formed using atomic layer deposition. Using atomic layer deposition, a uniformly thick protective layer can be formed even on complex 3D-shaped Fe-based catalyst particles, and the thickness of the protective layer can be controlled to a thin level.

[0070]

[0071] The process of forming a protective layer using an atomic layer deposition method can be performed by a conventional method, and after loading Fe-based catalyst particles into an atomic layer deposition facility, the process of injecting and depositing the protective layer raw material, the process of oxidizing or reducing, and the process of purging are combined into one cycle, and the cycle can be repeated multiple times. In the above process, water (H2O), ozone (O3), or oxygen (O2) plasma can be injected to form a metal oxide, and hydrogen gas can be injected to form a metal layer.

[0072]

[0073] Carbon dioxide conversion method

[0074] 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.

[0075] The selectivity for high-carbon hydrocarbons having 5 or more carbon atoms in a mixed hydrocarbon gas produced using the catalyst of the present invention can be 40% or more, preferably 45% or more. The catalyst of the present invention is characterized by simultaneously high carbon dioxide conversion rate and high selectivity for high-carbon hydrocarbons during a carbon dioxide conversion reaction using the catalyst by introducing the protective layer described above.

[0076] The above conversion reaction can be carried out without any particular limitation under conditions applicable to the thermochemical conversion reaction of carbon dioxide, and the reactor used in the present invention is not particularly limited. Furthermore, the temperature at which the reaction is carried out is also not particularly limited as long as it is a temperature sufficient for the conversion of carbon dioxide, and the catalyst of the present invention can minimize sintering even under high-temperature conditions by having a protective layer, thereby allowing the carbon dioxide conversion reaction to proceed stably even at relatively high temperatures.

[0077]

[0078] Hereinafter, the present invention will be described in more detail with examples and experimental examples to specifically explain the present invention. However, the present invention is not limited to these examples and experimental examples. The examples according to the present invention can be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more completely explain the present invention to those of average skill in the art.

[0079]

[0080] ingredient

[0081] Fe / Si, Fe / γ-Al, Fe / δ-Al, Fe bulk catalysts, Fe / Na, and Fe / K / Cu / Si catalysts were used as Fe-based catalyst particles. The Fe / Na catalyst refers to a catalyst in which Na, 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 a main catalyst component on a Si support, and Cu and K components are supported as co-catalyst components.

[0082]

[0083] Examples and Comparative Examples

[0084] The prepared Fe-based catalyst particles (0.5 g) were applied and loaded onto a square tray. The tray was then placed in a chamber within the ALD equipment, and the chamber temperature was set to 150°C and the process pressure to 1 Torr. Then, trimethylaluminum (TMA) at 20°C was pulse-injected into the chamber together with 100 sccm of nitrogen gas as a carrier gas for 3 seconds, maintained for 100 seconds, and purged for 20 seconds. This process was repeated three times. Then, purging was performed again for 600 seconds, and the process of injecting water instead of trimethylaluminum in the previous process for 3 seconds in a pulse, maintaining for 100 seconds, and purging for 20 seconds was repeated three more times. This process was considered one cycle, and the cycle was repeated 8 to 40 times to form a protective layer containing aluminum oxide on the surface of the Fe-based catalyst particles.

[0085]

[0086] The details of the catalysts manufactured in each example and comparative example are summarized in Tables 1 and 2 below. Meanwhile, in the case of Example 5-2, the conditions other than those of Example 5-1 were the same, but the amounts of TMA and water introduced were doubled to manufacture a catalyst having the same thickness of the protective layer but a higher coverage rate. In Example 5-3, the catalyst particles were pulverized and classified to reduce the particle size from the existing 300 to 500 μm to 100 to 300 μm, and then a protective layer was formed. In the case of Example 5-3, as the size of the catalyst particles decreased, the exposed surface area increased, and thereby the coverage rate of the protective layer increased.

[0087]

[0088] Comparative Example 1 Example 1 Comparative Example 2 Example 2 Comparative Example 3 Example 3 Fe-based catalyst particle type Fe / SiFe / γ-AlFe / δ-Al Coverage (%) - 14-11-24 Protective layer thickness (nm) - 5-5-5 Protective layer (Al) content (wt%) - 23-13-18.9 Catalyst specific surface area (m 2 / g)208291442.2697.313.7Fe Surface area (m2 / g)0.02110.1040.41780.1528Not measuredNot measured

[0089] Comparative Example 4 Example 4-1 Example 4-2 Example 4-3 Comparative Example 5 Example 5-1 Example 5-2 Example 5-3 Fe-based catalyst particle type Fe bulk catalyst Fe / K / Cu / Si Coverage (%) - 877839-11.716.729.8 Protective layer thickness (nm) - 125-222 Protective layer (Al) content (wt%) - 5.49.712-2.12.95.4 Catalyst specific surface area (m 2 / g)37.832.328.624.071.469.866.870.4Fe Surface area (m 2 / g)0.03310.13570.14010.0786Not measuredNot measuredNot measuredNot measured

[0090] Meanwhile, the characteristics measured in Tables 1 and 2 above were measured using the following method.

[0091] 1) Protective layer thickness: After depositing (sputtering) platinum (Pt) or carbon to a thickness of 100 nm on the protective layer of the catalyst particle, FIB (Focused ion beam) or Ar + Cross-sectional specimens were fabricated using ion milling. The thickness of the catalyst layer was measured by TEM analysis of the fabricated specimens.

[0092] 2) Protective layer content: The catalyst content was confirmed through ICP component analysis. 0.1 g of catalyst particles were dissolved in 1 ml of hydrochloric acid, diluted 10 times, and then ICP-OES analysis was performed. Meanwhile, the protective layer content refers only to the Al content included in the protective layer, excluding the Al content derived from the support.

[0093] Measurement equipment: ICP-OES Agilent 5110

[0094] Measurement conditions: RF Power 1300W, Torch Height 15mm, Plasma gas flow 15L / min, Sample Gas flow 0.8L / min, Aux. Gas flow 0.2L / min, Pump Speed ​​1.5ml / min

[0095] 3) Coverage: Calculated using the previously measured protective layer content, protective layer thickness, specific surface area of ​​the catalyst, and catalyst density, and calculated using the following formula.

[0096] Coverage = Catalyst content / (Protective layer thickness * Catalyst specific surface area * Theoretical density of catalyst)

[0097] 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. Meanwhile, if the Fe surface area decreases despite an increase in the protective layer, this is confirmed to be due to the catalyst particles clumping together during the reduction process, resulting in a decrease in the Fe surface area.

[0098]

[0099] Considering the results in Tables 1 and 2 above, the coverage was higher in the Fe bulk catalyst with a relatively large internal pore size than in the other catalysts, and it was confirmed that the coverage decreased as some pores were blocked as the thickness of the protective layer increased. On the other hand, in the case of the remaining catalysts using a support, the coverage was confirmed to be lower than in the case of using a bulk catalyst as the internal pore size became relatively small, and in all types of catalysts, it was confirmed that the specific surface area of ​​the catalyst decreased compared to the catalyst without a protective layer formed as the formed protective layer blocked some pores.

[0100]

[0101] Experimental Example 1. Measurement of conversion rate and selectivity in carbon dioxide conversion reaction using a catalyst.

[0102] Mixed hydrocarbons were produced from carbon dioxide using the catalysts manufactured in Examples 5-1 to 5-3 and Comparative Example 5. Specifically, the manufactured catalysts were placed in a reactor, heated to 500°C, and pretreated by flowing 5% CO2 / N2 (250 sccm) for 3 hours. Thereafter, the temperature inside the reactor was lowered to 350°C, and 25% CO2 / H2 (75 sccm) was continuously flowed for 6 hours under 20 bar pressure conditions to carry out the reaction.

[0103]

[0104] The reaction product formed as a result of the reaction was passed through a thermostatic water bath trap set to 0℃ to collect liquid hydrocarbons with a carbon number of 5 or more, and the gaseous product was analyzed in real time using gas chromatography. The reaction was performed continuously for more than 48 hours.

[0105] Carbon dioxide conversion rate and selectivity for hydrocarbons with carbon number of 5 or more were measured / calculated using the following methods.

[0106] 1) Conversion rate: Calculated using the following formula.

[0107] Carbon dioxide conversion rate = (input CO2 flow - exhaust CO2 flow) / (input CO2 flow) * 100%

[0108] 2) Selectivity: Calculated using the following formula.

[0109] Selectivity of gaseous products = (C A H B Flow rate * A) / (input CO2 flow rate - exhaust CO2 flow rate) * 100%

[0110] Selectivity for liquid hydrocarbons with 5 or more carbon atoms = 100% - (sum of selectivities for gaseous products)

[0111]

[0112] The measured conversion rate and selectivity values ​​are summarized in Table 3 below.

[0113] CO2 conversion rate (%) C5+ selectivity (%) Example 5-144.956.8 Example 5-246.157.6 Example 5-347.861.8 Comparative example 540.050.0

[0114] As can be seen from Table 3 above, when the catalyst of the present invention was used, it was confirmed that the carbon dioxide conversion rate and the selectivity for liquid hydrocarbons with a carbon number of 5 or more with high added value were higher than when the catalyst of the comparative example was used. Furthermore, in Examples 5-2 and 5-3, where the thickness of the protective layer was the same, but the content of aluminum in the protective layer was higher and the coverage was higher accordingly, higher conversion and selectivity values ​​were confirmed than in Example 5-1, and through this, it was confirmed that the conversion rate and selectivity can be improved by increasing the coverage under the same conditions.

[0115]

[0116] Experimental Example 2. Confirmation of changes in catalyst properties after heat treatment.

[0117] After heat treatment of the catalysts of Comparative Example 4 and Example 4-3, it was confirmed how the specific surface area of ​​the catalyst changed and how particle agglomeration occurred.

[0118] Specifically, heat treatment was performed for each catalyst at 700°C for 2 hours, and the results are summarized and shown in Fig. 1.

[0119] As can be seen from Fig. 1, the catalyst of Example 4-3 of the present invention showed a small change in specific surface area and less agglomeration of particles despite being heated under high-temperature conditions for a long time, whereas the catalyst of Comparative Example 4 showed a sintering phenomenon in which particles agglomerated, and thus the specific surface area was greatly reduced.

[0120] From this, it was confirmed 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 the surface.

Claims

1. Fe-based catalyst particles; and A protective layer formed on the surface of the catalyst particle; The coverage of the catalyst particle surface by the above protective layer is 10 to 90%, A catalyst for carbon dioxide conversion, wherein the protective layer comprises Al, Ce, Cu, Co, Mo, or an oxide or nitride thereof.

2. In paragraph 1, A catalyst for carbon dioxide conversion, wherein the thickness of the protective layer is 0.5 to 10 nm.

3. In paragraph 1, The surface area of ​​the catalyst particle surface not covered by the protective layer is 0.05 to 2 m 2 / g Catalyst for carbon dioxide conversion.

4. In paragraph 1, The specific surface area of ​​the above catalyst is 1 to 250 m 2 / g Catalyst for carbon dioxide conversion.

5. In paragraph 1, A catalyst for carbon dioxide conversion, wherein the content of the protective layer is 1 to 50 wt% based on the weight of the entire catalyst.

6. In paragraph 1, A catalyst for carbon dioxide conversion, wherein the above Fe-based catalyst particles are Fe bulk catalysts or catalyst particles in which Fe is supported as an active ingredient on a support.

7. In paragraph 6, The above Fe-based catalyst particles are Fe bulk catalysts, A catalyst for carbon dioxide conversion, wherein the surface coverage of the catalyst particles by the protective layer is 30% or more and 90% or less.

8. In paragraph 6, The above support is a catalyst for carbon dioxide conversion, wherein the catalyst is alumina or silica.

9. In paragraph 6, The above Fe-based catalyst particles are Fe / Si, A catalyst for carbon dioxide conversion, wherein the surface coverage of the catalyst particles by the protective layer is 10% or more and 20% or less.

10. In paragraph 6, The above Fe-based catalyst particles are Fe / γ-Al, A catalyst for carbon dioxide conversion, wherein the surface coverage of the catalyst particles by the protective layer is 5% or more and 15% or less.

11. In paragraph 6, The above Fe-based catalyst particles are Fe / δ-Al, A catalyst for carbon dioxide conversion, wherein the surface coverage of the catalyst particles by the protective layer is 20% or more and 30% or less.

12. In paragraph 6, The above Fe-based catalyst particles are catalyst particles in which Fe is supported as an active ingredient on a support. A catalyst for carbon dioxide conversion, wherein at least one selected from among Na, K, and Cu is further supported as a cocatalyst component.

13. In paragraph 6, The above Fe-based catalyst particles are Fe / K / Cu / Si, A catalyst for carbon dioxide conversion, wherein the surface coverage of the catalyst particles by the protective layer is 10% or more and 50% or less.

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

15. A method for converting carbon dioxide, comprising the step of synthesizing a mixed hydrocarbon gas by heating a reaction gas containing carbon dioxide in the presence of the catalyst of paragraph 1.

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